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Massoud

wrote in
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On Fri, 3 Feb 2017 19:34:45 +0000 (UTC), Massoud
wrote:

wrote in
m:

Hey All,
I have an old Baldor bench grinder. Probably 70 years old or older.
The motor is the type that uses a capacitor for starting and
running. There is no centrifugal starting switch. I know this type
of phase making scheme provides lower torque for starting so that
the motor takes longer to come up to speed. But this grinder takes 5
seconds to reach operating speed, 3400 rpm. I replaced the bearings
in the motor and it now spins very easily. There is a 3/4 wide 6
inch grinding wheel on one side and a light weight 6 inch diamond
wheel on the other side. The cap in the thing might be the original
cap. It is a large round tinned metal can with solder lugs. 330
volts and 400mfd. Could it be that it needs a new cap? I don't know
what kind of cap it is. Oil filled I imagine but from the high mfd
campared to all my other run caps could it be an electrolytic cap?
There is no sign of leaking and there are two places on the top of
the cap where it looks like holes were sealed with solder.
Thanks,
Eric

You have a good start up, so no need to replace the cap.

5 seconds seems like too long. My other two Baldor grinders spin up to
full speed in 2 seconds. These grinders don't have a centrifugal
starting switch either so I assume they are wired just like my older
grinder. I'm concerned the long starting time might lead to
overheating the windings after many starts.
Eric

First concern should be loosing the torque, meaning slows down when
loaded. They are AC cap and no polarities. Generally, oil filed can which
if they don't leak, survive many many years.

The start spin also is related to inertia and load of the rotor, so if
they are not exactly the same, don't expect the same time.

Mass