I am hoping this question isnt too basic for this forum but I am
trying to replace some rechargeable batteries (in a Roomba: I
understand that generally only one or two start malfunctioning over
time and that it is usually the same one). It MUST be easier than I am
finding it.

I can just about solder on a connection but these rechargeable C cells
(nickel metal hydride? I am pretty sure they aren't lithium!) always
seem to have some sort of electro-welded rectangular plate connecting
the batteries which wont come off with a normal soldering gun? Or do
I just have to apply an inordinate amount of heat at exactly the
position where the ;nick' seems to be in the plate? Given the amount
of heat I seem to have applied to it already with no effect
whatsoever, to me it seems that this might damage the cell?

Is there some trick to doing this please or am i supposed to use a
dremel wheel to cut the plates off, leaving just the electro-weld to
which I solder the wire for the new cell?

In article , Amanda Ripanykhazov wrote:
I am hoping this question isnt too basic for this forum but I am
trying to replace some rechargeable batteries (in a Roomba: I
understand that generally only one or two start malfunctioning over
time and that it is usually the same one). It MUST be easier than I am
finding it.

I can just about solder on a connection but these rechargeable C cells
(nickel metal hydride? I am pretty sure they aren't lithium!) always
seem to have some sort of electro-welded rectangular plate connecting
the batteries which wont come off with a normal soldering gun? Or do
I just have to apply an inordinate amount of heat at exactly the
position where the ;nick' seems to be in the plate? Given the amount
of heat I seem to have applied to it already with no effect
whatsoever, to me it seems that this might damage the cell?

Is there some trick to doing this please or am i supposed to use a
dremel wheel to cut the plates off, leaving just the electro-weld to
which I solder the wire for the new cell?

The connections are welded. Maybe several thousand degrees will
take it off. Normally you bend them off.

Soldering to batteries can be risky both safety and damage.
To solder, Dremel scratches in the metal. Use a very hot iron
at about 750 degrees F. Time is the important part. You want to
heat it up quickly and solder so it has time to cool. Metal strips can be replaced with ordinary
wire.

greg

I often wonder why people don't call the manufacturer first. Is it that
difficult?

I would contact iRobot and ask them what the recommended procedure is.

On the assumption that iRobot is not stupid, and knows that the batteries
will eventually have to be replaced, it seems reasonable that the wires from
the batteries connect to a push-on terminal on the main board. If this is
so, you'll have to get the iRobot batteries.

On Feb 19, 2:17*pm, "William Sommerwerck"
wrote:
I often wonder why people don't call the manufacturer first. Is it that
difficult?

I would contact iRobot and ask them what the recommended procedure is.

Thanks for that everyone: I will try it.

Obviously no one calls iRobot for this question. they just want to
sell their expensive batteries. The last thing hhey want is to advise
on how to take the battery compartment apart. They even go to the
length of putting special screws on it to prevent anyone taking it
apart (using a triangular headed screwdriver: Has ANYONE ever come
across that on any other unit of any type whatsoever?)

Amanda Ripanykhazov wrote:
I am hoping this question isnt too basic for this forum but I am
trying to replace some rechargeable batteries (in a Roomba: I
understand that generally only one or two start malfunctioning over
time and that it is usually the same one). It MUST be easier than I am
finding it.

I can just about solder on a connection but these rechargeable C cells
(nickel metal hydride?
You sure they're not sub-C?
They're spot welded.
DO NOT SOLDER TO THE NEW BATTERIES. GET BATTERIES WITH TABS AND
SOLDER TO THE TABS.
Replace 'em ALL at once. Weak ones will be killed by the new ones.
"Not exactly, but that's the result."
I am pretty sure they aren't lithium!)
If you're gonna replace cells, shouldn't you be CERTAIN
what they are? Last thing you want is a robot running around
your floors ON FIRE!
always
seem to have some sort of electro-welded rectangular plate connecting
the batteries which wont come off with a normal soldering gun? Or do
I just have to apply an inordinate amount of heat at exactly the
position where the ;nick' seems to be in the plate? Given the amount
of heat I seem to have applied to it already with no effect
whatsoever, to me it seems that this might damage the cell?

Yes, it will.
Is there some trick to doing this

If you're gonna solder on batteries,
Wear safety glasses. Put 911 on speed dial.
Order up a whole set of tabbed cells to replace the ones
(actually ALL of them)
you ruin by overheating. Make sure you understand the charging
regimen so you can order the correct type of cells.

Now you're ready to ruin some new cells. Have at it.

OR,
you can take it back where you bought it and say, "fix it!"

please or am i supposed to use a
dremel wheel to cut the plates off, leaving just the electro-weld to
which I solder the wire for the new cell?

Amanda Ripanykhazov wrote:
On Feb 19, 2:17 pm, "William Sommerwerck"
wrote:
I often wonder why people don't call the manufacturer first. Is it that
difficult?

I would contact iRobot and ask them what the recommended procedure is.

Thanks for that everyone: I will try it.

Obviously no one calls iRobot for this question. they just want to
sell their expensive batteries. The last thing hhey want is to advise
on how to take the battery compartment apart. They even go to the
length of putting special screws on it to prevent anyone taking it
apart (using a triangular headed screwdriver: Has ANYONE ever come
across that on any other unit of any type whatsoever?)
Yes, it's common to prevent people who don't know what they're doing
from hurting themselves and suing the company. Certification agencies like
UL make a distinction between things that require a tool to open
and relax requirements in those areas. But people are idiots,
so vendors use fasteners that require uncommon tools to protect
them from themselves.
Your post suggests that you need that protection, but you're insisting
on learning the hard way.

