Subject:
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Re: Overcharged NiCd Batteries?
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Newsgroups:
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lugnet.robotics.handyboard
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Date:
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Tue, 9 Apr 2002 20:32:39 GMT
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Viewed:
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7379 times
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Jeremy,
You hooked it straight to a 12V power supply? That's kind of a brutal way to
charge NiCad's. Who knows what that's going to do. If it's regulated at
500mA, then it should take just a little over two hours to charge a 1000mAh
pack, which is a bit on the fast side. NiCad batteries can be left on a
trickle charge for an indefinite period, although I think doing that is hard
on them in the long run- but we're talking years. "Trickle charge" is
typically 1/10 of the capacity of the cell, which is 100 mA for a 1000 mAh
cell, and it should take a bit over 10 to 12 hours to charge at that rate.
If you left it at 500mAh for 12 hours, they are probably cooked. The way
they get destroyed is they overheat and "vent"- they have a valve that lets
the electrolyte out before they explode.
NiCad cells have a "nominal" voltage of 1.2 volts, which is 9.6 volts for 8
cells. They can give up to 1.4 volts for a short burst with a fresh charge,
whch would explain your 11 volts. Even vented cells can show a voltage with
fresh charge, they just won't have any capacity.
You might be able to tell if the cells have vented visually. Is there a
white powder around the positive contact of any of the cells? Then they are
surely toast. If there isn't, that doesn't mean they are OK- it doesn't show
right away on all cells.
-Benton
P.S. I fly electric powered R/C planes, which teaches a lot about NiCads
very quickly.
In lugnet.robotics.handyboard, Jeremy Overesch writes:
> Overcharged NiCd Batteries?
>
> Hello,
>
> I recently built a handyboard and bought a set of 8 1000mAh NiCd batteries
> for it. I charged the batteries using the handyboard and a 12V 500mA DC
> adapter from radio shack. I only charged the batteries for approximately 12
> hours, and they seem to work fine. However, when I measure the voltage of
> the batteries, it's higher than 9.6 volts, when they dont work any more. I
> then tried a charger that charges at 150mA and left it on for approximately
> 16 hours. The charger had not turned off yet when I stopped charging. The
> batteries measured over 11 volts with no load. After draining the batteries
> once again, I measured the voltage when I had the handyboard turned on. It
> measured 7.8V. When I turn it off and unplug the batteries, the voltage
> slowly rises to 9.4V. Is this normal or should I get new batteries? I was
> also wondering if the 500mA power adapter is adequate for the 1000mAh batteries.
>
> Thank you for your time,
>
> Jeremy Overesch
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Message has 1 Reply:
 | | Re: Overcharged NiCd Batteries?
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| I'm sorry, I didn't explain myself well enough. I meant to say that I used the 500mA 12V power supply (block AC to DC transformer) by connecting it to the handyboard. From the specifications, the handyboard is supposed to be able to charge 800mAh (...) (23 years ago, 9-Apr-02, to lugnet.robotics.handyboard)
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Message is in Reply To:
| | Overcharged NiCd Batteries?
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| Overcharged NiCd Batteries? Hello, I recently built a handyboard and bought a set of 8 1000mAh NiCd batteries for it. I charged the batteries using the handyboard and a 12V 500mA DC adapter from radio shack. I only charged the batteries for (...) (23 years ago, 9-Apr-02, to lugnet.robotics.handyboard)
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