Black & Decker 10" Ball Bearing Grinder Capacitor Issue

[jonhdw]

Hello all, I am in need of some assistance from the bench grinder experts.

I just restored a B&W 10" Ball Bearing Grinder, and I have some questions about the value of capacitor to use in it. When I bought it, there was a 55uf cap inside, which I thought was low for a start capacitor on a 1hp motor. The standard is about 550uf for a motor that size, so that's what I put in it.

Once I completed the restoration, and turned it on, it seems to struggle to start. So I got to thinking, does this motor even have a start capacitor? It might be a run capacitor, which would explain the 55uf capacitor that came in it.

So does anyone know for certain if this particular grinder model has a start capacitor or a run capacitor? Also, what is the correct value capacitor to use in there so I don't do any permanent damage to the windings?

Thanks!

 

[American Locomotive]

Dos it have a centrifugal switch inside to disconnect the capacitor? Did it work fine with the old capacitor?

 

[yhprum]

Was your capacitor an original one?
On the centrifugal switch... if there is one you may be able to hear it click as the motor coasts down after cutting the power.

 

[jonhdw]

Yes there is a centrifugal switch. It started up with the old capacitor but ran poorly because the bearings were shot. I doubt it was the original capacitor but I could be wrong. I didn’t think it was original because the grinder is likely 80 years old and the value of the capacitor seemed way too low. So I replaced the bearings and the cap and painted it. Now it runs fine but starts rough. I just want to make sure I don’t cause any major damage to the windings.

 

[American Locomotive]

A run capacitor is usually an oil filled (metal can) or film capacitor. Start caps are usually electrolytic in a plastic or cardboard (if old) casing. The 55 uF cap may have been correct. A bench grinder isn't meant to start up under a load, and won't require much starting torque.

 

[jonhdw]

That makes perfect sense American Locomotive! I never thought about it that way with the lower starting torque requirements.