Re: (ET) Time for a NiMH Elec-trak

["David Roden" <etpost drmm net>]

I've read of at least one person who built a road EV using (I think) 3 or 
4 
Prius packs.  The capacity is limited.  They are supposedly just well 
matched D cell size modules.  (If they don't work out for your tractor or 
Prism, you could fit all your friends' and relatives' flashlights. ;-)

I also wonder if they're not optimised for high power use rather than 
cyclic 
use.  The Prius specs rate the pack at 28kW, IIRC, or about 100 amps peak, 
pretty darn good for a D cell.  In the Prius they are held between about 
50% 
and 80% SOC, which is how they get their long life.  Of course that uses 
only 30% of their capacity, but that's all the Prius needs since it seldom 
goes very far or very fast on battery alone.

I believe you can discharge NiMH strings in parallel, but I wouldn't 
advise 
charging them in parallel.  From what I understand, they don't share the 
charge very well.  You could use a contactor lashup to hook the whole 
shebang in series for charging.

You will need proper charge management, or you'll ruin them in short 
order.  
The usual algorithm is negative delta-V - the charger looks for a slight 
drop in on-charge voltage - but there may be others.  You'll definitely 
need 
a fairly smart charger.  A Brusa NLG512 might do the job for you.  Metric 
Mind sells them for around $4,000 each.  Email them and ask whether they 
have a profile for NiMH.  


David Roden - Akron, Ohio, USA

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