REMEMBER THE SAFETY GLASSES.

I'd send you a picture of the battery pack that exploded after I
"fixed it" but it exploded so violently that I never found most of it.
The hot electrolyte spots on my glasses was my learning experience.

Amanda Ripanykhazov wrote:
I am hoping this question isnt too basic for this forum but I am
trying to replace some rechargeable batteries (in a Roomba: I
understand that generally only one or two start malfunctioning over
time and that it is usually the same one). It MUST be easier than I am
finding it.

I can just about solder on a connection but these rechargeable C cells
(nickel metal hydride? I am pretty sure they aren't lithium!) always
seem to have some sort of electro-welded rectangular plate connecting
the batteries which wont come off with a normal soldering gun? Or do
I just have to apply an inordinate amount of heat at exactly the
position where the ;nick' seems to be in the plate? Given the amount
of heat I seem to have applied to it already with no effect
whatsoever, to me it seems that this might damage the cell?

Is there some trick to doing this please or am i supposed to use a
dremel wheel to cut the plates off, leaving just the electro-weld to
which I solder the wire for the new cell?




Hi Amanda, You might want to look at this link, it details what to expect.

http://www.robotreviews.com/hack2/battery.shtml

Theres a good link to thread of advice on which cells to buy etc

Good luck, I'm about to try the same on my Roomba, JC

In article
,
Amanda Ripanykhazov wrote:
I am hoping this question isnt too basic for this forum but I am
trying to replace some rechargeable batteries (in a Roomba: I
understand that generally only one or two start malfunctioning over
time and that it is usually the same one). It MUST be easier than I am
finding it.

I can just about solder on a connection but these rechargeable C cells
(nickel metal hydride? I am pretty sure they aren't lithium!) always
seem to have some sort of electro-welded rectangular plate connecting
the batteries which wont come off with a normal soldering gun? Or do
I just have to apply an inordinate amount of heat at exactly the
position where the ;nick' seems to be in the plate? Given the amount
of heat I seem to have applied to it already with no effect
whatsoever, to me it seems that this might damage the cell?

The easiest - but more expensive way is to buy 'tagged' cells. These can
them be soldered without damage to the cell - a very real possibility if
you solder to them direct. But since they're less common on the retail
market the prices tend to be high. You might find somewhere local that can
weld tags to batteries for you. If you're lucky like me. ;-)

--
*Despite the cost of living, have you noticed how it remains so popular?*

Dave Plowman London SW
To e-mail, change noise into sound.

On Feb 19, 4:18*pm, Archon wrote:
Amanda Ripanykhazov wrote:
I am hoping this question isnt too basic for this forum but I am
trying to replace some rechargeable batteries (in a Roomba: I
understand that generally only one or two start malfunctioning over
time and that it is usually the same one). It MUST be easier than I am
finding it.

I can just about solder on a connection but these rechargeable C cells
(nickel metal hydride? I am pretty sure they aren't lithium!) always
seem to have some sort of electro-welded rectangular plate connecting
the batteries which wont come off with a normal soldering gun? * Or do
I just have to apply an inordinate amount of heat at exactly the
position where the ;nick' seems to be in the plate? Given the amount
of heat I seem to have applied to it already with no effect
whatsoever, to me it seems that this might damage the cell?

Is there some trick to doing this please or am i supposed to use a
dremel wheel to cut the plates off, leaving just the electro-weld to
which I solder the wire for the new cell?

Hi Amanda, You might want to look at this link, it details what to expect..

http://www.robotreviews.com/hack2/battery.shtml

Theres a good link to thread of advice on which cells to buy etc

Good luck, I'm about to try the same on my Roomba, JC

Hi JC

Yes, I had seen that and have two batteries to do: So my problem is
probably in getting enough good cells in one of them if I can figure
out how (as Mike would put it) to join up two separate tabbed cells
without having a spot welder

It is noteworthy that the on line 'experience based' instructions say
that you can solder where there was spot welding beforehand. (They
dont tell how to get the tabs off in the instructions which I saw,
which is why I posted here)

Amanda Ripanykhazova

Hi Amanda,

Amanda Ripanykhazov wrote:
On Feb 19, 4:18 pm, Archon wrote:
Amanda Ripanykhazov wrote:
I am hoping this question isnt too basic for this forum but I am
trying to replace some rechargeable batteries (in a Roomba: I
understand that generally only one or two start malfunctioning over
time and that it is usually the same one). It MUST be easier than I am
finding it.
I can just about solder on a connection but these rechargeable C cells
(nickel metal hydride? I am pretty sure they aren't lithium!) always
seem to have some sort of electro-welded rectangular plate connecting
the batteries which wont come off with a normal soldering gun? Or do
I just have to apply an inordinate amount of heat at exactly the
position where the ;nick' seems to be in the plate? Given the amount
of heat I seem to have applied to it already with no effect
whatsoever, to me it seems that this might damage the cell?
Is there some trick to doing this please or am i supposed to use a
dremel wheel to cut the plates off, leaving just the electro-weld to
which I solder the wire for the new cell?
Hi Amanda, You might want to look at this link, it details what to expect..

