What is the proper way to charge these cells. I have a number of AA's
that are all weak. I have tried charging them at a constant rate of
about .050A overnight and they seem to come up and they will work but
don't last very long. Can these be charged manually as you would Nicads
or is there a special trick to this? Thanks, Lenny Stein, Barlen
Electronics.

wrote:

What is the proper way to charge these cells. I have a number of AA's
that are all weak. I have tried charging them at a constant rate of
about .050A overnight and they seem to come up and they will work but
don't last very long. Can these be charged manually as you would Nicads
or is there a special trick to this? Thanks, Lenny Stein, Barlen
Electronics.

Hi Lenny...

Respectfully suggest that that's because you aren't charging them,
you're just teasing them a little

Unless 50 mills is a mis-type, that is.

If you really have to charge them manually, then read the capacity
(current "normal" is 2500 mah) and charge them 10 percent (250 mils
in this case) for 14 hours.

Or better, buy yourself a nimh charger. If the budget is a concern,
then Walmart has an Eveready "dumb" charger that comes with two
AA's, all for only a little under 10 dollars (cdn).

If the budget isn't of concern, then there are "smart" chargers
available that will on an individual cell basis pre-determine the
state of charge, charge them to 100% quickly, and then leave them on
trickle (about your 50 mil rate) until you remove them.


Take care.

Ken

In article .com, " wrote:
What is the proper way to charge these cells. I have a number of AA's
that are all weak. I have tried charging them at a constant rate of
about .050A overnight and they seem to come up and they will work but
don't last very long. Can these be charged manually as you would Nicads
or is there a special trick to this? Thanks, Lenny Stein, Barlen
Electronics.


I kinda wish someone would write up the best ideas that work about various
batterys and charging methods, and methods to test each
for quality. In working with NIMH, I have yet to gather enough
information to really evaluate them properly.
I have some that seem to shut down prematurly powering a digital camera.
I think its just one cell acting up or something like that sometimes. I always wanted to build
a charger, like one charging position for each cell. I never liked charging them
in series or parallel. Each one should be individually handled.

greg

In article ,
(GregS) wrote:

In article .com,
" wrote:
What is the proper way to charge these cells. I have a number of AA's
that are all weak. I have tried charging them at a constant rate of
about .050A overnight and they seem to come up and they will work but
don't last very long. Can these be charged manually as you would Nicads
or is there a special trick to this? Thanks, Lenny Stein, Barlen
Electronics.


I kinda wish someone would write up the best ideas that work about various
batterys and charging methods, and methods to test each
for quality. In working with NIMH, I have yet to gather enough
information to really evaluate them properly.
I have some that seem to shut down prematurly powering a digital camera.
I think its just one cell acting up or something like that sometimes. I
always wanted to build
a charger, like one charging position for each cell. I never liked charging
them
in series or parallel. Each one should be individually handled.

greg


The Ansmann Energy 16 will handle up to 12 AA cells treating each
individually. It has a function that will automatically renew old cells
that seem to be failing. It will do that by its refresh mode. Any cell
that needs this will not effect the state of charge or the charge time
of any other cell.

--
To reply no_ HPMarketing Corp.

"GregS" wrote in message
...
In article .com,
" wrote:
What is the proper way to charge these cells. I have a number of AA's
that are all weak. I have tried charging them at a constant rate of
about .050A overnight and they seem to come up and they will work but
don't last very long. Can these be charged manually as you would Nicads
or is there a special trick to this? Thanks, Lenny Stein, Barlen
Electronics.


I kinda wish someone would write up the best ideas that work about various
batterys and charging methods, and methods to test each
for quality. In working with NIMH, I have yet to gather enough
information to really evaluate them properly.
I have some that seem to shut down prematurly powering a digital camera.
I think its just one cell acting up or something like that sometimes. I
always wanted to build
a charger, like one charging position for each cell. I never liked
charging them
in series or parallel. Each one should be individually handled.

greg


So far it seems Maha makes chargers that do a pretty good job. They have a
couple that are said to rejuvenate cells - - the MH-C204F and the MH-401FS.
I bought the more expensive MH-401FS because it charges and monitors each
cell individually, and can be set for either 2 hr or 5 hr rate. So far, my
NiMH AA cells are performing well in regular use in a 3-watt Luxeon
flashlight that pulls about an amp out of a pair of Energizer 2300 mAh cells

Chuck.

