Wednesday, May 13, 2009

Batteries Part 5 Lead-acid

Lead-acid batteries are heavy, don’t hold as much power as even a NiCad, and don’t tolerate complete discharging. Even a marine deep-discharge battery can only handle 50 or so cycles before failure, and a car battery will fail after only a few times. They use toxic materials, are nasty dirty batteries, and a pain to deal with. So, why do we still use so many of them?
Lead-acid cells have a voltage of 2.1v fully charged, and have a very level discharge curve, a discharged lead-acid cell will have a voltage of 2v. Lead-acid have a charge efficiency of 60%, just 3/5 of the power that you put in comes back out. The normal configuration is to have them in a common case to produce either 6v or 12v. Lead-acid batteries can discharge at a very high rate, almost as good as a NiCad. Their real strengths are their insensitivity to charge and their high shallow cycle rate. Lead-acid cells can be charged with a basic constant-voltage charger, fast or slow, they just don’t care. Trickle, fast, however they get fed power, they take it. Also, as long as they don’t get discharged more than 20%, they can provide thousands of cycles. Finally, a lead-acid battery is better than just about any other type at low temperature operation (believe it or not).
Lead-acid: cheap starter batteries. Any other use is suboptimal.


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