Some time ago we were at grandma's house and my mother was cleaning the carpet using a vacuum cleaner. Suddenly, the RPMs fell and the vacuum started smoking. I unplugged it fast and hoarded it

I decided to take a look at it today. After I clumsily broke the plastic shell, rendering it unusable, I finally got to the motor. Two dark amorphous chunks fell off it as I was shaking it and I'm pretty sure they shouldn't be there.
It's a 220V AC motor which I deduce has this diagram:

Each winding shows 1.2Ω DC resistance, so I guess it's not burned out. The motor shows 2Ω approximately.

I got some picks of the motor and the two chunks that fell off (can you tell I got a new camera?). What could they be? Is the insulating varnish between the winding wires supposed to be that spilled or could it have melted during the motor overheat? Where could the smoke have come from?

The vacuum cleaner has a very basic power control, but I haven't examined that yet.

I don't want to plug in the motor without a good chance of it running and not smoking to death.

Any input is appreciated.

 

Took a look at the control board. Nothing looks toast, no burn marks. It uses a BTA-600 TRIAC to control the AC input waveform.

 

Looks a bit like melted & burnt insulation. Generaly what kills vacume cleaners is blocked bags & filters, causing the motor to over heat. They rely on a reasonable airflow through them to cool the motor.

 

If a winding (either in the field or the rotor) develops a shorted turn it will still measure essentially the same DC resistance but will draw much higher current, since the short acts like a transformer with a shorted secondary. This short can be detected by a device called a growler.

If you want to try running the motor you could either use a Variac to allow slow application of the voltage (while monitoring the current), or place a power resistor of the appropriate size in series.

 

I 'm having trouble understanding why a winding short would act like a shorted secondary. Wouldn't it just simply leave out some wire turns? Any reading material, even inside AAC?

Would it be the same if the short was located in the field or in the rotor?

Luckily I have the vacuum cleaner's own TRIAC voltage control so I can give it a shot on the lowest setting. It's still quite a current though. Will see. I might add a resistor after all.

 

Vacume cleaners ive worked on with faulty armatures when runing will arc badly around the commutator.

 

I 'm having trouble understanding why a winding short would act like a shorted secondary. Wouldn't it just simply leave out some wire turns? Any reading material, even inside AAC?

Would it be the same if the short was located in the field or in the rotor?
..........

I know it seems counter-intuitive. But think of the shorted turn as a separate secondary turn on a transformer. Shorting that turn will generate large currents since it acts like a shorted transformer output, and the current is limited only by the resistance of the windings.

Not sure whether a short is worse in the field or rotor.

 

I have taken the motor apart today. The shaft would have serious trouble being turned by hand. I took out the brushes' contacts. They were badly chipped and jammed the rotor. I smoothed them with sandpaper. I oiled the bearings. Afterwards, the rotor would rotate smoothly. Then I took a look at the rotor windings. Two strands were badly burned.

I gave the motor a try @80V. It would rotate, but would also create an electrical hum, heat up fast and smell instantly. I didn't let it run for more than a few seconds at a time.

I decided to get rid of the whole system at the end. Too bad.

 

Did the brushes fall out/break contact? It appears to be a universal motor.

 

The brushes were in place, but the end of the contacts, touching the commutator (if that's the right word for it) was not uniformly ground. Flakes of carbon had fallen off, a bit had slid towards the shaft direction and carbon dust had filled partially the gap between the commutator contacts.

But the deadly blow to the motor was probably overheating. As I said in the first post, the motor started smoking for the first time after the vacuum was used on a thick carpet with a full bag, probably.

 

If you can ensure all the carbon is out between the commutator segments, it may work a bit, not perfectly , but work a bit. You can test for shorted winding by running it on 12VDC and checking the current draw with a current limiting power supply. If it goes full scale, try spinning it a bit, then the other way. If it just gets hot, you need a ew motor, rewinding those costs about the same ($100) if you have a winding shop in your area, have them put in new bearings/brushes as well and it'll be like new again..

 

It is sad that economics has driven companies to build 'disposable' products in this way. The added costs of sealing and making the motor serviceable, plus the cost of service are just more than the brainwashed consumers of the world are willing to put up with...they have been told this by the people selling the products for less...so the target for blame is very large and ignorant of their involvement in this merry go round of consumerism.

So ends the sarcastic business gospel of our modern times.

 

@thatoneguy

Can you elaborate a bit more on the test cases of the windings? What would I expect in either case?
In any case, the motor is shot, by now; this is just for educational purposes.
Was it normal that the carbon had spilled so much between the commutator gaps? I believe the vacuum cleaner was at about 5 years old, maybe a bit more.

And of course it's not worth repairing. I don't think the appliance itself cost more than 100euros.

@Kermit2

The only appliance that bothers me a lot that gets more and more cheap by the time is printers. Their cost goes down, but their quality goes way down. My last three printers didn't last more than two years. If you think about it, they cost less than the ink they consume.

 

The carbon in the commutator gaps may have built up to a point where many are shorted together. Run a dental pick between each one until it is clear, then re-measure, or try to run it at a lower voltage, if it won't budge at all, it's the bearings, which caused the windings to overheat.

 

The motor already runs, as I wrote in post #8, but defectively.

The bearings were a bit stiff, but not to the point that they wouldn't let the motor start. I 'll check the resistance of the motor after the cleaning, just out of curiosity.
The procedure could help isolate the root of the problem, albeit not solve it.

Thanks.

 

Cleaned the carbon from the gaps. Ran it for a bit and re-checked. Some carbon had already sneaked back in. I guess the brushes are of poor quality or have had their life cycle.

I ran the motor at 20VDC. It drew 3.3A. Its rating is 1400W. I think we can call it by those stats.