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Question:

Electric Motor Repair?

I have a large shop fan that is belt powered by an electric motor. Here a while back the fan stopped running and would just hum when it had power. If you pushed the fan blades it would start running. That told me that the likely suspect was the starter capacitor. Today I went to Grainger and picked up a replacement. Unfortunately they did not have a direct replacement but verified that the one they had would work. Came home.. hooked it up.. and it still will not start on its own. Although I did not mark down how it was connected months ago when I took it apart, it is only two wires and I could tell on the original piece where they were connected. Am I missing something here? Is there more to replacing a capacitor than just wiring a new one up? Or is there something else wrong. Thanks in advance!

Answer:

Maybe a blown commutator or something in the windings. My guess is commutator which can be cleaned sometimes. It won't start because the +/- thing the commutator does is fried. When you spin it, it catches the next mark and runs. As it runs, the inertia just skips over the bad spot. It's like a gear that's missing a tooth - it won't start, but once it gets going it will just pass over the missing tooth. It's hard to explain in words... Maybe it can be fixed, likely it can't. It means the motor is old, that's for sure.
what is the voltage of the motor? does the fan turn freely without the belt? does the motor shaft turn freely? if there is a bind in the motor then that may be what is preventing it from gaining momentum. try to run the motor without the belt. you may just need a new motor. EDIT: if the motor runs freely when disconnected than make sure nothing is binding up the fan... try some WD40 until the fan spins effortlessly... if that doesn't work than you probably need a new motor. The commutators, brushes and springs the others are talking about are mostly found on DC motors. you have an AC motor. your motor is probably a dual-voltage... i.e can be wired for 120V or 240V... make sure it is wired correctly by looking at the motor name plate/wiring diagram.
appears like a defective fan motor. maximum in all probability a useless spot on the armature or starter factors undesirable. the cost of restore will exceed the cost of the fan. go back it to the position you purchased it from, or purchase a clean one.
Sounds like it's dieing of old age to me. Anyway how big is this shop? 3/4 HP is a huge fan motor for a home shop. You may want to down size and replace the whole thing. Unless it's a huge shop 1/4 HP should more then do the job.
If the MFD and Voltage on the new capicator are within 10 % of the old capicator it will work....If the motor has a capicator it will ( Must) have a starter switch...The starter switch will be mounted inside the ode end bell as a general rule...The rotor shaft has a centrifugal device that operates the starter switch...If this device is stuck with the starter switch contacts open the motor won't start on its own...Grainger use to stock the switches....Don't know about now. If you decide to try to take the switch off...Be sure to tag EVERYTHING....If you have 2 leads to the capiucator it doesn't matter which wire goes where on the capicator... Be careful the switch is sort of fragile

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