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Old 18th Aug 2022, 1:47 pm   #1
IanNVJ35
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Default Causes of smoking motors

Its often the way, a vacuum or lawnmower works well and gets maintained as needed but the cause of failure is the motor starts smoking and it gets thrown out.

I have just had my Mum on the phone with the vacuum smoking from the motor as she was using it. I know its maintained well.

Asking around at work the consensus is that the windings just break down over time and fail. Has anyone found out the usual cause of smoke from a motor? I said I'd take a look before its condemned as its a nice old 70's Electrolux that used to belong to my Gran.
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Old 18th Aug 2022, 2:00 pm   #2
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Default Re: Causes of smoking motors

In my experience it's always a short in the winding of the rotor, which then behaves like a shorted transformer winding.

You get to know the smell of cooked varnish. Most recent example here was an old electric drill. The new one is so much lighter and torquier.
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Old 18th Aug 2022, 2:24 pm   #3
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Default Re: Causes of smoking motors

Our vacuum cleaner went up in smoke some years ago.
There was a RIFA capacitor lurking in it so it was an easy fix.
I diagnosed the fault with a sniff.
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Old 18th Aug 2022, 2:40 pm   #4
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Default Re: Causes of smoking motors

It depends on the type of motor. In this case we are dealing with a universal (series brush) motor and shorted turns on an armature coil are a prime suspect as mentioned. But on an older unit the commutator and brushes might be overheating due to the brushes being worn out and making poor contact, or a bearing might have seized.

But as Refugee says, interference suppressors going up in smoke (especially if the smoke is sudden and the motor continues running) are another possibility. I have seen at least three vacuum cleaners emit smoke from that cause.
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Old 18th Aug 2022, 3:47 pm   #5
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Default Re: Causes of smoking motors

Henry Vacuums are a classic apparently. Capacitor emits smoke and the whole machine often ends up in WEEE.

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Old 18th Aug 2022, 6:25 pm   #6
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Default Re: Causes of smoking motors

It was a Henry
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Old 18th Aug 2022, 6:40 pm   #7
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Default Re: Causes of smoking motors

After I left home my mum employed a cleaning lady (!). One day she rang and said the faithfull Electrolux Dolphin had started smoking while the cleaning lady had been using it on 'superboost'. I went round and stripped it down and found a motor sleeve bearing had seized and been spinning with the shaft, setting fire to the felt oiler. I rang the wholesaler and was told they did a 'compatible' motor made in eastern europe for around 20 quid. I fitted it and found it had ball races instead of sintered bearings. it ran perfectly for years after.
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Old 18th Aug 2022, 9:11 pm   #8
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Default Re: Causes of smoking motors

Thanks for the replies. Really helpful. I'm taking a look tomorrow and will let you know what I find.
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Old 18th Aug 2022, 9:16 pm   #9
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Default Re: Causes of smoking motors

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Originally Posted by G6Tanuki View Post
In my experience it's always a short in the winding of the rotor, which then behaves like a shorted transformer winding.

You get to know the smell of cooked varnish. Most recent example here was an old electric drill.
I've also found that to be the case on each occasion, never the field windings. Yes, the smell of burnt enamel insulation is truly awful and I bet quite toxic.
My most recent motor failure was in a SDS drill which was in good condition and hadn't had a huge amount of use. It was working fine, not being unduly stressed in any way then suddenly a muffled gurgling/buzzing sound and a release of smoke. and a rotten varnish stink. The armature windings being the problem and the drill was BER as a result.
I've had similar failures with vacuum cleaner motors. The 'best' one I had was a small Hoover cylinder vacuum cleaner which suddenly gave out a horrible buzzing sound with a lot of smoke. Had to quickly disconnect it and chuck it out the bungalow. Stunk the place out!

Sometimes early signs of armature winding failure can be picked up by noticing if there's excessive sparking around the brush to commutator segments. You can sometimes see darkened segments due to excessive heat. A whiff of ozone may also be evident because of the sparking. The Numatic George wet/dry cleaner I have is showing this problem at the moment so will look out for a replacement motor.

