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'[EE]: Showing NiCads who's boss'
2001\08\17@203251 by Jinx

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A couple of years ago I was given a cordless drill that
wouldn't charge. I found that one of the cells in the pack was
dead flat and was stopping the others charging up. At the
time I was told how to break down the high resistance
inside that flat cell, which I did, and the drill has been as
good as new since. But I can't remember the details of
what I did. I seem to recall applying 12 or 15V to it for a
few seconds, keeping an eye on when the meter swung
from 0 to a rapid charge (indicating that the insulating
dendrite barrier had been punched through) and then
removing said 12 or 15V and putting the pack into its
normal charger. Have I got it right ? There are one or two
appliances around here with what I think are dead cells
and I'd like to get them operational. As always, the cells
are an odd size and would be expensive to replace with
the manufacturer's "recommended" spare part

TIA

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2001\08\17@204514 by Tom Messenger

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Hi Jinx

You'll probably get lots of ideas on this one and I'll add my 2 cents here
now.

A common theory to explain the problem is that chemical dendrites grow
between the electrodes on the nicads. You didn't say nicad but you did say
power drill which up to lately have mostly used nicads.

In any case, when left 'dead' for a while, the dendrites form and keep a
given cell from charging because they effectively short it out.  The
solution I use often is as follows.

Dump a lot of current through the cell and fry the dendrites off. Monitor
the problem cell with a volt meter.  Charge up a big cap (say 100,000 ufd)
to 10, 15 or 20 volts. Using a low impedance delivery method, dump it into
the cell. At first, perhaps, the meter doesn't budge. Repeat several times
and usually, the cell voltage will suddenly jump up to over 1 volt. It will
continue up to 1.2 or 1.3 or so.  Burning out the dendrites can be done
with either polarity but forwards is best.

I usually hit the cell afterwards with one or two amps for one or two
minutes to get it well up the charging curve. At this point, you can charge
it with the usual nicad chargers.

On stuff you want to keep, try to keep the cells charged up.  Either use a
low trickle current or remember to charge them once every week or two.
When the cells get old enough to begin shorting out like this, they gladly
will short out again quickly.

It's best to apply this directly to each cell that needs it rather than to
the pack as a whole.

Good luck.

All the usual precautions apply.

At 12:30 PM 8/18/01 +1200, you wrote:
{Quote hidden}

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2001\08\17@204517 by Mike Kendall

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Years ago, I bought a book called "the battery book" put out by Tab I seem
to remember.  This guy burned out the dentrites on over a hundred batteries
to  get a percentage of recoverable batteries result.  He used the method
that was a little more homebrewed but better.  First, he put the batteries
in the refrigerator.  He used a very high current capacity device.....a car
battery connected backwards.  He would connect the cells backwards accross
the car battery for a second or two and then put it back in the
refrigerator.  This was done for a few burn cycles with a very good recovery
rate.   A note to anyone trying this as I've succesfully done it is to
connect the wires to the battery tabs and then connect the wires to the
battery posts.  The wires will leave arc spots.  Better to burn out the end
of some scrap wire and the car battery post will not be hurt.  I've done
this out in the field to handheld radio batteries very succesfully.
Regards,
Mike
{Original Message removed}

2001\08\17@212840 by Jinx

face picon face
> Dump a lot of current through the cell and fry the dendrites off.
> Monitor the problem cell with a volt meter.  Charge up a big
> cap (say 100,000 ufd) to 10, 15 or 20 volts. Using a low
> impedance delivery method, dump it into the cell

Now that sounds familiar. The rest of your post is new to me, as
is Mike Kendall's and I'll certainly be trying things out. And as you
say, others will their 2 cents worth so we'll see what develops
over the next couple of days. Thanks

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2001\08\17@214255 by Jim

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Some of the 'rapid chargers' sold to recharge
the batteries in (mainly) two-way radio equipment
seems to perform this function as well ... it's
probably just a result of the charge rate being
C/1 (versus the normal C/10) rate and not a
specific 'current pulse' as described below
that does the trick. I know the cells in the batt
pack for my 2M/70 cm transceiver are a lot
happier when occasionally zapped with the
rapid charger - I had to bring two cells in that
same pack 'back from the dead' using the
large cap method about 2 months ago and so
far they are looking good (the radio also has a
built-in DVM feature that reads the pack
voltage - easy to tell when a cell has 'shorted').

Jim



> Dump a lot of current through the cell and fry the dendrites off.
> Monitor the problem cell with a volt meter.  Charge up a big
> cap (say 100,000 ufd) to 10, 15 or 20 volts. Using a low
> impedance delivery method, dump it into the cell
>

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2001\08\17@234205 by Graeme Zimmer

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Occasionally I encounter a NiCad cell which has gone short-ciruit.......

