"DoN. Nichols" wrote in message
...
In article ,
larry g wrote:
I have been using a balanced rotary phase converter in the shop now for a
coupla years with no problems. Now I have acquired a couple of VFD
drives.
One of the drives is rated for 220V single or 3-phase. Should I use
these
drives fed from the single phase, or should I put them on the 3-phase
side
of the RPC? I'm leaning toward using them downstream of the RPC so that
the
VFD's are not derated. Is there any electrical reason not feed them from
the RPC?

The only reason that I can think of depends on how well balanced
the RPC is -- at the load which the VFD and its load produces. If the
balance is not petty good, you will likely get the same poor
distribution of current through the rectifier diodes at the input to the
VFD that running from single phase produces.


The rpc is ( hopefully ) currently for balanced for the average inductive
load that is expected to be placed upon it.

This includes the converter and the average motor load ( inductive ) this is
a resonant circuit.

If the system is up to this, it would follow that further resistive loading
( as in cnc equipment ) simply increases current draw, no ???

My system supplies to several cnc machines, there is little reactive loading
of motors other than the coolant pumps.

It seems to work fine, there is 50 hp of idler on a 100 and a 70 amp feeder,
to 4 cnc machines, rated average 40 amps each.

So far, no problems.

Knock on wood.......

G

--

SVL