🚀 go-pugleaf

In article <11AUG199210550479@rover.uchicago.edu> frank@rover.uchicago.edu writes:
>In article <1992Aug7.161224.29053@awdprime.austin.ibm.com>, dewey@vpdbox.austin.ibm.com writes...
>>All the talk about NiCad Memory and such, I decided to post this.
>> 
>>"One of the most useful and money saving kits you can buy!, The Nicad
>>Zapper Kit repairs those nicads that no longer will take a charge
>>due to the growth of interal 'whiskers'. The Zapper operates from
>>6VDC (battery not included) and develops 300 VDC which it momentarily
>>applies to the nicad to 'blow the whiskers' without damagaing the battery. 
>>Repairs about 90% of nicads in sizes AA to C cells. After zapping, the
>>nicad is ready to be fully charged again. Size of board: 2.6" x 2.7".
>>Complete with all parts, PC boards and instructions. Skill Level 3."
>> 
>> 
>>Anyone have any comments about such a device.
>
>	From one of Bob Pease's articles, a simpler zapper consists of
>	charging a 500ufd battery to around 12 volts, then discharging
>	it into the cell. If that doesn't work, up the cap by a factor of 10.
>
>	I have tried it, it does work, batteries with a dead short do come
>	back to life. Don't think 300 volts is necessary, main question is
>	how much energy (charge * voltage) to dump into a battery to blow
>	the wiskers. Like Bob's idea of starting out small, then going up
>	in capacitance in steps.

How about 120,000 ufd @ 55V.  I inherited a 7.5V cell phone pack with
two shorted cells.  A battery "reconditioner" (has caps to zap it for
whiskers), didn't heal it for long.  I zapped it with the above cap,
didn't work either.  The pack has some sort of positive temp coef
device which goes open circuit above about 1 amp or so.  Short circuit
protection.  This limits the amount of zap.  I popped open the pack
(AA cells, 700 mah or so), located the two shorted cells. I charged up
the cap to 55V, and administered it with clip leads and paper clips to
the cell casings (bad idea).  The paper clip vaporized (like a black-cat
firecracker), and burned a hole into the side of the cell, about 1/8"
deep (you could see the wrappings/foil).  It got rid of the short though.
I sealed it up right away with refrigeration epoxy.. Dunno how well
that pack will work.  My orig cell phone packs are still performing
well (approx 2200 charge/discharge cycles over 6 years now).. but
they have been "taken care of".  Slow charging (16 & 24 hour rates),
and discharged down to 1.1V per cell.  One pack shorted a cell last dec
from whiskers, but the cap zapped it ok (did not open it up to bypass
the current limiter).  

I have heard that pulse charging Nicads with 10X the current at 10%
duty cycle keeps the whiskers down. Any of you used chargers which
sense the slight voltage depression at end of charge to terminate
a "fast charge"?

--ghg