Electrical fault FIXED – vacuum cleaner

[AJB Temple]

We have a 3 year old Miele C3 Vacuum cleaner with Hepa filtration, which has unfortunately been operated (not by me) without the 9 layer filter bag correctly fitted. I am told that it was working one day and then not the next. Having disassembled it I am a bit stuck as to a repair. It’s a modular assembly really with three main parts: cable reel; control panel consisting of an on/off switch and a variable power control unit operated by plus and minus micro switches, and a motor unit.

When switched on the control panel lights up for a second or so then goes out. It does not switch the motor on. So power is getting the to control unit. The micro switches appear to work as I can use them to light up the different settings and the PCB looks immaculate. The on off switch is a simple push switch and responds correctly to a continuity test.

The motor is fed by three wires from the control panel: black (switch), brown (live) and blue (neural). With mains connected I can see with a test probe that the control unit is supplying power to the motor and cutting power when the switch is off. But the motor does not run.

The motor and attached fan spin freely by hand, and there is no evidence of dirt or damage (though some dirt has clearly been sucked through at some point).

I suspect a motor failure as it makes no attempt to start and is silent, but I can’t see how I can test it. It is encased in a mobile plastic case with no visible means of removal. It does not smell and there is no visible damage to the windings. There is no visible capacitor, though one may be hidden inside the plastic motor casing perhaps.

My question is, using my 240v test unit supplying mains power, can I connect a live and neutral feed to the encapsulated motor terminals, to test the motor, or will this damage it? I know I can buy a new genuine Miele motor for circa £150 (not worth it) or a copy for £48, but I would like to establish whether the motor is kaput first.

I realise that the most vulnerable part is the cable reel, which has no visible damage. Clearly it is providing power and switching, but I suppose there could be a continuity fault and I need to test that. I’ve had to order some connectors as the block units that Miele use are difficult to get probes into without risking damage.

Any ideas? I have never tested an electric motor. Thanks, Adrian

 

[9fingers]

Test for continuity across the motor terminals first before brute force application of mains power.
I would think the most likely problem will be with the brushes either due to wear or not freely sliding in their guides.
There will not be a starting capacitor in a brush motor.
Bob

 

[AJB Temple]

Thanks Bob.

There are four terminals in the connector block. Going left to right, 1 disused, 2 brown (live), 3 black (switch) and 4 blue (neutral).

I get 63.3 ohms across 2 and 3 (brown to black(, nothing across 2 and 4 (brown to blue), nothing across 3 to 4 (black to blue).

Brushes are not obvious. Typically these machines run for a couple of decades, so I would be surprised if the brushes are worn out.

 

[9fingers]

Thanks Bob.

There are four terminals in the connector block. Going left to right, 1 disused, 2 brown (live), 3 black (switch) and 4 blue (neutral). Would I be right to assume that I should get continuity across 2 and 4?

Brushes are not obvious but I will go and have another look on the bench now.

Fairly likely but not sure what a switch is doing on the motor but measure everything anyway

Bob

 

[AJB Temple]

There is no continuity beep off the multimeter (which works fine) across any combination of the terminals.

There isn't a switch on the motor - just the black wire which I assumed was a switch wire as a black wire loops in and out of the switch.

Anyway, the lack of any continuity through the motor is, I imagine, a bad sign?

 

[Lurker]

As Bob implies, hanging brushes are a common fault with brushed motors.

 

[9fingers]

Don’t use the beeper as you don’t know what threshold it is set to beep. measure resistance in ohms
Should be say under a 100 ohms

You tube has videos on most models of vacuum cleaner showing how to probe and get into things.
Bob

 

[AJB Temple]

See my second post above Bob - reading of 63 ohms across the brown to black terminals, otherwise nothing.

I've found a video on you tube that suggests that the triac inside the motor switch terminal may have failed. This means taking the motor fully apart, seeing if it is the triac and replacing it if I can get one. I feel a bit like I am guessing at faults though.

