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From: jb@lydia.mae.cwru.edu (Jim Berilla)
Newsgroups: sci.electronics
Subject: Re: 1 phase to 3 phase conversion
Message-ID: <1991Mar30.015157.27798@usenet.ins.cwru.edu>
Date: 30 Mar 91 01:51:57 GMT
References: <1991Mar28.191005.1653@rodan.acs.syr.edu>
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In article <1991Mar28.191005.1653@rodan.acs.syr.edu> mamiller@rodan.acs.syr.edu (Mark A. Miller) writes:
[ needs a single to 3 phase converter ]

Many companies make variable speed drives for 3 phase motors.  The smaller
ones (5 horsepower or less) can use single phase for input.  They also have
a number of useful features.  They can vary the speed of the motor (by
changing the output frequency) from about 30% to 150%.  They can provide a
soft-start by ramping the motor speed up over a period of time.  Overload
protection is usually built in.

They're not cheap, though.  About $800.00 for a 5 hp controller.  They're
small (9x12x6 inches for 5 hp), quiet, and easy to use.  Given time, you
could build your own, but I haven't seen any cookbook plans for building
them.  I've done some work with high power circuits like this, and the
first few weeks were spent watching power transistors turn into plasma.
Subtle problems can cause not-too-subtle results.  (If anybody's inter-
ested, the TL494 under some cases can clock the same output twice in a
row, rather than alternating the two outputs.  Mail me for the gory details.)

A freind of mine is using a 5 hp unit to run a 2 hp mill in his basement.
Works great.  The variable speed control is an added bonus.

Another person tried to run a 1 hp machine with a 1 hp controller.  I don't
know the details, but he said it didn't work.

One nice thing about 3 phase motors is that you can flip them into reverse
without waiting for it to stop.  I was tapping a bunch of holes on the mill
once, and that ability sure saved me a lot of time.  No overload indication
when going from full speed forward to full speed reverse.
-- 
      Jim Berilla / jb@falstaff.cwru.edu / 216-368-6776
"My opinions are my own, except on Wednesday mornings at 9 AM,
           when my opinions are those of my boss."