Single phase motor problem

[Fred]

I have an old single phase 110V 5.6amp 1/3HP 1200rpm induction motor
that operates a scroll saw..The motor ran well in the past but now it won't
start.
It just sits there drawing current. If I spin the motor by quickly moving
the belt
it will start.

It has capacitor start and the cap measures 84 mfd. Can't read the cap
rating clearly
but it looks like its a nominal rating of 72 mfd. I'm assuming the cap is OK
because
I can measure what seems to be a reasonable value.

Any ideas what the problem could be?

I apologize if this is not the right news group for this post.

 

[Bill Vajk]

Fred wrote:

I have an old single phase 110V 5.6amp 1/3HP 1200rpm induction motor
that operates a scroll saw..The motor ran well in the past but now it won't
start.
It just sits there drawing current. If I spin the motor by quickly moving
the belt
it will start.

It has capacitor start and the cap measures 84 mfd. Can't read the cap
rating clearly
but it looks like its a nominal rating of 72 mfd. I'm assuming the cap is OK
because
I can measure what seems to be a reasonable value.

Any ideas what the problem could be?

I apologize if this is not the right news group for this post.

Some motors have an internal cenrifugal switch that
disconnects the capacitor after the motor has started.
Could be yours has one and the switch is shot.

Otherwise the start winding itself could have failed.

 

[John Popelish]

Fred wrote:

I have an old single phase 110V 5.6amp 1/3HP 1200rpm induction motor
that operates a scroll saw..The motor ran well in the past but now it won't
start.
It just sits there drawing current. If I spin the motor by quickly moving
the belt
it will start.

It has capacitor start and the cap measures 84 mfd. Can't read the cap
rating clearly
but it looks like its a nominal rating of 72 mfd. I'm assuming the cap is OK
because
I can measure what seems to be a reasonable value.

Any ideas what the problem could be?

I apologize if this is not the right news group for this post.

The capacitor may have dried out and though showing almost nominal
capacitance, may have so mush series resistance that it cannot pass
the expected current. If you can verify the start switch function and
start winding continuity, replacing the cap is the next step.

--
John Popelish

 

[Jamie]

in the back of the motor there should be a weight switch that ingauges
the starter field.
when the motor gets spinning up to a speed enough to throw the switch
open it should do so thus disconnecting the starter field.
i don't know what kind of starter you have in that motor but you could
have a constant field starter which stays on all the time or a shaded
pole type field. in either case i would say that you have an open widing.


Fred wrote:

I have an old single phase 110V 5.6amp 1/3HP 1200rpm induction motor
that operates a scroll saw..The motor ran well in the past but now it won't
start.
It just sits there drawing current. If I spin the motor by quickly moving
the belt
it will start.

It has capacitor start and the cap measures 84 mfd. Can't read the cap
rating clearly
but it looks like its a nominal rating of 72 mfd. I'm assuming the cap is OK
because
I can measure what seems to be a reasonable value.

Any ideas what the problem could be?

I apologize if this is not the right news group for this post.