MEW 194 – Electric Motor Warning

[Michael GilliganParticipant @michaelgilligan61133]

Thank You …

[Michael GilliganParticipant @michaelgilligan61133]

I would just like to publicly thank Mike Joseph, for his timely warning about the internal wiring in old Electric Motors.

Based on Mike's advice; I have just had a look at the Hoover motor that I have been storing for years [in the hope of, one day, finding a good use for it].

Just like Mike's … the Rubber insulation was crumbling.

I recovered the four long "holding-it-together" screws, and the brass electrical terminals … The rest has gone to the Tip.

MichaelG.

[WALLACEParticipant @wallace]

Hi Michael.

I need to look at several.motors I have which are the same type as well – but, I’d be a lot more tempted to rewire them.

I don’t want to stir up the health and safety hornets nest, but I’ve converted a few 440 volt 3 phase motors to 240, with new cable, heatsink tubing to cover any soldered joins, tied it all down with wax string and finally coated it all with lashings of varnish.
To make sure it was all ok, I tested the insulation with a 500 volt ‘megga’.
It’s not just the meanness that appeals to me in rewiring a Hoover motor, I’ve also found that they run a lot smoother than a modern day one – and it does seem a shame to bin something that is probably repairable if you take care and have a reasonable understanding of what you’re doing.

W.

Edited By WALLACE on 03/09/2012 20:54:23

[Sub MandrelParticipant @submandrel]

I have a Hoover fractional and it's lovely. The wiring is intact, but I'm going to replace it with PVC covered wire soon.

I agree the quality is exception. plus it will work hard for agesw without getting more than warm.

Neil

[Michael GilliganParticipant @michaelgilligan61133]

Fair comment Wallace … you obviously have the skills, time, and patience.

I was quite disappointed to let the Hoover go; they're stylish as well as smooth running.

Oh well; there's a bit more space under the bench.

MichaelG.

[john fletcher 1Participant @johnfletcher1]

What a shame to discard a motor for such a simple fault, as Wallace says, its very easy to fix a motor. Just work with care,after all that is all the rewind people do. Also those motors are very silent running as they used sleeve bearings, modern ones use ball bearings.Ted

[Ady1Participant @ady1]

The old stuff is good quality gear made to last a lifetime

Needs fixed/refurbished every 20-30 years though

[Michael GilliganParticipant @michaelgilligan61133]

O.K. Guys … Don't rub it in !

[Always happens when I finally throw something away]

MichaelG.

[Ian S CParticipant @iansc]

We’v just replaced the air pump in the church pipe organ, the 1hp motor on the old pump was dated 1917, the bearings (two at each end with a ring oiler), 1″ long X 1″ dia. The wiring was replaced about 15/20yrs ago, the field coils double cotton covered over enamal, and the cotton was still OK, I wonder if the new motor will last as long? Ian S C

[Ian PParticipant @ianp]

Have you replaced the motor or the pump, or both? I know the guarantee had probably run out but what actually failed?

Ian

[Sub MandrelParticipant @submandrel]

If Ian was in the UK it would read "We've just replaced the air pump in the church pipe organ. the old pump was dated 1917 and the lad who works it just got a telegram from the queen and says he's retiring."

Neil

[Ian S CParticipant @iansc]

Nothing wrong with either the blower, or the motor, someone decided to modernise, the old blower was at the opposite end of the building, with a long length of ducting(leaky) to the organ at the front of the Church, the new one is inside the Organ. The old blower would be great for a forge.
Ian S C

[jason udallParticipant @jasonudall57142]

"with a long length of ducting(leaky) to the organ at the front of the Church"…

might not been better to replace DUCTING?.. odds is the fan etc was probalby mounter remotely for a reason…

BTW Ian , one of the successful (commercially) uses for stirling engins (C19) was to drive church organ pumps…quiet and easier to "use" than steam …. at least until electric motors…

[Sub MandrelParticipant @submandrel]

I was merrily machining away today when phut! the motor stopped and lights went out – the workshop box had tripped. Tried rpelacing the (5A) fuse still pop – right back to the house box!

Much mulit-metering which showed motor coils and insulation OK (>20Megohms) and also took the inside plate off – to show my motor is all PVC wiring in good condition, just the capacitor is rubber covered (but still good – and being external is visible). Didn't solve the problem though

Motor ran OK with NVR/filter box bypassed – it turned out the rectifier for the relays had gone dead short across the AC terminal. replaced and now OK.

I was surprised this blew, as it was out of the old mini-lathe control box, passing 300W for the motor, whereas I was only using it to provide enough for two.tiny relays – about 20ma.

Neil

[Sam StonesParticipant @samstones42903]

Gentlemen,

Every since our well-known brand of washing machine packed up some years ago, I have been suspicious about certain applications where PVC covered wiring had been installed.

After removing the cover of said machine, I found that spade terminals had been used to connect the mains supply to the built-in water heater. (I can't recall the heater Wattage.)

That’s fair enough, but on closer inspection, I discovered that a couple of cm's of PVC insulation leading away from both terminals had largely disappeared, exposing the solid copper wire, or what was left of it. The single strand copper wire was much thinner at the spade terminals, tapering to almost nothing. In fact, one of the copper leads was so thin it had failed and gone open circuit.

I contemplated the possibility that either the spade terminals or more likely the heater itself had been overheating. This would initiate a degradation process in the PVC insulation sufficient to produce hydrochloric acid. In turn, the acid would then attack the copper, thinning it even more, and thus accelerating failure.

I realise that there must be vast quantities of PVC cable in use, so is this an isolated case?

What do you think?

Sam

[Michael GilliganParticipant @michaelgilligan61133]

Footnote:

I just found this useful PDF document on Induction Motors in the Home Workshop.

MichaelG.

[ALAN EARLParticipant @alanearl64921]

JUST NOTICED THIS ON MOTORS DOES ANYONE KNOW HOW TO REVERSE ONE OF THESE HOOVER SINGLE PHSE MOTORS MINE DOES NOT HAVE AN EXTERNAL CAPACITOR AND LOOKING INSIDE I WAS UNABLE TO IDENTIFEY WHICH WIRES TO CHANGE OR IF IT CAN BE REVERSED A.EARL

[norman valentineParticipant @normanvalentine78682]

Alan, I am not an expert, so can't be relied on but I have one of those lovely Hoover motors. I wanted to fit it on a machine that needed to run in either direction. I identified the pairs of wires that fed each coil and after that it was quite easy following one of the diagrams in Tubal Cains "Model Engineers Handbook". I have to admit that I melted the capacitor at the first attempt but now it works fine.

Edited By norman valentine on 25/11/2014 16:28:39

[colin hawesParticipant @colinhawes85982]

My ancient 7" Drummond came with a lineshaft and an equally ancient Brooks motor with a contact starter. The motor failed twice through metal fatigue in the very visible windings. After I soldered the breaks twice, without having to dismantle anything, I decided I couldn't win and scrapped the motor. Colin

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