Re: Siemens SED2 VFD / Quincy 10 HP compressor troubles

On 2007-10-29, DoN. Nichols <dnichols@xxxxxxxxxxx> wrote:
According to Ignoramus10340 <ignoramus10340@xxxxxxxxxxxxxxxxxxxx>:
On 2007-10-29, Jon Elson <elson@xxxxxxxxx> 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.

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.
This will reduce the current surge through the caps -- at least until a
short power outage shuts off the VFD and then the power returns. If
this works, you may want to add a circuit to automatically add the caps
as you start up the VFD. Or -- you can give each additional cap its own
bridge rectifier, so you are not overburdening the built-in rectifier.


I found my 92 uF cap and will try it tonight to see if it makes any
difference. The question of "switching in" caps and "inrush current"
is relatively well studied. I am indeed concerned about burning the
rectifier. I do have a rectifier of my own. I will probably need to
get more caps.

i
.

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