Re: G201s repaired, now to bring up machine

--- Chris Brick <cbrick@t...> wrote:

> Mariss Freimanis wrote:
>
> > Your motor may have a shorted turn. Shorted turns
> > kill drives and usually cannot be detected with an
> > ohmmeter.
>
> Any tests that can be done? I have another motor I
> can throw in but since these are surplus, there's
> no telling what may be wrong with them. It may be
> time to bite the wallet and get new motors.
>

Note: Both of the following tests must be done
with the motor disconnected from the drive!

I'm pretty sure an inductance bridge would detect a
shorted turn. The winding with the short would have
a lower inductance than the other windings.

If you don't have an inductance bridge, there is
another test you could try. You need to be able
to spin the motor slowly but steadily. For example,
I'd chuck the motor shaft in my lathe chuck, set
the lathe for 50-100 RPM, and bring the toolpost
up next to the motor body to keep if from spinning.
When you spin the motor shaft, it acts like a
generator. The voltages across each winding
should be nearly the same. If one is low, it
probably has a shorted turn.

Be very careful measuring the voltages. Especially
if you spin the motor too fast, you can develop a
hundred volts or more at the terminals... Enough
to knock you on your rear, or worse.

Disclaimer: I have not done this test, but based
on what I know about motors, it should work.
Mariss, what do you think?

John Kasunich