The standard cure is to use a set of car jumper leads to briefly zap the
crook battery across your car battery.
(in the "charging" direction.....)

This will certainly remove the short, but please be aware that if you manage
to stick the leads to the battery, the resultant explosion will be somewhat
interesting.....

My experience is that the "cure" is seldom permanent. Once a NiCad becomes
flakey it is best to discard it......

............................ Zim

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2001\08\18@020722 by Ned Seith

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Jinx,

I have the commercially made NiCad Zapper in one of my junk piles.
I vaguely recall that it charged a capacitor to 40 VDC and discharged
the capacitor into the NiCad battery. If your interested, I could locate
the NiCad Zapper and forward the schematic to you.

Sincerely,
Ned Seith
Nedtronics
59 3rd Street
Gilroy, CA 95020
(408) 842-0858
spam_OUTnedTakeThisOuTspamnedtron.com

At 12:30 PM 8/18/01 +1200, you wrote:
{Quote hidden}

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2001\08\18@024336 by Jinx

face picon face
> Jinx,
>
> I have the commercially made NiCad Zapper in one of
> my junk piles. I vaguely recall that it charged a capacitor
> to 40 VDC and discharged the capacitor into the NiCad
> battery. If your interested, I could locate the NiCad Zapper
> and forward the schematic to you.
>
> Sincerely,
> Ned Seith

Ned, yes I would be interested if you can find the time. I've
just tried a 10000/50 cap at 15V and that seems to have
woken a battery up. I'll see how it does under normal charge.
Still a few more batteries to experiment on (I must be the
poster-boy for War On Waste !!) using other's suggestions

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2001\08\18@182227 by Jinx

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Treatment of Patient A (Black & Decker DustBuster) seems
to have been successful. It has two series NiCad. One battery
was zapped with 15V from a cap, the other had 15VDC put
to it until it started to charge. I left it on its charger overnight and
seems to be perfectly healthy this morning. Its caregiver tells
me it was used from new for just a couple of weeks about 3
years ago and then tossed in the drawer. Both cells were 0.00
and unchargeable before yesterday

Send in the next one please nurse..........

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2001\08\21@145351 by Jim Pruitt

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Ned, could I get the schematic info as well?

Thanks

Jim Pruitt



>>> EraseMEnedspam_OUTspamTakeThisOuTNEDTRON.COM 08/17/01 11:05PM >>>
Jinx,

I have the commercially made NiCad Zapper in one of my junk piles.
I vaguely recall that it charged a capacitor to 40 VDC and discharged
the capacitor into the NiCad battery. If your interested, I could locate
the NiCad Zapper and forward the schematic to you.

Sincerely,
Ned Seith
Nedtronics
59 3rd Street
Gilroy, CA 95020
(408) 842-0858
nedspamspam_OUTnedtron.com
At 12:30 PM 8/18/01 +1200, you wrote:
{Quote hidden}

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2001\08\21@171729 by Jinx

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> Ned, could I get the schematic info as well?

Ned was kind enough to send me a pdf. It's a little large
(300kB) for general mail, so I was hoping, with Ned's
permission, to summarise and gif it and put it up as a
web page. Should be able to do that today

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2001\08\25@194545 by Jinx

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I've uploaded the NiCad zapper circuit, with a strobe light for
comparison.

http://home.clear.net.nz/pages/joecolquitt/nicdzap.html

Notes with the circuit say that the neon lights when there is
approx 180VDC on the 470u zapping cap. A dead battery
should make a loud pop as the dendrites are vapourised.
Do not leave the unit charged for more than a few minutes
and the 470u may need to be reformed if the unit is not used
for several months

These are some notes from Ned Seith

"Transformer T1 has the appearance of a miniature audio coupling
transformer, however, as can be seen in the attached diagram that
appearance is deceptive and this is a most unusual transformer
probably with a turns ratio between 1:500 to 1:700. The transformer
has the following markings; a white index dot, KMJ  X, G, 18K and
is bound in yellow tape.

Transformer T2 is housed in a red plastic enclosure that is ¼" x ¼
and ½" tall. There are two wire leads protruding from the bottom
and one wire lead protruding from the top. The only marking is HEI.

The xenon flash tube X1 is about ¼" in diameter and about ¾" tall
with a dark charcoal colored glass. There are two wire leads
protruding from the bottom. There is a copper ribbon band around
the outside of the glass tube. The top wire lead from transformer
T2 is soldered to the copper ribbon on the xenon tube.

I am familiar with the trigger coil and the flash tube from Radio
Shack and these parts are entirely different"

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