DoN. Nichols wrote:
According to Ignoramus10340 :

On 2007-10-29, Jon Elson wrote:


Ignoramus3971 wrote:


[ ... ]


I thought that dropping to 220 under load was kind of normal?



No, it is NOT normal. Now, of course, you are running the VFD on single
phase, and it was not designed for that. So, I would expect a
significant voltage drop, maybe to as low as 300 V or so. That's what
the caps are for. But, 220 VDC is abnormal.


So, it sounds as though I need more caps.
Lots more, probably no way it will work at less than 1000 uF.



Beware -- more caps with the same rectifier may result in too
much current through the rectifier and thus burn out the rectifier.
Perhaps power up the VFD with the standard caps, then switch in an
additional one, then another, until you have the full set in place.
You can't do this! Connecting several hundred uF of caps (some charged,
some not) together with a switch will cause a HUGE bang, as loud as a
pistol shot, and the switch will be toast, the very fist time.

Larger VFD's, like my Tosvert 11 KVA drive, have a resistor and relay
circuit that slowly charges the cap bank before making the direct
connection. It wouldn't be real hard to make up such a circuit if it
doesn't already have something like this. You turn it on with a big 240
V light bulb or resistor in series, then short out the resistance after
a second, and before allowing the VFD to power the load.

Jon