230 v Ac Motor Surge damages motor frequently, I need surge protection ! Help

[Kedar264]

I am using a 230 v 18 watt shaded pole motor Ac water pump in my project ,it involves switching of motor at intervals of few seconds via relay

The back emp at turn off duration kills the motors winding some how I No protection causes very high surge upto 1.2kv so ,I tried 330 v mov in patrellel but didn't getting expected results . i also tried 220 pf 2kv capacitor in parellel but not working,please suggest me any better methods for surge protection here god will bless you!

Thanks

[HackedFridgeMagnet]

MOVs will limit voltage across windings.

What are the signs of damage? General Overheating or a short in one part of the coil? Or maybe signs of arcing?

But maybe you need to rethink your controller or your motor.

[Kedar264]

The motor is potted so there is no way to check ,but all I see is open circuit at the coil wires ,it may be damage in coil due to arcing

[SeanB]

You probably are doing too many starts on the motor. If you are switching the motor to regulate flow I would suggest using some water valves and running the motor full time, and use the valves and some orifices to bleed off water instead, so that you can switch in say up to 3 drains to reduce pressure before finally switching the motor off.

Adding the MOV across the motor will help protect the switch, but the current surge in starting the motor will cause issues with frequent stop start operation, you might want to look at zero cross switches to start the motor, just to reduce the current spike at turn on a little. With nthe zero cross switch you would need the MOV in any case, along with a snubber across the triac block to keep it from triggering on spikes.

[Ian.M]

I'd bet the winding has a non-resettable thermal fuse for safety, and as SeanB suggests, you are simply starting it far too frequently, so it overheats faster than the heat can be conducted away by the water and blows the thermal fuse.

Either get a different type of pump rated for frequent starting, or add a diverter loop to let the water recirculate controlled by a three port solenoid valve, again rated for frequent operation, so the pump can run continuously.  Only shut off the pump if it isn't going to be needed for at least five minutes.

[joeqsmith]

I assume when you state "relay", that's a TRIAC so you are turning off at the zero cross.

   

[Zero999]

You probably are doing too many starts on the motor. If you are switching the motor to regulate flow I would suggest using some water valves and running the motor full time, and use the valves and some orifices to bleed off water instead, so that you can switch in say up to 3 drains to reduce pressure before finally switching the motor off.

Adding the MOV across the motor will help protect the switch, but the current surge in starting the motor will cause issues with frequent stop start operation, you might want to look at zero cross switches to start the motor, just to reduce the current spike at turn on a little. With nthe zero cross switch you would need the MOV in any case, along with a snubber across the triac block to keep it from triggering on spikes.

A agree and if it's a centrifugal or impeller pump, rather than a displacement pump, then it's more efficient to simply block the inlet which will reduce the load on the motor, although you need to be sure it will still be adequately cooled, without the water flowing through it continuously.