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Motor continuity confusion in bench grinder

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Alpha-Dave

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Hi all,

Old machinery apears to be an emotional rollercoaster:

I picked up a Wolf bench grinder for £30 from Facebook, it turned out to be the 8” version rather than 6”, which was good.

24781803-5A50-496B-B3AD-8340F4F5CE65.jpeg


The seller plugged it in (having put on a temporary plug) and it ran ok. It ate some metal so all was good, I assumed, although the switch was a little gritty.

Getting it home and starting to clean it up, I removed the base to check the wiring to see how to add a new lead. It was quite crusty and corroded inside, and removing the large starting capacitor flexed some wires that have not been moved since 1950 (according to the date on the cap)!

00F0DA51-FA0F-4738-AB0C-99BBA62706E7.jpeg


Now looking at the insulation, it is crumbling away on the wires from the motor. Two of the 4 wires go to the switch, and 2 go to the capacitor.

F575D78C-9B79-49BE-8D52-B829DC01CCB1.jpeg


Using a continuity tester: the capacitor is continuous across its terminals, which seems bad. All 4 of the motor wires are connected to each other. None connect to the case (fortunately). Therefore I’m wondering if the insulation has completely broken down between the switch & cap and the motor, or is it possible it is wired ok?

Any thoughts welcome!

Many thanks!
 

Argus

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Perhaps that 70-year old wiring is trying to tell you something....................

It's likely, from that date that it's VIR cable.... (Vulcanised India Rubber outer sheath, with a waxed paper lining), which was prone to hardened crumbling when I ripped a lot of it out of buildings on it in the 60s.

The motor winding's varnish may be OK.......
New capacitor? Re-wiring?
 

guineafowl21

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Yes, you’ll need to strip down to the stator and rewire from there, and add a new cap.

It usually involves softening (heat gun) and untying the bindings to release the junctions between the winding wires and outgoing flex, soldering on new flex and retying. If you can’t find a local motor shop to do it, I’d be willing.
 

Alpha-Dave

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Having looked at the capacitor, I definitely thought a new one would be sensible, although unfortunately some of the paint has peeled, so it is 10 microfarads, but ?80 V AV. It must be at least 280V given UK 230V supply, but 380 or 480 ratings for running caps versus starting caps are both plausible.

9A1153AF-C0D9-41E8-903C-CFA552814BFE.jpeg

A quick google showed a post on a radio forum that says that this type of cap (visconel) has oil in it that may have carcinogenic compounds, so I will not be poking at it.
 

Alpha-Dave

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Perhaps that 70-year old wiring is trying to tell you something....................

It's likely, from that date that it's VIR cable.... (Vulcanised India Rubber outer sheath, with a waxed paper lining), which was prone to hardened crumbling when I ripped a lot of it out of buildings on it in the 60s.

The motor winding's varnish may be OK.......
New capacitor? Re-wiring?
Definitely a new cap and switch, and all wiring associated replaced.
 

Alpha-Dave

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Yes, you’ll need to strip down to the stator and rewire from there, and add a new cap.

It usually involves softening (heat gun) and untying the bindings to release the junctions between the winding wires and outgoing flex, soldering on new flex and retying. If you can’t find a local motor shop to do it, I’d be willing.
Unfortunately, I think you are right.

I need to get the flanges for the grinding wheels off the rotor before I can get the end caps off and look at the wiring; therefore I need to buy or make a bearing puller to get them off.

Thank you for the offer, I will see how it looks once fully apart.
 

guineafowl21

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I picked up a similar Wolf grinder for £10 recently, literally on the scrapheap. The scrappie said it was no good, but the fault was just a wire off the cap! Again, a TCC visconol but this one was still going strong. A very good grinder and well worth restoring.

I didn’t need a bearing puller to strip mine down.
 

Alpha-Dave

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Well a lot of very tiny taps with a copper mallet persuaded the flanges to move, so I was able to get to the end caps.

C6C2ACDB-BA0C-4256-9A08-E496BA17F9EB.jpeg


Then cutting the ancient heat shrink off the wires showed that the insulation really had perished.

184E57E8-6C1F-46CC-906E-88B56D1DB99B.jpeg


The windings on the stator look good though!

91C15C09-1A9B-4436-8C6D-7F7193A847EE.jpeg


and the laminations look good.

F027A412-6CDB-4840-B48F-CFD1F72FC636.jpeg


So now the questions are:
1) how to get the binding off (heat gun as guineafowl21 suggests; or send to a professional at this point)
2) what sort of wiring to replace the perished parts with (I guess I can just measure the conductor with calipers)
3) how to bind the new wire in and replace the binding.


8B78309E-0B05-46D4-9F4C-BBD68DEAAE66.jpeg


All thoughts & comments appreciated!
 
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Spectric

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That looks in a sorry state, although the windings look ok, cannot tell without testing though and so rather than end up with something electrically unsafe I would get that to a motor repair specialist to get it properly done and tested, you need an insulation tester to ensure that all the insulation is intact without unseen shorts. This test will measure resistance under an applied voltage, so any breakdown in insulation will be found.
 

Alpha-Dave

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After emailing, messaging and calling 4x local companies that offer motor repair, one said they could have a look at it.

They replaced the leads on the stator, tested it for leaks, and tested the old capacitor, which apparently is in good shape.

3B3CE4EB-AA4C-4497-AEF7-8566F7C4B076.jpeg



I have ordered a replacement switch, which will require a little modification to the case to fit, but sourcing a direct replacement was always unlikely.
 

Spectric

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Do you now know what the wires are, looks like four wires so they would have brought out the star point. It was much easier when they used to just bring out all six windings into the junction box and left it to yourself to determine the config, was essential in the days of the star delta starter.
 

Spectric

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That makes sense, and makes you appreciate how much simpler three phase motors are.
 

Alpha-Dave

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I bought a NVR switch from Axminster, then 30 min to cut and file a 22x42 mm hole in the front and some connector blocks and it’s working nicely.

Annoyingly the stone I bought is too wide (I should have checked), but the wire wheel I bought is excellent.

The next stage is to make a stand, and a box/cover for the wire wheel.
 
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