4 May
2017
4 May
'17
9:17 a.m.
On May 4, 2017, at 11:54 AM, Jon Elson via cctalk
<cctalk at classiccmp.org> wrote:
... But, you DO need a true sine wave source, and VFDs do not produce sine waves, they
put out 400 V PWM waveforms that look fine to a motor, but not good at all to electronic
loads.
I wonder how true that is. Consider that (for machines of this era) power supplies are
probably transformer input, to a rectifier and then a filter. The transformer would
smooth out the VFD output pulses, and whatever is left would definitely be removed by the
output filter. The only question I can see is whether the rectifier diodes have enough
reverse voltage margin to deal with whatever peaks pass through the transformer. (The
transformer itself certainly will, given normal insulation design/test practice for power
transformers.)
If the power supply is a swiching regulator, the details are slightly different but the
overall picture is similar. Then you begin with a rectifier, which would have to be able
to deal with the input spikes, followed by some amount of filtering. Once past that I
don't see any further issues.
An electronic circuit that looks at the incoming AC waveform directly would certainly have
issues with a VFD, but I can't think of too many examples of that. A KW-11/L is one
exception that comes to mind... :-)
paul