sarrett@harlie.ICS.UCI.EDU (Wendy Sarrett) (03/15/90)
A few days ago I posted a message asking about how to save an apparently
burnt out rechargable battery. At the request of one of the sci.electronics
readers I am posting the responces I recieved. The idea seems to be that
one must get a very strong current going through the thing.
Wendy
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From: Adam Denton <asd@mtqua.att.COM>
Usually these battery packs are 4-6 nickel-cadmium cells connected in
series. When they're overcharged, *all* of the cells become somewhat
damaged, but are usually serviceable. However, what often happens is
that one or more cells develop an internal 'short circuit' which prevents
the individual cell from ever being charged again.
There's a very fun way to fix these internally-shorted cells:
1) Get a very big capacitor, highest uF rating you can find;
try 4700-10000 uF at 50 volts.
2) Somehow, charge the capacitor up to the highest voltage you
can; use whatever power supplies you might have. The higher
the voltage, the better! (Voltage must be greater than battery-
pack voltage to be effective; preferably twice as much, or
even bigger). Usually 12V-50V will work.
3) Using thick wire, connect charged capacitor across battery pack
terminals, observing correct polarity. When you complete the
circuit, a SURGE of current will flow through the battery pack
(which can be up to 50 AMPERES!) which will "melt" the internal
shorts.
4) Repeat above as many times as you like; usually I do it 4-5 times.
5) Charge battery pack immediately, or else the 'shorts' can re-form.
This usually works, but bear in mind that the internal cells of the
battery pack probably have 'vented' and are thus no longer working
at 100% capacity. Also, you'll notice a big spark when you complete
the circuit, so watch out. Also, when you make the final connection
that completes the circuit, make sure it's *good* -- that is, if you do
it by, say, touching an alligator-clip jumper to the capacitor, make
sure that when you actually press the lead to the capacitor terminal,
you PRESS IT VERY HARD IMMEDIATELY. You want to keep all resistances as
small as possible, so you get a nice, high-current surge.
Hope this helps.
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From: Hans-Ove Frimodig <hoven@cd.chalmers.se>
1. Discharge a 1000uF capacitor through the battery a few times. Charge the
capacitor to approx. 20-30 V before each discharge.
2. Charge the battery with a current higher than normal charging current
(10 times higher is no problem for the battery) until the voltage across
the battery starts to inrease steady. This should take max 10-30 sec.
If it doesn't work, try step 1 and 2 again with more uF, Volts and Amps !!!grege@gold.GVG.TEK.COM (Gregory Ebert) (03/15/90)
>There's a very fun way to fix these internally-shorted cells: > > 3) Using thick wire, connect charged capacitor across battery pack > terminals, observing correct polarity. When you complete the > circuit, a SURGE of current will flow through the battery pack > (which can be up to 50 AMPERES!) which will "melt" the internal > shorts. > +++++++++++++++++++++++++++++++++++++++++++++++++ Ah-ha !! Zap, Sizzle, and fry to the rescue !!!!! +++++++++++++++++++++++++++++++++++++++++++++++++