http://www.robotreviews.com/hack2/battery.shtml

Theres a good link to thread of advice on which cells to buy etc

Good luck, I'm about to try the same on my Roomba, JC

Hi JC

Yes, I had seen that and have two batteries to do: So my problem is
probably in getting enough good cells in one of them if I can figure
out how (as Mike would put it) to join up two separate tabbed cells
without having a spot welder

It is noteworthy that the on line 'experience based' instructions say
that you can solder where there was spot welding beforehand. (They
dont tell how to get the tabs off in the instructions which I saw,
which is why I posted here)

In general, you don't want to remove the tabs unless absolutely
necessary. Use them as "attachment points" to which you *can*
solder. Trying to make a connection to the battery (cell)
itself is an exercise in frustration and danger (batteries don't
like heat; soldering irons are hot -- do the math)

If you *must* remove the tabs, you can usually just wiggle
them back and forth repeatedly until metal fatigue causes
them to fail. You will end up with a small cluster of
"bumps" on the battery case as the "welds" usually stay behind
(i.e., you will find an equivalent number of *holes* in the
removed tab)

Amanda Ripanykhazov wrote:
On Feb 19, 4:18 pm, Archon wrote:
Amanda Ripanykhazov wrote:
I am hoping this question isnt too basic for this forum but I am
trying to replace some rechargeable batteries (in a Roomba: I
understand that generally only one or two start malfunctioning over
time and that it is usually the same one). It MUST be easier than I am
finding it.
I can just about solder on a connection but these rechargeable C cells
(nickel metal hydride? I am pretty sure they aren't lithium!) always
seem to have some sort of electro-welded rectangular plate connecting
the batteries which wont come off with a normal soldering gun? Or do
I just have to apply an inordinate amount of heat at exactly the
position where the ;nick' seems to be in the plate? Given the amount
of heat I seem to have applied to it already with no effect
whatsoever, to me it seems that this might damage the cell?
Is there some trick to doing this please or am i supposed to use a
dremel wheel to cut the plates off, leaving just the electro-weld to
which I solder the wire for the new cell?
Hi Amanda, You might want to look at this link, it details what to expect.

http://www.robotreviews.com/hack2/battery.shtml

Theres a good link to thread of advice on which cells to buy etc

Good luck, I'm about to try the same on my Roomba, JC

Hi JC

Yes, I had seen that and have two batteries to do: So my problem is
probably in getting enough good cells in one of them if I can figure
out how (as Mike would put it) to join up two separate tabbed cells
without having a spot welder

It is noteworthy that the on line 'experience based' instructions say
that you can solder where there was spot welding beforehand. (They
dont tell how to get the tabs off in the instructions which I saw,
which is why I posted here)

Amanda Ripanykhazova

Hi Amanda, I haven't checked out the construction of the Roomba battery
as yet but I'm guessing your problem is the original links between the
batteries is not an easily solderable metal, maybe stainless steel?. In
the link I gave you they are replacing all the batteries so soldering to
the original batteries was not a required. The metal case of the
batteries can usually be soldered to but its not recommended as others
have stated. You may need a special flux and a high wattage iron to make
decent connection to the original welded tags. JC

Just to add, it's sometimes cheaper to buy a different make of battery
that may be on offer and rob it of its cells to fix another.

--
*Reality is a crutch for people who can't handle drugs.

Dave Plowman London SW
To e-mail, change noise into sound.

Just to add, it's sometimes cheaper to buy a different make of
battery that may be on offer and rob it of its cells to fix another.

This is not generally a good idea. Replacing the bad cells in one battery
with new, good cells, is likely to cause cell reversal during operation. You
should generally replace all the cells.

It's also useful to have some way of measuring each cell's capacity while
discharging it, so you can roughly match the cells' capacities.

Amanda Ripanykhazov wrote:
On Feb 19, 4:18 pm, Archon wrote:
Amanda Ripanykhazov wrote:
I am hoping this question isnt too basic for this forum but I am
trying to replace some rechargeable batteries (in a Roomba: I
understand that generally only one or two start malfunctioning over
time and that it is usually the same one). It MUST be easier than I
am finding it.

I can just about solder on a connection but these rechargeable C
cells (nickel metal hydride? I am pretty sure they aren't lithium!)
always seem to have some sort of electro-welded rectangular plate
connecting the batteries which wont come off with a normal
soldering gun? Or do I just have to apply an inordinate amount of
heat at exactly the position where the ;nick' seems to be in the
plate? Given the amount of heat I seem to have applied to it
already with no effect whatsoever, to me it seems that this might
damage the cell?

Is there some trick to doing this please or am i supposed to use a
dremel wheel to cut the plates off, leaving just the electro-weld to
which I solder the wire for the new cell?