"GregS" wrote in message
...
In article .com,
" wrote:
What is the proper way to charge these cells. I have a number of AA's
that are all weak. I have tried charging them at a constant rate of
about .050A overnight and they seem to come up and they will work but
don't last very long. Can these be charged manually as you would Nicads
or is there a special trick to this? Thanks, Lenny Stein, Barlen
Electronics.


I kinda wish someone would write up the best ideas that work about various
batterys and charging methods, and methods to test each
for quality. In working with NIMH, I have yet to gather enough
information to really evaluate them properly.
I have some that seem to shut down prematurly powering a digital camera.
I think its just one cell acting up or something like that sometimes. I
always wanted to build
a charger, like one charging position for each cell. I never liked
charging them
in series or parallel. Each one should be individually handled.

I agree. When a set of four is brand new they usually all charge in the same
time, but as they age it seems that one or two cells in the set will become
different from the others and will take much longer to charge. When that
happens I don't see how two different cells can be charged properly if
they're on the same circuit. That's why I like the Maha C401FS chargers that
have individual circuits for each cell. I also have a couple of the older
Maha C204Fs which reviewers all raved about, but because they charge cells
in pairs I now use them only occasionally for the conditioning feature.

N.

"Chuck Olson" wrote in message
...

[ . . . ]

So far it seems Maha makes chargers that do a pretty good job. They have a
couple that are said to rejuvenate cells - - the MH-C204F and the
MH-401FS.

Well, the C204F can condition cells by automatically deep-cycling them. The
C401FS does not have this feature.


I bought the more expensive MH-401FS because it charges and monitors each
cell individually, and can be set for either 2 hr or 5 hr rate.

Yes, the C401FS is my favorite charger too. While it's not cheap, I doubt
it's possible to get as good a charger at a better price. Absolutely, having
a separate circuit for each cell is a good idea, and I appreciate the
fast/slow charge switch too. Normally I use the slow rate because the cells
stay cooler, but it's often handy to have the faster rate available when I
need 'em in a hurry.

N.

Nostrobino wrote:
"GregS" wrote in message
...

In article .com,
" wrote:

What is the proper way to charge these cells. I have a number of AA's
that are all weak. I have tried charging them at a constant rate of
about .050A overnight and they seem to come up and they will work but
don't last very long. Can these be charged manually as you would Nicads
or is there a special trick to this? Thanks, Lenny Stein, Barlen
Electronics.


I kinda wish someone would write up the best ideas that work about various
batterys and charging methods, and methods to test each
for quality. In working with NIMH, I have yet to gather enough
information to really evaluate them properly.
I have some that seem to shut down prematurly powering a digital camera.
I think its just one cell acting up or something like that sometimes. I
always wanted to build
a charger, like one charging position for each cell. I never liked
charging them
in series or parallel. Each one should be individually handled.


I agree. When a set of four is brand new they usually all charge in the same
time, but as they age it seems that one or two cells in the set will become
different from the others and will take much longer to charge. When that
happens I don't see how two different cells can be charged properly if
they're on the same circuit. That's why I like the Maha C401FS chargers that
have individual circuits for each cell. I also have a couple of the older
Maha C204Fs which reviewers all raved about, but because they charge cells
in pairs I now use them only occasionally for the conditioning feature.

N.


Yeah, I've got several devices which take *three* AA's...makes it kind
of difficult to charge them, when my charger only does two at a time....

jak

"jakdedert" wrote in message
...
[ . . . ]
Yeah, I've got several devices which take *three* AA's...makes it kind of
difficult to charge them, when my charger only does two at a time....

Yes, I'll bet. I don't think I've ever had anything that took three AA
cells.

N.

Nostrobino wrote:
"jakdedert" wrote...
Yeah, I've got several devices which take *three* AA's...makes it kind of
difficult to charge them, when my charger only does two at a time....

Yes, I'll bet. I don't think I've ever had anything that took three AA
cells.

All four of my FRS radios take three AA cells each. I've seen (but wouldn't
own) flashlights that take three AAs.

--
If John McCain gets the 2008 Republican Presidential nomination,
my vote for President will be a write-in for Jiang Zemin.

