alt.energy.homepower

In article <+noZs_0802@>,
sylvan butler wrote:

> 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.

What about having separate parallel strings with separate chargers for
each string? Each string would have to have a diode to keep it
isolated, granted that loses 1/2 volt.

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