View Full Version : Grinder Capacitor

11-10-2009, 09:06 AM
I have a Harbor Freight 8" grinder, 3/4 hp, 3450 rpm. It starts fine and spins fine, HOWEVER, when I grind anything it slows to the point of stopping unless I remove the item. This is the case with a TIG tungsten or anything larger. grrrr!

So I opened the base and found a capacitor. It's marked: CBB60, 6mf +-5%, 250v, AC50hz, China. I read you can sort of check a cap with a digital VOM, so I set mine on the 200 scale and touched both cap ends, nothing. So I changed leads and the reading fluctuated up and down then stopped within a minute. I could not repeat this.

Any suggestions for further testing? Any recommendations for a replacement capacitor?

Thanks, Alex

PS I'm electrically challenged so be gentle.

11-10-2009, 10:41 AM
Sounds like you're misinterpreting the meter reading. Use the ohms scale, try going to a higher range. What is supposed to happen is that you'll get a momentary reading until the capacitor is charged, then it should read as an open circuit. Swap the leads and test again. Each time you swap leads, you're changing the charge on the cap so it should show some kind of reading as the charge reverses and builds again to the point where it no longer is taking current. Then the reading should show infinite again.

Digital meters are tricky in that if they can't resolve and display a reading quickly enough, they may not even show that there was a momentary current flow into the capacitor. Going to a higher resistance range usually lowers the amount of current that can flow from the meter, and thus increases the time it takes to charge the capacitor. That might give enough time for the meter to give an indication. But unless you reverse the leads for a second reading, there won't be another shot of juice going into the cap because it's already charged from the previous test.

11-10-2009, 12:51 PM
yep, analog meters are best for testing caps. Also, as I have read, Chinese motors are not what they are rated at. Your grinder may say 3/4 hp but may only be 1/4 or 1/3 hp.

scatter cat
11-10-2009, 03:17 PM
You should be able to get a new cap at any heating and air supply place.I am guessing here.The cap maybe just for the start circuit.Check your run windings in your motor if you can get to the leads.You might have a open coil in the windings somewhere. That would account for the no power.Check on the x1 ohms scale. The resistance in the windings will be pretty low usually around 1 or 2 ohms. Unless they are open. The start winding less than the run windings.

11-11-2009, 12:11 AM
Thanks for the advice, looks like I have more checking to do. I did use the 200k ohms scale, I guess I just wrote 200.