Nostrobino wrote:
"jakdedert" wrote in message
...
[ . . . ]

Yeah, I've got several devices which take *three* AA's...makes it kind of
difficult to charge them, when my charger only does two at a time....


Yes, I'll bet. I don't think I've ever had anything that took three AA
cells.

N.


At least half a dozen Motorola FRS radios and an LED flashlight, for
starters....

jak

On Sat, 24 Sep 2005 16:17:28 -0500, clifto wrote:

All four of my FRS radios take three AA cells each. I've seen
(but wouldn't own) flashlights that take three AAs.

Then you're missing out on a good thing. I have a small light
that uses a high intensity Luxeon LED powered by 3 AAA cells. It's
noticably brighter than 2D cell flashlights using krypton bulbs.
The light pattern is better too, although as with most LED lights,
there's no focusing.

ASAAR wrote:
On Sat, 24 Sep 2005 16:17:28 -0500, clifto wrote:
All four of my FRS radios take three AA cells each. I've seen
(but wouldn't own) flashlights that take three AAs.

Then you're missing out on a good thing. I have a small light
that uses a high intensity Luxeon LED powered by 3 AAA cells. It's
noticably brighter than 2D cell flashlights using krypton bulbs.
The light pattern is better too, although as with most LED lights,
there's no focusing.

My good LED flashlights take either two or four AA's. One of the "fours"
has seven white LEDs, a decent if not pinpoint pattern, and turned out
to be intrinsically safe in the bargain. (At least it's marked so; I
haven't turned on the gas to experiment.

Not having seen the Luxeon or any other LED lights with three cells,
I was referring to some old-style krypton-bulb three-AA flashlights
that just weren't worth the effort of carrying.

--
If John McCain gets the 2008 Republican Presidential nomination,
my vote for President will be a write-in for Jiang Zemin.

clifto wrote:
ASAAR wrote:

On Sat, 24 Sep 2005 16:17:28 -0500, clifto wrote:

All four of my FRS radios take three AA cells each. I've seen
(but wouldn't own) flashlights that take three AAs.

Then you're missing out on a good thing. I have a small light
that uses a high intensity Luxeon LED powered by 3 AAA cells. It's
noticably brighter than 2D cell flashlights using krypton bulbs.
The light pattern is better too, although as with most LED lights,
there's no focusing.


My good LED flashlights take either two or four AA's. One of the "fours"
has seven white LEDs, a decent if not pinpoint pattern, and turned out
to be intrinsically safe in the bargain. (At least it's marked so; I
haven't turned on the gas to experiment.

Not having seen the Luxeon or any other LED lights with three cells,
I was referring to some old-style krypton-bulb three-AA flashlights
that just weren't worth the effort of carrying.

I believe I stated specifically an LED flashlight. It was one of the
first ones available, from C. Crane. There are much better ones sold
nowadays; but until this one dies, I'm keepin' it. I get 50 hours from
a fresh set of alkaline AA's, and it will stay lit for an additional
*100* hours at reduced brightness. I usually use discarded RF
microphone batteries in it, but occasionally grab a set of NiMH's out of
the charger if I've no mic culls around at the moment.

jak

What is the group's opinion of the chargers that Radio Shack sells at
this time?

And for that matter their batteries also.

Thanks

TMT

On 25 Sep 2005 13:42:18 -0700, Too_Many_Tools wrote:

What is the group's opinion of the chargers that Radio Shack sells
at this time?

Several years ago when there were very few smart chargers
available from any sources, their "timer" chargers were fair to
good. They had one large smart charger that handled AAA through D
cells, but it was a dud. I found that when it finished charging,
the cells were only about 1/3 charged. I attempted to exchange it
but found that that model had been pulled from all of the stores.
As of early this year the only smart charger I've seen in any of the
local stores is a tiny little thing, probably not high on too many
lists because it's a fairly slow charger. But it has some nice
features. It appears to have 4 independent charging circuits (but
there's no easy way for me to verify this because it has only a
single LED indicator). It charges up to 4 AA or AAA cells, NiCad or
NiMH. Its best feature is that unlike my other finicky smart
chargers that too readily refuse to charge what they consider to be
marginal batteries, this one hasn't given up on any yet. And the
batteries that the other chargers refuse to charge still have most
of their original capacity and perform very well in everything I've
put them in, except for the other "smart" chargers. This little
charger, BTW, is the only one that isn't on the shelves with all of
the other chargers. It's stored with the battery powered toy racing
cars, with an Xmods logo. It sells for about $24, but comes with 8
of Radio Shack's standard AAA NiMH cells. Even though I have more
AAA batteries than I can use, I might get another of these chargers
because what they do, they do well, and if RS stops selling them I
doubt that I'll be able to find any other similar chargers.


