Re: induction motor question

Hi Gavin,

> Original Poster: Gavin Hubbard <ghub005-at-xtra.co.nz>
> Hello List.
> I am thinking of buying a second-hand 90 rpm (geared) induction motor
>to use for winding larger coils. I tested the motor in the shop but
>found a problem.
> The motor plate says to use a 15 uF start cap, but when I tried this
>(with a known good cap) it wouldn't start unless it was given a turn
>by hand. Obviously this would be no good for stop-start coil winding
>:-) I don't know much about induction motors, but I'm guessing that
>the motor plate does not take into account the extra torque needed
>to turn the gearbox(?) How do I fix this?

Have a look at the motor (only a screwdriver and a DVM are
needed) to see:

1.) If there is an internal centrifugal switch and if it closes properly
at stand still. I had the exact same problem you describe and I
found these contacts to be shot. It is only a little work to correct
this, however. Sometimes the contacts are just corroded or bent
too far apart. In my case I had to rebuild the switch, because the
contacts were beyond repair.

2.) If there is no internal switch (or even if there is), take a DVM
and measure the start-up windings directly where they enter the
actual motor winding core. Inifinity means the starter winding is
shot. If these are shot, pass up the motor for a different unit.

As the gearbox is already attached to the motor, I donīt think it
is a problem of a too small starting capacitance.

Coiler greets from Germany,