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Spockie-Tech
Site Admin
Joined: 31 May 2004
Posts: 3160
Location: Melbourne, Australia
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There is no cheap, easy way of charging a NiCd (or NiMh) battery *fast* without some form of temperature monitoring or voltage feedback to sense the "end-of-charge" point.
The quicker you want to pump current back into them, the better your charger needs to be to accurately sense when they are full and stop charging them, overcharging is the biggest killer of NiCd's. If you're prepared to stand there while they charge and constantly feel for them getting hot, you could monitor it manually, but it would be like watching grass grow..
The best "simple" example of a temperature controlled fast charger I've seen on the net is here.. http://www.capable.ca/rcstuff/fastchg.htm - It could be improved a lot with the replacement of all that discrete circuitry with a micro, and it will only charge 7-cell packs as shown, so dont build it expecting to charge 12 or 24v packs with it. Its aimed at the RC car guys with their 7.2v packs. It could be modified, but you will need someone with some serious electronic skills to assist.
I'm not sure how sensitive to ripple (non stable voltages) on their charging cycle they are though. Lead Acid Batteries are *very* sesitive to it. It does nasty things to the formation of the spongey lead structure created by the acid. Nicad chemistry might not be a little more tolerant, but its probably still a good idea to have the power supply as smooth as possible for maximum battery life. _________________ Great minds discuss ideas. Average minds discuss events. Small minds discuss people
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Sun May 22, 2005 2:16 pm |
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Spockie-Tech
Site Admin
Joined: 31 May 2004
Posts: 3160
Location: Melbourne, Australia
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Yep, If you want stuff from other people, then you generally have to offer them something in return.. Jobs are great for that kind of thing..
The good news is, walks on the beach, sleeping in on a rainy sunday morning and lots of other good things in life are still free..
The free things generally arent much good for Bot building or Cars though..
*ahem, back on topic Brett - where were we ? - ah yes, NiCad charging*
Might be interesting to hear from Jeff J (Still lurking out there Jeff ? - you've been quiet for a while again) - He uses 7.2v RC Car packs to power El-Bravo I believe.
If you dont mind having some pack connectors in your Bot to series daisy-chain them up to a useable voltage, yet still be able to seperate them to charge them with the low-voltage-only cheaper RC car chargers, then that might be an option to get away with cheaper chargers.
Its a lot easier (electronically) to turn 12v (from a car battery) into 7.2v charging than it is to step it up to a higher voltage required to charge a 12v (or more) pack, so your range of available chargers would be much greater for the lower voltage packs _________________ Great minds discuss ideas. Average minds discuss events. Small minds discuss people
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Mon May 23, 2005 9:48 pm |
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