phase converters for big iron

Kevin Handy kth at
Wed Apr 27 11:18:32 CDT 2005

Mike Gemeny wrote:

>You can build your own rotary phase converter from an old 3 phase motor. And 3 phase motors can be some of the cheapest to get second hand.
>It seems that a three phase motor will not start if a phase is missing, but if it is running it will continue to run if a phase is removed. The combination of the energized windings and the spinning rotor will have the effect of creating the third phase, although this is not an efficient state of affairs.
>In my home machine shop I first used a bank of capacitors to help synthesize the third phase. The bank of WWII tin caps was adjusted until the lathe motor was running with the least buzz.
>Then I added a three phase chipper. The first time I slammed the lathe from forward to reverse with the chipper I was surprised that the lathe reversed and the strain of reversing it could be heard in the chipper motor.
>Then I added a three phase grinder to the setup. But when the grinder was used alone the cap bank was the wrong size and the motor had a terrible buzz in it. So I released the drive belt on the lathe and turned on the lathe motor. Bingo! The buzz in the grinder was gone!
>So in this configuration I am in essence using the caps to start the lathe motor as a rotary phase converter for the grinder.
Note that you can now buy solid state phase converters.

I have a brother that switched to one in his wood-shop, and
it has many advantages: More efficient (cheaper to run);
more motors work with it; more power is available on
created phases; quieter; etc.

It works much better than the rotery ones he used to
use; which were designed as phase converters, not just
some large three pase motors; and his equipment
is much happier, too.

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