In the good old days, you could purchase just the armature rather than a complete motor for the Hoover washing machines which made a repair more economic.

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Old 18th Aug 2022, 11:25 pm   #10
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Default Re: Causes of smoking motors

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One of my better "skip finds", a treadmill. No doubt its owner thought it had a burnt-out motor and was BER.

In truth however, the white epoxy resin (?) material that had leached out of the armature just needed carefully filing away to restore normal operation.
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Old 18th Aug 2022, 11:29 pm   #11
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Default Re: Causes of smoking motors

I certainly dont like the brush contact pattern on that armature, Graham. Not very wide considering the width of the commutator. I would be checking the brush condition. I have several of these motors gleaned from the same source as you, along with the speed controller. New brushes are a few bob only and freely available. The motors are in fact VERY good quality.

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Old 19th Aug 2022, 9:30 am   #12
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Default Re: Causes of smoking motors

I have also had experience with these motors and found that stopping/smoking and stinking the place out was caused by lack of cooling. The "fan" fitted to the end of the motor near the brushes is inadequate, especially at low speeds. The plastic melting out of the armature is an early warning for imminent doom.
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Old 19th Aug 2022, 10:41 am   #13
IanNVJ35
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Default Re: Causes of smoking motors

I got the vacuum apart and upon opening the powerful burning smell was released in earnest. However I was pleased to see it was the 150nF capacitor that had melted and released a foul smelling brown fluid.

So just ordered a new one.

Thanks for the input, hopefully it's saved another item from wasteful disposal.

Out of interest what is the function of that capacitor?
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Old 19th Aug 2022, 10:48 am   #14
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Default Re: Causes of smoking motors

We had a Hoover (other makes are available) vacuum cleaner some years ago which exhibited this symptom. Turned out the problem was poor brush contact caused by large burrs on the brass brush holder, when the machine was new the ends of the brushes were tapered to aid bedding in, as they wore down the full size section stuck on the burr.
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Old 19th Aug 2022, 1:59 pm   #15
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Default Re: Causes of smoking motors

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Originally Posted by IanNVJ35 View Post
Out of interest what is the function of that capacitor?
Gets it through the RF interference emissions tests needed to get a CE mark etc.

David
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Old 19th Aug 2022, 3:59 pm   #16
IanNVJ35
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Default Re: Causes of smoking motors

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Quote:
Originally Posted by IanNVJ35 View Post
Out of interest what is the function of that capacitor?
Gets it through the RF interference emissions tests needed to get a CE mark etc.

David
As simple as that! Thanks.
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Old 19th Aug 2022, 5:38 pm   #17
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Default Re: Causes of smoking motors

Quote:
Originally Posted by IanNVJ35 View Post
I got the vacuum apart and upon opening the powerful burning smell was released in earnest. However I was pleased to see it was the 150nF capacitor that had melted and released a foul smelling brown fluid.
That's good to know the motor is OK.
Out of interest, was the suppression cap made by that well known company that supplies 'ultra safe and reliable' Class X caps?

Regards,
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Old 19th Aug 2022, 8:30 pm   #18
IanNVJ35
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Default Re: Causes of smoking motors

Symon, it was made by Rifa. A maker i have never heard from before.

Yes I'm pleased to find an easier fix. It's a good sturdy vacuum and unlike the tat available today actually can be disassembled for cleaning and servicing.
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Old 19th Aug 2022, 9:11 pm   #19
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it was made by Rifa.
Now that's a surprise!

Ian, Those old Electrolux cleaners were excellent, really well built and meant to be serviceable.

I had a decent early 1980s Philips cylinder cleaner that was also great. It had a good quality open construction motor for good ventilation. Sadly, it had to be scrapped due to water being sucked into the motor which caused a lot of corrosion in the impeller. If I had dealt with it soon after the water had got into the motor I could have cleaned and dried everything out.

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Old 19th Aug 2022, 9:24 pm   #20
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Default Re: Causes of smoking motors

Just to clarify Ian, (and as Symon alludes to) RIFA are renowned for dramatic failure!

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