Re: Phase Converter

If you want to just get the motor spinning, remember that you only
need a fraction of the amps to get 50% RPM on the motor. The soft
start motor starters or very small VSD's can be 1/4 of the hp (or
less) to get motor spin near 80% of speed.

I'm not positive but I think the amp draw is a square root function,
so 1/4 amps will spin it 50% and 1/16 amps will spin it 1/4 speed.
We used to test large hp motors with small VSD's to verify operation,
just keep under the VSD rate hp (amps) and you can get it to spin.
Once it is moving that fast, the amp draw to get it spinning full
speed is vastly reduced.

Dave

--- In CAD_CAM_EDM_DRO@y..., "Mr. sausage" <sirsausage@h...> wrote:
> 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@p...>
> >Reply-To: CAD_CAM_EDM_DRO@y...
> >To: CAD_CAM_EDM_DRO@y...
> >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/
> >
> >OFF Topic POSTS: General Machining
> >If you wish to post on unlimited OT subjects goto:
> >aol://5863:126/rec.crafts.metalworking or go thru Google.com to
reach it if
> >you have trouble.
> >http://www.metalworking.com/news_servers.html
> >
> >http://groups.yahoo.com/group/jobshophomeshop I consider this as
a sister
> >site to the CCED group, as many of the same memembers are there,
for OT
> >subjects, that are not allowed on the CCED list.
> >
> >
> >
> >Post messages: CAD_CAM_EDM_DRO@y...
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> >List Owner
> >
> >
> >
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> >
> >
>
>
>
>
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