Hi Amanda, You might want to look at this link, it details what to
expect.

http://www.robotreviews.com/hack2/battery.shtml

Theres a good link to thread of advice on which cells to buy etc

Good luck, I'm about to try the same on my Roomba, JC

Hi JC

Yes, I had seen that and have two batteries to do: So my problem is
probably in getting enough good cells in one of them if I can figure
out how (as Mike would put it) to join up two separate tabbed cells
without having a spot welder

It is noteworthy that the on line 'experience based' instructions say
that you can solder where there was spot welding beforehand. (They
dont tell how to get the tabs off in the instructions which I saw,
which is why I posted here)

Amanda Ripanykhazova

Amanda, Lark Battery (www.larkbattery.com) should be able to sell you what
you need. Their contact info is
LARK BATTERY CENTER
8302 NW 39th Expressway
Bethany, OK. 73008
(405) 946-5275


Send them an email describing what you need and get a quote from them. They
will sell you individual cells with tabs so you can build the battery
yourself, or if you wish, they will construct the battery for you (at no
additional charge). I have done business with them before, and I can
attest to their quality.
You will have to describe the battery construction or send a picture so
they can construct it. From the web link posted above, it looks to be 12
sub-C cells in series, arranged in a 6x2 pack. There appears to be some
additional wiring attached to the pack, so you'll have to attach it to the
new pack.
Lark Battery are good folks. No affiliation; just a satisfied customer.

Cheers,
--
David
dgminala at mediacombb dot net

On 20/02/2010 12:17 PM, William Sommerwerck wrote:

Just to add, it's sometimes cheaper to buy a different make of
battery that may be on offer and rob it of its cells to fix another.

This is not generally a good idea. Replacing the bad cells in one battery
with new, good cells, is likely to cause cell reversal during operation. You
should generally replace all the cells.

I think that's what he means. Rob one (unusable brand) battery to
replace the cells of your (wanted brand) battery. As long as the cells
themselves are the same, it's all good.

It's also useful to have some way of measuring each cell's capacity while
discharging it, so you can roughly match the cells' capacities.

The cells are sometimes stamped, if not, you can get a clue from the
label of the battery case (the outside plastic case). They may not give
you too much information other than the brand and model, but they
usually do state the Ampere/hour capacity.

On Feb 19, 10:54*am, Amanda Ripanykhazov
wrote:
I am hoping this question isnt too basic for this forum but I am
trying to replace some rechargeable batteries (in a Roomba: I
understand that generally only one or two start malfunctioning over
time and that it is usually the same one). It MUST be easier than I am
finding it.

Two cautions: if this is a battery of multiple cells in series, you
must
replace ALL cells at once. It is important that all the cells have
the same batch number and age if they are charged and discharged
in series.

Second caution, the contents of these (NiCd or NiMH) is a caustic
liquid, buy tabbed cells rather than trying to get the case up to
soldering
temperature. The tab ends can take solder temperature or spotwelding
without hazard.

"William Sommerwerck" wrote in
:

I often wonder why people don't call the manufacturer first. Is it
that difficult?

I would contact iRobot and ask them what the recommended procedure is.

On the assumption that iRobot is not stupid, and knows that the
batteries will eventually have to be replaced, it seems reasonable
that the wires from the batteries connect to a push-on terminal on the
main board. If this is so, you'll have to get the iRobot batteries.





Or take the pack to a Batteries Plus store or other rebuilder and have a
new pack built. Usually at a lower cost than a new OEM pack.

--
Jim Yanik
jyanik
at
localnet
dot com

"William Sommerwerck" wrote in
:

Just to add, it's sometimes cheaper to buy a different make of
battery that may be on offer and rob it of its cells to fix another.

This is not generally a good idea. Replacing the bad cells in one
battery with new, good cells, is likely to cause cell reversal during
operation.

You also have OLD cells with lots of charge cycles mixed with new cells,and
the old cells will fail sooner.

You should generally replace all the cells.

Agreed.

It's also useful to have some way of measuring each cell's capacity
while discharging it, so you can roughly match the cells' capacities.


agreed.

--
Jim Yanik
jyanik
at
localnet
dot com

On Feb 19, 7:42*pm, Jim Yanik wrote:
"William Sommerwerck" wrote :

Just to add, it's sometimes cheaper to buy a different make of
battery that may be on offer and rob it of its cells to fix another.

This is not generally a good idea. Replacing the bad cells in one
battery with new, good cells, is likely to cause cell reversal during
operation.

You also have OLD cells with lots of charge cycles mixed with new cells,and
the old cells will fail sooner.

You should generally replace all the cells.

Agreed.

It's also useful to have some way of measuring each cell's capacity
while discharging it, so you can roughly match the cells' capacities.

agreed.

--
Jim Yanik
jyanik
at
localnet
dot com

You can solder to the tabs or to the remains of the tabs where you
have pulled them off. Scratch the metal before you solder to get them
to take the solder. Use flux also. Replace all batteries, using NMH
rather than NiCad, as they have larger capacity. they are sub-C, I
have had to replace my wife's roomba batteries, so know first-hand

On 20/02/2010 12:42 PM, Jim Yanik wrote:

This is not generally a good idea. Replacing the bad cells in one
battery with new, good cells, is likely to cause cell reversal during
operation.

You also have OLD cells with lots of charge cycles mixed with new cells,and
the old cells will fail sooner.

Sure, but surplus battery packs would more then likely be very similar,
if not a little on the depreciated side.

On 20/02/2010 2:16 PM, hr(bob) wrote:

... Replace all batteries, using NMH
rather than NiCad, as they have larger capacity...

This can't usually be done, because the end of charge algorithms on the
smart chargers won't won't be compatible with the different cell technology.
It's very possible a charger for NiCads can grossly overcharge NiMh.
You had better HOPE the circuitry has a timeout value, otherwise you'll
melt them down to a shapeless blob.
If nothing else, this will bring the life of your new NiMh's down.

Even float charging (which was routinely done in cheap equipment for
NiCads) is a bit iffy when you get to NiMH cells.

