Electric Motor Clicking and Twitching When Switched Off

[aesmith]

Hi,
The motor in question is a single phase 230V induction motor driving a planer thicknesser. I don't see a data plate The machine was donated so I don't know it's history. There are a bunch of safety interlocks but if all those are satisfied, guards in place etc, the machine runs and I have no special reason to think it's not full power.

Pressing Start you get a good clunk presumably from a relay, and the machine runs. When you hit Stop it runs down taking a few seconds, but then once stopped it sits making little knocking noises and twitching a little. It does this for a few seconds.

If any of the safety switches are wrong, then when you hit On it does the same. Instead of just nothing happening, it starts knocking and twitching for a few seconds. No relay closing noise.

Before I start dismantling or tracing wires does this ring any bells? Without opening it up the safety switches all look to be wired back to the control box, then only one cable to the motor.

 

[roofman]

Sounds like a cap is not discharging

 

[Gareth J]

I don't know how it does it but I've a bench saw that's single phase and when you hit the stop button, it ramps down to a gentle but controlled stop. There are associated odd motor noises. This differs from just cutting the power, if you do that, it freewheels to a stop taking much longer as the intertual if the blade is significant.

Maybe, yours has a similar "controlled stop" feature that's a bit out of whack or something.

 

[aesmith]

Sounds like a cap is not discharging

Would/could that be a capacitor that's energised when there's supply to the machine, but the start relay not closed? Charged by the action of pressing the start button?

 

[aesmith]

Maybe, yours has a similar "controlled stop" feature that's a bit out of whack or something.

There could well be something like that. From the manual of a later variant ..

"Note. There is an electronic braking system on your machine, which works by switching
the ‘run’ capacitor. When you stop the machine after it has been running, you will hear a
“click, click” sound as the brake activates, and the motor will slow down quite quickly.
Please be aware that the effectiveness of the braking action is dependent on the ‘run’
capacitor being fully charged; this takes a finite time after the motor has been started.

If you start and then stop the machine very quickly, without allowing sufficient time for
the ‘run’ capacitor to charge fully, the switching occurs (i.e. you will hear the clicking
sound) but there is no apparent braking action."

 

[Zedd]

Sounds like the capacitor is discharging after shutoff. I would check the start/run capacitor first before tearing into the wiring

 

[aesmith]

Maybe, yours has a similar "controlled stop" feature that's a bit out of whack or something.

I think this is probably it. For a start there are more wires to the motor than just L and N.

Copying your test if I pull the power the cutter block takes 15 seconds to stop. Stopping using the control, it stops in around 5 seconds followed by 10 seconds of knocking/twitching.