Subject: Re: Running 3 phase motor on 2 phase

From: [email-masked] (Kevin Pinkerton)
Date: 26 Jan 1996 11:53:13 GMT

It Metal Web News and it can be found at:

 http://tbr.state.tn.us/~wgray/index.html

Good stuff there.

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From: [email-masked] (James Kirkpatrick)
Date: 26 Jan 96 09:02:41 MST

In article <[email-masked]>, [email-masked](Eric Saville ) writes:
|>I am trying to get a hold of a schematic for a circuit to run a 3 phase
|>motor on 2 phase converter. I recently saw a posting that said they
|>were available at web site http://plains.uwyo.edu /"metal, when I try
|>access it I recieve an error- forbiden. Can any one provide me with the
|>schematic, or tell me another way to get them. Thank you.

Well, first you got the plains address wrong.  The character before
"metal" is not supposed to be a quote, it is the tilde character.
On many keyboards this is left of the "1" key, shifted.  In other words:
      http://plains.uwyo.edu /~metal

Second, I'm afraid I've not yet gotten a 3-phase article in place at the
above.  However, check out:

  http://tbr.state.tn.us/~wgray/howto/ph-conv/ph-conv.html

Jim

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From: 73744,2077/GO:[email-masked]
Date: 26 Jan 1996 18:58:18 GMT

In <[email-masked]>, [email-masked] (Jonathan M. Elson) writes:
>Eric Saville ([email-masked]) wrote:
>: I am trying to get a hold of a schematic for a circuit to run a 3 phase
>: motor on 2 phase converter. I recently saw a posting that said they
>: were available at web site http://plains.uwyo.edu /"metal, when I try
>: access it I recieve an error- forbiden. Can any one provide me with the
>: schematic, or tell me another way to get them. Thank you.
>

Don't be shy about trying a converter.  However if you make one, make a rotary
converter.  Lindsay Publishing has a book on how to do it.  The same info is probably on
the net.

I have a 10HP 3 phase air compressor, two stage, that I run in my garage off
the rotary phase converter I assembled.  It works fine.  I did have to back off the
cutout pressure on the compressor to avoid overcurrents in the compressor motor.
That is due to the fact that the converter is not entirely efficient in developing
3 phase power.  However, the low cost of used industrial compressors more than
makes up fo some slight inefficiencies of a converter.  If I ran the compressor
10 hrs a day.  I might consider a commercial single to 3 phase converter.

However, this type of homebrew converter can easily start the 10HP compressor.

Also, 10HP single phase motors are very hard to come by.

Good Luck,

Dave

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From: [email-masked] (darylb)
Date: Fri, 26 Jan 1996 17:00:31 +0000

In article <[email-masked]>, [email-masked]
(Jonathan M. Elson) wrote:
> snip... REAL 2 phase has a 90
> degree phase shift between the two phases, and it CAN be converted to REAL
> 3 phase with a simple center-tapped transformer, called a Scott-T.  But
> you probably don't have 2 phase power with the 90 degree phase shift.
> ...snip

I have never heard of this 2 phase power. Where is it used and why...what
are its advantages? How do you convert a 90deg phase shift to three 120deg
legs with a center tapped transformer?
Very curious
Daryl

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From: [email-masked] (Tony Jucewicz)
Date: 27 Jan 1996 08:06:06 -0500

Eric, try /~metals on the url. I just tried, and got through fine. It listed
"3 phase motor comming soon". Not sure what that means, but the site does
work.
Tony

Eric Saville ([email-masked]) wrote:
: I am trying to get a hold of a schematic for a circuit to run a 3 phase
: motor on 2 phase converter. I recently saw a posting that said they
: were available at web site http://plains.uwyo.edu /"metal, when I try
: access it I recieve an error- forbiden. Can any one provide me with the
: schematic, or tell me another way to get them. Thank you.
-- 
Tony Jucewicz   [email-masked]         Stone is forever ########
http://www.voicenet.com/~tonyspg             And EVER ################
BBS (610)346-9047    Stonework "HOW-TO"      And YES, EVER ###########

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From: [email-masked] (Paul Amaranth)
Date: 26 Jan 1996 14:26:26 GMT

In article <[email-masked]> [email-masked] (Jonathan M. Elson) writes:
>What do you mean by 2 phase.  Do you mean 220 with a neutral?  That is not
>really 2 phase, just center-tapped single phase.  REAL 2 phase has a 90
>The so-called phase converters are really a starting capacitor and relay.
>it drops out after the motor starts, and you get very little torque from
>it.  I used a cedarburg converter on my 1/2 HP Bridgeport for years, and it
>was a real trick to do any roughing cuts without stalling the mill.  I 
>finally got a Drivecon 1/2 HP variable speed drive (which takes 1 phase in)
>and now the motor never stalls.  I used to be able to stall it by holding the
>spindle with my hand!  I don't want to try that trick now!
>
>Unfortunately, the Drivecon gets expensive for the larger models.
>

Using a 3 phase idler motor generates "real" 3 phase within limits and
allows you to get close to 100% of the rated power on your tools.  The
metal web article is an excellent treatise on this subject.  You can
probably build one for $100-$150, maybe less depending on how fancy
you want to get and what you can scrounge.  As somebody else pointed
out the URL is http://tbr.state.tn.us/~wgray/index.html

I have absolutely no interest in trying to stall my mill (1hp Bridgeport)
using my hand :-)

The variable speed inverter is a really neat technology which gives you
infinitely variable speed.  If you can afford it, this has a lot of
advantages.  I did some looking into this a while back to see if it
was reasonable to build one from scratch.  I concluded that it's possible,
but going much over 1HP would get difficult (i.e. expensive).  These
things work by changing your 220AC into DC and then synthesizing the
correct three phase waveforms.  You can cheat a little by making a
stepped square wave instead of a true sinewave without getting into
too much trouble, but the more sophisticated devices use pulse width
modulation techniques to get the correct Voltage/Current characteristics
as seen by the load as well as varying the frequency with the motor
speed.  Controlling 220V at 15-20A is not trivial (in other words $$$)

--
Paul Amaranth  Manager User Services - office: (810) 370 4541 (also voicemail)
               (e-mail)     [email-masked]         
   Mosaic page: http://www.acs.oakland.edu/links/amaranth/amaranth.html

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From: "D. Hall" <[email-masked]>
Date: 28 Jan 1996 03:20:24 GMT

Stay away from that 2-phase stuff, It'll bite you in the ass. All you need the third leg
for is to start the motor, it runs on single phase. Put a small 3-Phase motor in line to
the motor you want to run. Start it by hand(rotation) hit it with juice, it will excite
the third leg so you can start what you wanted to run.

Dale