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Old 09-25-2011, 06:33 PM   #8 (permalink)
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Originally Posted by IamIan View Post
I think that is the reason people don't use this method.

If you manage to get ~85% efficiency ... getting 30A @ 900V from 12V looks like about ~2,650 Amps from the battery side

... snip ...
I see a silly math error in my example, where 6 batteries would service 6 inverters. And I have not been clear that there is a separate pair of fork truck batteries feeding each DC to AC inverter. My apologies.

I agree that 2650 amps would be far more difficult to deal with than purchasing different equipment.

Let's try this example again with better numbers. 6 pairs of fork truck batteries. Each pair gives 12V at 500A to one AC to DC converter (DC Converter) which is sized better. Each 5000W (instead of 1750W) DC Converter puts out 30A at 150VDC, assuming 85% efficiency. String the 6 DC Converter outputs together in series to get 30A at 900 VDC.

This discussion of theory ignores the fact that I'm over the GVRW for the truck, and assumes that I successfully cool the heat sinks well enough that nothing melts.

The two biggest costs for an EV, from what I've read, are the battery pack and the controller. I have access to cheap big heavy batteries that are low voltage, and a cheap controller which is very high voltage. I've come up with this goofy idea to make the two work together. And I want to do it safely.

I'm nervous because I have not seen this method used thus far. I'm not arrogant enough to think that I'm the first to think of this. It's been thought of before and rejected for some very good reasons that I'm looking for. If I can find a solution to those good reasons - I'll try it.

One reason is inefficiency. Losing 15% of your battery power is a huge penalty. Not only is it lost, but I must find a way to get rid of the heat from all of those heat sinks - fans, liquid cooling, whatever. If I can carry 15% extra (cheap) battery to balance that off, and find a reasonable way to get rid of the heat, that one seems surmountable.
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