How to store to retain it for possible future use?

deliberately discharged and then unattended outside of pc
charged up in pc and then unattended outside of pc
charged via otherwise unused pc once a month? 6 monthly ? yearly ? and then
removed from pc
stored in a fridge? or just a cool dry place or a warm place

N_Cook wrote:
How to store to retain it for possible future use?

deliberately discharged and then unattended outside of pc
Will destroy it.

charged up in pc and then unattended outside of pc

Yes.

If you have an antistatic bag and a moisture abosrber, put them in it and
seal it. Keep cool, but do not freeze (as the UNIX fortune program used to say).

In case any one wonders, the cells themselves are not affected by static,
but the electronics inside the battery pack are.

If you are the cautious type, place the anti static bag inside a sealed
zip lock bag. If the cells leak, the electrolyte is extremely corrosive.

I have no proof, just a feeling, but I would not place them in bag and seal
it using a vacuum food sealing system. The cells are designed to not leak
at seal level air pressure, not a vacuum.

Geoff.

--
Geoffrey S. Mendelson, Jerusalem, Israel N3OWJ/4X1GM

Anti-static bags are conductive. Not like metal, but they conduct. Make sure
the battery's contacts are covered.

On Thu, 1 Oct 2009 14:29:37 +0100, "N_Cook" wrote:

How to store to retain it for possible future use?

http://en.wikipedia.org/wiki/Lithium-ion_battery#Shelf_life
Store at about 50% charge in the coldest place you can find. Warm to
room temperatures before using.

"At a 100% charge level, a typical Li-ion laptop battery that is full
most of the time at 25 °C or 77 °F will irreversibly lose
approximately 20% capacity per year...."

deliberately discharged and then unattended outside of pc

That will blow up the battery.

charged up in pc and then unattended outside of pc

Full charge will eventually self-deteriorate the battery.

charged via otherwise unused pc once a month? 6 monthly ? yearly ? and then
removed from pc

Nope. Lifetime is measured in charge cycles. That would just
decriment the number of charge cycles available.

stored in a fridge? or just a cool dry place or a warm place

Cool. Cold is better, but don't freeze. Optionally store in sealed
plastic bag to prevent condensation when removed from fridge.


--
Jeff Liebermann
150 Felker St #D http://www.LearnByDestroying.com
Santa Cruz CA 95060 http://802.11junk.com
Skype: JeffLiebermann AE6KS 831-336-2558

On Thu, 01 Oct 2009 09:34:43 -0700, Jeff Liebermann
wrote:

On Thu, 1 Oct 2009 14:29:37 +0100, "N_Cook" wrote:

How to store to retain it for possible future use?

http://en.wikipedia.org/wiki/Lithium-ion_battery#Shelf_life
Store at about 50% charge in the coldest place you can find. Warm to
room temperatures before using.

"At a 100% charge level, a typical Li-ion laptop battery that is full
most of the time at 25 °C or 77 °F will irreversibly lose
approximately 20% capacity per year...."

that's seriously dated and extremely inaccurate. It doesn't explain
the packs that are ten years older (or more) and still can demonstrate
2/3rds of original capacity. Unfortunately some of these references
seem to never track reality.

deliberately discharged and then unattended outside of pc

That will blow up the battery.

That's also an extreme view, assuming discharge to the "normal"
end-point and *not* to zero volts per cell (which is geberally
precluded by the pack protection module anyway).

Have you ever witnessed that occur? The normal decomposition of cells
allowed to deteriorate from EOD is non-spectacular, just a quiet
process without the leakage that say an alkaline primary would
exhibit.

charged up in pc and then unattended outside of pc

Full charge will eventually self-deteriorate the battery.

The things that determine the rate of loss_of_usable_capacity are
temperature and state-of-charge. Also simple choices (not generally
available to the user of consumer appliances) play a big part in cycle
life. Lowering the end-of-charge voltage from 4.20 to 4.10 returns a
trebling of cycle life in return for a small reduction in usable
capacity.

charged via otherwise unused pc once a month? 6 monthly ? yearly ? and then
removed from pc

Nope. Lifetime is measured in charge cycles. That would just
decriment the number of charge cycles available.

It isn't that simple.

stored in a fridge? or just a cool dry place or a warm place

Cool. Cold is better, but don't freeze. Optionally store in sealed
plastic bag to prevent condensation when removed from fridge.

On Fri, 02 Oct 2009 09:15:31 +0800, who where wrote:

On Thu, 01 Oct 2009 09:34:43 -0700, Jeff Liebermann
wrote:

On Thu, 1 Oct 2009 14:29:37 +0100, "N_Cook" wrote:

How to store to retain it for possible future use?

http://en.wikipedia.org/wiki/Lithium-ion_battery#Shelf_life
Store at about 50% charge in the coldest place you can find. Warm to
room temperatures before using.

"At a 100% charge level, a typical Li-ion laptop battery that is full
most of the time at 25 °C or 77 °F will irreversibly lose
approximately 20% capacity per year...."

that's seriously dated and extremely inaccurate. It doesn't explain
the packs that are ten years older (or more) and still can demonstrate
2/3rds of original capacity. Unfortunately some of these references
seem to never track reality.

How recent a web page would you consider to be adequately up to date?

More pages that say basically the same thing:
http://www.batteryuniversity.com/parttwo-34.htm
http://powerelectronics.com/portable_power_management/battery_charger_ics/proper_care_extends-li-ion-battery-0425/

http://www.apple.com/batteries/
If you use your iPod, iPhone, or notebook in temperatures higher
than 95° F (or 35° C), you may permanently damage your battery’s
capacity. That is, your battery won’t power your device as long on
any given charge. You may damage it even more if you charge the
device in these temperatures. Even storing a battery in a hot
environment can damage it irreversibly.

http://www.centralhobbies.com/instructional/lithium.html
3. Don't charge up the battery pack just to store it away. When
storing for long periods of time, keep the battery at a 40% charge
level.

More if you want them.... Google for "Li-Ion battery care".

deliberately discharged and then unattended outside of pc

That will blow up the battery.

That's also an extreme view, assuming discharge to the "normal"
end-point and *not* to zero volts per cell (which is geberally
precluded by the pack protection module anyway).

Agreed. However, the OP didn't specify how he plans to discharge the
battery. I had visions of discharging the battery pack outside of the
laptop (or whatever).

Have you ever witnessed that occur? The normal decomposition of cells
allowed to deteriorate from EOD is non-spectacular, just a quiet
process without the leakage that say an alkaline primary would
exhibit.

Witnessed what? Having a Li-Ion battery die from excessive discharge?
Yep, but with LiPo batteries in model airplanes. They don't have the
protection found in most laptops and cell phones. The motor is fully
able to fly the battery into the ground. Two to perhaps five such
cycles is all that's required to kill the battery.

charged up in pc and then unattended outside of pc

Full charge will eventually self-deteriorate the battery.

The things that determine the rate of loss_of_usable_capacity are
temperature and state-of-charge. Also simple choices (not generally
available to the user of consumer appliances) play a big part in cycle
life. Lowering the end-of-charge voltage from 4.20 to 4.10 returns a
trebling of cycle life in return for a small reduction in usable
capacity.

I had the opportunity to verify part of that on a small scale. Four
identical LiPo batteries.
1. 100% charge refreshed every two weeks at room temperature.
2. 100% charge refreshed every two weeks in my fridge.
3. 50% charge refreshed every two weeks at room temperature.
4. 50% charge refreshed every two weeks in my fridge.
Unfortunately, 50% charge was largely a guess and my not have been
accurate. The 2 week interval was also not exact. None of the
batteries were discharged with any load other than self-discharge.

At the end of 6 months, I used a West Mtn Radio battery analyzer to
see what was left.
http://www.westmountainradio.com/CBA.htm
I returned all the batteries to room temperature, let them stabilize
for a day, and charged them all to 100%. I then tested them and
generated discharge graphs at rated Amp-Hr capacity.
1. 60% of rated capacity
2. 85% of rated capacity
3. 98% of rated capacity
4. 98% of rated capacity.
The above numbers are from my fading memory and may not be exact. I
think I can post the corresponding graphs, if I can find the data. The
laptop I was using for testing crashed and I'm not sure if I had
backed up the data.

charged via otherwise unused pc once a month? 6 monthly ? yearly ? and then
removed from pc

Nope. Lifetime is measured in charge cycles. That would just
decriment the number of charge cycles available.

It isn't that simple.

True. It never is that simple.

stored in a fridge? or just a cool dry place or a warm place

Cool. Cold is better, but don't freeze. Optionally store in sealed
plastic bag to prevent condensation when removed from fridge.

So, since you indicate that everything I posted is wrong, how should
one store a Li-Ion battery?

--
# Jeff Liebermann 150 Felker St #D Santa Cruz CA 95060
# 831-336-2558
# http://802.11junk.com
# http://www.LearnByDestroying.com AE6KS

On Thu, 01 Oct 2009 20:22:26 -0700, Jeff Liebermann
wrote:

On Fri, 02 Oct 2009 09:15:31 +0800, who where wrote:

On Thu, 01 Oct 2009 09:34:43 -0700, Jeff Liebermann
wrote:

On Thu, 1 Oct 2009 14:29:37 +0100, "N_Cook" wrote:

How to store to retain it for possible future use?

http://en.wikipedia.org/wiki/Lithium-ion_battery#Shelf_life
Store at about 50% charge in the coldest place you can find. Warm to
room temperatures before using.

"At a 100% charge level, a typical Li-ion laptop battery that is full
most of the time at 25 °C or 77 °F will irreversibly lose
approximately 20% capacity per year...."

that's seriously dated and extremely inaccurate. It doesn't explain
the packs that are ten years older (or more) and still can demonstrate
2/3rds of original capacity. Unfortunately some of these references
seem to never track reality.

How recent a web page would you consider to be adequately up to date?

More pages that say basically the same thing:
http://www.batteryuniversity.com/parttwo-34.htm
http://powerelectronics.com/portable_power_management/battery_charger_ics/proper_care_extends-li-ion-battery-0425/

http://www.apple.com/batteries/
If you use your iPod, iPhone, or notebook in temperatures higher
than 95° F (or 35° C), you may permanently damage your battery’s
capacity. That is, your battery won’t power your device as long on
any given charge. You may damage it even more if you charge the
device in these temperatures. Even storing a battery in a hot
environment can damage it irreversibly.

http://www.centralhobbies.com/instructional/lithium.html
3. Don't charge up the battery pack just to store it away. When
storing for long periods of time, keep the battery at a 40% charge
level.

More if you want them.... Google for "Li-Ion battery care".

You've rolled a number of points into one. I was referring
speciically to their 20% p.a. loss of capacity claim, which is a
crock.

deliberately discharged and then unattended outside of pc

That will blow up the battery.

