# Opposite grinder rotation



## calstar (Nov 30, 2017)

Recently picked up a grinder(Doer,1/2hp, 1725rpm, 120v) at a garage sale to use with wire wheels.  Rotation is opposite to what is usually found, it rotates from the bottom up, not the top down.  Here is a marginal photo(if needed i can take a better one), the only black/hot wires are a pair labeled T2 and T3, will switching these reverse rotation direction?  I can use it as but have been standing on the back side or side so I get the top down rotation, would be nice to correct it.



thanks, Brian


----------



## jim18655 (Nov 30, 2017)

Picture/attachment isn't showing up.


----------



## jim18655 (Nov 30, 2017)

Any name plate/wiring diagram?


----------



## markba633csi (Nov 30, 2017)

Hi Brian, yes you should be able to reverse it.
There should be two windings, and the cap goes to one of them.  You'll need to
swap the ends of the winding that connects to the cap or swap the run winding ends. 
First step: Get some masking tape and a sharpie and label all the wires; draw a diagram how it's connected now.
Then disconnect all the connections and locate the two windings with a ohmmeter or continuity checker
at that point you can wire it back up.
I'll do a little sketch and post it to make the wiring a bit clearer.
Mark


----------



## markba633csi (Nov 30, 2017)

Does it make a clicking noise when it comes to a stop? In other words is there a centrifugal switch in there?
It's either a capacitor start motor or a capacitor run motor.  Capacitor run motors don't click.


----------



## markba633csi (Nov 30, 2017)

Here is a diagram which is most likely how your motor is wired now.
What you want to do is either swap A and B  or  C and D  to reverse. 
Locating A and B with a meter would be easiest, you'll get a steady low ohms reading.
When measuring C and D you'll get a funny reading that will start off low and go high (infinite ohms) because of the cap. (the centrifugal switch is normally closed when the motor is off)


	

		
			
		

		
	
Mark


----------



## markba633csi (Nov 30, 2017)

If that were a permanent split cap or PSC, also called a "capacitor run" motor, the centrifugal switch would be absent, the cap would
just connect to point C, but otherwise would be reversible the same way. 
M


----------



## calstar (Nov 30, 2017)

Is the pic showing up now? I can see it on this end. No wiring diagram on motor. It makes a click so there is a centrifugal switch. Thanks for the diagram Mark, I'll look for continuity. Yeah, I almost always label and photo when I'm working on things, ALWAYS when its electrical.

Brian


----------



## Eddyde (Nov 30, 2017)

Be carful! It could it be that the grinder was dissembled at some point and put back together backwards. That is to say, the guards & base facing the wrong way. I recently restored a bench grinder and realized that was a possible error. You can determine if the motor rotation is correct by checking which way the shaft nuts are threaded, if the nuts will tighten by holding them and turning the shaft in the direction it is now rotating, the rotation is correct. If you reverse the motor the nuts would want to loosen, possibly creating a dangerous condition.


----------



## markba633csi (Nov 30, 2017)

Good point Ed
Check that Brian, I hadn't thought of it, but I was wondering why it would be backwards in the first place
M


----------



## Holescreek (Nov 30, 2017)

I've never run into a 3 phase motor that wouldn't change directions just by swapping one of the two leads.


----------



## woodchucker (Nov 30, 2017)

Holescreek said:


> I've never run into a 3 phase motor that wouldn't change directions just by swapping one of the two leads.


it's not a 3 phase motor I don't believe. That's why it has a capacitor.


----------



## Holescreek (Nov 30, 2017)

You're right.  "3 phase " just stuck with me when I read T2 and T3.


----------



## cathead (Nov 30, 2017)

Would it be physically possible to rotate the motor 180 degrees so the wheel on the other side of the motor?  
Then it would rotate as you would like and no need to reverse the motor electrics.


----------



## calstar (Nov 30, 2017)

Eddyde said:


> Be carful! It could it be that the grinder was dissembled at some point and put back together backwards. That is to say, the guards & base facing the wrong way. I recently restored a bench grinder and realized that was a possible error. You can determine if the motor rotation is correct by *checking which way the shaft nuts are threaded*, if the nuts will tighten by holding them and turning the shaft in the direction it is now rotating, the rotation is correct.* If you reverse the motor the nuts would want to loosen*, possibly creating a dangerous condition.



Well.... this morning I noticed that the left hand wheel(looking at from the front) is a right hand thread, its usually the right wheel that has the right hand thread, so the rotation is correct for the shaft in this position. I don't want to rebuild it, will just continue to use it from the back side, or maybe drill a hole in the base and mount the switch on the other side(i'll post a pic if I do it), so now the back is the front.  The guards are not a problem, it didnt come with them and I'm using it for wire wheels only.

Thanks again for all the help,  Brian


----------



## markba633csi (Nov 30, 2017)

Sounds like someone took the rotor out and re-installed it wrong.  Anyhow, forewarned is forearmed.  Ciao. 
Mark


----------



## 1holla (Dec 23, 2017)

just change the two wires marked A and B in the schematic above.


----------

