Faulty motor or caps?

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Old 01-28-17, 02:36 AM
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Faulty motor or caps?

Hi, I'm hoping somone can point me in the right direction to get an electric motor working as it should.
I have a woodworking machine with three single phase motors. The motors appear to share a start and run capacitor. Two of the motors run as expected but the third has started humming and not turning. It was working well then wasn't used for a couple of weeks and now has this problem. If I start the motor (disconnected from the cutters so no load) by hand it will turn but at a lower speed and very little torque. It will do this in either direction. Any thoughts anyone?
 
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Old 01-28-17, 04:55 AM
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You can test a Capacitor.
Warning; Capacitors hold a charge for long periods and can knock you across the room even though they are not connected to any wires.
1. Disconnect the machine from the power, unplug or turn off the disconnect.
2. Discharge the Capacitor by using an insulated screwdriver, touch the connections of the capacitor together.
3. Using a multimeter, set it to continuity, ohm test. and touch the test leads to the capacitor. This will charge it using the multimeters battery
4. Switch the multimeter to voltage test
5. Test the capacitor for voltage, the meter should spike for a second and then read 0
6. This is the capacitor discharging.

It would help to know the type of motor. Make, model, HP, voltage, frame size, etc., etc.
Some motors have a centrifugal start switch. It may be stuck and need lubricated.
HERE is a good video
 
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Old 01-28-17, 05:29 AM
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Thanks for your reply and the video link

I don't think the motors have centrifugal switchs because the start switch, common to all three motors, has a start position and then springs back to the run position. I've always thought that this is doing the job of the centrifugal switch. There is also a selector switch to pick which motor operates.

I will test the capacitors as suggested and visually. I'll also get the motor details.

The machine has three motors. The spindle molder motor is the problem one. The saw motor is identical and is working as expected. The planer motor is a bit bigger and also works fine. This makes me think the caps are ok but from what I've read online the motor is behaving as if there is a problem with the caps.
 
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Old 01-28-17, 05:38 AM
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If you listen closely, you can hear a centrifugal switch click as the motor is turned off and slows down. It's the sound of the springs returning the weights to the original position.
 
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Old 01-28-17, 07:01 AM
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If I start the motor (disconnected from the cutters so no load) by hand it will turn but at a lower speed and very little torque. It will do this in either direction. Any thoughts anyone?
That is consistent with a winding short, or low capacitance run capacitor. I've never seen motors sharing capacitors, but I suppose its possible.
 
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Old 01-28-17, 10:18 AM
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There is also a selector switch to pick which motor operates.
Does that mean that only one motor ever runs at one time ?
 
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Old 01-28-17, 10:57 AM
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Yes, only one motor runs at a time.
I'll try and post a picture of the switches.

I've assumed the capacitors were shared as I can only see two however that might only be half accurate as I'll tell you in a second.

I've done a few tests as well as I can, but this is new for me.

No visible signs of a problems on either capacitor.

As I said before the saw and spindle molder motors are identical, the planer motor is bigger and a different make. The planer motor runs with either of the capacitors disconnected but I can't hear a switch noise when the motor slows. This motor is not very accessible so I suppose it is possible that there are other capacitors within the casing but they must be smaller than the two I can see. I'll try and have a closer look tomorrow.

One of the caps is rated at 50uF. If I do the test Electromen suggested the AC voltage spikes at 1V then drops. With this capacitor disconnected the saw motor hums but doesn't start so I'm guessing this is the start capacitor?

The other is rated at 156/200 uF. The saw motor runs with this capacitor disconnected.
The voltage spikes at 4V then drops.

I guess I could test the motor by swapping the wires around on the two matching motors but this is trickier than it sounds because of access.
 
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Old 01-28-17, 11:01 AM
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The start switch is on the left. I have to turn it to AVV to start the motor then when I release it springs back to 1
 
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Old 01-28-17, 11:03 AM
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What's the Make and Model of the machine?
 
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Old 01-28-17, 11:06 AM
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Since that has a manual start and you can only select one motor at
a time...... there would only need to be two capacitors.

The 156/200uf 330vac is the start cap.
The 50uf 370vac is the run cap.

That meter test is only a general indication of quality.
It certainly couldn't hurt to change both.
 
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Old 01-28-17, 12:22 PM
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The machine is a Sicar 260. Its an italian machine from the 80's. I'm not in the US by the way.

That was my thoughts on the capacitors, no reason not to share them.

I guess I need to test the motor.
 
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