That's also an extreme view, assuming discharge to the "normal"
end-point and *not* to zero volts per cell (which is geberally
precluded by the pack protection module anyway).

Agreed. However, the OP didn't specify how he plans to discharge the
battery. I had visions of discharging the battery pack outside of the
laptop (or whatever).

If it is a laptop pack recent enough to care about, it will contain a
pack protection module which will preclude discharge beyond a LVCO
point, typically 3.0v, and will also preclude excessive discharge
current. Nothing unsafe about a DYI discharge on that pack.

If it is a single cell from a cellphone or similar, different story.
these tend to have minimal inbuilt protection (if any) and rely
heavily on the host device for the customary protective functions.

Have you ever witnessed that occur? The normal decomposition of cells
allowed to deteriorate from EOD is non-spectacular, just a quiet
process without the leakage that say an alkaline primary would
exhibit.

Witnessed what? Having a Li-Ion battery die from excessive discharge?
Yep, but with LiPo batteries in model airplanes. They don't have the
protection found in most laptops and cell phones. The motor is fully
able to fly the battery into the ground. Two to perhaps five such
cycles is all that's required to kill the battery.

No protection means all bets are off.

charged up in pc and then unattended outside of pc

Full charge will eventually self-deteriorate the battery.

The things that determine the rate of loss_of_usable_capacity are
temperature and state-of-charge. Also simple choices (not generally
available to the user of consumer appliances) play a big part in cycle
life. Lowering the end-of-charge voltage from 4.20 to 4.10 returns a
trebling of cycle life in return for a small reduction in usable
capacity.

I had the opportunity to verify part of that on a small scale. Four
identical LiPo batteries.
1. 100% charge refreshed every two weeks at room temperature.
2. 100% charge refreshed every two weeks in my fridge.
3. 50% charge refreshed every two weeks at room temperature.
4. 50% charge refreshed every two weeks in my fridge.
Unfortunately, 50% charge was largely a guess and my not have been
accurate. The 2 week interval was also not exact. None of the
batteries were discharged with any load other than self-discharge.

At the end of 6 months, I used a West Mtn Radio battery analyzer to
see what was left.
http://www.westmountainradio.com/CBA.htm
I returned all the batteries to room temperature, let them stabilize
for a day, and charged them all to 100%. I then tested them and
generated discharge graphs at rated Amp-Hr capacity.
1. 60% of rated capacity
2. 85% of rated capacity
3. 98% of rated capacity
4. 98% of rated capacity.
The above numbers are from my fading memory and may not be exact. I
think I can post the corresponding graphs, if I can find the data. The
laptop I was using for testing crashed and I'm not sure if I had
backed up the data.

No need. I've seen numbers on these before, and Evgenij Barsukov has
posted comment on this previously in sci.chem.electrochem.battery.

charged via otherwise unused pc once a month? 6 monthly ? yearly ? and then
removed from pc

Nope. Lifetime is measured in charge cycles. That would just
decriment the number of charge cycles available.

It isn't that simple.

True. It never is that simple.

stored in a fridge? or just a cool dry place or a warm place

Cool. Cold is better, but don't freeze. Optionally store in sealed
plastic bag to prevent condensation when removed from fridge.

So, since you indicate that everything I posted is wrong, how should
one store a Li-Ion battery?

I never suggested that everything you posted is wrong, far from it.
But several points were amiss and they attracted specific comment.

I have seen numerous manufacturer-derived articles recommending 50-60%
SOC and cool/cold but not freezing as the optimum storage condition
for maximised life. I see nothing at all wrong with this approach
*if* maximum life is the sole objective. If OTOH the user wants to be
able to pull the cell/battery out of storage and into service without
an intervening warm-up or recharge, maybe a higher SOC is warranted.
Like many things relating to Li-XX cells, it is a tradeoff.

The extra life obtained by reducing the EOC voltage is well documented
and well worth it in laptop applications BUT the end user doesn't get
to choose. The manufacturer is out to deliver (well, promise) the
maximum discharge runtime he can, and he doesn't give a rats how long
the pack lasts in service.

I have a pack from an olde Acernote Lite 370 series dated 9637, so it
is just over 13 years old. It is stored with, but not *in*, the
machine. About once every year or so I pull that out and run it until
the machine shuts down, then recharge it to 100% (sic). It delivers
about 1.3 hours, compared to 2.5+ when new. That is stored at 100%
and room temperature (32S/116E).

I also have several test packs of 18650 cells left over from a project
about five years ago when I designed a commercial Li-XX charger. They
were shelved at 4.20v and currently all are above 3.9v. I haven't
bothered to measure their storage capacity because I have no reason,
but I can assure you that they wouldn't show that sort of cell voltage
if they had lost 20% of original capacity per year.

On Thu, 1 Oct 2009 07:12:28 -0700 "William Sommerwerck"
wrote in Message id:
:

Anti-static bags are conductive. Not like metal, but they conduct.

Especially the cheap ones that motherboards and such come in with the
crosshatch patterns on the outside of the bag. Never put a motherboard
down on the outside of one or you can discharge the CMOS battery if left
long enough.

In article , Jeff Liebermann
wrote:

http://en.wikipedia.org/wiki/Lithium-ion_battery#Shelf_life
Store at about 50% charge in the coldest place you can find. Warm to
room temperatures before using.

SNIP

Cool. Cold is better, but don't freeze. Optionally store in sealed
plastic bag to prevent condensation when removed from fridge.


Jeff,

"coldest place you can find" versus "don't freeze".

Which is it?

--- Joe

On Fri, 02 Oct 2009 15:36:03 -0700, ess (Joe) wrote:

In article , Jeff Liebermann
wrote:

http://en.wikipedia.org/wiki/Lithium-ion_battery#Shelf_life
Store at about 50% charge in the coldest place you can find. Warm to
room temperatures before using.

Cool. Cold is better, but don't freeze. Optionally store in sealed
plastic bag to prevent condensation when removed from fridge.

"coldest place you can find" versus "don't freeze".
Which is it?

The coldest place you can find that doesn't freeze the battery. I
would think you could decode that from what I wrote. Freezing is 0C
so anything between that and somewhat below room temperature is a good
target.

The fridge at 5 to 8C is about as cold as I would think necessary. Any
colder runs the risk of freezing the battery. If that's too
difficult, room temperature is fine. Just don't let the battery get
hot.

Before using the battery, let it warm up to room temperature.

--
Jeff Liebermann
150 Felker St #D http://www.LearnByDestroying.com
Santa Cruz CA 95060 http://802.11junk.com
Skype: JeffLiebermann AE6KS 831-336-2558

On Fri, 02 Oct 2009 14:03:46 +0800, who where wrote:

http://www.batteryuniversity.com/parttwo-34.htm

You've rolled a number of points into one. I was referring
speciically to their 20% p.a. loss of capacity claim, which is a
crock.

Guilty as charged and you're correct, but not for commodity Li-Ion
laptop batteries as the OP apparently is using. According to:
http://www.batteryuniversity.com/parttwo-34.htm

Temp 40% storage charge 100% storage charge
0C 96% after 1 yr 94% after 1 yr
25C 96% after 1 yr 80% after 1 yr
40C 85% after 1 yr 65% after 1 yr
60C 75% after 1 yr 60% after 3 months

Kinda looks like about 20%/yr loss with 100% charge at room temp. My
abbreviated test showed a 40% loss with 100% charge at room temp in 6
months. I'll agree with the Wikipedia numbers until someone specified
a specific chemistry and testing method (that I can perform with my
West Mtn Radio CBA II tester).

However, you are correct that there are new and improved chemistries
that do not have anywhere near the self discharge and
self-deterioration rate of commodity laptop batteries. Eagle Picher
makes Lithium-CFX batteries, that claim a self discharge rate of less
than 1%/year at room temperature.
http://www.edn.com/article/CA6672104.html
These batteries are made to operate at body temperature (37C) and must
therefore not suffer from self-deterioration at elevated storage
temperatures.

If it is a laptop pack recent enough to care about, it will contain a
pack protection module which will preclude discharge beyond a LVCO
point, typically 3.0v, and will also preclude excessive discharge
current. Nothing unsafe about a DYI discharge on that pack.

True. The battery pack has enough electronics inside to protect
itself from excessive discharge. Under Windoze, one can set an alarm
and a shutdown point based on battery capacity. The default threshold
is about 10%. I've never tested this to determine if it works.
Presumably, if you don't want to run the battery down to below perhaps
25% capacity, setting a shutdown threshold below this point is wasted
effort. Similarly, if there's a protection threshold inside the
battery pack, it's certainly not labeled or easily determined.

If it is a single cell from a cellphone or similar, different story.
these tend to have minimal inbuilt protection (if any) and rely
heavily on the host device for the customary protective functions.

Yep. Model airplanes and helicopters are even worse. All the
protection electronics is in the external battery charger. It
protects against fatal overcharge, but does nothing for excessive
discharge.

No protection means all bets are off.

Yep.

No need. I've seen numbers on these before, and Evgenij Barsukov has
posted comment on this previously in sci.chem.electrochem.battery.

(...)

I never suggested that everything you posted is wrong, far from it.
But several points were amiss and they attracted specific comment.

No problem. However, I'll stand on the Wikipedia 20%/year loss at
100% charge at room temperature for commodity laptop batteries. My
results were even worse. I'll concede that there are new chemistries
that offer substantial improvements in self-discharge and
self-deterioration, but I haven't seen any in laptops.

I have seen numerous manufacturer-derived articles recommending 50-60%
SOC and cool/cold but not freezing as the optimum storage condition
for maximised life.

Same here. That's also my recommended storage condition.

I see nothing at all wrong with this approach
*if* maximum life is the sole objective. If OTOH the user wants to be
able to pull the cell/battery out of storage and into service without
an intervening warm-up or recharge, maybe a higher SOC is warranted.
Like many things relating to Li-XX cells, it is a tradeoff.

Well, of course. I mentioned (twice) that one should let the battery
warm to room temperature before using. I don't know what will happen
if the battery is either charged or discharge at near freezing
temperatures, but it probably will not do anything useful.

The extra life obtained by reducing the EOC voltage is well documented
and well worth it in laptop applications BUT the end user doesn't get
to choose. The manufacturer is out to deliver (well, promise) the
maximum discharge runtime he can, and he doesn't give a rats how long
the pack lasts in service.

The user can set the Windoze low battery warning to trip at a much
higher level than the ridiculously low default value of 10%. That
will prevent excessive discharge.

I have a pack from an olde Acernote Lite 370 series dated 9637, so it
is just over 13 years old. It is stored with, but not *in*, the
machine. About once every year or so I pull that out and run it until
the machine shuts down, then recharge it to 100% (sic). It delivers
about 1.3 hours, compared to 2.5+ when new. That is stored at 100%
and room temperature (32S/116E).

