Restoring Thor 6002 bench grinder - wiring question

[timsch]

I picked up a Thor 6002 bench grinder yesterday at an estate sale. The shaft spun pretty freely, but the bearings could probably use some lube.



I offered $5 since it was obvious that it needed a new power cord. I got it home and opened it up to find it needed a new start capacitor and a full rewire. Any recommendations on what start capacitor? It's got a curved bracket with around a 1.5" radius for holding a cylindrical cap. I'd think the biggest 220V cap that'll fit would be good, but I'm no electronics guru.



I can't find a wiring schematic on this model so I'm gonna have to rely on some more general resources, y'all being one of the best ones I have. It's a 220V grinder. How do I identify which wires is which coming from the armature? This will be 2 hots and a neutral, with a 4th for ground coming from the power cord, right?

 

[Watthour]

Be careful about the cap voltage rating. Many are rated with one DC value and a completely different AC value.

Using a conventional formula for start capacitor sizing:

C(µF) = W x Motor Eff x 1000 ÷ ( VAC² x Hertz ) = µF

And plugging in your values:

C(µF) = 378 x 80 x 1000 / (240 x 240 x 60) = 12.346 µF.

Based upon that, and presuming this is indeed a start capacitor, and NOT a start-run capacitor, a 15µF would be suitable.

Note that I used 240V for the "V" value since that is very likely what your system is delivering, and possibly higher. Providers have been bumping line voltages over the past few decades in order to satisfy demand and maintain a reasonable power factor in their distribution systems.

Given the probable peak voltage the application will see (RMS voltage x √2) in a single-phase system, a 470V rating would be suitable for a 240 system. Going below a 420V rating could result in a spectacular failure of the capacitor insulation.

It looks like that is also a relatively common value to find commercially:

https://www.mouser.com/c/passive-components/capacitors/?capacitance=15%20uF&voltage%20rating%20ac=470%20VAC

 

[Watthour]

As for the motor wiring, with a dedicated 220V wound stator (according to the nameplate), there will be no "neutral" wire in the makeup/connection box. That other wire is likely the part-winding tap that is for connection of the start capacitor. If you open the unit to service the bearings, you should be able to observe the wire connections, and also see if there is a centrifugal start switch. If the switch is NOT present, the capacitor could be used as a start/run type, and sizing would necessarily be different.

 

[Watthour]

Interesting that your photo looks a lot like the unit of page 28 of this catalog:

http://www.blackburntools.com/articles/rose-tools-catalog-archives/pdfs/thor-ca1930-no-39a.pdf

 

[John T]

Good info Watthour !!!!!!! I knew all that stuff yearssssssssssssssssssssssss ago but Ive slept a lot since lol

John T

 

[timsch]

Got it open with a little persuasion. More wiring surprises.



I thought maybe I sheared them pulling it apart, but the breaks don't look new. I wonder how that happened, whether those are just cut, or whether that was a centrifugal start switch that got removed.... I'm not familiar with the inners of these types of machines.

Here's how those three wires connect to the stator.



Yes, that looks to be the unit in the catalog. I couldn't find a catalog date with a quick glance. I wonder when it was from, and how much $96 would be these days.

 

[Watthour]

The centrifugal start switch is present, as expected, but is obviously disconnected. That will need to be reconnected, and the end bell reassembled to the stator/frame.

The more difficult part will be determining what wires are connected to what windings. One of your photos shows a tag on one of the wires, and that could be critical information. I could guess at what is what, but careful measurement with a high-current ohmmeter might be necessary to determine which wire is the main/run winding (which is usually low resistance), which wire is the start winding (usually higher resistance), and which is common to both through the switch.

 

[Watthour]

Also, the stator appears to be in good condition, so the unit hasn't likely been overloaded or overheated. It could be a viable piece once it's all figured out and turning on good bearings. They don't make them like they used to, and having a good piece of iron as a bench grinder is a definite plus.

 

[timsch]

Thanks for all of the replies, Watthour. I agree with your last statement, and I'm looking forward to restoring this.

Regarding reconnecting the centrifugal start switch, the wires as they are look just long enough to connect if the end bell is not removed, which doesn't look feasible. Maybe there were longer lengths and the middle sections were cut out for some reason. Unless told otherwise, I'll plan on splicing in some wire between those remaining pieces.

The wire tag unfortunately is illegible. Maybe it means something by itself....I don't know.

Before posting initially, I checked for resistance on each of the three wires coming from the windings, one probe on the wire and the other on the outer surface of the stator. Infinite resistance on all three wires, although one wire did cause the multimeter to flash some resistances, which were in the high MOhm range.

 

[timsch]

Checking wires, the black wires and the red have continuity. The yellow wire looks to be just a straight run from the power input side to the centrifugal switch side. All wires have infinite resistance with the frame.

I've looked for a wiring schematic for this grinder with no success. A general search turned up this from Milwaukee:

This looks like it's pretty close to what mine should be, I'd guess.

 

[Watthour]

Possibly more like this:

https://www.electricalvolt.com/wp-content/uploads/2023/02/cap1-768x461.png?ezimgfmt=ng:webp/ngcb1

 

[timsch]

Possibly more like this:

https://www.electricalvolt.com/wp-content/uploads/2023/02/cap1-768x461.png?ezimgfmt=ng:webp/ngcb1

Figuring out how my wiring would fit to match that diagram, I only come up with one possibility. Here's the same with B Y R labeling. There was only one place I could fit the yellow. Red and black meet on top only because they have continuity.

Any other possibilities?

 

[caterpillar guy]

On facebook groups there is a group that does old motors from turn of the century 1900 and older to more modern ones. I think it goes by antique electric motors . They helped me with an old induction repulsion motor I was working on cleaning it up and rewiring it. for new lwads to connect to.