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What would make a 1 hp single phase motor increase in rpm by 25%

What would make a 1 hp single phase motor increase in rpm by 25%

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  #1  
Old 11-11-19, 02:56 PM
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What would make a 1 hp single phase motor increase in rpm by 25%

120v -Single phase- no VFD- after years it simply turning substantially faster that if was last week
 
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Old 11-11-19, 03:53 PM
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Are you talking about motor shaft? How and what are you using to measure RPM to make this comparison?
 
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Old 11-12-19, 09:56 AM
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It could be a resistive neutral at the utility..., do you notice lights getting unusually brighter at times ? Or a resistive neutral on that motor circuit. Check the neutral splices at every switch and junction box all the way back to the panel, including the panel. A resistive ( corroded or slightly loose ) neutral connection can sometimes cause unusually high voltage when another circuit is drawing amperage. It could also be a winding issue within the motor. Depending on how old the motor is, the frequency of use, etc.
 
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Old 11-12-19, 10:01 PM
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It could be a resistive neutral at the utility...,
What the heck is that.
 
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Old 11-13-19, 07:18 AM
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Perhaps the motor centrifugal starting switch had been stuck for some time, and finally it freed itself, causing the motor to run at its full rated normal RPM?
 
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Old 11-13-19, 07:22 AM
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What the heck is that.
Apparently it's a thing.

resistive neutral when a heavy load dips the voltage on one side, the voltage raises on the other.
 
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Old 11-13-19, 08:10 AM
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Electric induction motor's rotor synchronous speed is determined by the voltage frequency and the number of magnetic poles formed by the stator's run coil windings. If the induction motor is a non-synchronous design, the motor's rotor speed will be less than synchronous due to something called slip. Slip is not a constant and can result in a small RPM change (not 25%). Operating the non-synchronous motor beyond design torque will also cause motor rotor RPM to decrease. What does the motor nameplate state for RPM?
 
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