No real tricks, just a few techniques that can make battery pack
building/rebuilding easier.

Don't reuse old cells or the old welded connecting strips for new battery
packs. If the old cells have leaked, the pack connector copper leads may
also be damaged if the leakage has reached the ends of the stranded copper
leads. The liquid that's leaked out of the cells can wick up into the
stranded copper leads.
Replace the pack leads with the same gage wire (or larger) if any damage is
visible.

Choose new cells of the correct physical size and reasonable capacity,
fresh, flat top cells with soldering tabs already attached. Solder the tabs
to connect the cells together, not wires or other material directly to the
cells. Some dealers will add tabs to cells for free.

Cells with tabs used to be made with the 2 tabs oriented 180 degrees apart
(looking down at the top of the cell, one tab points left, the other tab
points right).
The cells I purchased recently from 3 different sources have the tabs both
pointing in the same direction.
Lay the cells out side-by-side in a line with alternating + & - tabs
adjacent to each other, and all the tabs pointed upward.
To get the tabs to meet and overlap, make a 45 degree bend close to the
welds, which changes the direction of the tab to 90 degrees.
By making the 45* bend close to the weld, the tabs won't stick out past the
sides of the cells.

Clean the tabs and tin them with solder using flux.. as they overlap, tin
the top of one tab, and the bottom of the other. With the cells neatly hot
glue tacked together, apply an additional small amount of solder to the area
where the tinned tabs overlap, and press the tabs together with a tool until
the solder cools.
I place a small square of fiberglass tape under the joined tabs as extra
insurance so the + tabs can't short circuit to the cell case (even though
there is an insulating washer under the plastic skin).

If the original battery pack utilized a thermal protection device, one
should definiely be installed in the new pack. Many times a thermal switch
is marked with the temperature rating. Temperature rise during charging can
be detrimental to the useful life of the battery pack, and also to the
capacity of the cells.
Thermal protection switches with leads can be soldered to tabs of the cells.
The polyswitch types of devices should be spot welded directly to the cells.
Any other components (diodes, precision resistors) that were part of the
original battery pack should be checked for normal values.

Connector leads can be soldered to the appropriate tabs, and shrink tubing
over the soldered connection and the end of the lead will offer some
support/strain relief for the leads.

There are dealers that also sell the shrink wrap to cover the cells, for
making a neat and secure battery pack.

A few simple guidelines will prevent most problems.
Don't solder directly to cell terminals.
Don't allow cells to get hot while charging.
Don't overcharge battery packs. One of the best ways to prevent overcharging
is to use a manually reset timer to limit the amout of time for charging.
Don't over-discharge battery packs. When the device/tool starts to run
slower, stop using it and recharge the battery pack.

Many rechargeable consumer devices are supplied with very poor quality
chargers (just a transformer and a diode was the cheapest method).
If you can't get a reasonable service life from the battery packs, you might
consider choosing another method of charging the battery, whether that means
removing it to connect it to a better quality charger, or modifying the
device with an external connector for safely connecting a better quality
charger.

In some cases, it's just better to have more than one battery pack, that can
be easily swapped by means of an external connector.

--
Cheers,
WB
..............


"Amanda Ripanykhazov" wrote in message
...
I am hoping this question isnt too basic for this forum but I am
trying to replace some rechargeable batteries (in a Roomba: I
understand that generally only one or two start malfunctioning over
time and that it is usually the same one). It MUST be easier than I am
finding it.

I can just about solder on a connection but these rechargeable C cells
(nickel metal hydride? I am pretty sure they aren't lithium!) always
seem to have some sort of electro-welded rectangular plate connecting
the batteries which wont come off with a normal soldering gun? Or do
I just have to apply an inordinate amount of heat at exactly the
position where the ;nick' seems to be in the plate? Given the amount
of heat I seem to have applied to it already with no effect
whatsoever, to me it seems that this might damage the cell?

Is there some trick to doing this please or am i supposed to use a
dremel wheel to cut the plates off, leaving just the electro-weld to
which I solder the wire for the new cell?

Just to add, it's sometimes cheaper to buy a different make of
battery that may be on offer and rob it of its cells to fix another.

This is not generally a good idea. Replacing the bad cells in one battery
with new, good cells, is likely to cause cell reversal during operation.
You
should generally replace all the cells.

I think that's what he means. Rob one (unusable brand) battery to
replace the cells of your (wanted brand) battery. As long as the cells
themselves are the same, it's all good.

Perhaps. But the principle stands -- replace all the cells.


It's also useful to have some way of measuring each cell's capacity
while discharging it, so you can roughly match the cells' capacities.

The cells are sometimes stamped, if not, you can get a clue from the
label of the battery case (the outside plastic case). They may not give
you too much information other than the brand and model, but they
usually do state the Ampere/hour capacity.

It's ampere-hour, not Ampere/hour. Big, big difference.

Cells with the same mAh rating from the same company nevertheless vary in
capacity. I've had to return new cells for replacement because they were way
out of spec.

... Replace all batteries, using NMH
rather than NiCad, as they have larger capacity...

This can't usually be done, because the end of charge algorithms
on the smart chargers won't won't be compatible with the different
cell technology. It's very possible a charger for NiCads can grossly
overcharge NiMh. You had better HOPE the circuitry has a timeout
value, otherwise you'll melt them down to a shapeless blob.
If nothing else, this will bring the life of your new NiMh's down.

