alt.energy.homepower

On 18 Feb 2008 07:27:46 -0500, nicksanspam@ wrote:
> wrote:
>>The problem, particularly in series parallel strings, is if one goes
>>bad, replacing it can jeopordize the rest. They NEED to be well
>>balanced to work well and live long.
>
> How well-balanced? How can we measure that?
> Series resistance? Self-discharge rate?

off the top of my head...
* I-V curves during charge and discharge (they'll be different) which
is a way to derive internal resistance, but internal resistance
is never constant, hence the curves.
* charge acceptance (applied voltage and current resulting in how much
charge in the cell) which is implied by the I-V curves but not defined
since absorption time at full voltage can vary
* Ah capacity is not terribly critical if the other parameters were to
match, but in practice they won't match if Ah doesn't match

It's actually a lot more complex than matching transistors for an
amplifier, so typically we punt. In practice cells are never perfectly
matched, so periodic equalization charges are necessary to compensate.
The greater the mismatch, the more frequently equalization is needed,
and equalization is tough on batts.

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