Update 2 on Quincy compressor and VFD

I have found approximately 170 microfarads of extra capacitance, in
bits and pieces. Wired them in. Set the V/f curve to linear (setting
0). I set the max frequency to 20 Hz.
With that, the compressor spins, runs, pumps, and the motor goes to
33% of its proper RPM. DC Bus Voltage drops from 320 volts to
approximately 255 volts when the motor is in action.
So it is a little victory, sort of.
Trying to set frequency to 25 Hz results in the motor getting stuck
and stopped.
So, it seems that extra capacitance helps, but I need much more.
I have ordered extra capacitors on eBay (electrolytic type, rated at
500 VDC).
I hope that maybe 1,000 uF would be about right.
Perhaps, for conservatism, I will supply them from a separate
rectifier, I have a pair of IRKDL71-06S02 rectifiers. It would be a
mess and I would prefer not to do it.
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And don't lose sight of your ultimate objective, which is to "flip" this package for a profit. If your eBay listing reads "... with 3 phase VFD modified to run single phase", it might scare off bidders. "Modified" is not a good word to use to describe a VFD.
Reply to
Bob Engelhardt
You got it. You are right. I will try to do it without extensive modification. I do not consider adding an extra capacitor to be a big modification.
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"Custom Fitted with..."
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Reply to
Gunner Asch
If you are adding capacitors to a VFD that is designed to accommodate just that, you are not modifying the VFD.
Joe Gwinn
Reply to
Joseph Gwinn
now you just have to find a buyer that wants a compressor with a VFD drive, and is willing to pay extra for it. If their shop has 3 phase already.......
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That proves the problem is where we expected it to be. But, 255 V is still really low. You should be able to develop 90 V RMS at that cap voltage (half of 255/1.414). Hmmm, (90/240) * 60 Hz = 22.5 Hz, so that is right on the money, too.
Well, you need a hold-up time of about 8 ms, and the line current for 10 Hp at 340 VDC is about 22 A, so 1000 uf (0.001 F) will sag at a rate of 22,000 V/sec. Ugh, if I did this right, it will still lose 176 V between line peaks. This doesn't sound right, but I don't see my error. Increasing the cap bank to 5000 uF (wow, that's a lot of caps at 500 V) would reduce the sag to about 34 V, which is probably the kind of voltage ripple you are aiming for (~10%).
Reply to
Jon Elson

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