Checking and testing an electric motor Advice Please

[R1chard]

I have a cement mixer which suddenly went wrong. There was no leak to earth or overload trip.
It doesn’t rotate normally and then if it’s given a bit of help it struggles and turns in small slow jerky movements....
I have tried to replace the capacitor with a similar one, to no avail. This is the extent of my knowledge and edge of my comfort zone.

I have dissembled the motor and accessed the windings. I believe this is an induction motor (no rotor coil or brushes) and tested the wires emerging from the coil without any continuity error across the two white capacitor wires nor across the three other wires but I’m flying blind.
Visual inspection of the windings does show a little “scorching” and the resin is a little brittle but no more than I would expect on an older motor.
Any ideas?

 

[Spectric]

Hi

Just get a new motor, it will be faster and cheaper than trying to fix the old one. Infact check on the price of a new mixer first as a new motor may not be sensible. These things tend to not be over engineered because nothing survives the abuse given to them by builders who just get the customers to share the bill.

 

[EddyCurrent]

Are you describing the motor operation when it is installed in the mixer or when it's out on a bench ?

 

[Sideways]

Capacitor failure and faults with the switchgear are two of the most likely causes. This includes oxidation / corrosion of connections so check and clean.
My assumption is that this is a single phase motor.
It could be a permanent split capacitor type where the cap is always in circuit.
Given the mass of a cement mixer and inertia to be overcome while starting, it could well be a capacitor start type. In these a larger value cap is in circuit for a second or so and switched out of the circuit as soon as it's up to speed by a centrifugal switch on the end of the motor. Horrid things, they are a regular cause of unreliability and source of vibration. If it's one of these, clean the contacts and check the connections. They are a simple mechanism and it should be pretty obvious.
If there's a short somewhere inside the windings, that will be much harder to find but is one of the less likely faults.
Hope this helps...

 

[R1chard]

Are you describing the motor operation when it is installed in the mixer or when it's out on a bench ?

When it’s installed.