Motor start capacitor

[jrjr2u]

I have an old 3/4hp motor that has a starting issue. I removed the load and the motor spins freely. When I turn it on it sometimes won't start by itself. It will hum but given a little spin it will take off and run ok. I checked the cap and it seems to be in spec. It shows no signs of bulging or leaking. The cap is rated 150mfd and my meter shows it at 163. The start switch seems to be working as it should. Can the cap show in spec yet still cause this? Motor is made in Taiwan and dated 1977. It's a 120v motor.

 

[Besoeker3]

Time to replace it ?

 

[jrjr2u]

Time to replace it ?

Probably, that's why I was asking

 

[jrjr2u]

This looks to be compatible - What do you think?

https://www.amazon.com/FidgetGear-Cylinder-150MFD-Starting-Capacitor/dp/B07QXZWQXG/ref=sr_1_3?crid=3PFXQIQE8OCUC&keywords=Start%2BCapacitor%2B150&qid=1681928012&s=industrial&sprefix=start%2Bcapacitor%2B150%2Cindustrial%2C101&sr=1-3&th=1

 

[ActionDave]

Is there any vertical play in the shaft? A worn bearing, especially a sleeve bearing will spin freely but will bind up when current hits windings.

 

[jrjr2u]

Is there any vertical play in the shaft? A worn bearing, especially a sleeve bearing will spin freely but will bind up when current hits windings.

Nope the bearings all seem good, no play and spin freely.

 

[ActionDave]

I wouldn't change the capacitor until I checked the starting circuit.

 

[ActionDave]

Nope the bearings all seem good, no play and spin freely.

It would only take a few thousandth of an inch to matter.

 

[jrjr2u]

So back to my original question - Can the cap show in spec yet still cause this occasional failure to start?

 

[synchro]

So back to my original question - Can the cap show in spec yet still cause this occasional failure to start?

It might measure the correct capacitance, but have too large an ESR (equivalent series tesistance). That could cause not only voltage drop, but insufficient phase shift as well.

 

[jrjr2u]

It might measure the correct capacitance, but have too large an ESR (equivalent series tesistance). That could cause not only voltage drop, but insufficient phase shift as well.

Cool that's an easy place to start then. It is 40+ years old after all! Thanks

 

[steve66]

And you have continuity through the start winding? Just wondering -Are you trying to start the motor with a load, or unloaded?

 

[xformer]

So back to my original question - Can the cap show in spec yet still cause this occasional failure to start?

Sometimes weak or leaky capacitors can read good from meter voltage, but at line voltage do not operate sufficiently.

 

[augie47]

If the cap checked o.k. I'd be most interested in the start circuit... a dirty centrificul switch perhaps ?

 

[jrjr2u]

And you have continuity through the start winding? Just wondering -Are you trying to start the motor with a load, or unloaded?

Yes on continuity and no load.

 

[jrjr2u]

If the cap checked o.k. I'd be most interested in the start circuit... a dirty centrificul switch perhaps ?

Time will tell. I am replacing the cap, just cause I can, and will tear it down if that doesn't rectify the issue.

 

[jrjr2u]

Sometimes weak or leaky capacitors can read good from meter voltage, but at line voltage do not operate sufficiently.