Electric Motor starting problem

[Greg Peterson]

Picked up an old Montgomery Wards scroll saw this past summer. The motor is a 1/3 HP, fan rated, thermo protected motor.

I have to cycle the power switch three to four time to get the motor to run. The first power cycle of the switch causes the motor to make a short, 1/4 revolution or so and then it stops. Two or three more power cycles and the motor finally comes to life.

Any idea's? No starters on the exterior of this motor. Just a smooth cylindrical housing. I'm wondering if the fan rating of the motor is a clue.

[Rod Sheridan]

Hi, one thought that comes to mind is that a motor rated for fan duty may;

1) not have enough breakout torque to start a reciprocating piece of machinery

2) Not be capable of cooling itself without the airflow generated by the fan it's meant to drive.

If the motor starts fine without the scroll saw connected, it's item #1.

If the motor doesn't start without the scroll saw, take it apart and clean the centrifugal starting switch, and make sure the start winding isn't open.

The cooling issue will show up with a long run under load. If the motor trips the thermal protector, you'll know it needs airflow.

Regards, Rod.

[Daniel Simon]

Sounds to me like you need a new capacitor. It might be located on the inside.

[Mike Seals]

Picked up an old Montgomery Wards scroll saw this past summer. The motor is a 1/3 HP, fan rated, thermo protected motor.

I have to cycle the power switch three to four time to get the motor to run. The first power cycle of the switch causes the motor to make a short, 1/4 revolution or so and then it stops. Two or three more power cycles and the motor finally comes to life.

Any idea's? No starters on the exterior of this motor. Just a smooth cylindrical housing. I'm wondering if the fan rating of the motor is a clue.

Check the E bay for the motor part number. I found a guy that sells lots of replacement motors for older equipment. Prices were very reasonable.

[Greg Peterson]

FWIW, this is also a split phase motor.

The starting problem is independent of a load being present.

[Rod Sheridan]

Hi Greg, now you're on to the starting switch and start winding inside the motor.

If the start switch doesn't close when the motor is stopped, the start winding won't have any current, so the motor won't start.

While you have it apart, check that the start winding isn't open, since one again, no current in the start winding will result in a no start condition.

Regards, Rod.

[Marcus Ward]

My dust collector was doing the same thing, turns out it was dust inside the switch. Start with the easy stuff.

[Greg Peterson]

Yeah, I've done some research and it seems the problem lies somewhere in the starting circuit or switch.

Thanks for the idea's and input. I'll take a stab at the easy stuff. Anything more complicated probably would warrant getting a new motor.

[Greg Peterson]

Well, problem solved. After opening the motor up and blowing it out and cleaning the starter contact, I couldn't find anything within the motor that look out of place or obviously dysfunctional. So prior to reassembly, I turned my attention to the SPST switch that was wired up to the motor. Bingo! Replaced it with a new SPST switch and now it fires up just fine. The motor is whisper quiet and smooth as silk. Wish I could say the same for the scroll saw. Going to have to dig a little deeper into it inners.