>NiMH are not as awesome as you may think in traction application.
>They require a BMS in full discharge application unlike hybrids. As
>a Vectrix owner I know there drawback well, and like almost all
>Vectrix owners, I am planning to upgrade to lithium. NiMH has a
>higher internal resistance, this make them more expensive to charge
>and they generate a lot of heat when used, unlike lithium they need
>active cooling systems as well as a BMS.
NiMH dry cells doubtless have higher internal resistance than the
murdered flooded wet cells, and some brands are substantially better
than others. (tho 3 banks of good D cells, 12 pounds, still starts my
car.) If they're getting hot, Vectrix probably runs them too hard.
Sounds like they should be doubled up in amp-hours to reduce currents.
>And even the low density LiFePo carry more charge per pound. But if
>I can't talk you out of wanting some Ni cells stop by any Vectrix
>forum as many of us are switching to lithium you can pick up used
>cells on the cheap.
A typical NiMH AA cell is: 1.2 V * 2.5 AH / 30g = 100 WH/Kg.
A NiMH D cell is: 1.2 V * 10 AH / 163g = 73 WH/Kg.
(Derate for weight of packaging & connections.) The D cells handle
higher currents - more than 4 * the AA cell.
A spec I saw for some LiFePO3 - a while back - was 60 WH/Kg.
and for some flooded NiMH, also a while back, also 60 WH/Kg.
Craig
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