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Hydrashift electrical gremlins

wfissell

Plastic
Joined
Apr 18, 2018
Location
Nashville, TN
Hi,

my victory was short lived. Motor cuts out after a few minutes use. Wait a while, then it will restart. Seemed like a thermal issue. Opened the back. Transformer warm and smells hot. Do these fail, commonly?

thank you
 
Fail commonly? No.

Warm as in too hot to touch?

Do you have the correct heaters in the motor starter for the voltage that you're feeding to the motor? And are the motor leads correctly connected for the voltage?
 
Hi,

Motor leads, yes. Heaters, dont know. It all appears to be factory. The transformers are fine, I think- I checked and they are putting out the correct voltages even when the motor has stopped.

On a little more detective work, it only happens at high speed - 1050 or 1400 under load albeit a tiny load. I suspect an overload protector is kicking in. I ran it with panel door open and there was an audible 'pop' when the motor stopped. A little later I could restart.

Is there a thermal overload protection in there? I have the schematic that was parked in the door of the electrical panel, but I didnt see a distinction between fuse and thermal overload.

I appreciate all your help!

Bill
 
The only transmormer(s) would most likely be for a low voltage control circuit for the motor starter coils. There is probably no "thermal protection"- just overcurrent protection provided by the heaters on the motor starters themselves. If your machine was, at one time wired for 440 and then later reconnected for 240 volt operation and the heaters were not changed for the higher motor current, you could be tripping one of them. Its also possible one of the heaters is defective and false tripping. If you are not familiar with motor starts and how they work:
A Look at Thermal Overload Heaters in Motor Starters - YouTube
 
Dan has likely hit on the problem: a machine with heaters for 440v input, but now running on 220v. Since the current will roughly double when the voltage is cut in half, the heaters think that the motor is drawing too much current, and they open the circuit to protect the motor windings from overheating.

The "pop" you heard was probably the magnetic contactor on the motor starter dropping out when the heaters cut the circuit to the magnet winding. Which is exactly what it should do when the heaters sense an over current to the motor. The heaters are automatic reset once they cool, although the control circuits are usually designed so that the motor will not also automatically re-start, which could be dangerous, so a motor re-start requires the machine operator.

If you have trouble identifying the correct heaters for your motor starter, post some photos of the inside of the electrical cabinet and of the nameplate on the drive motor. The charts for the heaters from the various manufacturers (General Electric, Allen-Bradley, etc.) are online, but they can be a bit confusing to decipher, especially if you're not familiar with them.

Typically, when the input voltage to a machine is changed, three things must also be changed: (1) the heaters [typically two on the motor starter on older machines, but three on newer ones]; (2) the connections to the control circuit transformer [usually a diagram is present on the transformer ID plate showing how to make the connections depending on the input voltage]; and (3) the motor winding leads.
 
That was exactly the problem. It had the N26 heaters which would be appropriate for 440 not the N35 which would be the correct choice for 220. Ordered 2 NOS and well see what happens!
 








 
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