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I am repurposing some Sanyo nimh ev batteries for my solar system.Each "Stick" battery consists of 5 cells and they are 6 volts each stick of 5.I am wiring two of them together to get 12volts and 6.3 amps each.i have a total of 48 pairs that is a combined 12 volts 302 amps.What I need to know is what kind of charge controller on this scale would work for this battery type?
I assume these are Ford Escape/Fusion hybrid 5 "D" cell sticks?
First, you absolutely, positively MUST NOT parallel NiMH in any way. Things will go bad very very quickly.
NiCd and NiMH have a relatively unique characteristic of exhibiting a voltage DROP when they hit full charge. If you have two cells/batteries in parallel, one will hit full charge first, its voltage will drop, and the charger/parallel element will begin discharging into the fully charged cell(s), generate more heat and drop lower in voltage. Your first clue is usually the smell of the too-hot shrink.
This is called thermal runaway. Zero chance of a fire except for the shrink possibly burning off or anything flammable nearby igniting. 100% chance of destroying your cells.
The only way you can make this work is to parallel each element AFTER a diode that prevents backflow into the cell. This means that each and every element needs it's own charger, i.e., a 2S4P 12V battery would need 4 12V chargers - one for each 2S "12V".
There's a reason you NEVER find NiMH cells in parallel. This is it. True EV NiMH batteries like in the EV1 or Rav 4 were large format cells - none in parallel. Just much bigger cells and a lot of them in series.