You have it backwards. NiMH cells are usually pushed to a higher
end-of-charge voltage than nicads. Charging NiMH cells on a nicad charger
will, if anything, undercharge them.

In article ,
William Sommerwerck wrote:
Just to add, it's sometimes cheaper to buy a different make of
battery that may be on offer and rob it of its cells to fix another.

This is not generally a good idea. Replacing the bad cells in one
battery with new, good cells, is likely to cause cell reversal during
operation. You should generally replace all the cells.

Well, yes. I wasn't suggesting otherwise. The majority of cordless tools
use sub-C sizes of different types and capacities - and of course number
according to the voltage. If you can buy one on special offer it might be
able to supply a set of cells to replace those in the faulty unit at a
lower cost than buying individual tagged replacement cells. I've done just
this a few times. For example, with the move to LI cells some are selling
off their NiMH cells at discount. Same with NiCads.

It's also useful to have some way of measuring each cell's capacity while
discharging it, so you can roughly match the cells' capacities.

Usually on the battery case or tool spec if not the individual cells.

--
*The more I learn about women, the more I love my car

Dave Plowman London SW
To e-mail, change noise into sound.

It's also useful to have some way of measuring each cell's capacity
while discharging it, so you can roughly match the cells' capacities.

Usually on the battery case or tool spec if not the individual cells.

Let me repeat this... The capacity printed on the cell is its nominal
capacity. It is NOT the capacity of that particular cell. Individual cells
can sometimes differ 20% or more from this value -- usually on the low side.

It's important to match the capacity of nicad and NiMH cells, because they
have a very abrupt cutoff. This means that one cell can drop way low, while
the other cells are at a voltage high enough to continue powering the
device. If you let the device run long enough after this point, the weak
cell will drop to zero volts, then reverse, possibly causing it to leak or
explode.

"William Sommerwerck" wrote in
:

... Replace all batteries, using NMH
rather than NiCad, as they have larger capacity...

This can't usually be done, because the end of charge algorithms
on the smart chargers won't won't be compatible with the different
cell technology. It's very possible a charger for NiCads can grossly
overcharge NiMh. You had better HOPE the circuitry has a timeout
value, otherwise you'll melt them down to a shapeless blob.
If nothing else, this will bring the life of your new NiMh's down.

You have it backwards. NiMH cells are usually pushed to a higher
end-of-charge voltage than nicads. Charging NiMH cells on a nicad charger
will, if anything, undercharge them.




many NiCd chargers use a temp sensor to determine a full charge,and that
will kill NiMH.

--
Jim Yanik
jyanik
at
localnet
dot com

In article ,
William Sommerwerck wrote:
Usually on the battery case or tool spec if not the individual cells.

Let me repeat this... The capacity printed on the cell is its nominal
capacity. It is NOT the capacity of that particular cell. Individual
cells can sometimes differ 20% or more from this value -- usually on the
low side.

And you think makers of low end tools care about this?

It's important to match the capacity of nicad and NiMH cells, because
they have a very abrupt cutoff. This means that one cell can drop way
low, while the other cells are at a voltage high enough to continue
powering the device. If you let the device run long enough after this
point, the weak cell will drop to zero volts, then reverse, possibly
causing it to leak or explode.

Despite having used re-chargeable batteries from long before they became a
domestic item, I've never known one to explode. But then I've always
insisted on decent chargers.

--
*Why is the man who invests all your money called a broker?

Dave Plowman London SW
To e-mail, change noise into sound.

You have it backwards. NiMH cells are usually pushed
to a higher end-of-charge voltage than nicads. Charging
NiMH cells on a nicad charger will, if anything, undercharge
them.

Many NiCd chargers use a temp sensor to determine a full
charge,and that will kill NiMH.

Nicad chargers do not generally have temperature sensors, unless they're
built into the battery pack. Furthermore, a NiMH cell can tolerate higher
temperatures than a nicad so, again, a charger designed for nicads is likely
to shut off too soon rather than too later.

I worked for several months at Microsoft Hardware. One of my projects was
documenting Microsoft's rapid charger for its cordless mice. Though nicad
and NiMH cells are more alike than different, the latter are usually pushed
to higher charging cut-off voltages and temperatures. A nicad charger is not
likely to damage NiMH cells.

"Wild_Bill" wrote in
:

Don't overcharge battery packs. One of the best ways to prevent
overcharging is to use a manually reset timer to limit the amout of
time for charging. Don't over-discharge battery packs. When the
device/tool starts to run slower, stop using it and recharge the
battery pack.

Many rechargeable consumer devices are supplied with very poor quality
chargers (just a transformer and a diode was the cheapest method).
If you can't get a reasonable service life from the battery packs, you
might consider choosing another method of charging the battery,
whether that means removing it to connect it to a better quality
charger, or modifying the device with an external connector for safely
connecting a better quality charger.

My wife & I each have coldless drills, which we use intermitently for
household repairs & projects. The only way to make sure we have a
charged battery handy for emergencies is to leave one in the chargers.
Even though these are reasonably high quality chargers (Ryobi & DeWalt),
I'm sure we are shortening the life of the batteries.

It occured to me that one option might be to put the chargers on a timer,
so that they are on for half an hour a day. That should top them off,
without cooking them. The catch is that I'm not sure what sort of load
the charger presents when it is off. I could just end up discharging the
battery through (at a minimum) diode leakage. As long as the leakage is
low, that might actually be OK, ot it could produce a nasty memory effect
in the NiCd's.

