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OxxAndBert
28th Jan 2019, 06:54 PM
Picked up a nice 6" Glen (Glentanner) bench grinder on the weekend, but unfortunately its doesn't run.

Checked the start capacitor, its fine. Centrifugal switch is also OK.

I'm a confused about the windings though.
To start with, this is what I'm assuming is the circuit and winding relationship. The switch is the centrifugal switch:
https://uploads.tapatalk-cdn.com/20190128/7f25f059912db120b81d7786aeafba25.jpg

If I check the resistance across the line connections to the motor, I get an open circuit ( I expected to get low resistance from the run winding if the winding was good)
If I remove the capacitor and check the resistance across the terminals that connect to it - I get low resistance (centrifugal switch closed). Thats what I'd normally expect, but not if the run winding was open circuit.

Its got me a bit baffled so thinking I'm making a wrong assumption somewhere.

Steve

BobL
28th Jan 2019, 07:05 PM
Sounds like the main winding is OC.

OxxAndBert
28th Jan 2019, 07:05 PM
This is the inside.
Red terminals go to start cap.
Blue to main on/off switch.

https://uploads.tapatalk-cdn.com/20190128/bbe4ff54ab7e3da5926f22ada4d83d99.jpg

Steve

OxxAndBert
28th Jan 2019, 07:57 PM
Sounds like the main winding is OC.

That's what I thought initially, but then I can't explain how I get continuity at the capacitor connections if the main winding is OC.

Steve

BobL
28th Jan 2019, 08:15 PM
Earths OK?

OxxAndBert
28th Jan 2019, 09:06 PM
Earths OK?

None of the windings are shorted to earth if that's what you're asking.

Think it's making a bit more sense now.

https://uploads.tapatalk-cdn.com/20190128/ad6e65662b4649d63a382946f43eca2c.jpg

If I remove the start cap, then AC 0 ohms
AD 38 ohms
AB OC

If I connect CD, then AB is still OC, so seems that it's broken between B and F.

Does that make sense?

Steve

BobL
28th Jan 2019, 09:59 PM
None of the windings are shorted to earth if that's what you're asking.

Think it's making a bit more sense now.
If I remove the start cap, then AC 0 ohms
AD 38 ohms
AB OC

If I connect CD, then AB is still OC, so seems that it's broken between B and F.

Does that make sense?

Yep - well done!

OxxAndBert
29th Jan 2019, 08:47 PM
The culprit. Guessing a dry solder joint that get a bit hot. Prized apart slightly for your viewing pleasure :)

https://uploads.tapatalk-cdn.com/20190129/8ab7a5d10f954ba1c3c6e2277b17606f.jpg

Steve

BaronJ
29th Jan 2019, 09:08 PM
Hi Steve,

Good work on finding that bad joint ! A quick rub with some sandpaper and solder them back together. Don't forget to put some insulating sleeve on as well.

OxxAndBert
30th Jan 2019, 09:56 PM
Cleaned it up and soldered back together, with some fiberglass "spaghetti tube" over the joint, and bit of 5 min Araldite to keep everything in place.

https://uploads.tapatalk-cdn.com/20190130/abbaaae7a808cd12fdd826350c611b02.jpg

Tests out fine electrically, but will grab a couple of new bearings tomorrow before I put it back together. Bearings aren't bad but may as well take the opportunity while it's apart.
Unless anyone knows of a reason behind the single metal shield bearings fitted, it will be getting double rubber sealed ones!

Steve

BaronJ
31st Jan 2019, 07:05 AM
Hi Steve,

As far as I'm aware only the friction of the rubber seal against the inner surface.

When I put new bearings into the 8" grinder that I refurbished, I only used single metal shielded ones.

377902
I posted pictures quite some time ago. :)

OxxAndBert
31st Jan 2019, 03:02 PM
Thanks Baron. The obsessive side of me says that using metal shields in an environment with grinder dust is asking for a reduced bearing life, but obviously in practice its non-issue.
I bought 2 of each types at the bearing shop today. Will see how I feel tonight as to which ones I fit ;)

Steve

BaronJ
31st Jan 2019, 08:31 PM
Good Morning Steve,

FWIW there is no venting on the grinder that I refurbished, so there isn't any airflow through the motor to drag grinding dust into the bearings. To be honest the only grinders I've seen with vented motors, have been the pedestal type where the motor is in the base of the column, and they get really filthy with particles from belt wear.

So I don't think it will make any difference which ones you fit.

OxxAndBert
31st Jan 2019, 08:55 PM
Fair comment. Think I'll just fit the metal shielded ones then and save the RS for something more deserving ;)

Steve

OxxAndBert
1st Feb 2019, 07:31 PM
All back together and purring like a kitten :)

Just have to decide which wheels to put on it.

Steve