And for that matter their batteries also.

Their NiMH batteries are green, and have been for far too long.
They're good batteries, but unless they were recently changed, still
have the same modest 1800 or 850 mah capacity that they've had for
several years. If you are considering getting their NiCads, watch
out, as they have two types. One is OK, but the other has a
capacity and weight that's only about 1/2 of the better type.

Thanks for the response.

I am a bit surprised that the market has not had better offerings.
While I do not regularly follow this market (and that is why I ask the
advice from those more knowledgable), I was under the impression that
NiMH had been out for awhile and that I assumed that manufacturers had
developed offerings to fill the market need...apparently not to the
extent I had assumed.

Could one determine if a charger is doing a cell individually by
charging only one cell at a time?

I also note that Radio Shack has an overnight charger and a fast
charger that does AA through D sizes. Is there an advantage in having a
slower charging rate? In other words, are the "fast charging" NiHM
batteries have a problem that the slower charging batteries don't?

TMT

On 25 Sep 2005 13:42:18 -0700, "Too_Many_Tools"
wrote:

What is the group's opinion of the chargers that Radio Shack sells at
this time?

And for that matter their batteries also.

Thanks

TMT

When it comes to rechargeable batteries and chargers, I've found that
this site offers a good selection, and decent prices.

Note: I am in no way connected to this site, its owner, or anything;
just thought it might be helpful to any who are looking for
rechargeables or chargers.

http://www.thomas-distributing.com/index.htm


73 de Bill, KB8EB

Thanks for the lead.

While we are on the subject, what is the shelf life of NiMH batteries
if they are left in their original containers?

If one buys a package and puts it on the shelf for let's say five
years, will the battery work as if you had charged it when you first
bought it?

I had also forgotten to ask...is there a FAQ for NiMH batteries?

Thanks

TMT

"Too_Many_Tools" wrote in message
oups.com...
I also note that Radio Shack has an overnight charger and a fast
charger that does AA through D sizes. Is there an advantage in having a
slower charging rate? In other words, are the "fast charging" NiHM
batteries have a problem that the slower charging batteries don't?

Theoretically speaking, slow charging will give more recharge cycles before
the cell is worn out. However, with a decent delta-v charger doing fast
charging, it's less of an issue these days. In the past, fast charging cells
using the timer method was brutal and could often result in overheating and
overcharging.

Dave

"Too_Many_Tools" wrote in message
oups.com...
What is the group's opinion of the chargers that Radio Shack sells at
this time?

And for that matter their batteries also.

Thanks

TMT


Here's a very good place to get the latest on chargers and batteries
http://candlepowerforums.com/vb/forumdisplay.php?f=9

Chuck

Thanks for the lead.

TMT

What does a smart charger do when compared to just charging NIMH cells
at ten percent of their capacity, (as I do nicads now) ? What are the
characteristics of the charge cycle with the different types of
chargers and can a circuit to do this be built to handle batteries of
different voltages and capacities? Lenny,.

"Too_Many_Tools" wrote in message
ups.com...
Thanks for the lead.

While we are on the subject, what is the shelf life of NiMH batteries
if they are left in their original containers?

If one buys a package and puts it on the shelf for let's say five
years, will the battery work as if you had charged it when you first
bought it?


Theoretically, yes. In practice, it's possible for them to deteriorate.

