Re: [CAD_CAM_EDM_DRO] Phase Converter

Raymond Heckert wrote:

> Tim, do you, or anyone on-list know how to build a VFD??

Sure, there's a kit from international Rectifier for the power section, then
you buy a chip from Intel or Motorola with a $9900 development package,
and you spend a year tinkering with code. Plan on spending $150,000
to get it working. (I know, been there, done that!)

> I need something
> to start a 15 hp, 3-phase motor, sort of softly. I have single-phase 230vac
> at up to 100 amps. I can get around in 'discrete' electronics pretty well,
> so I wouldn't have a problem building one. Is it just a matter of charging
> a few joules into two big D.C. cap's front-to-back, and feeding a magic
> sinewave set of SCR's through a filter, or is it a real beastie? Reply
> off-line, if this gets to be OT.

No, you can't use SCR's, there's no practical way to turn them off. Back
in the "old" days, there were cycloconverters and real inverters made
with SCRs, they were the size of refrigerators - like walk-in boxes, even!
Now, we use IGBTs, but it will cost you $350 to get a power block good
for 15 Hp. Driving the IGBTs is a job for a real pro - I'm close now, after
blowing up a couple thousand $ of FETs and IGBTs, I pretty well understand
the problems.

Buy a surplus VFD from Dealer's Electric or find one on eBay. You should be
able to find one for under $300 with a little patience. If you need the full 15 Hp
output of the motor, you will need a 20 - 25 Hp VFD, at least. If you won't
need the full 15 Hp, you can probably get by with a good 15 Hp VFD, especially
if you keep it in a reasonably cool environment.

I would say you are completely off your rocker to try to build one of these
yourself when you can just buy them for less than the cost of ONE set of
parts. And, be assured, if you built it yourself, one set would not be ANYWHERE
near enough!

Jon