Single phase motor repair help

[tpolley]

I have never messed with ac motors before. I've been researching YouTube and Google to try and learn how to fix this motor.

I picked up a free drill press. Previous owner said it needed a new motor. It's 120 volt single phase. 1700rpm. 7.5amp. Typical drill press motor. The motor was unhooked and sitting on the floor next to it when I picked it up. That's all I know about it's original symptoms.

Before I did anything I looked at the motor and saw the start capacitor had leaked so I assumed all it needed was a start capacitor. I replaced the capacitor with that of a similar value. I temporarily mounted the motor and turned it on. It just hummed and didn't turn. I had to turn the shaft by hand to get it going. Even then as it was spinning it was humming really loud.

I checked the resistance on the windings. The start winding is 0.5 ohms. The run winding is 1.5 ohms. Everything I read online says the start winding should be higher resistance than the run winding. Opposite of what I found on mine.

Plus, if you look at the picture, the start winding is black. I thought it was supposed to be black because it was so evenly coated black. But now I'm not sure. I think the start winding is burned up.

 

[tpolley]

Also, I did check the centrifugal switch for continuity and it seems to be making good contact.

 

[Lightning rod]

yes, the winding is toast.
it should also smell pretty bad

 

[RPH]

Winding is fried. Even the wrapper shows heat damage. New motor time.

 

[Davefr]

Yep, start winding is fried. If a split phase induction motor doesn't release the start winding after a few seconds it will fry. Usually caused by a bad capacitor or defective centrifical switch.

 

[nadogail]

When the smoke leaked out of your motor it became a Door Stop.

 

[wyliesdiesels]

yeah thats toasty! it even annealed part of the run winding as shown by the darker colored copper on the left

 

[American Locomotive]

Yup, start winding definitely smoked. Either the smoked windings took the capacitor out, or a bad cap made the windings smoke.

FWIW: A friend of mine had a drill press with a bad start winding. He just disconnected the winding, and hand-started the drill press.

 

[Norcal]

Odd motor, with 120 volt rating over the normal 115V, used for motors & does not have HP, or NEMA frame number.

 

[dogdog]

easier to just get a replacement motor with the same or higher rating 3/4 hp motor is not much. As long as it is the same frame, rpm, and shaft diameter. The winding is shorted mentioned in multiple replies. So if you are attached to that particular motor, have a motor shop rewind it.? Not sure how much it will cost.

 

[PoorUB]

Odd motor, with 120 volt rating over the normal 115V, used for motors & does not have HP, or NEMA frame number.

Pretty sure that is a OEM motor, probably a Clarke drill press. Typical Chinese import.

7.5 Amps should work out to be about 3/4 HP.

 

[Norcal]

Pretty sure that is a OEM motor, probably a Clarke drill press. Typical Chinese import.

7.5 Amps should work out to be about 3/4 HP.

I had decided not to comment about the likely ChiCom origin.

 

[fitter30]

Purchased replacement motors by amps not hp. Most motors like that have a sf of 1. Service factor of 1 is a cheap motor can't be run at over amps. 1.15 sf is a better motor can run at 15% above name plate amps.

 

[Innovate1]

Yup, start winding definitely smoked. Either the smoked windings took the capacitor out, or a bad cap made the windings smoke.

FWIW: A friend of mine had a drill press with a bad start winding. He just disconnected the winding, and hand-started the drill press.

That's an option but not too convenient. You just have to be sure to give it a start in the right direction. In college a prof in a motors class told of helping a friend with a motor on the feed auger for a pellet stove or some sort of stove. After being shown it could be hand started they started it in the wrong direction and it pulled some of the burning bits out of the stove! Or at least that was the story told.

 

[Zeke]

Motors are not cheap but many power tools are. For instance you can buy a little CM table saw of the old belt type for 20 bucks. You will get at least a 3/4 HP motor.

 

[tpolley]

Alright, I scrapped the original motor. I did find an old Dayton motor in my dad's barn that should be compatible. I checked the tag on the motor and configured it for 120v. I know the hot side is switched, but does it matter to the motor which side gets the hot and which gets the common?

 

[dogdog]

No... for that type of ac induction motor, direction of rotation is dependent on how the start winding is configured. which it looks like its your T5 ,T8 is the start winding.

 

[Norcal]

Alright, I scrapped the original motor. I did find an old Dayton motor in my dad's barn that should be compatible. I checked the tag on the motor and configured it for 120v. I know the hot side is switched, but does it matter to the motor which side gets the hot and which gets the common?

Sometimes a diagram will spec one line as "Ungrounded Line" that is where the hot would be landed if wired for 120V but if nothing is speced then don't worry about it.