Dave

On 26 Sep 2005 14:56:38 -0700, "
wrote:

What does a smart charger do when compared to just charging NIMH cells
at ten percent of their capacity, (as I do nicads now) ?

you mean 10% under their max. capacity ? How do you
define/test/measure those 10% ?
IIRC and per specs. one needs an 120% capacity charge to have a cell
fully charged

What are the
characteristics of the charge cycle with the different types of
chargers and can a circuit to do this be built to handle batteries of
different voltages and capacities? Lenny,.

it detects the -dV/dt notch that occurs when batteries are fully
charged .. I think Maxim (sp?) has a number of IC's that can be used
to build a home made charger with such characteristics .. it may be
worth the effort for the fun of building I don't think it will save
you a dime compared to commercially available units ..
FWIW

"imbsysop" wrote in message
news
On 26 Sep 2005 14:56:38 -0700, "
wrote:

What does a smart charger do when compared to just charging NIMH cells
at ten percent of their capacity, (as I do nicads now) ?

you mean 10% under their max. capacity ? How do you
define/test/measure those 10% ?
IIRC and per specs. one needs an 120% capacity charge to have a cell
fully charged

He said charging *at* ten percent of capacity, e.g. charging 2000mAh cells
at 200mA. That's the long-established rate for standard (as opposed to fast)
charging of such cells, I believe.

N.

On Tue, 27 Sep 2005 09:01:23 -0400, "Nostrobino"
wrote:


"imbsysop" wrote in message
news
On 26 Sep 2005 14:56:38 -0700, "
wrote:

What does a smart charger do when compared to just charging NIMH cells
at ten percent of their capacity, (as I do nicads now) ?

you mean 10% under their max. capacity ? How do you
define/test/measure those 10% ?
IIRC and per specs. one needs an 120% capacity charge to have a cell
fully charged

He said charging *at* ten percent of capacity, e.g. charging 2000mAh cells
at 200mA. That's the long-established rate for standard (as opposed to fast)
charging of such cells, I believe.

sorry for my bad reading .. :-)

caveat of that method is that it is time controlled and one never
knows the discharge state of the batteries when charging starts so the
"timer run" for "full" is impossible to define .. with a -dV/dt
charger nothing to worry about anymore. have been using one for 4
years now and my NiMh's still feel like brand new ..
FWIW

imbsysop wrote:

snip

you mean 10% under their max. capacity ? How do you
define/test/measure those 10% ?
IIRC and per specs. one needs an 120% capacity charge to have a cell
fully charged

Hi...

Suspect that you'll find that 120% isn't sufficient. You'll need
about 140%

Ken

"imbsysop" wrote in message
...
On Tue, 27 Sep 2005 09:01:23 -0400, "Nostrobino"
wrote:


"imbsysop" wrote in message
news
On 26 Sep 2005 14:56:38 -0700, "
wrote:

What does a smart charger do when compared to just charging NIMH cells
at ten percent of their capacity, (as I do nicads now) ?

you mean 10% under their max. capacity ? How do you
define/test/measure those 10% ?
IIRC and per specs. one needs an 120% capacity charge to have a cell
fully charged

He said charging *at* ten percent of capacity, e.g. charging 2000mAh cells
at 200mA. That's the long-established rate for standard (as opposed to
fast)
charging of such cells, I believe.

sorry for my bad reading .. :-)

caveat of that method is that it is time controlled and one never
knows the discharge state of the batteries when charging starts so the
"timer run" for "full" is impossible to define ..

Yes, good point.


with a -dV/dt
charger nothing to worry about anymore. have been using one for 4
years now and my NiMh's still feel like brand new ..
FWIW

You're way ahead of me on this and I'm afraid I don't know what -dV/dt
means. Is that something related or similar to the "FLEX negative pulse"
charging that Maha advertises (which is also Greek to me)?

N.

On Tue, 27 Sep 2005 13:13:19 GMT, Ken Weitzel
wrote:



imbsysop wrote:

snip

you mean 10% under their max. capacity ? How do you
define/test/measure those 10% ?
IIRC and per specs. one needs an 120% capacity charge to have a cell
fully charged

Hi...