The Acernote Light 370 was delivered with NiMH batteries, but later
LiIon batteries were made available.

Why do you discharge the battery before charging? As I understand it,
LiIon doesn't have a memory problem.

I also have several test packs of 18650 cells left over from a project
about five years ago when I designed a commercial Li-XX charger. They
were shelved at 4.20v and currently all are above 3.9v. I haven't
bothered to measure their storage capacity because I have no reason,
but I can assure you that they wouldn't show that sort of cell voltage
if they had lost 20% of original capacity per year.

Agreed. 3.92v is the highest voltage that a LiIon-Cobalt cells will
deliver. You did something right because my 6 month experiment showed
deterioration in both room temperature batteries.

--
Jeff Liebermann
150 Felker St #D http://www.LearnByDestroying.com
Santa Cruz CA 95060 http://802.11junk.com
Skype: JeffLiebermann AE6KS 831-336-2558

On Fri, 02 Oct 2009 23:22:02 -0700, Jeff Liebermann wrote:
On Fri, 02 Oct 2009 15:36:03 -0700, ess (Joe) wrote:

In article , Jeff Liebermann
wrote:

http://en.wikipedia.org/wiki/Lithium-ion_battery#Shelf_life
Store at about 50% charge in the coldest place you can find. Warm to
room temperatures before using.

Cool. Cold is better, but don't freeze. Optionally store in sealed
plastic bag to prevent condensation when removed from fridge.

"coldest place you can find" versus "don't freeze".
Which is it?

The coldest place you can find that doesn't freeze the battery. I
would think you could decode that from what I wrote. Freezing is 0C
so anything between that and somewhat below room temperature is a good
target.

only if the battery uses pure water as it's electrolyte.

On Sat, 03 Oct 2009 03:47:36 -0500, AZ Nomad
wrote:

On Fri, 02 Oct 2009 23:22:02 -0700, Jeff Liebermann wrote:
On Fri, 02 Oct 2009 15:36:03 -0700, ess (Joe) wrote:

In article , Jeff Liebermann
wrote:

http://en.wikipedia.org/wiki/Lithium-ion_battery#Shelf_life
Store at about 50% charge in the coldest place you can find. Warm to
room temperatures before using.

Cool. Cold is better, but don't freeze. Optionally store in sealed
plastic bag to prevent condensation when removed from fridge.

"coldest place you can find" versus "don't freeze".
Which is it?

The coldest place you can find that doesn't freeze the battery. I
would think you could decode that from what I wrote. Freezing is 0C
so anything between that and somewhat below room temperature is a good
target.

only if the battery uses pure water as it's electrolyte.

Sigh... I guess I have to do the necessary Google searching.

http://www.nationmaster.com/encyclopedia/Lithium-ion-battery%23External-links
Many authors suggest that freezing Li-ion batteries may be
detrimental. However, most Li-ion battery electrolytes freeze
at approximately -40 °C. Household freezers rarely reach below
-20°C. Published experiments demonstrate that freezing (even
below -40°C) is unharmful if the battery is fully warmed to room
temperature before use. More details are given in the book
"Characteristics and Behavior of 1M LiPF6 1EC:1DMC Electrolyte at
Low Temperatures" by L.M. Cristo, T. B. A****er, U.S. Army
Research, Fort Monmouth, NJ.

Seems that it's safe to put a Li-Ion battery in the freezer. However,
many web pages suggest the proper storage conditions are 0C to 20C at
40% charge. For example:
http://www.idxtek.com/pdf/tech_info/T-004.pdf (camera battery)

Incidentally, I just received ten RAZR cell phone batteries from a
vendor in China. All arrived charged to about 30-40%.


--
Jeff Liebermann
150 Felker St #D http://www.LearnByDestroying.com
Santa Cruz CA 95060 http://802.11junk.com
Skype: JeffLiebermann AE6KS 831-336-2558

On Sat, 03 Oct 2009 08:26:56 -0400, Meat Plow
wrote:

On Sat, 03 Oct 2009 00:10:54 -0700, Jeff Liebermann
wrote:

snip
No problem. However, I'll stand on the Wikipedia 20%/year loss at
100% charge at room temperature for commodity laptop batteries.

My Asus model MNB600's battery has lived at pretty much full charge
and at room and above temperature for 5 years with not a significant
loss of capacity. It still goes around 2.5 hours speed stepped down to
800 mhz and about 1 hour at full speed 1.8 ghz.

If the battery lived INSIDE your laptop, it's not at room temperature.
Laptops run hot.

One of my enrolled agent customers used IBM A31/A31p laptops as their
main computahs. The grand plan was to make it easy to take them on
interviews at clients homes, but that rarely happened. The batteries
were at 100% charge, inside a hot laptop, for 24x7x365. After 2.5
years, all the batteries were essentially dead with perhaps 10 minutes
runtime.

Rhetorical question:
Why don't UPS manufacturers use Li-Ion batteries?

--
Jeff Liebermann
150 Felker St #D http://www.LearnByDestroying.com
Santa Cruz CA 95060 http://802.11junk.com
Skype: JeffLiebermann AE6KS 831-336-2558

On Sat, 03 Oct 2009 05:47:19 -0700, Jeff Liebermann wrote:
On Sat, 03 Oct 2009 03:47:36 -0500, AZ Nomad
wrote:

On Fri, 02 Oct 2009 23:22:02 -0700, Jeff Liebermann wrote:
On Fri, 02 Oct 2009 15:36:03 -0700, ess (Joe) wrote:

In article , Jeff Liebermann
wrote:

http://en.wikipedia.org/wiki/Lithium-ion_battery#Shelf_life
Store at about 50% charge in the coldest place you can find. Warm to
room temperatures before using.

Cool. Cold is better, but don't freeze. Optionally store in sealed
plastic bag to prevent condensation when removed from fridge.

"coldest place you can find" versus "don't freeze".
Which is it?

The coldest place you can find that doesn't freeze the battery. I
would think you could decode that from what I wrote. Freezing is 0C
so anything between that and somewhat below room temperature is a good
target.

only if the battery uses pure water as it's electrolyte.

Sigh... I guess I have to do the necessary Google searching.

http://www.nationmaster.com/encyclopedia/Lithium-ion-battery%23External-links
Many authors suggest that freezing Li-ion batteries may be
detrimental. However, most Li-ion battery electrolytes freeze
at approximately -40 ?C. Household freezers rarely reach below

Thanks you for verifying that the phrase "freezing is 0C" was complete
bull****.

On Sat, 03 Oct 2009 10:25:53 -0400, Meat Plow
wrote:

"room and above temperature" The battery pack is on the front ledge it
does not get hot from the laptop but gets "above" room temperature.
Just how much "above room temperature" I don't know never measured it
but it's surly not warm to the touch as the rear end is where the fans
and heat sink are located.

Laptop monitor software to display battery temperature.
http://www.passmark.com/products/batmon.htm

It would be interesting if the protection circuit in the battery pack
also logged temperature. That would be sufficient to estimate battery
life and alert the user that the battery is too hot.

I've seen many including HP batteries go belly up in a short time.

Yep. Seen any Li-Ion battery chargers that have a settable EOC (end
of charge) adjustment? I haven't. One could program it to stop
charging at perhaps 80% of charge, and somewhat extend the life of
batteries that are in 7x24x365 laptops. Also useful for the spare
batteries that I carry in the bag. Left fully charged, they also tend
to die early.

Rhetorical question:
Why don't UPS manufacturers use Li-Ion batteries?

Aw, you're no fun...

Still waiting for fuel cell laptop batteries. Polyfuel died in
August. Ultracell is selling mostly to the military.
http://www.ultracellpower.com/sp.php?rugged
Most of the major Japanese manufacturers have announced and even
demonstrated products, but nothing I can buy, yet. Grumble...

--
Jeff Liebermann
150 Felker St #D http://www.LearnByDestroying.com
Santa Cruz CA 95060 http://802.11junk.com
Skype: JeffLiebermann AE6KS 831-336-2558

On Sat, 03 Oct 2009 00:10:54 -0700, Jeff Liebermann
wrote:

On Fri, 02 Oct 2009 14:03:46 +0800, who where wrote:

(snip)

If it is a laptop pack recent enough to care about, it will contain a
pack protection module which will preclude discharge beyond a LVCO
point, typically 3.0v, and will also preclude excessive discharge
current. Nothing unsafe about a DYI discharge on that pack.

True. The battery pack has enough electronics inside to protect
itself from excessive discharge. Under Windoze, one can set an alarm
and a shutdown point based on battery capacity. The default threshold
is about 10%. I've never tested this to determine if it works.
Presumably, if you don't want to run the battery down to below perhaps
25% capacity, setting a shutdown threshold below this point is wasted
effort. Similarly, if there's a protection threshold inside the
battery pack, it's certainly not labeled or easily determined.

The Windoze setting is purely for functionality - so the user can bail
before the pack pulls the plug and causes that "You didn't shut
Windoze down properly, so I'm doing a disc scan" screen on restart.

The pack protection modules we used were preset to open the series FET
switch at 3v0. If you look at the discharge curve of Li-Ions at
constant current (or with a constant load impedance) you will notice a
distinct droop below about (from memory here) 3v3. While cell
deterioration starts at/below 2v5 there is very little useful capacity
gained by proceeding below 3v0.

If it is a single cell from a cellphone or similar, different story.
these tend to have minimal inbuilt protection (if any) and rely
heavily on the host device for the customary protective functions.

Yep. Model airplanes and helicopters are even worse. All the
protection electronics is in the external battery charger. It
protects against fatal overcharge, but does nothing for excessive
discharge.

No protection means all bets are off.

Yep.

No need. I've seen numbers on these before, and Evgenij Barsukov has
posted comment on this previously in sci.chem.electrochem.battery.

(...)

I never suggested that everything you posted is wrong, far from it.
But several points were amiss and they attracted specific comment.

No problem. However, I'll stand on the Wikipedia 20%/year loss at
100% charge at room temperature for commodity laptop batteries. My
results were even worse. I'll concede that there are new chemistries
that offer substantial improvements in self-discharge and
self-deterioration, but I haven't seen any in laptops.

Cost. Commodity chemistries have been around for over a decade and
are cheaper than newer solutions that aren't into the same part of the
volume/cost curve yet. Remember that the laptop manufacturer
generally sees the battery pack as a non-warranted item (wear and
tear), and even when it IS warranted it only has to function for that
period without any capacity guarantee. So cheap is good for them.

I have seen numerous manufacturer-derived articles recommending 50-60%
SOC and cool/cold but not freezing as the optimum storage condition
for maximised life.

Same here. That's also my recommended storage condition.

