Induction motor problem.

Does it have a capacitor to make sure it spins in the right direction?

The noise is probably the centrifugal switch closing and bringing the starter winding back into circuit.

In theory at least, the only thing which should be able to stop a single-phase induction motor once it has started (other than a supply interruption) is a physical overload. Neither the capacitor nor the starter winding should be in circuit once the shaft is up to speed and the centrifugal switch has opened.

So... is the switch operating correctly?

Or is the load perhaps too heavy compared with the nominal power output?

Finally, has some misfortune befallen the running winding?

That was my initial thought, but surprised the 'Chack' is only heard when stalled and power switched off for a few seconds.

The centrifugal switch doesn't seem to be behaving in a way I might expect. I'm wondering if this is a thermal switch.

There may be 3 windings, 2 for normal running where one uses a capacitor to provide a phase change, and a third winding to provide extra torque at start-up using a thermal cut-out?

Without some more details I can't see how we can help.

Fredxx has brought this to us :

The few seconds, is that before, or after it has stopped rotating?

I read that the motor was already stalled and a 'chack' was heard a few seconds after it is switched off. And that it would then restart ok.

The OP really needs to clarify. As I said we need more details.

Does this help?

Greatly. The 'chack' is well after the motor is stalled, that implies some sort of thermal switch which resets where power is removed.

Centrifugal switches are noisy but also tend to make a noise also as they run up.

It's also not obvious if this a capacitor start or split phase motor.

It seems to run fine for while when under load and then stop. What happens if you apply this level of load immediately after coming up to speed.

Does the motor get hot if you leave it running with no load? If it stays cold then it's either a faulty thermal cut-out switch or a faulty capacitor, where the capacitor value has dropped through some internal failure.

The "Chack" comes after I switch off at the switch (first clack, the mains switch), but before I myself say "Clack!".

This is an old motor (70 yrs?), and I m not sure it's got a thermal cut-out. It's only been run for a few seconds today, as in that clip. Switch on, comes up to speed, load applied, slows, stalls, switched off, "clack".

If I run it without the belt and it gets warm, is that indicative of a capacitor problem? I assume that there's a capacitor in the cylinder attached to the side of the motor. How do I tell if it's a "capacitor start or split phase motor", please?

To add to that, if I run it for several minutes with no load, it does not get warm, and the "Clack!" comes about 14s after switching off at the switch.

Is the winding warm after you have loaded the motor and when it has stalled?

I could not hear any typical centrifugal style switch kick in as it spun up, so probably not capacitor start. The bulge on the motor will contain a run cap. If that is failing you won't get enough phase shift to drive the motor, and that could explain the lack of torque.

Not obvious what is "clacking" though. Has this go a "motor starter" switch / cutout? (often combined with NVR start / stop buttons)

I would test the cap, and also buzz out the windings (both stator and rotor) and check nothing is open circuit. Has the motor got a speed rating on its plate?

I thought it might be a "sticky" centrifugal switch. The bellhousing at the non-pully end has some sort of contacts in and that seems to be where the noise comes from, but it's hard to say. It's rather greasy in there. Perhaps I will drag it out, take the cover off, and see what happens whe it's switched on then off.

It's switched on and off by a brass fronted toggle switch, like an old light switch. Up for off, down for on. Here:

I will have a poke about. The motor's plate is here:

What does "buzz out the windings" mean?

I doubt the rotor will have a winding?

The stator windings must be ok, or it wouldn't spin up. The motor stays cool, which implies the windings have integrity. If just a single winding is energised it would just sit there.

The fact it can stall and stay that way without load imply a switch of some sort. The delay in de-energising and the 'clack' sound implies a thermal effect.

Some motors have two capacitors, one for running and one for starting, and so giving a good starting torque as well as efficiency at normal working rpm. It is usual for a centrifugal switch to switch the start capacitor out of the circuit, but I'm wondering if this has been replaced with some cheapskate thermal switch which is kept hot in normal running.

The fact it spins up implies the start capacitor is ok, but wondering if there is a running capacitor which has failed. The motor should still run but have a poor load capability and when stalled wouldn't be able to restart. Hence my question about stalling from a load that is applied quickly.

I expect all the working gubbins is going to be in the power-bulge. I would suggest the OP opens this up and shows us what is in there. If there are two caps then the running one may have failed.

I'll jhave a look maybe tomorrow. What does a thermal cut-out look like, on something of this age? I am not at all sure it'll have such a thing. It's a minimum of 70 years old, and could be over 80.

Check them for electrical continuity.

Correct. As you have remarked, AC motors have stators (the frame) and rotors. Only the stator has a winding. With DC motors, it's completely different.

Yup, if it stuck on that will leave the start cap in circuit...

About as far from a direct online starter as you can get then :-)

Yup, looks like it. Check both bulges - the lower one is probably just the terminal housing.

Use a multimeter on a resistance range to establish that the windings are not open circuit.

(it's a four pole motor, so will have more than one set)

You can also use a multimeter on a resistance range to check the cap - you should see an initial low resistance that then rises and keeps rising. Easy to see on an analogue meter, but also not bad on a good digital one with a bar graph.

It might look like a centrifugal switch stuffed full of gunk! :-)

(I probably have something of similar vintage on my planer)

That did cross my mind but ones I've seen have been dry.