Suspect that you'll find that 120% isn't sufficient. You'll need
about 140%

well I was just reporting a "general" statement .. I know that it
should be 140% as charger manufacturers as well as charger IC
manufacturers use an 1.4 loss factor when charging so they actually
dimension their chargers for an 140% overcharge :-)

On Tue, 27 Sep 2005 09:32:02 -0400, "Nostrobino"
wrote:


"imbsysop" wrote in message
.. .
On Tue, 27 Sep 2005 09:01:23 -0400, "Nostrobino"
wrote:


with a -dV/dt
charger nothing to worry about anymore. have been using one for 4
years now and my NiMh's still feel like brand new ..
FWIW

You're way ahead of me on this and I'm afraid I don't know what -dV/dt
means. Is that something related or similar to the "FLEX negative pulse"
charging that Maha advertises (which is also Greek to me)?

whoops .. yes it is probably the same thing the Maha guys mean ..

what is refered to is that, at "full" charge NIMH's and NiCd's exhibit
a short steep voltage raise followed rather quickly by a sudden small
voltage drop. This is commonly refered to as a -dV/dt aka a negative
voltage increase per time .. modern chargers detect this dip and act
accordingly, mostly switching to so called "trickle" charging ..
HTH

On Tue, 27 Sep 2005 16:01:06 +0200, imbsysop wrote:

You're way ahead of me on this and I'm afraid I don't know what -dV/dt
means. Is that something related or similar to the "FLEX negative pulse"
charging that Maha advertises (which is also Greek to me)?

whoops .. yes it is probably the same thing the Maha guys mean ..

what is refered to is that, at "full" charge NIMH's and NiCd's exhibit
a short steep voltage raise followed rather quickly by a sudden small
voltage drop. This is commonly refered to as a -dV/dt aka a negative
voltage increase per time .. modern chargers detect this dip and act
accordingly, mostly switching to so called "trickle" charging ..

I don't think so. dV/dt just refers to monitoring the changing
slope of voltage vs. time. That could be done with any type of
charging circuit, even an extremely simple one based on little more
than a capacitor and a diode, and maybe a current limiting resistor.
Charging using pulses of current (used by my old, but poorly
designed RayOVac renewable alkaline/NiCad charger) is supposed to be
a better method. Possibly more efficient. But adding negative
pulses (slightly discharging between positive charging pulses)
supposedly leaves the chemical structure of the battery in a better
state. i.e., the batteries retain their fullest capacity for a
greater number of charge cycles. Whether that's completely true or
an oversimplification I can't say, as I don't recall reading it in a
white paper or fact sheet from a battery manufacturer's website.

"ASAAR" wrote in message
...
On Tue, 27 Sep 2005 16:01:06 +0200, imbsysop wrote:

You're way ahead of me on this and I'm afraid I don't know what -dV/dt
means. Is that something related or similar to the "FLEX negative pulse"
charging that Maha advertises (which is also Greek to me)?

whoops .. yes it is probably the same thing the Maha guys mean ..

what is refered to is that, at "full" charge NIMH's and NiCd's exhibit
a short steep voltage raise followed rather quickly by a sudden small
voltage drop. This is commonly refered to as a -dV/dt aka a negative
voltage increase per time .. modern chargers detect this dip and act
accordingly, mostly switching to so called "trickle" charging ..

I don't think so. dV/dt just refers to monitoring the changing
slope of voltage vs. time. That could be done with any type of
charging circuit, even an extremely simple one based on little more
than a capacitor and a diode, and maybe a current limiting resistor.
Charging using pulses of current (used by my old, but poorly
designed RayOVac renewable alkaline/NiCad charger) is supposed to be
a better method. Possibly more efficient. But adding negative
pulses (slightly discharging between positive charging pulses)
supposedly leaves the chemical structure of the battery in a better
state. i.e., the batteries retain their fullest capacity for a
greater number of charge cycles. Whether that's completely true or
an oversimplification I can't say, as I don't recall reading it in a
white paper or fact sheet from a battery manufacturer's website.

Dang, this is an interesting discussion. (Defined as "any discussion that
leaves me knowing more coming out than I did going in.")

N.

On Tue, 27 Sep 2005 21:53:02 +0200, imbsysop wrote:

You're way ahead of me on this and I'm afraid I don't know what -dV/dt
means. Is that something related or similar to the "FLEX negative pulse"
charging that Maha advertises (which is also Greek to me)?

whoops .. yes it is probably the same thing the Maha guys mean ..

what is refered to is that, at "full" charge NIMH's and NiCd's exhibit
a short steep voltage raise followed rather quickly by a sudden small
voltage drop. This is commonly refered to as a -dV/dt aka a negative
voltage increase per time .. modern chargers detect this dip and act
accordingly, mostly switching to so called "trickle" charging ..

