Good basic video understanding and diagnosis of three phase motors

[Greg Pack]

You tube is awesome! This brief video (less than 15:00) might help many of you understand how a three phase motor works, and how to diagnose problems with your three phase motor. It includes testing procedures with a multimeter and megohmeter.

https://www.youtube.com/watch?v=6H_MkhwAmz4



BTW, I use a supco M500 megger with "idiot lights" to test a short to ground. They are about $100 and worth owning if you work on your own equipment.

 

[I.B. Washincars]

My dad always recommended the "float" test. Throw the motor in the river. If it floats, it's bad. If it sinks, it's good.

 

[madscientist]

That works for witches too, right?

 

[cantbreak80]

My dad always recommended the "float" test. Throw the motor in the river. If it floats, it's bad. If it sinks, it's was good.

Fixed it for ya.

 

[mjwalsh]

You tube is awesome! This brief video (less than 15:00) might help many of you understand how a three phase motor works, and how to diagnose problems with your three phase motor. It includes testing procedures with a multimeter and megohmeter.

https://www.youtube.com/watch?v=6H_MkhwAmz4

BTW, I use a supco M500 megger with "idiot lights" to test a short to ground. They are about $100 and worth owning if you work on your own equipment.

cfcw,

Thanks for the worthwhile link. We did not get into three phase until 1987 so our 3 phase motors were relatively new then but not so new anymore. Since we have close to 15 three phase motors ... that kind of info could prove to be helpful. From the video ... I learned that with my very precise digital Fluke 325 clamp on meter I can check for the balanced amp draw that I never thought of before. We have gotten into inverter duty motors recently.

I am not sure how much finding out that the insulation has weakened will help us much though. Is there a less costly solution than rewinding or brand new ... if we catch the insulation problem at an early stage?

mike walsh www.kingkoin.com

 

[Greg Pack]

I am not sure how much finding out that the insulation has weakened will help us much though. Is there a less costly solution than rewinding or brand new ... if we catch the insulation problem at an early stage?

mike walsh www.kingkoin.com

The insulation problem can be monitored, but when it is shorted there is not much you can do except replace the motor.

For me, where the shorting/megger comes into good use is In Bay Automatics that have multiple motors in the hostile environment AND possibly moving power cords that can open or short. i have a fusion X, and there are fifteen motors on the gantry. Mine are connected into VFDs, which can be quite costly to replace. A shorted motor can take one of those out, and also reportedly cause crazy problems by voltage/current swings.

In my early days, I replaced a lot of bad motors due to a bad power cord, and until recently, was throwing away motors that apparently just had moisture in them. When you see how simple the interior of a three phase motor is you realize why you so rarely have to fool with them.


Interior moisture can also cause a motor to test bad with a megger. You can pull the bell housing off and dry it in low heat in an oven.