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Old 09-25-2011, 07:41 PM   #10 (permalink)
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Originally Posted by thingstodo View Post
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.
6 inverters each rated 5,000 watts each , don't usually come very cheap... unless you have a very good source for them.

Also remember those peak rating numbers on inverters are only for surges ( a few seconds ) ... if you run the inverters for any significant amount of time at more than the continuous rating , you have a good chance of burning them out to an early death.

What kind of Lead Acid batteries are you considering? Do you have any model numbers or specs on them?

Lead is heavy to start with ... and Lead usually doesn't like high Amp current rates very much either ... plus the Peukert effects of the harder you push them the less you get out of them ... if you are pushing them too hard they might not have a very long service life under the stress either.

And as you already noted ... even if you get ~85% efficiency ... those inverters alone will be pumping out over ~5kw of heat ... plus the additional heat from the batteries themselves ... plus the additional heat from the 900V VFD ... plus the additional heat from motor.

What kind of motor is it? Do you have any model numbers or specs? ... If the only reason to need this step up to 900V is to use the VFD as a motor controller ... than we can look at other motor controller prices ... which will put a cap on what the VFD + Inverters would have to be under to be a cost effective alternative.
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