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Old 09-25-2011, 02:12 PM   #4 (permalink)
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Originally Posted by Ryland View Post
What is a VFD?
I would guess that a DC to DC converter like you are talking about is going to be about 85% efficient, just judging from other DC to DC converters that I've seen, but finding one that will deal with 6v is going to be hard and finding one that can deal with the high amps that you are talking about (500 amps or more) is going to be the really hard part.
I would be happy with 85%. Re-using fork truck batteries is inexpensive and carrying a couple more for decreased efficiency seems reasonable. I need 35 HP out, so I'll need about 41 HP in.

A VFD, or Variable Frequency Drive, also referred to as an Adjustable Speed Drive (ASD) is an industrial motor controller. It takes three phase AC in, converts to DC - usually with 6 diodes in a bridge, has some DC filtering capacitors and inductors, then uses pulse width modulation to 'build' AC at the frequency that you want your motor to run and sends it out. This would replace the 'Curtis' controller, or the ReVolt Cougar.

The off-the-shelf DC to AC inverter I've tried takes 12V in and puts out 150- 155VDC. With 85% efficiency, that would be 12V in at 170A continuous, 340A peak. Output would be just over 11A continuous at 150VDC.

I should have said 'two fork truck batteries in series' for each inverter.

The DC output of the inverters appears to be isolated from the input terminals, and more importantly, isolated from the heat sinks. I'm testing so far - planning to put multiple inverters in series to add voltage, perhaps multiple strings of inverters to get the required current.

I need about 30A at 900VDC. That should give me 35 HP, about what I expect that 'SalvageS10' will need to make highway speed.

I've read about all of the AC conversions that I can find. No one seems to be using this method. I expect there are one or more reasons for that. I'm trying to figure out what the issues are and work around them.
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