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- Path: sparky!uunet!gatech!purdue!mentor.cc.purdue.edu!noose.ecn.purdue.edu!en.ecn.purdue.edu!ghg
- From: ghg@en.ecn.purdue.edu (George Goble)
- Newsgroups: sci.electronics
- Subject: Re: Nicad Zapper
- Message-ID: <1992Aug16.220410.15327@en.ecn.purdue.edu>
- Date: 16 Aug 92 22:04:10 GMT
- References: <1992Aug7.161224.29053@awdprime.austin.ibm.com> <11AUG199210550479@rover.uchicago.edu>
- Organization: Purdue University Engineering Computer Network
- Lines: 51
-
- 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
-