 

[9fingers]

All bets are off for remote fault analysis if there is some sort of electronic switch integrated in the motor. Wtf would they do that??
I think I’ve a c3 awaiting repair in the garage. Picked it up on freecycle. I could possibly take a look tomorrow and see if I can be more helpful?

Bob

 

[AJB Temple]

Thanks Bob, that would be helpful. I have now realised that this domestic vacuum was used for over an hour to clear up a large amount of dust from angle grinder surfacing of concrete. Clouds of superfine dust. It's a bit annoying.

Within the motor unit, as part of the terminal connector, there is apparently a small PCB with a Triac soldered to it. As I understand it, this is a form of solid state AC switch alongside possibly a heat overload fuse.

There are two pairs of brushes apparently and they can get clogged. Full motor strip required to get to them (fan off casings off, armature out, armature back cover off so that brushes can be reinstalled).

 

[9fingers]

I got a similar sounding story from the lady who gave me my cleaner. I think it still runs but noisy.

Once I’ve done my chores I’ll take a look at it.
Bob

 

[9fingers]

Hi Adrian,

I've just got home from visiting family to find the vacuum I have here is an S8 model.
I will still take a dive in tomorrow in the hope that the innards might be similar
Cheers
Bob

 

[AJB Temple]

Thanks Bob, S8 was precursor to the C3 and they are very similar I believe. Best, Adrian

 

[Cabinetman]

Well if it’s dust got into where the brushes are, you don’t have anything to lose by trying the age old trick of a really good thump, it may just dislodge what’s stopping the brushes touching the thingy – you see I know all about these motors lol.
You never know it may work, stranger things have happened.

 

[9fingers]

Well if it’s dust got into where the brushes are, you don’t have anything to lose by trying the age old trick of a really good thump, it may just dislodge what’s stopping the brushes touching the thingy – you see I know all about these motors lol.
You never know it may work, stranger things have happened.

Technically known as percussive maintenance I believe?

Bob

 

[MY63]

If dust is the issue would the application of compressed air help.

 

[John Brown]

Lord Finchley tried to mend the Electric Light
Himself. It struck him dead: And serve him right!
It is the business of the wealthy man
To give employment to the artisan.

Hillaire Belloc.

 

[9fingers]

Lord Finchley tried to mend the Electric Light
Himself. It struck him dead: And serve him right!
It is the business of the wealthy man
To give employment to the artisan.

Hillaire Belloc.

This particular "artisan" has pm'd the op with an offer to fix the offending motor!

Bob

 

[John Brown]

Lord Finchley tried to mend the Electric Light
Himself. It struck him dead: And serve him right!
It is the business of the wealthy man
To give employment to the artisan.

Hillaire Belloc.

This particular "artisan" has pm'd the op with an offer to fix the offending motor!

Bob

Nice of you.
It was merely in jest, I hasten to add...

 

[AJB Temple]

OP has replied. Thanks Bob.

 

[AJB Temple]

Just to conclude this, it transpires that Bob here (9Fingers) actually knows magic. Thanks Bob.

The triac, in the motor connector unit, needed to be replaced and Bob did some cleaning out and other fixey uppy stuff and the machine is now hot to trot.

As an aside, my extremely lovely and tolerant wife decided that this was a good opportunity to buy a cordless vacuum cleaner as well. She did not wish to make "landowner tax avoider Dyson" even richer so she bought a top of the range VAX with two batteries. These each last 40 minutes they claim. Lies, but not damned lies.

Makers and reviewers of battery powered stick vacuums claim they are as powerful as corded ones. This is, in my view, total cobblers. Especially on carpets the HEPA filtered Miele knocks the VAX (with power brush and idiotically named turbo mode) into a cocked hat then sucks it out again.

Miele will remain in use for the carpeted areas. I am gradually getting rid of carpets throughout the house, but it will be the year after next before I get round to the last two rooms, which will be stone.

 

[AndyP]

Aye he is a wizard, that Bob.

While in the UK it was hard to imagine life without carpets. Only one bedroom here is carpeted rest of the house tiled or parqueted. Wouldn't have it any other way now.