Any thoughts or comments?

Thanks!

Doug White

Let me repeat this... The capacity printed on the cell is its
nominal capacity. It is NOT the capacity of that particular
cell. Individual cells can sometimes differ 20% or more from
this value -- usually on the low side.

And you think makers of low end tools care about this?

What does that have to do with the issue at hand?

Cells from the same production run are likely to have similar capacities.
But this isn't always true.

If you are making up your battery pack, you should break in the cells and
measure their capacities, assembling the batteries from cells within a few
percent of each other.


It's important to match the capacity of nicad and NiMH cells, because
they have a very abrupt cutoff. This means that one cell can drop way
low, while the other cells are at a voltage high enough to continue
powering the device. If you let the device run long enough after this
point, the weak cell will drop to zero volts, then reverse, possibly
causing it to leak or explode.

Despite having used re-chargeable batteries from long before they
became a domestic item, I've never known one to explode. But then
I've always insisted on decent chargers.

I've never had the problem, either. But the charger has nothing to do with
it. I was talking about discharge (see above).

The safest way to handle a multi-cell battery pack is to run it until it
just begins to show a drop in performance, then charge it. This reduces the
chance of any cell being driven into reversal.

The more cells in the battery, the greater the chance of reversal.

My wife & I each have coldless drills, which we use intermitently
for household repairs & projects. The only way to make sure we
have a charged battery handy for emergencies is to leave one in
the chargers. Even though these are reasonably high quality
chargers (Ryobi & DeWalt), I'm sure we are shortening the life of
the batteries.

You probably are. I would not charge the batteries until they began to run
down, then recharge no more than four hours (or whatever the manual
recommends as the maxium charging time).

I own an inexpensive 12V Ryobi drill, which gets similar intermittent use.
The charger /does not/ shut off automatically. Indeed, there is nothing to
indicate that the charge is complete! I am very careful about when and how
long I charge it.

The battery does not quickly self-discharge. I've never had a time it wasn't
ready. So, after each use, I'll recharge it for 15 minutes or so.

A 12V battery pack has eight nicad cells. It's important not to repeatedly
run down the battery, as you're increasing the chance of reversing the
lowest-capacity cell in the pack.


It occured to me that one option might be to put the chargers on a timer,
so that they are on for half an hour a day. That should top them off,
without cooking them.

A half hour a week -- or even a month -- would probably be enough.


The catch is that I'm not sure what sort of load the charger presents
when it is off. I could just end up discharging the battery through (at a
minimum) diode leakage.

That would be several hundred K.

"William Sommerwerck" wrote in
:


A 12V battery pack has eight nicad cells. It's important not to
repeatedly run down the battery, as you're increasing the chance of
reversing the lowest-capacity cell in the pack.

my 9.6V Makita stick has EIGHT cells,wouldn't a 12V pack have TEN cells?
1.2V per cell.


--
Jim Yanik
jyanik
at
localnet
dot com

In article ,
William Sommerwerck wrote:
It's important to match the capacity of nicad and NiMH cells, because
they have a very abrupt cutoff. This means that one cell can drop way
low, while the other cells are at a voltage high enough to continue
powering the device. If you let the device run long enough after this
point, the weak cell will drop to zero volts, then reverse, possibly
causing it to leak or explode.

Despite having used re-chargeable batteries from long before they
became a domestic item, I've never known one to explode. But then
I've always insisted on decent chargers.

I've never had the problem, either. But the charger has nothing to do
with it. I was talking about discharge (see above).

I've often run re-chargeables flat - although not intentionally. There'd
have to be a *vast* imbalance before one blew up. And indeed in practice
the cells don't all fail together, so even the very best makes will
exhibit just the effect you're talking about when old.

The safest way to handle a multi-cell battery pack is to run it until it
just begins to show a drop in performance, then charge it. This reduces
the chance of any cell being driven into reversal.

Yes.

The more cells in the battery, the greater the chance of reversal.

I've not actually experienced it. So put it in the same sort of pigeon
hole as memory effect. ;-)

--
*We waste time, so you don't have to *

Dave Plowman London SW
To e-mail, change noise into sound.

"Jim Yanik"


many NiCd chargers use a temp sensor to determine a full charge,and that
will kill NiMH.

** Utter nonsense.

Temp detection is the MAIN way of detecting the end point when charging
NiMH cells.

The PROBLEM comes with NiCd chargers that use VOLTAGE peak detection -
cos NiMH cells never drop voltage like NiCds do.



..... Phil

"William Sommer******"


Nicad chargers do not generally have temperature sensors, unless they're
built into the battery pack. Furthermore, a NiMH cell can tolerate higher
temperatures than a nicad so, again, a charger designed for nicads is
likely
to shut off too soon rather than too later.


** What an utterly STUPID non sequitur !!!



I worked for several months at Microsoft Hardware. One of my projects was
documenting Microsoft's rapid charger for its cordless mice. Though nicad
and NiMH cells are more alike than different, the latter are usually
pushed
to higher charging cut-off voltages and temperatures. A nicad charger is
not
likely to damage NiMH cells.

** ********.

Chargers that are looking for the battery voltage to peak then come DOWN
will NEVER stop if NiMH cells are being used instead of NiCd.


...... Phil

many NiCd chargers use a temp sensor to determine
a full charge, and that will kill NiMH.

