Re: [CAD_CAM_EDM_DRO] Phase Converter

If you just want to "start a 15 hp, 3-phase motor, sort of softly", you can
probably use what's commonly called a "soft start". These *are* SCR
controlled devices which essentially are large light dimmers. The firing
circuitry is not trivial for these either, but no where nearly as
unforgiving as inverter drives. I designed the "smart" 68HC16 based ones
manufactured by www.eaco.com.

An example of a 125 HP starter on ebay can be seen at
http://cgi.ebay.com/ws/eBayISAPI.dll?ViewItem&item=1716212325

>From: Jon Elson <elson@...>
>Reply-To: CAD_CAM_EDM_DRO@yahoogroups.com
>To: CAD_CAM_EDM_DRO@yahoogroups.com
>Subject: Re: [CAD_CAM_EDM_DRO] Phase Converter
>Date: Tue, 26 Mar 2002 18:56:27 +0000
>
>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
>
>
>Addresses:
>FAQ: http://www.ktmarketing.com/faq.html
>FILES: http://groups.yahoo.com/group/CAD_CAM_EDM_DRO/files/
>
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>
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>
>
>
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