OT Motor Temp

I got a call today, and wanted to get some opinions. a customer has a reznor heater in his metal powder blending facility. The 115v 1ph motor for the fan burnt up after a year. The local hvac guy figured the open motor was a problem with conductive dust, and ordered a sealed motor from reznor for this heater. The voltage to the motor is 105v steady, and the motor is running at the nameplate FLA of 6.8A. The motor is heating up, and shutting off via the thermal switch. They replaced the motor once, thinking the first sealed motor may be bad, with the same results.

The voltage was a little low, but everything looked ok. The motor is the same size as the original, and was ordered through the oem for this heater. Any ideas why it might be overheating, while running at FLA. the starting cap was replaced with the motor, checked ok, and it's starting strong.

The voltage to the motor is 105v steady

That is barely within 10%. What is the voltage at the source? Wire size and the length of run could be causing the voltage drop.

Is the fan belt driven? I had this same problem on a swamp cooler a while back. Tore apart the centrifugal switch thinking that was the problem, replaced the motor when that didn't work. I finally realized that the there was a variable pulley on the motor and it was turned all the way in so basically the motor didn't have the power to turn the fan that fast. The really deceptive part of all this was that when it was having problems the motor never over amped just got hotter than Hades. Turned out the pulley and everything started working just fine.

Uh what is ambient temperature around the motor.

Dust etc - has anyone cleaned the fan blades thus reducing load torque demand?

IF belt drive fan good suggestion on checking drive ratio. Also would consider checking bearnigs - uhh when if ever did we oil those poor bearings?

For sure I would look into low voltage - it may not be THE problem but it for sure is not helping any.

Dan Bentler

Even though you are at FLA you should never really run at this current level for extended periods of time. As several metioned you really need to check the mechanical side of your system. Only other thing I could see is the motor may be underrated for the job.

Two things I noticed
1. the Single Phase start winding is shorted out and not used after the motor has been started.
2. What is the power requirements of the task.
You may be running a 1 KW motor on a 2 KW load requirement.
the FLA is the maximum the motor can supply -
OR
Additional cooling for the motor may be needed.