I see nothing at all wrong with this approach
*if* maximum life is the sole objective. If OTOH the user wants to be
able to pull the cell/battery out of storage and into service without
an intervening warm-up or recharge, maybe a higher SOC is warranted.
Like many things relating to Li-XX cells, it is a tradeoff.

Well, of course. I mentioned (twice) that one should let the battery
warm to room temperature before using. I don't know what will happen
if the battery is either charged or discharge at near freezing
temperatures, but it probably will not do anything useful.

The extra life obtained by reducing the EOC voltage is well documented
and well worth it in laptop applications BUT the end user doesn't get
to choose. The manufacturer is out to deliver (well, promise) the
maximum discharge runtime he can, and he doesn't give a rats how long
the pack lasts in service.

The user can set the Windoze low battery warning to trip at a much
higher level than the ridiculously low default value of 10%. That
will prevent excessive discharge.

Yes (see earlier) but I was referring to end-of-charge setpoint.

I have a pack from an olde Acernote Lite 370 series dated 9637, so it
is just over 13 years old. It is stored with, but not *in*, the
machine. About once every year or so I pull that out and run it until
the machine shuts down, then recharge it to 100% (sic). It delivers
about 1.3 hours, compared to 2.5+ when new. That is stored at 100%
and room temperature (32S/116E).

The Acernote Light 370 was delivered with NiMH batteries, but later
LiIon batteries were made available.

Yep, I have both here (two 370's) and the NiMH is thoroughly rooted.


Why do you discharge the battery before charging? As I understand it,
LiIon doesn't have a memory problem.

It doesn't, but the only way I can sensibly evaluate it's usable
capacity is by measuring runtime.

I also have several test packs of 18650 cells left over from a project
about five years ago when I designed a commercial Li-XX charger. They
were shelved at 4.20v and currently all are above 3.9v. I haven't
bothered to measure their storage capacity because I have no reason,
but I can assure you that they wouldn't show that sort of cell voltage
if they had lost 20% of original capacity per year.

Agreed. 3.92v is the highest voltage that a LiIon-Cobalt cells will
deliver. You did something right because my 6 month experiment showed
deterioration in both room temperature batteries.

These are cheap (Chinese) 18650 commodity cells which my client
imports. Far from special. To evaluate the prototype charger I set
the EOC to 4v20 and did cyclical testing on packs of 1/2/3/4 cells.
There were some interesting points to emerge from this, but somewhat
O/T for this thread.

On Sat, 03 Oct 2009 06:35:31 -0700, Jeff Liebermann
wrote:

Rhetorical question:
Why don't UPS manufacturers use Li-Ion batteries?

Not-so-rhetorical answer: Cost. SLA's are cheaper commodities and
also require less attention (cost) to safety aspects. Weight and
kJ/kg don't matter in a UPS.

Rhetorical question: Why don't UPS manufacturers use a decent
charging circuit in their SLA-backed UPS's?

On Sat, 03 Oct 2009 10:27:21 -0700, Jeff Liebermann
wrote:

Yep. Seen any Li-Ion battery chargers that have a settable EOC (end
of charge) adjustment? I haven't.

Yes, the design I did allowed selection of 4v10 and 4v20 EOC.

(Technically it isn't the EOC point, rather the transition from CC to
CV charging. True end-of-charge is generally triggered when the
charge current at constant voltage tapers off to a predetermined
figure like 10% of the CC rate. But it does set the final charged
state and voltage).

One could program it to stop
charging at perhaps 80% of charge, and somewhat extend the life of
batteries that are in 7x24x365 laptops. Also useful for the spare
batteries that I carry in the bag. Left fully charged, they also tend
to die early.

That was one reason for the selection to be available. Unfortunately
(as I mentioned earlier) laptop manufacturers have one objective -
maximum runtime for minimum cost.

who where wrote:

That was one reason for the selection to be available. Unfortunately
(as I mentioned earlier) laptop manufacturers have one objective -
maximum runtime for minimum cost.

And weight. If cost and reliability were more important, they would use
nickle metal hydride cells. The cells are almost indestructable, easy to
charge, have no reputation of early failure or catching fire, and so on.
They can be reconditioned by draining them completely, which they actually
seem to do well with unlike any of the lithium cells.

Somewhere along the way, people decided that expensive lithium cells were
"in" and nickle metal hydride cells were for flashlights and $10 MP3 players.

This is IMHO one of the great failings of portable device design in this
century. What surprises me is that no one has picked up on this in the
"climate change" crowd, lithium cells use rarer materials and are much more
dangerous to the environment if dumped in the trash, which is where most of
them end up. (or worse, a recylce heap in China.)

Geoff.

--
Geoffrey S. Mendelson, Jerusalem, Israel N3OWJ/4X1GM

Why don't UPS manufacturers use a decent
charging circuit in their SLA-backed UPS's?

What are the differences between decent and indecent charging circuits?

On Sun, 4 Oct 2009 06:24:04 +0000 (UTC), "Geoffrey S. Mendelson"
wrote:

who where wrote:

That was one reason for the selection to be available. Unfortunately
(as I mentioned earlier) laptop manufacturers have one objective -
maximum runtime for minimum cost.

And weight. If cost and reliability were more important, they would use
nickle metal hydride cells. The cells are almost indestructable, easy to
charge, have no reputation of early failure or catching fire, and so on.
They can be reconditioned by draining them completely, which they actually
seem to do well with unlike any of the lithium cells.

and invariably a much higher self-discharge rate, although more
recently this has improved a lot (although *after* Li-Ion gained
widespread acceptance).

Somewhere along the way, people decided that expensive lithium cells were
"in" and nickle metal hydride cells were for flashlights and $10 MP3 players.

Weight and volumetric superiority were the main attractions,
particularly for cellphones. You could fit about twenty of my Nokia
GSM phone's pack inside the NiXX pack for my old Motorola analog flip.

This is IMHO one of the great failings of portable device design in this
century. What surprises me is that no one has picked up on this in the
"climate change" crowd, lithium cells use rarer materials and are much more
dangerous to the environment if dumped in the trash, which is where most of
them end up. (or worse, a recylce heap in China.)

which is the *same* as dumped in the trash :-(

Don't get me started on CFL's ...

On Sun, 4 Oct 2009 04:58:52 -0700, "William Sommerwerck"
wrote:

Why don't UPS manufacturers use a decent
charging circuit in their SLA-backed UPS's?

What are the differences between decent and indecent charging circuits?

Quite simple really.

Decent ones recharge the SLA's with a sensible regime that supports
longevity while providing a reasonable recovery after disharge.

Indecent ones overcharge the SLA's and fsck them.

who where wrote:

Somewhere along the way, people decided that expensive lithium cells were
"in" and nickle metal hydride cells were for flashlights and $10 MP3 players.

Weight and volumetric superiority were the main attractions,
particularly for cellphones. You could fit about twenty of my Nokia
GSM phone's pack inside the NiXX pack for my old Motorola analog flip.


That's not really fair. My Motorola flip used 6 volts, and needed about 1 amp
to transmit while you were speaking. It used the AMPS system which was basicly
FM radio.

It also needed 50ma on standby.

My current cellphone (a really cheap Alcatel GSM) has a 450ma 3.6 volt battery.

In Nimh terms that would be 3 cells each 1/2 AAA size. Not much bigger or
heavier, if at all then the lithium battery in it. It would also be ok to run
it down to zero, and with the new cells last a year without discharging
(or about a week in the phone, even with it off), and go through 1,000 cycles
before dying.

As for relative size, you could put 5 or 6 of the Alcatel phones in the
1600mah pack for the flip. I actually had a lithium battery for it, it was the
size of the 600mah nicad, but held 1000mah. Cost around $100.

Geoff.
--
Geoffrey S. Mendelson, Jerusalem, Israel N3OWJ/4X1GM

On Sun, 04 Oct 2009 11:07:27 +0800, who where wrote:

On Sat, 03 Oct 2009 10:27:21 -0700, Jeff Liebermann
wrote:

Yep. Seen any Li-Ion battery chargers that have a settable EOC (end
of charge) adjustment? I haven't.

Yes, the design I did allowed selection of 4v10 and 4v20 EOC.

User selectable? That sure would be nice. If so, that's the first
charger I've seen that offers any manner of early EOC control by the
user. Sometimes, it's internally selectable by a jumper, pot, or
component selection. However, I've never seen it user accessible much
less properly documented.

(Technically it isn't the EOC point, rather the transition from CC to
CV charging. True end-of-charge is generally triggered when the
charge current at constant voltage tapers off to a predetermined
figure like 10% of the CC rate. But it does set the final charged
state and voltage).

I think (not sure) that simply disabling the CV part of the charge
cycle would be sufficient to stop charging at about 80% of full
charge.

One could program it to stop
charging at perhaps 80% of charge, and somewhat extend the life of
batteries that are in 7x24x365 laptops. Also useful for the spare
batteries that I carry in the bag. Left fully charged, they also tend
to die early.

That was one reason for the selection to be available. Unfortunately
(as I mentioned earlier) laptop manufacturers have one objective -
maximum runtime for minimum cost.

Yep. The math for calculating how far down a Li-Ion battery pack is
discharged is fairly simple if I make a number of assumptions. Load
can be estimated by removing the battery, and running the laptop
solely on the charger. Measure the charger current while using as
much power as possible (full LCD backlight, run a DVD movie, no CPU
slowdown). It's usually fairly close to the current rating of the
charger. If you're lazy (like me), just use the charger current spec.

Estimating the average load and duty cycle is not easy. I use 10% of
maximum, which is probably wrong for many applications and users, but
is a fair starting point. I'm also ignoring charger efficiency which
I assume is fairly high.

Using a handy IBM Thinkpad R40 as an example, the charger is rated at:
16v 4.5A. 16v * 4.5A = 72 watts.
Using my 20% duty cycle guess, we have an average load of 14.4 watts.

The battery is rated at 14.4v 4000ma-hrs or:
14.4 * 4A-Hr = 57.6 watt-hrs.

So, if we fully charge the battery, and run it to depletion, we can
theoretically have:
57.6 watt-hrs / 14.4 watts = 4 hrs.
My R40 typically will run about 2 hrs which is down to perhaps 50% of
full charge. I should probably do the same calculation with one of
the new Netbook computers, which is more sensitive to battery
selection but are also conveniently rated in hours of operating time.

Most of the vendors use MobileMark 2007 ($400) software for
determining their battery run time under a controlled work load:
http://www.bapco.com/products/mobilemark2007/index.php
See
http://www.bapco.com/support/technical_documents/Mobilemark2007_Whitepaper.pdf
Section 2.5 and 4.4 have battery run time criteria which is rated down
to 7% of battery capacity. Little wonder they get inflated run time
numbers.

Note:
Run time = how long the laptop or battery will run.
Life time = how long the battery will last before replacement.

