william_b_noble wrote:
so, after wanting a milling machine for a few years, I broke down and bought
one - this one
http://cgi.ebay.com/ws/eBayISAPI.dll...tem=7556615290
to be specific. I've mailed $$ to the manufacturer in Sweeden who will send
me the manual (cheap, 55 euros), so now while I'm waiting for delivery, I'm
turning my attention to the next problem - how to power it.

You will notice that it says it's 440V - I don't know if the motors, etc are
dual voltage or not, but my garage doesn't have 440 in it. Of course I can
use a transformer and a bunch of VFDs or a rotary phase converter, or ....
but I wonder what the group experience might be. I can also rewind the
motor for 220 and use an off the shelf VFD, or I can modify a 440V VFD so it
accepts a DC input and then make a DC power supply (e.g. full wave doubler)
to supply it from the 220, or .......

so, what do you think?

I've tried both. I found that connecting a 3ph transformer to a RPC
caused the transformer to heat up quickly. I actually burned one out.
I imagine that part of the problem was the fact that the RPC was't
balanced with caps as well as it should have been.

I have had more luck with using a single phase transformer to boost the
voltage up the voltage needed by the VFD and feeding a VFD designed for
3ph input with single phase (but at approximately the right voltage).
This is simply a matter of connecting the two single phase conductors to
two of the three line in terminals on the VFD. The VFD should be
derated, but in a milling application I don't see it being terribly
important as the starting load is low and the machine if used by a
hobbiest is gernerally not pushed too hard.

Since large single phase transformers are hard to come by, I am
experimenting with using 3ph transformers to boost the single phase
input. In a week or so I will get a used VFD I bought on ebay hooked up
to such a transformer so that I can try it out and let you know how it goes.

stan