• Scam Alert. Members are reminded to NOT send money to buy anything. Don't buy things remote and have it shipped - go get it yourself, pay in person, and take your equipment with you. Scammers have burned people on this forum. Urgency, secrecy, excuses, selling for friend, newish members, FUD, are RED FLAGS. A video conference call is not adequate assurance. Face to face interactions are required. Please report suspicions to the forum admins. Stay Safe - anyone can get scammed.

Grinder starter problems

DPittman

DPittman

Ultra Member
For those people that know something about electric motors (I'm not one of them)...

If the video comes through it will explain things better than my garble below...

If loaded once before getting up to full speed the motor shuts off and then will try again and fail and shut off again several times before finally being able to get to full speed. It seems to do this repeatedly with no load at startup. It has done this in the past but seemed to have fixed itself after several startups. This time it doesn't seem to remedy itself.

( i just put on a new wheel and don't have it completely balanced yet so there is some extra vibration)


Ok the video is too large to post....I will go research on other methods
 
The starter capacitor is optional on some motors; it shifts the phase slightly to aid in startup (single phase motor) for the starter winding. If the switch is toast you can burn up the starter windings. Usually the ones I've dealt with just won't start at all if the capacitor is gone. Assuming it is single phase, those two components are the usual suspects. It can be tough to get to. Sometimes you have to pull the shaft to access it. The switch is speed controlled, so loading will affect it.

There...I'll let someone smarter than me chime in now...I've exhausted my knowledge of AC motors.
 
Long ago we had an old motor off of an appliance of some sort ( furnace, dryer, washing machine or something) that we used with a buffing wheel on it. To get it going you had to give the wheel a spin with your hand and then immediately flip it on or else it would just buzz or seemed liked it wanted to start backwards. We ran that for years like that.
 
That's the capacitor for sure in that example. You see it on air conditioners all the time. Spin the fan and it starts up. The buzzing is a dead giveaway...but it also means you are putting the starter coil in danger of burning up. Easy, inexpensive fix.
 
See the capacitors under the motor - you have to take the housing off and they are in the base. Did you abuse it recently? I had a motor like that and the problem was a burnt winding. Also can check the centrifugal switch kicking in and out.

If it was me I would see the capacitors in the base and replace these first. You can get them cheap off aliexpress. Once capacitor issue is dealt with look into other issues.

The problem through is not 100% sure sign of capacitor issue - notice that capacitor for start is there to make the motor move - once it moves it is not used. Yours moves but then cuts out - it moved initially so start capacitor is no longer the issue IMHO. Run capacitor is there to make things smooth - i.e. it will still run with it dead or mostly dead. Yours cuts in and out - it cannot really be the centrifugal switch as well as your grinder is moving - its job is also done.

It feels to me like one of the windings is turned on and off intermediately. Maybe bad connection or loose connection? I can see that the grinder is not well balanced (as say a Baldor is) thus maybe something was shaken loose? Maybe check that first before any capacitor work. You can also check windings while at it.
 
Give it a really good spin and switch it on once you have spun it (keep your hands safe) if it runs up to speed, your switch of centrifugulality is probably not working correctly - possibly stuck open or contact are dirty/bad. I have also seen where the capacitor connections have come off...
 
The vibration is not the problem as it was doing that before when it was balanced. It started by grinding before the motor got up to speed,
20201212_134859.jpg
and has done this years ago but seemed to reset itself somehow (there is no manual reset button on the unit).
I don't see a centrifugal switch in the owners manual.
Is all the info I needed to order a capacitor just the info seen on the capacitor in the picture?
 
CalgaryPT said:
Do you have a VOM, or even one with a capacitance setting?

Click to expand...
Yes yes I do, but embarrassingly I don't really know how to use all the functions.
However that video was great and very helpful. I think I might be able to test my capacitor myself but for now, I put things back together and if I can find the same capacitor online somehow, I will order it and then test my old one for knowledge sake.

It sounds like it is very likely the capacitor. I've had this bench grinder for 22 years so I guess if capacitors deteriate, then mine is probably due.
 
Do the capacitor check like PT is suggesting because its pretty quick. Pay attention to the pre-discharge unless you like shocking surprises LOL.
But a bum centrifugal switch still could be the root cause. If its not functioning properly, you will just burn up the next capacitor and/or a collection of these things can adversely affect (read burn out) motor windings.
 
And if you don't have a CS then then there is some electronic equivalent. It could be integrated into the switch or relay or some such black thingy (my electrical knowledge rapidly diminishing here).
I had a video saved but cant find it. This one possibly? John, where are you? LOL

 
DPittman said:
Yes yes I do, but embarrassingly I don't really know how to use all the functions.
However that video was great and very helpful. I think I might be able to test my capacitor myself but for now, I put things back together and if I can find the same capacitor online somehow, I will order it and then test my old one for knowledge sake.

It sounds like it is very likely the capacitor. I've had this bench grinder for 22 years so I guess if capacitors deteriate, then mine is probably due.
Click to expand...
You can generally use a cap up to 20% greater, so in your case 30 uF. But the voltage must be the same as or greater. So in your case at least 250VAC. As the voltage goes up, so will the size of the cap, which could be an issue if space in the motor is tight. If you can't find one online, a motor repair shop should have one. Good place to start because its cheap. Next step is the switch.
 
Last edited:
PeterT said:
Good overview of centrifugal switch.
Click to expand...
BTW - this guy's videos are great. I've watched lots of them in the past. There's something about his presentation style that is so humble you think, "I can do that too."
 
You must log in or register to reply here.
Back
Top