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Single phase motor

Dangerstevie

New Member
I have a single phase 2hp motor powering my compressor. Unfortunatly its packed up for some reason, when i switch the motor on it buzzes, turns very slowly and then trips my 15A fuse in the garage. I have stripped the motor down and everything seems ok, nothing seems to be broken.

The motor has 4 wires coming from it, 2 white & 2 red. There was a capacitor attached to the motor too, but i cannot remember how this was wired and stupidly i just whipped off the connections without thinking.

What tests can i carry out to troubleshoot the cause of the problem?

Thanks
 

be80be

Well-Known Member
I would say you have a bad capacitor 1 white and 1 red go to the capacitor
 

Hero999

Banned
It could also be a shorted winding.
 

Dangerstevie

New Member
I have tested all of the wires for continuity with the housing which would indicate a shorted winding and none of them have continuity, the meter just stays on 1.
 

Dangerstevie

New Member
Ok cool, ill check that in a bit. What are the 4 wires? from what i have been reading and common sense would lead me to believe its a reversible motor? would this be a reasonable assumption?
 

be80be

Well-Known Member
It not 1 white and 1 red go to the capacitor if it was reversible you have 6 to 8 wire
 

Hero999

Banned
I have tested all of the wires for continuity with the housing which would indicate a shorted winding and none of them have continuity, the meter just stays on 1.
That isn't a fail safe method of detecting a shorted winding.

It only proves the winding isn't shorted to the case. It doesn't prove that some of the varnish hasn't burnt off neighbouring turns causing them to short together.

They are four wires because a phase shifting capacitor needs to be added to enable it to start.
 

be80be

Well-Known Member
If he had ohm out the windings and new what they should be would help but you pulled all the wires off with out marking them the first thing you should of checked was the power going to the motor at the motor then check the capacitor to see if it is shorted and make sure it reads the right capacitance And I would of ask who you loan it to if it had let it get hot maybe even smoked a little and if they said no and didn't lie It's the cap that went bad But you said it ran slow and if so you should of smelt smoke when you tried it If not your back to maybe a bad capacitor. O one more thing on all the motors I have work on in 25 years if it has the wire like you said 2 white and 2 red 1 white and 1 red go to power what left go to the cap and it did care which red or which white or they would have been white red black brown and some times blue
 
Last edited:

gerty

Member
What voltage iis it wired for? 120 or 220.
2 HP will max out a 15a circuit at 120v, and that's provided nothing else is plugged in on the same circuit.
Can you take a voltage measurement, at the motor, while it's trying to start.
 

Dangerstevie

New Member
its running on 240v, i bought the compressor off a friend cheap because he said he couldn't get it to work and it just whirred and nothing turned. I think it may be better for me to buy a new motor. This motor seems like its a lot of hassle.
 

Diver300

Well-Known Member
It sounds like it is a single phase induction motor. They need a capacitor to make them turn in a known direction.

With no load, and with no capacitor, you should be able to get it to run by powering the red leads, and leaving the white leads disconnected, as long as you give it a flick so that it is spinning when you turn on the power.

For normal running, the red leads are connected to the mains, and the white leads are connected via the capacitor. That should make it run from standstill in one direction. Reverse the white leads to reverse direction.
 

Dangerstevie

New Member
ok cool, ill bang the terminals together tonight and jazz it up see if that works taking the cap out of the equation. if it doesn't ill just have to change the fuse again.
 

Dangerstevie

New Member
so if i join the reds together and leave the whites disconnected, then power the reds it wont work??? in your previous post thats exactly what you said to do.
 

be80be

Well-Known Member
2 of the wires are for the capacitor 2 are for the power the capacitor is there to start the motor I have not ever seen 1 that will start with out the capacitor that has 4 wire and if you would tell me what brand your motor is I try to post you the wiring for it.
in your previous post thats exactly what you said to do.
Not me I said 2 to the capacitor and 2 to the power then you posted it running on 240volts.
 

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