--
Jeff Liebermann
150 Felker St #D http://www.LearnByDestroying.com
Santa Cruz CA 95060 http://802.11junk.com
Skype: JeffLiebermann AE6KS 831-336-2558

On Sun, 04 Oct 2009 11:27:07 -0400, Meat Plow
wrote:

Laptop monitor software to display battery temperature.
http://www.passmark.com/products/batmon.htm

Interesting.

The point is that it is possible to monitor the operating temperature
of the battery and then offer suggestions on how to prolong the
battery life based on the measurements. It's also possible to predict
imminent battery failure with this information. However, in our
consumption based society, such things are rarely supplied.

Rhetorical question:
Why don't UPS manufacturers use Li-Ion batteries?

UPS's spend much of their life with fully charged batteries. They
also tend to run rather warm inside. This combination is not
compatible with Li-Ion batteries, which die prematurely when run hot
and fully charged. If run like a typical UPS (which is almost never
run), it would make a great battery killer. The reduction in weight
and hazardous substances might be beneficial for some applications,
but there's little demand for lightweight or non-toxic backup power.
One might do better using capacitors instead of a battery.

Still waiting for fuel cell laptop batteries. Polyfuel died in
August. Ultracell is selling mostly to the military.
http://www.ultracellpower.com/sp.php?rugged
Most of the major Japanese manufacturers have announced and even
demonstrated products, but nothing I can buy, yet. Grumble...

I have a lead acid jumpstart pack boasting a 900 amp (heh) surge and a
200 watt inverter. Never used it in that configuration but I would
assume several hours of usage would not be out of reason.

Huh? I was pitching fuel cell (methanol) power systems, not lead
acid. Read what I wroth. Pour your booze into the fuel cell and get
enough power to run your computah for a few hours.

Also, it's not "surge". It's probably "xxxxx cranking amps" or some
such contrived measurment designed to avoid specifying standardized
amp-hr battery capacity. Pick one:
http://en.wikipedia.org/wiki/Car_battery#Terms_and_ratings


--
Jeff Liebermann
150 Felker St #D http://www.LearnByDestroying.com
Santa Cruz CA 95060 http://802.11junk.com
Skype: JeffLiebermann AE6KS 831-336-2558

On Sun, 04 Oct 2009 11:02:14 +0800, who where wrote:

Rhetorical question: Why don't UPS manufacturers use a decent
charging circuit in their SLA-backed UPS's?

Many years ago, I accused APC of intentionally setting the charger in
some models to prematurely destroy batteries and create hazardous
conditions (bulging, leaky, and overheating batteries). Specifically,
the early APC 1400RH 4ru model was the major culprit.
http://www.LearnByDestroying.com/pics/home/apc1400.jpg
It has 4ea 12V 7A gel cells in a series-parallel derangement. We had
about 35 of these installed at various installations, all of which
rapidly ate batteries. Eventually, these UPS's were removed when it
was found that the batteries had bulged and leaked so much that
extraction was impossible. I ended up with most of them and tried
redesign the charging circuit. APC was totally uncooperative. I
don't want to go into the details, but eventually APC released a
totally new 1400RH model, with a slightly improved charging circuit.

During this adventure in frustration, I learned a few things about UPS
charging philosophy. The customers want the batteries to recover as
fast as possible after being run for a while. That's because power
outages tend to come in clusters, like during a storm. Fast recharge
is an important requirement. Given the choice of long battery life
and fast recharge, most customers will choose fast recharge. More to
the extreme, when faced with the possibility of killing the battery
just to get it charged quickly, most customers will accept the cost of
a new battery pack rather than risk any additional server downtime.

So, rather than a modern staged charging system, that tapers off near
the EOC, and is intentionally easy on the battery, the typical UPS
battery charger is designed to get as close to 100% of charge as
quickly as possible and never mind going into overcharge. That
results in dramatic changes in EOC threshold with aging batteries,
connector losses, manufacturing variations, etc. Basically, you can
have long battery life, or fast recharge, but not both.

My current guess(tm) is that UPS charging circuits are designed first
for fast charge and secondarily for maintaining as close to 100%
charge as possible. Both of these are detrimental to long battery
life, so the charging is selected for a "reasonable" battery life of
about 3 years (depending on model).

Some of my previous rants on the subject:
http://groups.google.com/group/sci.electronics.repair/msg/e99a0f155fc198c0
http://groups.google.com/group/sci.electronics.repair/browse_thread/thread/cf5ea1e3f3a01d4f/

--
Jeff Liebermann
150 Felker St #D http://www.LearnByDestroying.com
Santa Cruz CA 95060 http://802.11junk.com
Skype: JeffLiebermann AE6KS 831-336-2558

On Sun, 04 Oct 2009 10:09:19 -0700, Jeff Liebermann
wrote:

On Sun, 04 Oct 2009 11:07:27 +0800, who where wrote:

On Sat, 03 Oct 2009 10:27:21 -0700, Jeff Liebermann
wrote:

Yep. Seen any Li-Ion battery chargers that have a settable EOC (end
of charge) adjustment? I haven't.

Yes, the design I did allowed selection of 4v10 and 4v20 EOC.

User selectable? That sure would be nice. If so, that's the first
charger I've seen that offers any manner of early EOC control by the
user. Sometimes, it's internally selectable by a jumper, pot, or
component selection. However, I've never seen it user accessible much
less properly documented.

Ah, I didn't say external ;-) It was an on-board jumper selection,
so the user would need to crack the case. This charger was for
"commercial/industrial" users and supplied as a companion device to
their custom 1/2/3/4-cell packs. T'was documented for the vendor so
he could set it to best suit the end-user application.

(Technically it isn't the EOC point, rather the transition from CC to
CV charging. True end-of-charge is generally triggered when the
charge current at constant voltage tapers off to a predetermined
figure like 10% of the CC rate. But it does set the final charged
state and voltage).

I think (not sure) that simply disabling the CV part of the charge
cycle would be sufficient to stop charging at about 80% of full
charge.

(Checks project report ...) On my 18650 testing, transition occurred
at ~59% when charging at 0.55C. Asthere is obviously a finite ohmic
impedance characteristic, transition would occur later at lower rates.

One could program it to stop
charging at perhaps 80% of charge, and somewhat extend the life of
batteries that are in 7x24x365 laptops. Also useful for the spare
batteries that I carry in the bag. Left fully charged, they also tend
to die early.

That was one reason for the selection to be available. Unfortunately
(as I mentioned earlier) laptop manufacturers have one objective -
maximum runtime for minimum cost.

Yep. The math for calculating how far down a Li-Ion battery pack is
discharged is fairly simple if I make a number of assumptions.

(snip)

Estimating SOC is a *lot* easier, trivial linear calculation. From
fully charged (and preferably "rested"), discharge until the PACK
shuts off the pooter. Observe run time. Deicde what % you want left
in your pack, repeat above and terminate when that proportion of the
full runtime remains.

On Sun, 04 Oct 2009 10:59:04 +0800, who where wrote:

The Windoze setting is purely for functionality - so the user can bail
before the pack pulls the plug and causes that "You didn't shut
Windoze down properly, so I'm doing a disc scan" screen on restart.

That only happens with FAT and FAT32. NTFS has a journaling
filesystem:
http://en.wikipedia.org/wiki/USN_Journal
which does not require a fsck if the user or battery protection
circuit suddenly pulls the plug.

Incidentally, no kudos to Western Dismal for selling their Passport
series of USB drives with FAT32, thus insuring that pulling the plug
will trash some recently written data. I reformat or use Windoze
"convert.exe" all of these to switch to NTFS.

The pack protection modules we used were preset to open the series FET
switch at 3v0. If you look at the discharge curve of Li-Ions at
constant current (or with a constant load impedance) you will notice a
distinct droop below about (from memory here) 3v3. While cell
deterioration starts at/below 2v5 there is very little useful capacity
gained by proceeding below 3v0.

Well yes.... any storage device, with a low internal series resistance
will exhibit a fairly flat discharge curve followed by an abrupt
droop. See the first graph at:
http://www.mpoweruk.com/performance.htm
The problem is that the sharp knee is somewhere between 5% and as
little as 1% of capacity. To prevent running the battery into the
ground (and possibly reverse polarizing some of the cells when
connected in series), the dropout point is as close to the beginning
of the droop as possible. That's fine for a new battery, but as the
battery ages, the same threshold slowly moves up the charge curve as
the terminal voltage decreases. I don't think any of the SOC chip
vendors compensate for this.

No problem. However, I'll stand on the Wikipedia 20%/year loss at
100% charge at room temperature for commodity laptop batteries. My
results were even worse. I'll concede that there are new chemistries
that offer substantial improvements in self-discharge and
self-deterioration, but I haven't seen any in laptops.

Cost. Commodity chemistries have been around for over a decade and
are cheaper than newer solutions that aren't into the same part of the
volume/cost curve yet.

Agreed. It does take time for new technology to decrease in price.
However, there little incrimental benefits to switching to a superior
chemistry or technology. For a few percentage points increase in
performance, the exponential increase in cost makes it a bad
investment. Mediocrity tends to be permanent until a new mass market
can be found, or until some external influence (environment, scarcity
of materials, hazards, safety, etc) demands a replacement. Methinks
we'll be seeing the commodity Li-Ion battery, with its 20% capacity
loss per year, for quite some time.

Remember that the laptop manufacturer
generally sees the battery pack as a non-warranted item (wear and
tear), and even when it IS warranted it only has to function for that
period without any capacity guarantee. So cheap is good for them.

Generally true but there are exceptions. The Sony manufactured
batteries full of metal shavings that would catch fire with little
provocation was covered under various warranties. I had 4 laptop
batteries (out of maybe 200) replaced under this warranty. However,
for general use, you're correct. There is no battery warranty. About
10 years ago, I received 4ea Compaq Presario 1620 series laptops, each
with a spare battery. Most of the batteries died within 5 months
including the ones that were left in the original packaging and not
used until tested. Compaq (pre-HP) declared this to be "normal
battery life" and refused to do anything. 3rd party Li-Ion battery
packs were somewhat better and lasted about a year. We switch to the
older NiMH batteries, which were half the price, and lasted 3 years.
Your horror stories may vary.

The user can set the Windoze low battery warning to trip at a much
higher level than the ridiculously low default value of 10%. That
will prevent excessive discharge.

Yes (see earlier) but I was referring to end-of-charge setpoint.

Ok, got it. Still, the Windoze low battery warning feature is quite
useful. I have mine set to warn me at 40% and shut down at 25%. Too
soon to tell if this will extend the life of the battery pack.

