Success! Elect. Motor Start Capacitor

Scott Farris

Scott Farris

Well-known member
Help, is anyone up to speed on 120V capacitors for starting single phase motors? (To keep this duck/decoy related, its the wicked old motor on my bench drill press that I use for hollowing out my decoys.) The Capacitor is AEROVOX 130-165 MFD 125 VAC. I can find 130-156 or 145-174 µF Ratings. My problem is I don't know if it's better to match the 130 end or bracket the upper end. At the moment I pretend the motor is an outboard and wrap a starter cord around the drive pulley and give her a yank and hit the on switch to start the motor. Works but seems a bit risky for a $3.65 part.

Thanks!
Scott
 
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Scott

Unless the motor starts under heavy load you should be fine with the 130-156 uF start cap. Is the centrifugal switch good? Could be dirty contacts.
 
Yep that one should be fine. MFD=microfarad=uF
I agree with the centrifugal switch, make sure you can hear it releasing to let it run on the run coil and hear it close when slowing down to return to the starting coil. You should be able to tell the difference in sound.

Becuase if it isnt closing back when it drops below the speed you wont be able to re start it without physically spinning the shaft to cause the run winding to turn on.
 
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Thanks guys, I hadn't thought of the [font=Verdana,Arial,Helvetica]centrifugal switch. Since it's out of site out of mind. For the price I'll give the capacitor a try before taking the bell off. I haven't heard the switch noise but not knowing what I'm listening for make the diagnosis questionable.

Thanks a lot!
Scott
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Just when you first start the motor, at roughly 75% full speed the centrifugal switch will open leaving just the run winding in. So once you start it, it should only be like a second before you hear a click noise, and the same when you turn it off. It may be too small to hear it, or maybe its not happening and thats why you arent hearing it but anyways, A capacitor start motor that doesnt start is the majority of the time a burnt or worn out cap.
 
maybe left field in your situation but have you checked the voltage? I just "helped" a friend with his belt driven fan he came home with. The wire on the receptacle was burning back from a poor connection in the wall and he wasn't getting enough power. His power tools and other small consumers worked fine. Just a thought.
 
Package arrived from McMasters yesterday with a new capacitor. Unsolderd the old capacitor, crimped new connectors to fit the new capacitor, with the new capacitor attached but just hanging in space I plugged the anchient drill press in and hit the switch. Success! It started right up. Heck it even starts after I finished assembling the capacitor housing to the motor.

Thanks for all the input and the fears of bad [font=Verdana,Arial,Helvetica]centrifugal[/font] switches and low voltage ;^)

[font=Verdana,Arial,Helvetica]A capacitor start motor that doesnt start is the majority of the time a burnt or worn out cap. [/font]
Click to expand...
Sometimes its good to be in the simple majority!

Thanks guys!

Scott
 
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Scott, I have to start my bench grinder by spinning the wheel and then turning it on. I think you've shamed me into installing a new capacitor! Doug
 
Doug,

Good luck to you, I hope it goes as easy for you. Unfortunately it does take a bit of the fun out of getting the motor started, but it sure is convenient.


Scott
 
It has been a few years since this thread was active, but maybe you can help me with the capacitor problem I'm facing.
[font=Verdana,Arial,Helvetica]The Capacitor I have is Philips 124-149 MFD 125 VAC. I can find 130-156 or 145-174 µF Ratings.
The problem is I don't know if it would better to match the 130 end or bracket the upper end.[/font]
Appreciate any help on this.
 
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