I don't think so. dV/dt just refers to monitoring the changing
slope of voltage vs. time. That could be done with any type of
charging circuit, ..

I think you are largely missing the point .. the formula describes the
mathematical differential function (integration) that describes the cell
behaviour at full charge .. the charger doesn't particpate in this except
for detecting this "endpoint" by working as a dt integrator.

I'm fully aware of the formula and what it represents, at least
mathematically. But this is not the proper forum to discuss
integral calculus and derivatives. But your point that it was
"probably the same thing the Maha guys mean ..", and was also
referring to FLEX negative pulse charging seems to be incorrect.
Are you saying that all of the smart chargers that monitor "-dV/dt"
use pulse charging circuits? I thought they were used only by some
of them. And that not all of those also utilize negative charge
pulses. If I'm mistaken could you provide some documenting links?

"ASAAR" wrote:

But adding negative pulses (slightly discharging between
positive charging pulses) supposedly leaves the chemical
structure of the battery in a better state. i.e., the
batteries retain their fullest capacity for a greater number
of charge cycles.

As I understand it, PCR (periodic current reversal) has a
beneficial effect on the physical structure of a metallic
cathode as it's formed, rather than a chemical effect.

In fact, I believe PCR is required in electroplating, otherwise
the plated material is too spongy to be useful. In a battery,
this can mean dendrite formation.

My own electroplating experiments (without PCR) when I was
young produced very soft deposits.

John

On Wed, 28 Sep 2005 08:02:35 +1000, John Henderson wrote:

But adding negative pulses (slightly discharging between
positive charging pulses) supposedly leaves the chemical
structure of the battery in a better state. i.e., the
batteries retain their fullest capacity for a greater number
of charge cycles.

As I understand it, PCR (periodic current reversal) has a
beneficial effect on the physical structure of a metallic
cathode as it's formed, rather than a chemical effect.

Right. That's why I added the word "structure". If I thought it
only affected the chemical soup (or paste?) I would have worded it
differently. I don't know if the PCR's benefit is related to NiCad
dendrite formation, but I assumed it would either prevent something
like that, or the opposite, keeping the cathode from being eroded in
a manner similar (but chemically, not physically) to the way halogen
lamps redeposit vaporized metal back onto the filament.

On Tue, 27 Sep 2005 16:45:02 -0400, ASAAR wrote:

On Tue, 27 Sep 2005 21:53:02 +0200, imbsysop wrote:

You're way ahead of me on this and I'm afraid I don't know what -dV/dt
means. Is that something related or similar to the "FLEX negative pulse"
charging that Maha advertises (which is also Greek to me)?

whoops .. yes it is probably the same thing the Maha guys mean ..

what is refered to is that, at "full" charge NIMH's and NiCd's exhibit
a short steep voltage raise followed rather quickly by a sudden small
voltage drop. This is commonly refered to as a -dV/dt aka a negative
voltage increase per time .. modern chargers detect this dip and act
accordingly, mostly switching to so called "trickle" charging ..

I don't think so. dV/dt just refers to monitoring the changing
slope of voltage vs. time. That could be done with any type of
charging circuit, ..

I think you are largely missing the point .. the formula describes the
mathematical differential function (integration) that describes the cell
behaviour at full charge .. the charger doesn't particpate in this except
for detecting this "endpoint" by working as a dt integrator.

I'm fully aware of the formula and what it represents, at least
mathematically. But this is not the proper forum to discuss
integral calculus and derivatives. But your point that it was
"probably the same thing the Maha guys mean ..", and was also
referring to FLEX negative pulse charging seems to be incorrect.
Are you saying that all of the smart chargers that monitor "-dV/dt"
use pulse charging circuits? I thought they were used only by some
of them. And that not all of those also utilize negative charge
pulses. If I'm mistaken could you provide some documenting links?

I agree on your points .. I was not aware of the "newer"(?) negative
pulse charging systems that probably do a better job in preserving the
microcrystaline structure of the "internal chemical battery soup" ...
as to "smart chargers" is there any other method that can be
considered "intelligent" than monitoring the voltage dip ? If a
charger doesn't use this method, I for one would not qualify it as an
"intelligent charger"

On Wed, 28 Sep 2005 08:02:35 +1000, John Henderson
wrote:

"ASAAR" wrote:

But adding negative pulses (slightly discharging between
positive charging pulses) supposedly leaves the chemical
structure of the battery in a better state. i.e., the
batteries retain their fullest capacity for a greater number
of charge cycles.

