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.
i
Reply to
Ignoramus10340
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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.
Bob
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.
i
Reply to
Ignoramus1285
"Custom Fitted with..."
Gunner
"[L]iberals are afraid to state what they truly believe in, for to do so would result in even less votes than they currently receive. Their methodology is to lie about their real agenda in the hopes of regaining power, at which point they will do whatever they damn well please. The problem is they have concealed and obfuscated for so long that, as a group, they themselves are no longer sure of their goals. They are a collection of wild-eyed splinter groups, all holding a grab-bag of dreams and wishes. Some want a Socialist, secular-humanist state, others the repeal of the Second Amendment. Some want same sex/different species marriage, others want voting rights for trees, fish, coal and bugs. Some want cradle to grave care and complete subservience to the government nanny state, others want a culture that walks in lockstep and speaks only with intonations of political correctness. I view the American liberals in much the same way I view the competing factions of Islamic fundamentalists. The latter hate each other to the core, and only join forces to attack the US or Israel. The former hate themselves to the core, and only join forces to attack George Bush and conservatives." --Ron Marr
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.......
Reply to
Tony
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%).
Jon
Reply to
Jon Elson

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