On 6/17/21 8:45 PM, Gregg Eshelman via Emc-users wrote:
Everything I've read on VFDs says do not feed them from a transformer.
WHY? Every VFD is being run from a transformer! What's
that thing up on a pole beside your house, or on a pad
behind your industrial shop? Yes, it is a transformer.
There really is no reason to NOT use a suitable transformer
to provide the correct voltage to a VFD.
First, you need to be sure your VFD can run off single-phase
power. If not specifically rated for it, then up-sizing the
VFD for 1.5 to 2X the motor rating will usually be fine.
Nor can you put a transformer between the VFD and the motor.
Yes, this is generally correct.
Most of them say *nothing* should be between the VFD and the motor, direct
connection only. The one on my 1943 Monarch 12CK lathe recommends a noise
filter on the input side to prevent noise feeding back into the line from the
VFD from getting to other stuff on the circuit.
Your 1943 Monarch does not have a VFD. The 10EE lathes had
two different schemes, depending on year. The old ones had
an AC motor-driven DC generator, the later ones (1960 or so)
had a thyratron drive for a shunt-wound DC motor. (Or,
maybe you are using a VFD to provide 3-phase power to the
motor-generator.)
Jon
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