Motor capacitors

[Jcb33]

Hello,
Looking for some help on a motor.
A farmer that lives down the road from me has a motor on his bin dryer fan that has an issue.
A year ago the centrifugal switch went bad so I replaced that and the capacitors because they looked rough too, everything has been going good till recently. The switch went bad again (it had some rust on it which was making it stick), replaced that and it seemed to be good. He called a couple days later and said he started it up and it started fine then made a terrible noise and tripped the OL.
I went over reset the OL took the cover off the side of the motor and started it, it seems like as soon as the switch flips to the run mode it starting a making a noise, the capacitors sparked at the Spade locations, the start capacitors smoke, and then I quickly shut it down.
Some of the Spade connections were loose so I replaced those and tried again and got the same results.
Should I just replace all the capacitors and try it again. I don't think that is the main problem but I don't know.
I didn't have any more time to do any more trouble shooting, but in my limited motor work I've never came across this before.
Thanks
It's a 7.5hp 240V single phase motor.

 

[ptonsparky]

Take it to a motor shop. We replace capacitors on those fans often enough, but an immediate subsequent failure sends it to a shop. Have the bearings replaced while it’s there. Rewinding that size is not usually done anymore.

 

[ActionDave]

I think your farmer's motor is on its last leg. Blown starting caps are often the canary in the coal mine. Having a starting switch stuck puts stress on other parts of the motor.

If the start caps stay in the circuit too long they will burn up or blow up. If it is a cap start motor and the start winding stays in the circuit too long it will burn up. If it is a cap start, cap run motor and the starting caps are bad the motor will try to start off the running cap and it will go bad.

 

[kwired]

Hello,
Looking for some help on a motor.
A farmer that lives down the road from me has a motor on his bin dryer fan that has an issue.
A year ago the centrifugal switch went bad so I replaced that and the capacitors because they looked rough too, everything has been going good till recently. The switch went bad again (it had some rust on it which was making it stick), replaced that and it seemed to be good. He called a couple days later and said he started it up and it started fine then made a terrible noise and tripped the OL.
I went over reset the OL took the cover off the side of the motor and started it, it seems like as soon as the switch flips to the run mode it starting a making a noise, the capacitors sparked at the Spade locations, the start capacitors smoke, and then I quickly shut it down.
Some of the Spade connections were loose so I replaced those and tried again and got the same results.
Should I just replace all the capacitors and try it again. I don't think that is the main problem but I don't know.
I didn't have any more time to do any more trouble shooting, but in my limited motor work I've never came across this before.
Thanks
It's a 7.5hp 240V single phase motor.

Are you certain the switch actually opened? If it did current through start caps should cease and this won't happen. If switch did open but you still have current through start caps then they possibly are not connected correctly or there maybe is a ground fault allowing current to still pass through them. Run capacitor always has current, the centrifugal switch just puts the start caps in parallel to the run until the speed is enough to open the switch.

Is possible your centrifugal mechanism is malfunctioning and not allowing it to open the switch. They do wear out and can hang up.

 

[paulengr]

Ultimately this points to why a potential relay is such a better option. A potential relay monitors the voltage across the coils. At first the motor is a dead short so low voltage. Once voltage climbs high enough it opens the start cap. As a fail safe many of them have say a 2 second timer, too. Nothing mechanical to get gummed up and fail inside the motor.

 

[Jraef]

There are basically two parts to a centrifugal switch, the switch contacts, and the centrifugal mechanics. If you replaced only the contact set, but the mechanical parts are still gummed up, you go right back into the same boat. But also if the bearings are going bad, even if you replaced the mechanical parts, the wobbly bearings may be tearing it up again right away. That's why Tom's suggestion to just take it in to a motor shop or replace it makes the most sense.