Motor starter problem

[T. J.]

Hello everyone,

I have a new (to me) lathe that I’m having electrical issues with. When I attempt to start the motor, it jogs for a fraction of a second and that’s it. Opening the control cabinet, I can see the motor starter (the middle one in the attached photo) visibly spark, but it doesn’t stay engaged. I can manually push the contactors (with an insulated screwdriver) and it will start the motor and stay engaged.

Does this mean the motor starter needs to be replaced or is there something else I need to check first?

 

[markba633csi]

What brand and model of machine is it? What voltage is it connected to?
Has it been rewired? Looks like fairly new wiring, cable ties, etc.

Most contactor machines have a transformer tap that needs to match the supply voltage
Is the right-most contactor actuating? It should pull first when the machine is powered up,
then the other two are for forward and reverse

 

[T. J.]

It’s a Ganesh GT-1340. It’s connected to 240V 3-phase. It’s a fairly new lathe, so I think the wiring is original.

The contactor on the right is controlled by the master power switch and it works properly. The middle one is forward and the left one is reverse. Reverse and forward are both behaving the same, so that probably rules out an issue with the contactors themselves. There is a transformer in there that wasn’t visible in my photo. I’ve attached another photo that shows it.

 

[o0norton0o]

I recall powermatic table saws had magnetic switches that were known to do exactly what you describe. You would push the start button and the motor would start, but wouldn't stay engaged when you released the button..... A new magnetic switch cured the problem.... (we had 2 of these saws in my shop and on the day the switch broke Mike would rig it to bypass the switch so he could work all day, using the service disconnect to turn the saw on and off until the new starter switch came)

 

[T. J.]

I just had a thought. The two wires supplying power to the transformer are labeled R & T. I’m pretty sure T is connected to the generated leg from my phase converter. Would that cause the issue? If so, I can rewire so that the transformer is supplied by the two non-generated legs.

That would be an easy fix…

 

[markba633csi]

That might cause the issue- try rewiring that
If that isn't it then the next step would be checking the transformer output voltages
Do you have an electrical diagram for the machine?

 

[mksj]

I just had a thought. The two wires supplying power to the transformer are labeled R & T. I’m pretty sure T is connected to the generated leg from my phase converter. Would that cause the issue? If so, I can rewire so that the transformer is supplied by the two non-generated legs.

That would be an easy fix…

Yes, that would cause the transformer voltage to drop on starting the motor which would cause the contactor coil to drop out or chatter. It is a common problem seen with the use of PRC's, it is always stated not to power the control systems with the wild leg.

 

[T. J.]

It will be a day or two before I have time, but I will try that and report back. I can swap the wires in a junction box on the back of the machine and avoid having to change anything inside the cabinet.

 

[David2011]

T.J., all I know about this is seeing that some machines need to have the transformer set to the right voltage whether 208-220-240. If it's that sensitive and you're have a voltage drop, sounds like you're on the right track.

BTW- thanks for all of the advice on the Index mill. I'm really enjoying it. What a solid machine!

 

[den-den]

You are probably on the right track. In case that is not the issue or for others with similar issues (motor turns while you press the start button but stops when the start button is released). This is often caused by either bad auxiliary contacts or an open in the "stop" circuit. Note: an open in the "stop" circuit will prevent the motor from being energized at all IF the wiring is done correctly.