ac single phase motor won't rotate even by hand

Sirrick · Sep 28, 2022

hello!!
hope anybody can help me.

I have an AC single phase 220v 1.5HP motor that won't rotate when plugged in even when I try to do it by hand, it is kind of magnetically locked, and just hums.
when unplugged, it rotates easily.
I tested it with a new capacitor that I'm 100% sure is OK (I took it from another motor that is working properly, after testing it, I took it back, and still working fine).
I tested the resistance from the connectors and the readings are in the picture. the resistance between each connector and ground is infinity.
there is no centrifugal switch or any other kind of switch.

any ideas?

thanks in advance!

westward10 · Sep 28, 2022

Just replace the capacitor they don't cost much to rule it out.

Sirrick · Sep 28, 2022

westward10 said:
Just replace the capacitor they don't cost much to rule it out.

thanks, I already did, same thing

Sirrick · Sep 28, 2022

Sirrick said:
hello!!
hope anybody can help me.

I have an AC single phase 220v 1.5HP motor that won't rotate when plugged in even when I try to do it by hand, it is kind of magnetically locked, and just hums.
when unplugged, it rotates easily.
I tested it with a new capacitor that I'm 100% sure is OK (I took it from another motor that is working properly, after testing it, I took it back, and still working fine).
I tested the resistance from the connectors and the readings are in the picture. the resistance between each connector and ground is infinity.
there is no centrifugal switch or any other kind of switch.

any ideas?

thanks in advance!

ok, this is weird and I would like to know the reason if anybody knows.
what I did, was just completely disassembled it, clean it a little because it was not really dirty, I assembled it again and now it works like a charm.

Rockingit · Sep 28, 2022

I'd have thought the most likely explanation is that there was some very slight misalignment on the bearings which meant that whilst you were able to spin it by hand the electromotive forces/fields weren't exactly in synch to start the spin. Just a hunch.

Lucien Nunes · Sep 28, 2022

Most likely, before you disassembled it, when energised the rotor was dislocating radially from its central position and was making contact with the stator, and physically blocking the movement. I.e. the radial movement was magnetic but the effect you felt on the shaft was friction. Now you have realigned it, the rotor doesn't touch. It can be a sign of worn or damaged bearings.

Until I read your last post, I was going to say that the readings looked valid and if the capacitor was OK, whatever might be wrong, I would expect it to run.