maybe replace start capacitor?

[Randall J Cox]

Have a 1 hp, 12 amp, 125V, single phase 6x48" belt sander with 12" disc sander. Thing must weigh 200 lbs! (same one Grizzly sells but with a different name as its older). Anyway, used it for years then moved and it started popping 20 amp circuit breakers. I replaced all the bearings about 5 years ago and it runs smooth as silk. Sometimes it pops breaker on startup and sometimes it doesn't. (I swapped breakers and same result.) As these caps are cheap, thought I would replace it to see if that is the problem. It only has one cap, the start cap and no run cap. The writing on the start cap says 400mf, 125V and Type 129. My Q is what does "Type 129" mean? And is it logical that a weak start cap could pop a 20 am circuit breaker? The existing one is certainly not burned, it looks new but know it isn't as I have had this sander since 2007. Thanks. Randy

[Michael Schuch]

Like you said capacitors are cheap so you might as well give it a try. But that doesn't sound like the issue from your description. If it were me I would clamp an ammeter around one of the legs of the power cord and take a reading at startup and when running.

If replacing the capacitor doesn't fix the problem then I think the next step would be to replace the motor so you might as well start with the capacitor.

Edit: If the motor has a centripetal starting switch that might be sticking which would keep the capacitor from disengaging after the motor is up to speed which could cause the breaker to pop. If the centripetal switch is bad a motor swap might be easier than tracking down a replacement switch depending on the motor manufacture. Or blowing out the motor and the starter switch then adding a drop of oil might fix the problem.

[Aaron Inami]

"Type 129" is likely just a model number for that particular capacitor.

Here's some options for the motor start/run capacitor:

https://www.mouser.com/c/passive-components/capacitors/motor-start-capacitors-motor-run-capacitors/?capacitance=400%20uF%20to%20480%20uF
(https://www.mouser.com/c/passive-components/capacitors/motor-start-capacitors-motor-run-capacitors/?capacitance=400%20uF%20to%20480%20uF)
The PSU40015A model is slightly smaller in diameter (it's 36mm diameter instead of 46mm).

The PSU40065A model has a higher voltage rating of 165VAC and would be more durable for long term or hard use.

[glenn bradley]

+1 on checking the centrifugal switch (https://en.wikipedia.org/wiki/Centrifugal_switch)mechanism. I swapped a couple caps before I figured out it was the switch. Both were in expensive at the time.

[Randall J Cox]

I have ordered a new start cap as I have it all apart and it was on the bottom of the unit and it might be a cheap fix. Once installed if that doesn't fix, will go after the centrifugal switch mechanism. I remember dressing the points on it when I installed the new bearings some years ago. Now I wait for the start cap to arrive. Had lunch with a hot rodder friend who worked in a motor rebuild shop and he also said probably the centrifugal switch. Appreciate the comments! Randy

[Mikail Khan]

A clamp on ammeter will be helpful in troubleshooting. They cost about $30.

MK

[Ronald Blue]

Just curious, does the breaker pop immediately or does it get up or almost up to speed before it trips? If you had to file the contacts on the centrifugal switch before it's possible it has the contacts welded together now. Just throwing possibilities out there. Hopefully the start capacitor resolves the issue.