As I understand it, PCR (periodic current reversal) has a
beneficial effect on the physical structure of a metallic
cathode as it's formed, rather than a chemical effect.

In fact, I believe PCR is required in electroplating, otherwise
the plated material is too spongy to be useful. In a battery,
this can mean dendrite formation.

My own electroplating experiments (without PCR) when I was
young produced very soft deposits.

Well in a previous life I used to work in Nikkel electroplating but we
always used "straight" DC .. Our biggest enemy in deposits quality was
actually copper :-) which made the deposits brittle. But times may
have changed :-)
FWIW

"ASAAR" wrote in message
...
On Tue, 27 Sep 2005 21:53:02 +0200, imbsysop wrote:

I'm fully aware of the formula and what it represents, at least
mathematically. But this is not the proper forum to discuss
integral calculus and derivatives. But your point that it was
"probably the same thing the Maha guys mean ..", and was also
referring to FLEX negative pulse charging seems to be incorrect.
Are you saying that all of the smart chargers that monitor "-dV/dt"
use pulse charging circuits? I thought they were used only by some
of them. And that not all of those also utilize negative charge
pulses. If I'm mistaken could you provide some documenting links?


A year or so ago, I bought the MH-C401FS battery charger with "FLEX NEGATIVE
pulse charging" feature. I wanted to find out what their charging procedure
was that produced such good results. I have a chart recorder that will trace
a line on a paper graph at an adjustable speed of paper movement. The
process I wrote in my notes is as follows:

"As soon as a battery is inserted in the holder, the controller switches
1000 mA charging current through a cycle of 1/4 sec on, followed by 3/4 sec
off, and it does this for 66 seconds before settling down to a nearly
continuous charge rate. I say nearly continuous because the charging is
switched off for 9.6 milliseconds four times per second. This continues
until about 50 minutes into the charging process when the charging current
is turned off for about 1 minute, and then continues for another 50 minutes
or until the charging process is stopped by the detection of a slight drop
in battery voltage, at which time the green light is lit and the charging
switches to a trickle charge by turning on the 1000 mA for only 1/4 second
every 4 seconds. So that's what happens to the current - - but I have no
idea when the microprocessor looks at battery voltage."

The chart recorder was set to display zero current at chart center so that
any reversal of current that might be described as "Flex Negative charging
current" would be displayed as a negative value. The charging current never
went negative! But this run was done on a set of new cells, so maybe the
"Flex" part didn't need to be executed. I can imagine applying a momentary
resistive load would result in a "negative" pulse of charging current, so it
might happen, but I never saw it.

Chuck

John Henderson writes:

"ASAAR" wrote:

But adding negative pulses (slightly discharging between positive
charging pulses) supposedly leaves the chemical structure of the
battery in a better state. i.e., the batteries retain their
fullest capacity for a greater number of charge cycles.

As I understand it, PCR (periodic current reversal) has a beneficial
effect on the physical structure of a metallic cathode as it's
formed, rather than a chemical effect.

There are at least 2 effects.

In fact, I believe PCR is required in electroplating, otherwise the
plated material is too spongy to be useful. In a battery, this can
mean dendrite formation.

My own electroplating experiments (without PCR) when I was young
produced very soft deposits.

This has been knowm by electroplates since the year dot. Almost all EP
is done by ofset AC current so as the get a sound solid plate. If the
metal is prone to growing dendrite of crystals, the current reversal
is concentrated at the dendrite and quickly removes it.

The other effect is stopping an `overvoltage' layer forming and the
resultant gassing off. This is also known as surface charge, and can be
quite significant.

Sealed NiCd and NiMH cells generate a lot more heat once they are fully
charged, and this temp rise reduces the series resistance of the cell
*LOTS*. It is this that causes the drop in voltage rise rate on charge
and discharge that can be used to signal end of charge.

Note that with NiCds, charging at low tempps is VERY bad news. Keep
them above 20C at the start. I don't know if this is a problem with
NiMH cells.

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