Re: [CAD_CAM_EDM_DRO] Phase Converter

From: "Tim Goldstein" <timg@...>
Date: Mon, 25 Mar 2002 15:42:36 -0700

I have built a phase converter (it worked just fine) and then I bought a
VFD. I am much happier with the VFD than with the phase converter. Not only
does the VFD handle the phase conversion, but it lets me ramp up and ramp
down the mill so that when it starts there is no huge power draw and when I
shut it down it comes to a stop in about 1/4 of the time that it did with
the phase converter.

If you are determined to build a phase converter there are about 4 links in
the list off the FAQ page.

Tim

There styles of machine where a VFD is not an optimal solution. One
with several motors is one where you may be better off with a
converter. The other (at a minimum you will have to rewire) is one
with a magnetic starter. To save some stress on their output
transistors, the VFD's I have, ramp the motor up slowly. They don't
like having a motor just cut in, and in the case of magnetic starters,
you have to put the converter after the starter, and use its controls
to start and stop the motor. If you just plug your machine into a
VFD, without providing power for the starter relay, it won't have any
voltage to engage, with the VFD set for "stop".

My buddy has your basic huge Van Norman universal mill. We are just
getting it running. I am loaning him a VFD so we can get some work out
of it asap... Our first attempts to use it were less than an
unqualified success.

It has a 3hp spindle motor, with separate 2hp feed and (less than 1hp)
coolant motors. It also has a magnetic starter for each of these. If
you have the VFD running, and hit the spindle start button, it can
overcurrent trip the VFD. If you try to use the VFD's controls,
without re-wiring things, the start relay has no juice to engage
before you tell the VFD to run.

For now (we are just getting it back on-line) we will just wire
straight from VFD to the spindle motor, and not try to power the feed
or coolant motors. The switch box on the side is a pretty tangled
mess, with 3 separate starter's, a big rotary switch to select what
you want active (spindle, spindle and feed, spindle and coolant, all
three...) so we aren't going to tackle it right now...

-dp-
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