Incidentally, some interesting reading on SOC (state-o-charge)
technology:
http://www.mpoweruk.com/soc.htm

--
Jeff Liebermann
150 Felker St #D http://www.LearnByDestroying.com
Santa Cruz CA 95060 http://802.11junk.com
Skype: JeffLiebermann AE6KS 831-336-2558

On Sun, 04 Oct 2009 10:46:55 -0700, Jeff Liebermann
wrote:

On Sun, 04 Oct 2009 11:02:14 +0800, who where wrote:

Rhetorical question: Why don't UPS manufacturers use a decent
charging circuit in their SLA-backed UPS's?

Many years ago, I accused APC of intentionally setting the charger in
some models to prematurely destroy batteries and create hazardous
conditions (bulging, leaky, and overheating batteries). Specifically,
the early APC 1400RH 4ru model was the major culprit.
http://www.LearnByDestroying.com/pics/home/apc1400.jpg
It has 4ea 12V 7A gel cells in a series-parallel derangement. We had
about 35 of these installed at various installations, all of which
rapidly ate batteries. Eventually, these UPS's were removed when it
was found that the batteries had bulged and leaked so much that
extraction was impossible. I ended up with most of them and tried
redesign the charging circuit. APC was totally uncooperative. I
don't want to go into the details, but eventually APC released a
totally new 1400RH model, with a slightly improved charging circuit.

During this adventure in frustration, I learned a few things about UPS
charging philosophy. The customers want the batteries to recover as
fast as possible after being run for a while. That's because power
outages tend to come in clusters, like during a storm. Fast recharge
is an important requirement. Given the choice of long battery life
and fast recharge, most customers will choose fast recharge. More to
the extreme, when faced with the possibility of killing the battery
just to get it charged quickly, most customers will accept the cost of
a new battery pack rather than risk any additional server downtime.

I suspect there's a bit of assumption in there. Most consumers of
"small/desktop/soho" UPS don't have the slightest clue how they work
or what goes on with them. The manufacturer makes assumptions on the
buyer's behalf, but obviously slanted towards the manufacturer's ends.
I have found UPS owners who maintain that they had to have failed
units refurbed by the mnaufacturer.

So, rather than a modern staged charging system, that tapers off near
the EOC, and is intentionally easy on the battery, the typical UPS
battery charger is designed to get as close to 100% of charge as
quickly as possible and never mind going into overcharge. That
results in dramatic changes in EOC threshold with aging batteries,
connector losses, manufacturing variations, etc. Basically, you can
have long battery life, or fast recharge, but not both.

You can achieve a *reasonable* compromise if a bit of effort is spent
on charger design. SLA's are best fed with a current-limited constant
voltage regime. Bulk charge recovery is achieved under the CL phase,
and setting the limit high to achieve fast replenishment isn't of
itself a battery-killer. BUT once the reasonable SOC has been
achieved and even before transition occurs, the CV fgure should be
reduced. And float voltage should similarly be reduced in recognition
that the average UPS spends say an hour a year (max) on discharge.
They don't need to be kept at 100%. They *should* be kept at a
sustainable (aka survivable) float condition, and if that loses
capacity the user needs then the user should have bought a better
sized unit.

None of this is news to you of course.

As an aside, I have equipped a several torches here with 6V 4Ah SLA's
in place of the original dry cell (4F?) pack (and changed to a 6V
krypton lamp). These are recharged as required using the Unitrode/TI
UC3906, to whose charge regime I continually refer people when they
enquire about care and feeding of SLA's. The current batch of SLA's
are over 10 years old.

My current guess(tm) is that UPS charging circuits are designed first
for fast charge and secondarily for maintaining as close to 100%
charge as possible. Both of these are detrimental to long battery
life

Yep.

so the charging is selected for a "reasonable" battery life of
about 3 years (depending on model).

IMOE there you are being kind to the UPS makers.

I've also experienced the drama of extracting dried/cracked/swollen
SLA's from their enclosures. Just like laptop manufacturers, UPS
makers are guilty of self-serving design without regard for the
downstream cost to the end user.

Some of my previous rants on the subject:
http://groups.google.com/group/sci.electronics.repair/msg/e99a0f155fc198c0
http://groups.google.com/group/sci.electronics.repair/browse_thread/thread/cf5ea1e3f3a01d4f/

On Mon, 05 Oct 2009 10:17:21 +0800, who where wrote:

Ah, I didn't say external ;-) It was an on-board jumper selection,
so the user would need to crack the case.

Grumble. That's what I want on my chargers. Actually, what I want is
complete control over just about every parameter involved in charging,
but would create its own collection of problems. The market for such
things is probably fairly small.

This charger was for
"commercial/industrial" users and supplied as a companion device to
their custom 1/2/3/4-cell packs. T'was documented for the vendor so
he could set it to best suit the end-user application.

I'll bet that the vendor does NOT supply this information to the
customer. Like I previously mumbled, I haven't seen any Li-Ion
chargers that give the customer any EOC control.

I think (not sure) that simply disabling the CV part of the charge
cycle would be sufficient to stop charging at about 80% of full
charge.

(Checks project report ...) On my 18650 testing, transition occurred
at ~59% when charging at 0.55C. Asthere is obviously a finite ohmic
impedance characteristic, transition would occur later at lower rates.

Ok, bad guess on my part. Maybe estimating the time needed for a CV
charge to get to 100%, and cut it in half to get 80%.

Yep. The math for calculating how far down a Li-Ion battery pack is
discharged is fairly simple if I make a number of assumptions.

(snip)

Estimating SOC is a *lot* easier, trivial linear calculation.

I wasn't looking for the SOC. That can be done by counting coulombs
(amps and seconds). What I was calculating was the run time of the
computer until the battery pack gives up. That's the mysterious
specification offered my many laptop vendors that reeks of science
fiction and cooked data. The number of variables involved in an exact
calculation is sufficiently high that most vendors will simply use an
empirical number, rounded up to the nearest integer.

From
fully charged (and preferably "rested"), discharge until the PACK
shuts off the pooter. Observe run time. Deicde what % you want left
in your pack, repeat above and terminate when that proportion of the
full runtime remains.

No problem except you don't specify what the computer is doing while
discharging the battery. There's a huge difference between sitting at
standby keeping the dynamic RAM alive, and beating up the CPU with
compressed video, spinning DVD drive, and full brightness
backlighting. It's as bad as the spec for the number of pages a laser
printer toner cartridge will deliver.


--
Jeff Liebermann
150 Felker St #D http://www.LearnByDestroying.com
Santa Cruz CA 95060 http://802.11junk.com
Skype: JeffLiebermann AE6KS 831-336-2558

On Sun, 04 Oct 2009 19:48:53 -0700, Jeff Liebermann
wrote:

On Mon, 05 Oct 2009 10:17:21 +0800, who where wrote:

Ah, I didn't say external ;-) It was an on-board jumper selection,
so the user would need to crack the case.

Grumble. That's what I want on my chargers. Actually, what I want is
complete control over just about every parameter involved in charging,
but would create its own collection of problems. The market for such
things is probably fairly small.

Indeed. You'd want one (or two), I'd keep a couple, a few more into
the s.e.d types, and probably a dozen for the rest_of_world.

It was a jumper on pin headers, extending it to the front panel would
be a snap.

The controller I used was the MAX1737. You get a certain amount of
flexibility designing around it, and we (the client and I) preferred
their regime to the others we considered.

This charger was for
"commercial/industrial" users and supplied as a companion device to
their custom 1/2/3/4-cell packs. T'was documented for the vendor so
he could set it to best suit the end-user application.

I'll bet that the vendor does NOT supply this information to the
customer. Like I previously mumbled, I haven't seen any Li-Ion
chargers that give the customer any EOC control.

The selection was vendor-made based on the end user's stated role, and
was selected in_conjunction_with pack sizing. Any time the role
looked like prolonged high SOC and temperatures above 30C, he'd go
with 4v10 and the pack size would then be determined. He didn't want
premature failures, unlike laptop makers who don't give a rats.

I think (not sure) that simply disabling the CV part of the charge
cycle would be sufficient to stop charging at about 80% of full
charge.

(Checks project report ...) On my 18650 testing, transition occurred
at ~59% when charging at 0.55C. Asthere is obviously a finite ohmic
impedance characteristic, transition would occur later at lower rates.

Ok, bad guess on my part. Maybe estimating the time needed for a CV
charge to get to 100%, and cut it in half to get 80%.

It's linear - CC - in CL mode.

Yep. The math for calculating how far down a Li-Ion battery pack is
discharged is fairly simple if I make a number of assumptions.

(snip)

Estimating SOC is a *lot* easier, trivial linear calculation.

I wasn't looking for the SOC. That can be done by counting coulombs
(amps and seconds). What I was calculating was the run time of the
computer until the battery pack gives up. That's the mysterious
specification offered my many laptop vendors that reeks of science
fiction and cooked data. The number of variables involved in an exact
calculation is sufficiently high that most vendors will simply use an
empirical number, rounded up to the nearest integer.

From
fully charged (and preferably "rested"), discharge until the PACK
shuts off the pooter. Observe run time. Deicde what % you want left
in your pack, repeat above and terminate when that proportion of the
full runtime remains.

No problem except you don't specify what the computer is doing while
discharging the battery. There's a huge difference between sitting at
standby keeping the dynamic RAM alive, and beating up the CPU with
compressed video, spinning DVD drive, and full brightness
backlighting. It's as bad as the spec for the number of pages a laser
printer toner cartridge will deliver.

Maybe I missed your objective. I understood it to be determining when
to stop discharge (in the laptop) to achieve a chosen SOC. Any time
you are playing with discharge the laptop activity is fundamental, but
for a known target SOC it isn't hard to invoke a known task (eg screen
saver) and do the linear maths.

On Sun, 04 Oct 2009 19:35:03 -0700, Jeff Liebermann
wrote:

On Sun, 04 Oct 2009 10:59:04 +0800, who where wrote:
The pack protection modules we used were preset to open the series FET
switch at 3v0. If you look at the discharge curve of Li-Ions at
constant current (or with a constant load impedance) you will notice a
distinct droop below about (from memory here) 3v3. While cell
deterioration starts at/below 2v5 there is very little useful capacity
gained by proceeding below 3v0.

Well yes.... any storage device, with a low internal series resistance
will exhibit a fairly flat discharge curve followed by an abrupt
droop. See the first graph at:
http://www.mpoweruk.com/performance.htm
The problem is that the sharp knee is somewhere between 5% and as
little as 1% of capacity.

It wasn't a sharp drop that we saw. More of a curve than a cliff.

To prevent running the battery into the
ground (and possibly reverse polarizing some of the cells when
connected in series), the dropout point is as close to the beginning
of the droop as possible. That's fine for a new battery, but as the
battery ages, the same threshold slowly moves up the charge curve as
the terminal voltage decreases. I don't think any of the SOC chip
vendors compensate for this.

