What is the trick to replacing rechargeable batteries please

[John Tserkezis]

On 20/02/2010 2:16 PM, hr(bob) hofmann@att.net 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.

 

[Wild_Bill]

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" <dmanzaluni@googlemail.com> wrote in message
news:a25715e6-9ba6-41be-887a-5b36c9b77c8e@c5g2000vbh.googlegroups.com...

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?

 

[William Sommerwerck]

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.

 

[William Sommerwerck]

... 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.

 

[William Sommerwerck]

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.

 

[Dave Plowman (News)]

In article <hlnd8g$ctl$1@news.eternal-september.org>,
William Sommerwerck <grizzledgeezer@comcast.net> 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 dave@davenoise.co.uk London SW
To e-mail, change noise into sound.

 

[Jim Yanik]

"William Sommerwerck" <grizzledgeezer@comcast.net> wrote in
news:hlocs4$nma$1@news.eternal-september.org:

... 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

 

[William Sommerwerck]

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.

 

[Doug White]

"Wild_Bill" <wb_wildbill@XSPAMyahoo.com> wrote in
news:XWMfn.332226$IU1.175326@en-nntp-04.dc1.easynews.com:

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

 

[William Sommerwerck]

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.

 

[William Sommerwerck]

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.

 

[Dave Plowman (News)]

In article <hloeai$tpd$1@news.eternal-september.org>,
William Sommerwerck <grizzledgeezer@comcast.net> 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 dave@davenoise.co.uk London SW
To e-mail, change noise into sound.

 

[Jim Yanik]

"William Sommerwerck" <grizzledgeezer@comcast.net> wrote in
news:hlosrd$bog$1@news.eternal-september.org:

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

 

[Dave Plowman (News)]

In article <hlosd1$99k$1@news.eternal-september.org>,
William Sommerwerck <grizzledgeezer@comcast.net> 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 dave@davenoise.co.uk London SW
To e-mail, change noise into sound.

 

[Phil Allison]

"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

 

[Phil Allison]

"William Sommerwanker"

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.

** BOLLOCKS.

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

 

[William Sommerwerck]

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.

 

[William Sommerwerck]

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.

** BOLLOCKS.
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".

 

[Phil Allison]

"William Sommerwanker"

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.

** YOU have it backwards - you PITA FOOL !!!

NiMH cells can show a meaningful voltage drop at the end of charge.

** But generally do NOT.

YOU ARE WRONG !!!

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.

** TOTALLY CONTRADICTS YOUR CLAIM at the top of this post.
----------------------------------------------------

Get a fucking brain - imbecile !!!

Chargers that use voltage detection usually also use temperature
detection,

** Bullshit.

PISS OFF PITA OLD FART !!


..... Phil

 

[William Sommerwerck]

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