AC Induction motor not working

[rrrileyeric]

I've encountered a small problem when working with my motor; when power goes into the motor, it locks up and it is much harder to move the shaft. However when the motor is switched off entirely and there is no power entering the motor, the shaft is easy to move with my hand and it spins freely. Are there any ideas as to why this problem is occuring?

 

[Grossel]

My best guess - given that no soft start and the motor is a "true" 3 phase motor (i.e. not with capacitor) - is that there is a break in a winding, so that you don't get a rotating field as inside as you're supposed to.

But - I think it's better to start with the type of motor (images, rating plate, what equipment it is used for) in order to suggest what may be wrong.

 

[vu2nan]

In the case of a single-phase motor, a failed start capacitor could be the likely cause.

 

[Diver300]

You may be able to get it rotating by hand and then power it on, and it will keep spinning.

I don't know the situation, and only a few mechanical loads will be safe to start like that, and you should not risk injury.

A lot of types loads will not allow a motor to accelerate, but if you can disconnect the load by taking a belt off or similar, it could be a useful tests.

If starting like that works, and it's a single-phase motor, then it's the starting capacitor that has failed or become disconnected. If starting like that works on a three-phase motor, one phase has become disconnected.

On either type of motor, the disconnection could be a break in the winding.

 

[rjenkinsgb]

That can also happen with a failed bearing or something mechanically loose / misaligned.

Once power is on, the magnetic field pulls the rotor and stator against each other at some point and the lock up.

 

[MaxHeadRoom78]

If Spinning it and applying power at the same time and this works in either direction, then as already mentioned, the start/run cap.