I'm not aware of any that do. But with the (IIRC) Mitsumi chips we
used, there was less need than with say nickel chemistries. The
module monitored cell voltage differences, and would prevent operation
if the differences exceeded a preset threshold value. With EOD set at
3v0 (average cell), there is no way any cell would get near to 2v5.

No problem. However, I'll stand on the Wikipedia 20%/year loss at
100% charge at room temperature for commodity laptop batteries. My
results were even worse. I'll concede that there are new chemistries
that offer substantial improvements in self-discharge and
self-deterioration, but I haven't seen any in laptops.

Cost. Commodity chemistries have been around for over a decade and
are cheaper than newer solutions that aren't into the same part of the
volume/cost curve yet.

Agreed. It does take time for new technology to decrease in price.
However, there little incrimental benefits to switching to a superior
chemistry or technology. For a few percentage points increase in
performance, the exponential increase in cost makes it a bad
investment. Mediocrity tends to be permanent until a new mass market
can be found, or until some external influence (environment, scarcity
of materials, hazards, safety, etc) demands a replacement. Methinks
we'll be seeing the commodity Li-Ion battery, with its 20% capacity
loss per year, for quite some time.

just like the corner of the engine bay on automobiles still features
lead-acid ....

Remember that the laptop manufacturer
generally sees the battery pack as a non-warranted item (wear and
tear), and even when it IS warranted it only has to function for that
period without any capacity guarantee. So cheap is good for them.

Generally true but there are exceptions. The Sony manufactured
batteries full of metal shavings that would catch fire with little
provocation was covered under various warranties. I had 4 laptop
batteries (out of maybe 200) replaced under this warranty.

That's an identified manufacturing fault, totally different from a
wear-and-tear situation.

However,
for general use, you're correct. There is no battery warranty. About
10 years ago, I received 4ea Compaq Presario 1620 series laptops, each
with a spare battery. Most of the batteries died within 5 months
including the ones that were left in the original packaging and not
used until tested. Compaq (pre-HP) declared this to be "normal
battery life" and refused to do anything. 3rd party Li-Ion battery
packs were somewhat better and lasted about a year. We switch to the
older NiMH batteries, which were half the price, and lasted 3 years.
Your horror stories may vary.

The user can set the Windoze low battery warning to trip at a much
higher level than the ridiculously low default value of 10%. That
will prevent excessive discharge.

Yes (see earlier) but I was referring to end-of-charge setpoint.

Ok, got it. Still, the Windoze low battery warning feature is quite
useful. I have mine set to warn me at 40% and shut down at 25%. Too
soon to tell if this will extend the life of the battery pack.

Incidentally, some interesting reading on SOC (state-o-charge)
technology:
http://www.mpoweruk.com/soc.htm

On Mon, 05 Oct 2009 16:45:09 +0800, who where wrote:

It was a jumper on pin headers, extending it to the front panel would
be a snap.

I was thinking more of something with a built in ethernet or USB port.
All the charge parameters can be setup on a web page. Once one has a
suitable processor, adding features such as battery history, battery
test, counterfeit detection, run time calculation, and fire detection
are mostly software. I'm half way inspired to design and build one
for myself but suspect that I can't make much money on it at consumer
price levels.

The controller I used was the MAX1737.
http://www.maxim-ic.com/quick_view2.cfm/qv_pk/2217
You get a certain amount of
flexibility designing around it, and we (the client and I) preferred
their regime to the others we considered.

Ok, but that's pure analog. Analog is not a problem but it does limit
what weird things can be done with a Li-Ion charger. I was thinking
more in the way of a digital (i.e. PIC controller) design, such as:
http://www.microchip.com/stellent/idcplg?IdcService=SS_GET_PAGE&nodeId=1406&dDocName =en024090
http://ww1.microchip.com/downloads/en/DeviceDoc/51515a.pdf
and increasing the output current capabilities to run larger battery
packs. For example, when the battery pack is in the charger and
allegedly fully charged, it would be fairly easy to apply a load and
discharge it for perhaps a minute or more. The asymptote of the
terminal voltage curve can be extrapolated to produce an estimated
runtime. Some of the remote battery management systems already do
this quite accurately. One could also include some RAM and add a data
logger and coulomb counter (amp-seconds). The area under the current
curve is the charging and discharging energy. This would give a good
clue as the battery packs comparative quality (something that I
suspect the manufacturers would not be interested in supplying).

The selection was vendor-made based on the end user's stated role, and
was selected in_conjunction_with pack sizing. Any time the role
looked like prolonged high SOC and temperatures above 30C, he'd go
with 4v10 and the pack size would then be determined. He didn't want
premature failures, unlike laptop makers who don't give a rats.

Good plan. However, there's always going to be the customer that
plugs in a new battery pack, runs it as long as possible, and then
proclaims that they're not getting the specified run time.

Maybe I missed your objective. I understood it to be determining when
to stop discharge (in the laptop) to achieve a chosen SOC. Any time
you are playing with discharge the laptop activity is fundamental, but
for a known target SOC it isn't hard to invoke a known task (eg screen
saver) and do the linear maths.

It was to see how close to a full charge was being used and where the
battery droop detection was set. That's measured in coulombs
(watt-seconds) or run time (hours). I have a Kill-a-Watt meter that
measures power consumption from the 117VAC line. I run the laptop
only from the charger, with the battery removed, for about 30 minutes
(the limit of my attention span), doing what I consider to a typical
applications mix. The Kill-a-Watt meter records the watt-seconds
(actually watt-hrs) used. It also compensates for power factor. I
throw in the switcher efficiency of about 85-90%:
http://www.energystar.gov/index.cfm?c=ext_power_supplies.power_supplies_cons umers
and calculate the energy consumption per hour of use. I use that as
the average load for run time calculations.

--
Jeff Liebermann
150 Felker St #D http://www.LearnByDestroying.com
Santa Cruz CA 95060 http://802.11junk.com
Skype: JeffLiebermann AE6KS 831-336-2558

On Mon, 05 Oct 2009 16:57:03 +0800, who where wrote:

Well yes.... any storage device, with a low internal series resistance
will exhibit a fairly flat discharge curve followed by an abrupt
droop. See the first graph at:
http://www.mpoweruk.com/performance.htm
The problem is that the sharp knee is somewhere between 5% and as
little as 1% of capacity.

It wasn't a sharp drop that we saw. More of a curve than a cliff.

Sorry. I shouldn't have said "abrupt". It does tend to dribble off
with a rather soft knee. Also, if you have several mixed cells in
series, of different ages, the knee will appear at different points in
the discharge curve for each cell. The knee will also be less
defined. (A good reason not to mix different age cells).

To prevent running the battery into the
ground (and possibly reverse polarizing some of the cells when
connected in series), the dropout point is as close to the beginning
of the droop as possible. That's fine for a new battery, but as the
battery ages, the same threshold slowly moves up the charge curve as
the terminal voltage decreases. I don't think any of the SOC chip
vendors compensate for this.

I'm not aware of any that do.

AN AGING MODEL FOR LITHIUM-ION CELLS
http://etd.ohiolink.edu/send-pdf.cgi/Hartmann%20Richard%20Lee%20II.pdf?acc_num=akron122 6887071
Warning: 278 page of a grad student's dissertation.
Skipping to Chapter VI - Conclusions, where it says:
A direct correlation was found between the cell capacity and
the open-circuit voltage of a fully discharged cell. Cell
resistance increased at a linear rate throughout the life
of the cells.

But with the (IIRC) Mitsumi chips we
used, there was less need than with say nickel chemistries. The
module monitored cell voltage differences, and would prevent operation
if the differences exceeded a preset threshold value. With EOD set at
3v0 (average cell), there is no way any cell would get near to 2v5.

The circuit doesn't monitor individual cells. I would think that one
cell with a bad case of premature aging might cause problems. I'm
beginning to think that I'm worrying over a non-problem. Never mind.

--
Jeff Liebermann
150 Felker St #D http://www.LearnByDestroying.com
Santa Cruz CA 95060 http://802.11junk.com
Skype: JeffLiebermann AE6KS 831-336-2558

On Mon, 05 Oct 2009 09:09:13 -0700, Jeff Liebermann
wrote:

On Mon, 05 Oct 2009 16:45:09 +0800, who where wrote:

It was a jumper on pin headers, extending it to the front panel would
be a snap.

I was thinking more of something with a built in ethernet or USB port.
All the charge parameters can be setup on a web page. Once one has a
suitable processor, adding features such as battery history, battery
test, counterfeit detection, run time calculation, and fire detection
are mostly software. I'm half way inspired to design and build one
for myself but suspect that I can't make much money on it at consumer
price levels.

The controller I used was the MAX1737.
http://www.maxim-ic.com/quick_view2.cfm/qv_pk/2217
You get a certain amount of
flexibility designing around it, and we (the client and I) preferred
their regime to the others we considered.

Ok, but that's pure analog. Analog is not a problem but it does limit
what weird things can be done with a Li-Ion charger.

The brief was "KISS". The end-users were real industrial users, and
quite disinclined to fiddle of even treat the pack and charger as
other than a black box.

I was thinking
more in the way of a digital (i.e. PIC controller) design, such as:
http://www.microchip.com/stellent/idcplg?IdcService=SS_GET_PAGE&nodeId=1406&dDocName =en024090
http://ww1.microchip.com/downloads/en/DeviceDoc/51515a.pdf
and increasing the output current capabilities to run larger battery
packs. For example, when the battery pack is in the charger and
allegedly fully charged, it would be fairly easy to apply a load and
discharge it for perhaps a minute or more. The asymptote of the
terminal voltage curve can be extrapolated to produce an estimated
runtime. Some of the remote battery management systems already do
this quite accurately. One could also include some RAM and add a data
logger and coulomb counter (amp-seconds). The area under the current
curve is the charging and discharging energy. This would give a good
clue as the battery packs comparative quality (something that I
suspect the manufacturers would not be interested in supplying).

The selection was vendor-made based on the end user's stated role, and
was selected in_conjunction_with pack sizing. Any time the role
looked like prolonged high SOC and temperatures above 30C, he'd go
with 4v10 and the pack size would then be determined. He didn't want
premature failures, unlike laptop makers who don't give a rats.

Good plan. However, there's always going to be the customer that
plugs in a new battery pack, runs it as long as possible, and then
proclaims that they're not getting the specified run time.

If they weren't getting the specified run time, it would be the result
of improper sizing (vendor fault or user-supplied misinformation), or
faulty pack or charger (vendor responsibility). Easily resolved.

Recall that the pack size was chosen AFTER the CV limit was
determined.

Maybe I missed your objective. I understood it to be determining when
to stop discharge (in the laptop) to achieve a chosen SOC. Any time
you are playing with discharge the laptop activity is fundamental, but
for a known target SOC it isn't hard to invoke a known task (eg screen
saver) and do the linear maths.