** Utter nonsense.

Temp detection is the MAIN way of detecting the end point
when charging NiMH cells.

The PROBLEM comes with NiCd chargers that use VOLTAGE
peak detection - cos NiMH cells never drop voltage like NiCds do.

Sorry, Phil, you've got it backwards.

NiMH cells can show a meaningful voltage drop at the end of charge. In
general, the harder the cell is charged, the greater the drop.

If you can place a thermistor on or near the NiMH cell, detecting the
temperature rise is usually the easiest and cheapest way to terminate
charge. This is particularly true if you're not hitting the cell hard and
don't have a big enough minus delta V to reliably detect.

Chargers that use voltage detection usually also use temperature detection,
as a belt-and-suspenders safety feature. One exception is the MAHA C9000
which uses only delta V (as far as I can tell), because it's hard to read
the cell's temperature through the plastic base of the charger.

Nicad chargers do not generally have temperature sensors, unless
they're built into the battery pack. Furthermore, a NiMH cell can
tolerate higher temperatures than a nicad so, again, a charger
designed for nicads is likely to shut off too soon rather than too later.

** What an utterly STUPID non sequitur !!!

Why don't you think before yelling?

NiMH cells can be rather brutally charged without damaging them, at a rate
that most nicads would not tolerate. (MAHA recommends at least 0.5C for its
NiMH cells, but I grew up with nicads, so I tend to set the charger between
0.2C and 0.4C.) Thus, the temperature sensor in a NiMH charger is likely to
be set higher than in a nicad charger. Placing NiMH cells in such a charger
will likely lead to undercharging the cell, rather than blowing it up.


I worked for several months at Microsoft Hardware. One of my projects
was documenting Microsoft's rapid charger for its cordless mice. Though
nicad and NiMH cells are more alike than different, the latter are
usually
pushed to higher charging cut-off voltages and temperatures. A nicad
charger is not likely to damage NiMH cells.

** ********.
Chargers that are looking for the battery voltage to peak then come
DOWN will NEVER stop if NiMH cells are being used instead of NiCd.

Again, you have it backwards. Perhaps, you brainless ignoramus, you might
like to discuss this with the engineers I worked with.

You're an object lesson in the dangers of discussing something before being
certain you're sure you know what you're talking about, in "open mouth,
insert foot".

Why do you think I should be afraid of you, you pitiful excuse for a human
being?

"You're nothing but a pack of cards." -- Alice

"William Sommer******"

Nicad chargers do not generally have temperature sensors, unless
they're built into the battery pack. Furthermore, a NiMH cell can
tolerate higher temperatures than a nicad so, again, a charger
designed for nicads is likely to shut off too soon rather than too
later.

** What an utterly STUPID non sequitur !!!

Why don't you think before yelling?

** JESUS H. CHRIST !!!!!!!!!!!!!!!!!!!!!!!!

YOU are one ARROGANT ****ING IDIOT

There is NO sense in you para above at ALL !!


NiMH cells can be rather brutally charged without damaging them, at a rate
that most nicads would not tolerate.

** ABSOLUTE ******** !!!!!!!!!!!

The reverse is the case.


Thus, the temperature sensor in a NiMH charger is likely to
be set higher than in a nicad charger. Placing NiMH cells in such a
charger
will likely lead to undercharging the cell,

** READ the very first line in this post.

YOUR WORDS !!!!!

Makes NONSENSE of your idiotic claims.

YOU DEMENTED ****WIT !!!!!!!!!!!!



I worked for several months at Microsoft Hardware. One of my projects
was documenting Microsoft's rapid charger for its cordless mice. Though
nicad and NiMH cells are more alike than different, the latter are
usually pushed to higher charging cut-off voltages and temperatures.
A nicad charger is not likely to damage NiMH cells.

** ********.

Chargers that are looking for the battery voltage to peak then come
DOWN will NEVER stop if NiMH cells are being used instead of NiCd.

Again, you have it backwards.


** YOU have it BACKWARDS

YOU ****ING DEMENTED IDIOT !!!!!!!!!


Perhaps, you brainless ignoramus, you might
like to discuss this with the engineers I worked with.

** Let them and YOU SUCK on this ****HEAD:

http://www.powerstream.com/NiMH.htm

" The minus delta V bump that is indicative of end-of-charge is much less
pronounced in NiMH than NiCad, and it is very temperature dependent. To make
matters worse, new NiMH batteries can exhibit bumps in the curve early in
the cycle, particularly when cold. Also, NiMH are sensitive to damage on
overcharge when the charge rate is over C/10. Since the delta V bump is not
always easy to see, slight overcharge is probable. For this reason
PowerStream does not recommend using minus delta V as a termination
criterion for nickel metal hydride batteries. "

And:

http://www.mpoweruk.com/chargers.htm

" dT/dt Charge system NiMH batteries do not demonstrate such a pronounced
NDV voltage drop when they reach the end of the charging cycle as can be
seen in the graph above and so the NDV cut off method is not reliable for
ending the NiMH charge. Instead the charger senses the rate of increase of
the cell temperature per unit time. When a predetermined rate is reached the
rapid charge is stopped and the charge method is switched to trickle charge.
This method is more expensive but avoids overcharge and gives longer life.
Because extended trickle charging can damage a NiMH battery, the use of a
timer to regulate the total charging time is recommended. "


FOAD you PITA IMBECILE !!!



..... Phil