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Single Phase Electric Motor Issues

Single Phase Electric Motor Issues

Single Phase Electric Motor Issues

(OP)
So I installed a 30in by 30in Dayton Upblast exhaust fan on a roof. The last exhaust fan's bearings failed and the shroud was torn up from the blower blades. I used the Single Phase Motor that was in the original in the new unit. I got the proper pulley, set up the V belt, and wired for low voltage at 120VAC. I tested the motor in the shop and it ran no load without any problems. When it was installed however it ran for 5 seconds shut off for 20 secs and continued in that loop. The motor began to get hot after running through that loop three times. I plan on opening up the motor and checking continuity throughout, but I was wondering if anybody is experienced this before.

RE: Single Phase Electric Motor Issues

Did you by any chance check the voltage supplied to the motor?
It sounds as if you may be feeding 240 Volts to a 120 volt motor.
Or the problem may be mechanical; the belts may be too tight or the bearings may still be bad.
But 5 seconds to heat up, probably the wrong voltage.

Bill
--------------------
"Why not the best?"
Jimmy Carter

RE: Single Phase Electric Motor Issues

(OP)
120VAC was measured on the supply with nothing wired to it. I think the belt may be too tight so I'm going lossen it.

RE: Single Phase Electric Motor Issues

if the fan bearings failed, the motor bearings may have as well. Bench testing with no load may not have revealed it though.


" We are all here on earth to help others; what on earth the others are here for I don't know." -- W. H. Auden

RE: Single Phase Electric Motor Issues

(OP)
I've already ordered a new motor but if I can salvage this one for another project it would be great.

RE: Single Phase Electric Motor Issues

The power used by a fan is proportional to the cube of the rpm. Even a small oversize on the motor pulley can overload the motor.

RE: Single Phase Electric Motor Issues

Quote (OP)

The last exhaust fan's bearings failed and the shroud was torn up from the blower blades.
If the blades jammed and stalled the motor for any length of time, the motor may be in the last stages of burnout.

Bill
--------------------
"Why not the best?"
Jimmy Carter

RE: Single Phase Electric Motor Issues

Quote:

If the blades jammed and stalled the motor for any length of time, the motor may be in the last stages of burnout.

It's a single phase with internal temp tripping, so probably not so much.

Keith Cress
kcress - http://www.flaminsystems.com

RE: Single Phase Electric Motor Issues

"It's a single phase with internal temp tripping, so probably not so much."
That thermal protection device is mass produced. It will generally protect a motor from the first jam-up, but if a motor is left jammed and cycling on auto resetting thermal protection, all bets are off.
When I was working in the turd world a power outage every Sunday for maintenance was common. There was a combination of four wire wye:delta transformer banks and single phase switching when the power was restored.
This put about 50% voltage on two thirds of each residential circuit until the second phase was closed.
All of the refrigerators and freezers had been without power for several hours and tried to start. With 50% voltage they all stalled.
The thermal protection would cut out shortly after full voltage was restored, but every weekend, somewhere in town, one or two hermetic compressor motors would fail. This was popularly attributed to "Power Surges".
Thermal protection is good but not perfect.
Small protection devices were available and common. The protection combined a voltage monitoring circuit which cut off the output if the voltage was too low or too high and a three minute timer before re-energizing.
A couple of shorted turns may give the observed symptoms for a short while before total failure.

Bill
--------------------
"Why not the best?"
Jimmy Carter

RE: Single Phase Electric Motor Issues

Did u measure the current of the motor?

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