In article , Ignoramus20106 says...

That made me think, I just used a way to run a 3 phase motor on single
phase power, by adding a capacitor. Can I make an electronic device
made of capacitors and perhaps a timeout or some other relay, that
would simply start 3 phase motors. That would obviate the need for the
idler.

Congratulations, you just invented single phase motors!

You need either a centrifugal switch, or a potential relay,
to implement the idea.

You cannot:

a) plug reverse motors like that, or
b) develop the entire nameplate horsepower

Jim


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Ignoramus20106 wrote:
So, I made a self starting phase converter that starts an idler using
a start capacitor.

That made me think, I just used a way to run a 3 phase motor on single
phase power, by adding a capacitor. Can I make an electronic device
made of capacitors and perhaps a timeout or some other relay, that
would simply start 3 phase motors. That would obviate the need for the
idler.

My own thought here is to wire it like the self starting capacitor
works: a cap between leg 1 and 3.

After starting, the 3 phase motor can run on single phase.

The only disadvantage to this that I can think of, is possibly low
starting torque. Perhaps that can be rectified by wiring it using
some other method.

I am sure that people smarter than me have already thought about all
these things, but I am curious about this question.

i


I've got a couple of 3ph. pedestal grinders that I run with sort of low
starting capacitance (slow starting, the 12" takes about 3 seconds to
come up to speed) and no extra switches or anything, just leave the
capacitors in the circuit. They seem to no mind running that way, used
'em for a few years now.

John

Ignoramus20106 wrote:
So, I made a self starting phase converter that starts an idler using
a start capacitor.

That made me think, I just used a way to run a 3 phase motor on single
phase power, by adding a capacitor. Can I make an electronic device
made of capacitors and perhaps a timeout or some other relay, that
would simply start 3 phase motors. That would obviate the need for the
idler.

My own thought here is to wire it like the self starting capacitor
works: a cap between leg 1 and 3.

After starting, the 3 phase motor can run on single phase.

The only disadvantage to this that I can think of, is possibly low
starting torque. Perhaps that can be rectified by wiring it using
some other method.

I am sure that people smarter than me have already thought about all
these things, but I am curious about this question.

I converted a power hacksaw to single phase by this method five years
ago. I had separate start and run capacitors, a potential relay and a
contactor. It was also a dual wound motor (two completely separate
windings, a four pole and a six pole) so I had a rotary switch to change
between the two. It ended up being a fairly complicated project! The
worst part was that the motor had both sets of windings permanently
connected in the star configuration, so I had to open it up, cut the
star points and solder on new leads. The machine worked fine, except
that it needed a little more start capacitance than my book recommended,
probably because it has a lot of inertia. It uses a 1 3/4 hp motor,
which is unusually rated at 1 3/4 hp on both speeds. Unfortunately it
stopped working last winter, and I haven't yet had chance to figure out
what's wrong with it. I can post some pictures if you're interested.

Best wishes,

Chris