It was to see how close to a full charge was being used and where the
battery droop detection was set. That's measured in coulombs
(watt-seconds) or run time (hours). I have a Kill-a-Watt meter that
measures power consumption from the 117VAC line. I run the laptop
only from the charger, with the battery removed, for about 30 minutes
(the limit of my attention span), doing what I consider to a typical
applications mix. The Kill-a-Watt meter records the watt-seconds
(actually watt-hrs) used. It also compensates for power factor. I
throw in the switcher efficiency of about 85-90%:
http://www.energystar.gov/index.cfm?c=ext_power_supplies.power_supplies_cons umers
and calculate the energy consumption per hour of use. I use that as
the average load for run time calculations.

The problem with those meters is that - being cheap/chinese - they
tend to poorly handle the line current "blips" into a rectifier. And
even if they returned true RMS, that doesn't itself reflect the actual
power drawn in those circuits.

On Mon, 05 Oct 2009 09:35:49 -0700, Jeff Liebermann
wrote:

On Mon, 05 Oct 2009 16:57:03 +0800, who where wrote:

Well yes.... any storage device, with a low internal series resistance
will exhibit a fairly flat discharge curve followed by an abrupt
droop. See the first graph at:
http://www.mpoweruk.com/performance.htm
The problem is that the sharp knee is somewhere between 5% and as
little as 1% of capacity.

It wasn't a sharp drop that we saw. More of a curve than a cliff.

Sorry. I shouldn't have said "abrupt". It does tend to dribble off
with a rather soft knee. Also, if you have several mixed cells in
series, of different ages, the knee will appear at different points in
the discharge curve for each cell. The knee will also be less
defined. (A good reason not to mix different age cells).

All the more reason to use a pack protection module that monitors (and
responds to) cell voltage differences.

To prevent running the battery into the
ground (and possibly reverse polarizing some of the cells when
connected in series), the dropout point is as close to the beginning
of the droop as possible. That's fine for a new battery, but as the
battery ages, the same threshold slowly moves up the charge curve as
the terminal voltage decreases. I don't think any of the SOC chip
vendors compensate for this.

I'm not aware of any that do.

AN AGING MODEL FOR LITHIUM-ION CELLS
http://etd.ohiolink.edu/send-pdf.cgi/Hartmann%20Richard%20Lee%20II.pdf?acc_num=akron122 6887071
Warning: 278 page of a grad student's dissertation.
Skipping to Chapter VI - Conclusions, where it says:
A direct correlation was found between the cell capacity and
the open-circuit voltage of a fully discharged cell. Cell
resistance increased at a linear rate throughout the life
of the cells.

Without reading his/her dissertation, I'm not sure what (s)he's
measuring. What does (s)he define as a fully discharged cell, and how
does (s)he achieve that state?

But with the (IIRC) Mitsumi chips we
used, there was less need than with say nickel chemistries. The
module monitored cell voltage differences, and would prevent operation
if the differences exceeded a preset threshold value. With EOD set at
3v0 (average cell), there is no way any cell would get near to 2v5.

The circuit doesn't monitor individual cells.

The modules we used certainly did. There was a connection to each
series connection node. (And in assembly the connections had to be
made in the correct order.)

I would think that one
cell with a bad case of premature aging might cause problems.

That is exactly what the module preempted.

I'm
beginning to think that I'm worrying over a non-problem. Never mind.

On Tue, 06 Oct 2009 11:33:22 +0800, who where wrote:

AN AGING MODEL FOR LITHIUM-ION CELLS
http://etd.ohiolink.edu/send-pdf.cgi/Hartmann%20Richard%20Lee%20II.pdf?acc_num=akron122 6887071
Warning: 278 page of a grad student's dissertation.
Skipping to Chapter VI - Conclusions, where it says:
A direct correlation was found between the cell capacity and
the open-circuit voltage of a fully discharged cell. Cell
resistance increased at a linear rate throughout the life
of the cells.

Without reading his/her dissertation, I'm not sure what (s)he's
measuring. What does (s)he define as a fully discharged cell, and how
does (s)he achieve that state?

See Pg 24 (section 2.2.2). He lists 3 methods along with their
limitations. I think (not sure) he's using coulomb counting
(amp-hrs). Section 2.2.3 follows with capacity measurement, which is
necessary to calculate the SOC. There's too much to quote. However,
you wanted the discharge point, and that's not covered directly. He
hints at:
For lead acid and lithium-ion batteries, the relationship
between the stabilized open circuit voltage, Eocs, and the
SOC is approximately linear (Wang & Stuart, 2002).
which implies that he uses 100% SOC as one point and extrapolates a
linear plot to zero SOC somewhere on the knee of the curve. However,
he also notes that it's temperature dependent, has hysteresis, and
requires substantial time to stabilize the terminal voltage. Unless I
missed something, he doesn't really specify how to measure the knee.

I won't pretend to understand all of it, especially since I'm buried
in work tonight and am having problems with (paying) distractions.
Maybe tomorrow.

The circuit doesn't monitor individual cells.

The modules we used certainly did. There was a connection to each
series connection node. (And in assembly the connections had to be
made in the correct order.)

OK, I'm impressed(1). That's the way battery packs should be built
and monitored. However, why stop at monitoring individual cells? I
prototyped NiCad and NiMH battery packs where each cell was also
charged individually. It's (fairly) well known that you can charge
these cells at almost any rate, as long as they're under 100% SOC. Go
over even slightly, and the cell gets very hot, very quickly. I've
built simulated chargers to do this and was able to charge NiCads
successfully at up to 20C (20 times rated capacity) to about 95% SOC.
Incidentally, the failures were rather impressive, including 2 small
fires, which might explain why such fast charging is not commercially
acceptable. I'm tempted to try the same tests with Li-Ion, but have
not been sufficiently inspired or bribed to do so.

(1) Note: I'm not easily impressed.

--
# Jeff Liebermann 150 Felker St #D Santa Cruz CA 95060
# 831-336-2558
# http://802.11junk.com
# http://www.LearnByDestroying.com AE6KS

On Tue, 06 Oct 2009 11:26:50 +0800, who where wrote:

The brief was "KISS".

KISS is often a euphemism for "cheap".

The end-users were real industrial users, and
quite disinclined to fiddle of even treat the pack and charger as
other than a black box.

True. There are probably some safety issues involved. It would not
do to have the customer twiddle the charging characteristics and
potentially turn the battery pack into a incendiary or explosive
device.

If they weren't getting the specified run time, it would be the result
of improper sizing (vendor fault or user-supplied misinformation), or
faulty pack or charger (vendor responsibility). Easily resolved.

Nope. There's also the possibility of creative testing. The
applications mix used for testing battery life by MobileMark 2007:
http://www.bapco.com/products/mobilemark2007/index.php
has a huge effect on measured battery life. However, there's nothing
standard about the selection of test apps, which could easily be
tweaked by the equipment vendor. I'm starting to see this with
Netbooks, where fairly long battery run times are predicted, but
rarely demonstrated. I had an Acer Aspire One (9" screen) and
currently an Asus 700. Neither has come close to the rated run time
when I use them normally at a local coffee shop.

Recall that the pack size was chosen AFTER the CV limit was
determined.

Good. That covers the vendor in case anyone actually tests for the
claimed capacity or run time.

Just thinking about it, there's enough info here to build a table or
graph of the calculated battery life versus run time terminating at
different EOC's. As you note, the closer to depletion I run the
battery pack, the shorter the battery life (measured in charge
cycles).

... The Kill-a-Watt meter records the watt-seconds
(actually watt-hrs) used. It also compensates for power factor. I
throw in the switcher efficiency of about 85-90%:
http://www.energystar.gov/index.cfm?c=ext_power_supplies.power_supplies_cons umers
and calculate the energy consumption per hour of use. I use that as
the average load for run time calculations.

The problem with those meters is that - being cheap/chinese - they
tend to poorly handle the line current "blips" into a rectifier. And
even if they returned true RMS, that doesn't itself reflect the actual
power drawn in those circuits.

Well, yes. The frequency and transient response of these meters is
rather lousy. My guess(tm) is that it has to be about 10 times lower
than the 50/60Hz it's trying to measure. That would put it at about
5Hz (200msec), which is not all that horrible. Also, the filter caps
in the typical laptop will smooth out most transient current spikes so
that the meter never sees the spikes. I don't have a power line
impairment tester to check this, but can probably trace out the
schematic to see how it works. Here's the patent with block diagram
and description:
http://www.google.com/patents?id=G3MDAAAAEBAJ&dq=6095850

The top photo is the inside of the older 4 button version. The lower
photo is the current 5 button version:
http://802.11junk.com/jeffl/pics/drivel/slides/kill-a-watt.html

Litigatory trivia:
http://greenpatentblog.com/2008/12/24/smartlabs-enjoined-parties-smart-management-focuses-issues-in-energy-meter-litigation/

--
# Jeff Liebermann 150 Felker St #D Santa Cruz CA 95060
# 831-336-2558
# http://802.11junk.com
# http://www.LearnByDestroying.com AE6KS

On Mon, 05 Oct 2009 22:53:17 -0700, Jeff Liebermann
wrote:

On Tue, 06 Oct 2009 11:26:50 +0800, who where wrote:

The brief was "KISS".

KISS is often a euphemism for "cheap".

The end-users were real industrial users, and
quite disinclined to fiddle of even treat the pack and charger as
other than a black box.

True. There are probably some safety issues involved. It would not
do to have the customer twiddle the charging characteristics and
potentially turn the battery pack into a incendiary or explosive
device.

If they weren't getting the specified run time, it would be the result
of improper sizing (vendor fault or user-supplied misinformation), or
faulty pack or charger (vendor responsibility). Easily resolved.

Nope. There's also the possibility of creative testing. The
applications mix used for testing battery life by MobileMark 2007:
http://www.bapco.com/products/mobilemark2007/index.php
has a huge effect on measured battery life. However, there's nothing
standard about the selection of test apps, which could easily be
tweaked by the equipment vendor. I'm starting to see this with
Netbooks, where fairly long battery run times are predicted, but
rarely demonstrated. I had an Acer Aspire One (9" screen) and
currently an Asus 700. Neither has come close to the rated run time
when I use them normally at a local coffee shop.

Remember these are industrial applications, NOT pooters.

Recall that the pack size was chosen AFTER the CV limit was
determined.

Good. That covers the vendor in case anyone actually tests for the
claimed capacity or run time.

Just thinking about it, there's enough info here to build a table or
graph of the calculated battery life versus run time terminating at
different EOC's. As you note, the closer to depletion I run the
battery pack, the shorter the battery life (measured in charge
cycles).

Whoa, where did I say that? IMOE there is no discharge end impact on
cycle life.

(snip rest)