Dyson flame thrower

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DiyNutJob

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My DC20 died on me with a horrifying never heard before noise that I am unable to describe. Having taken out the motor, I could see there's not much meat on the motor brushes. The commutator was carbonized. I cleaned that up through sanding. I put the old carbon brushes back and tested the motor stand-alone to see if it's any better. The motor was firing out a 6 inch tongue of flame. Instantly, the commutator was carbonized again.

The price of a new set of non-oem brushes is half the price of a non-oem and non-standard motor. I am agonizing over which to go for.

The worn brushes would suggest I just need a set of new brushes. What is the chance of the motor being kaput? It runs, except also throws out unusual amount of flames.
 
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Sparks normally occur when the brush is so worn down that the brush spring is hitting the commutator.

Some products, eg Festool, have little sprung loaded plastic inserts that pop out when the carbon brush wears down (thereby protecting the commutator).

Based on your description, I guess that the windings are ok. I might be wrong but if they were damaged, I would not expect any current to flow through them. That said, I might be wrong.
 
Although you polished the commutator did you remove all the carbon build up between the comm segments and from the surrounding area.
If the windings were damaged, theres very little chance of getting the armature to rotate.
 
The motor could not be disassembled. I could access the commutator and that's about all. The gaps were thoroughly cleaned with a needle. Since the motor actually runs, the windings are probably OK. It's the flames that make me hesitate if there is something more serious than just the brushes that is wrong. I never seen anything like it. The brushes are melting onto the commutator. It's a 1.6kw motor.
 
foxhole said:
Try local tip , Dyson always outnumbered any other brands 3 to 1.
Click to expand...

Years ago, I had a customer that was an early adopter of Dyson vacuums. She loved the fact that whenever it stopped working they would collect it the next day for repair. Over a two year period, it was repaired 4 times.

My Miele Cat and Dog vacuum cleaner is 15 years old and has never needed to be repaired...
 
DiyNutJob said:
The motor could not be disassembled. I could access the commutator and that's about all. The gaps were thoroughly cleaned with a needle. Since the motor actually runs, the windings are probably OK. It's the flames that make me hesitate if there is something more serious than just the brushes that is wrong. I never seen anything like it. The brushes are melting onto the commutator. It's a 1.6kw motor.
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It is definitely NOT a 1.6kw motor! Don't know where you got that information from but, if it was 1.6kw, you would struggle to vacuum for long before the weight got to much for you.

Just googled a new motor for the Dyson C20 and you can get a new replacement for "22.50 on Amazon.
Not a genuine Dyson but claims to fit the DC20 amongst others.

 
Yeah . It seems to be 1600W

My Miele is 2200W.

My festool dust extractors are rated lower than that that but only because they have power take off for the tools and are limited to a total of 2300W.
 
After much research, I am getting a £2.5 set of carbon brush that needs soldering. If that fails, I will get a new motor for £16. I see a reasonable chance of success with the new brush. I think the flames were to do with the high speed the motor ran at.
 
DiyNutJob said:
After much research, I am getting a £2.5 set of carbon brush that needs soldering. If that fails, I will get a new motor for £16. I see a reasonable chance of success with the new brush. I think the flames were to do with the high speed the motor ran at.
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I would suggest the flames were from the overheated carbon brushes, overheated due to high current demand due to shorted turns in the motor/commutator.
 
Do you mean shorted windings? You may be right. Owing to difficult access, I didn't test with multimeter. Now I have and found 1 commutator bar has higher resistance than others: 1.5 Ohm compared to 0.4 Ohm in an adjacent bar test. The motor looks to be gone or has a limp. I ordered before testing and wasted £2.5.
 
DiyNutJob said:
Do you mean shorted windings? You may be right. Owing to difficult access, I didn't test with multimeter. Now I have and found 1 commutator bar has higher resistance than ,others: 1.5 Ohm compared to 0.4 Ohm in an adjacent bar test. The motor looks to be gone or has a limp. I ordered before testing and wasted £2.5.
Click to expand...

You cannot really be certain, testing with a meter. There used to be a gadget, (name??), which plugged into the mains. It has windings like a transformer, with the laminations forming a large V on top. You drop the motor into that, and (from memory) use a hacksaw blade to short the segments, listening to the change in the buzz, to confirm no shorted turns.
 
It is certain the motor runs. Even if it runs with a limp, it may still be OK if the utility of it is not noticeably impacted.

I ran the bar to bar test a few more times and getting 0.4 Ohm for most of the bars. A couple at 0.1 and 0.2. One at 1.5 and one at 2.6. None of the bars were shorted to the axle ground.

There is still hope the motor will work OK. I am ignoring the interweb talks that said a variance of more than 10% in the resistance readings is bad. I can see the motor running therefore it can't be bad. It may not be like-new, but I am not expecting it to be after 20 years of light use. I am also ignoring the talk of it catching fire. If I don't get burning smells, it's acceptable.

There are some indications that motors are designed to fail incrementally. This means there is some tolerance for partial failures before the motor becomes completely useless.
 
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