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Re: [TCML] single phase synchronous motor

Have you tried running the motor as a capacitor run motor?

On the net, there are circuits for running three phase motors off a single phase with a motor run cap connected to the third winding. I don't know for sure if the motor would run synchronously with this arrangement or not, but it would be relatively simple to try. Many amateur machinists hook up one beefy freewheeling motor in this way to generate three phase power from single phase for metal working equipment. I don't see why you couldn't just use the freewheeling motor alone to drive your gap.

Just to be sure to use motor run capacitors, and not the much cheaper motor start capacitors. Usually, run caps have deep drawn aluminum or steel cases, like microwave oven caps, while start caps usually come in plastic cases. Motor start caps will overheat and fail spectacularly if run for more than a few seconds.

Generally, these arrangements use a larger capacitance value to get the motor up to speed, and then you drop out part of the capacitance for a smaller value for the steady state run condition. You can use a relay controlled with a manual start switch to implement this function.


On 1/26/2015 12:07 PM, twoten wrote:
I'm trying to find a 120v 1200rpm synchronous motor to spin my 6
electrode rotating spark gap. I have a 1200 rpm synchronous motor but
it's 3-phase and 230volts. I have been looking into microcontroller
solutions and building my own 3-phase motor driver. I have a vfd that
can spin the motor at the proper rpm but the phase drifts slowly around
the clock as seen by my homemade 120hz led strobe light.. Existing vfd's
don't have inputs for zero crossing signals and so can't be phase locked
to the line. If anyone knows where I can find a motor or even if they
exist please let me know. Thanks in advance!

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