The conversation seems to be over, but I have been out of touch about=20
the solar-charging of
NiMH (or Lead-Acid) batteries, and I am trying to catch up..

I just completed a three-year testing period, mostly to address problems=20
with solar battery charging> I'll pass along what we discovered:

1. Battery case temperature MUST be closely monitored. The ideal=20
charging point is VERY temperature-dependent. You will need to reduce or=20
suspend the charging current on hot days.

2. NiMH batteries are MUCH better than lead-acid systems in reliability=20
and weight. But the NiMH packs are VERY expensive.and until the costs=20
come down, you will probably specify lead-acid instead.

3. There are wonderful chips to charge NiMH packs. But these chips work=20
when the supply is steady. Unfortunately, solar charging doesn't work=20
that way: most of tne time the sun winks on and off behind clouds. This=20
fact plays hell with those smart charging chips. We were able to get a=20
reasonable, reliable charge by charging a large electrolytic then=20
release a "charge burst" into the battery when the level was exactly=20
correct You have a different current algorithm.for each type.

Everyone knows that the best battery is Lithium-Ion, but the problem=20
with overcharging and overtemperature is so serious that I don't=20
consider LiIon at all for solar applications.

I'll be glad to answer questions.

--Bob Axtell



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