Re: RCD he say 'click' ? The winner is ...

[T i m]

"Ed Sirett - Property maintainer and registered gas fitter." ;-)

Ed said "In a place I run, the damp pump windings have gone short circuit (4.4 Ohms @ 3V DC)"

Well the 'winner' in that the 'fault' causing the clicky thing under the stairs to do it's thing *seems* to be the wachine machine main motor?

Firstly I'd like to mention that I wasn't 100% correct with my first fault description in that the machine was infact 'On' but the door was open (I assumed nothing much would be live in there in this state). With the machine off and the power on, all was fine.

So, had a clean up in there (mainly belt rubber) and no sign of wet, mice, purple worms or currents (flowing in any direction).

I then gleaned a general connection path, removing and testing the connectors to various mains connected loads (and testing in-between) till I came to the main motor. With that disconnected the machine did everything else perfectly (but my whites weren't getting white, Doh!) ;-(

I pulled the motor and measured 45.5k ohms between either stator winding end and ground and 1.6 ohms across it?

So, at 45.5 it's not a 'short' to ground so what else would cause that sort of resistance (the 'breaking down' of a winding insulation possibly?).

Q1, is there anything *I* can do about that? (strip the motor and clean it with something (if so what?). Spray it with WD40 (that fixes everything, right? )

Q2, (and assuming the answer to Q1 is yes). Is 1.6 ohm 'ok' for a stator winding (the wires are pretty thick)?

Q3, could someone tell me if an RCD cares if the current through the live must come back through the neutral or the earth? ;-)

All the best and thanks again to all for the replies (I actually read them all so that makes me the saddest of all of us!)

T i m

p.s. Sorry if I missed anyone else mentioning a possible motor fault (I did check / isolate / rule-out filters / caps where possible as well ta .

[Stefek Zaba]

I could - but you'd have to promise never, NEVER to tell anyone else ;-)

[T i m]

Ok, I won't .. just whisper it then ..

T i m ;-)

[Ian Stirling]

The RCD measures the current flowing in live and neutral. If these differ by more than the set point (often 30/100mA) the RCD shuts off the current in a specified time (often 20ms). If the motor you have measures 45K from live-earth, then it may well exceed the trip point, though a naive calculation would only lead to 240/45000 =

5.3mA, it may well not be a perfect resistor.

First, if it's in a washing machine, it may have gotten wet. The first thing I'd try is to put it in an oven at 100C for 2 hours.

(on a tray, not touching the bottom of the oven).

If this cures it, as the water is likely to be dirty, you really should wash the motor. Dissasemble, remove bearings, wash with hot soapy water, rinse with hot water, and air dry. Examine bearings to see if any water has gotten in them. If it has, they really need replaced.

If it's not improved after baking, then it's probably a film of carbon/grease from the brushes and environment shorting to the case, or an overheated bit on a winding where the insulation is breaking down. You need to find and remove it by scraping/...

[T i m]

And that was only at 9V or whatever my DMM uses .. one assumes that could get worse at 300V AC ?

I don't think it's been wet (as in leak etc) but it could have been in a fairly high humidity (it's near the bathroom, tumble dryer (although that's externally vented) and kitchen (her steamer). Mind you it's been like that for a good few years now (~10) ?

Understood.

Ok, I was about to ask why you would dry it out then to wash it but the first stage is a test ..

Again, not 'water' .. and the bearings feel very smooth etc ..

Ok, well the brushes only have about 1.5mm of 'spring' left in them so I dare say there is a lot of carbon around. I didn't know if washing in something like white spirit / parrafin would be ok?

Ok .. any cleaning / testing effort has got to be better than £200 for a new motor ..(well, within reason) ;-(

All the best Ian .. ;-)

T i m

[John]

I'd want to see at least 5 Meg but preferably 100 Meg to infinity so your winding insulation is down and the motor in all probability has "had it". The cause could be waqter causing an initial tracking over then a burnt track remaining. What did you measure it with by the way? A megger will show up these sort of faults far better than an ohm meter but should be used with care if electronics are involved

You could try slowly drying it out but like as not it won't be any good afterwards anyway

Could be it reactance/impedance that matters here but if your windings insulation is down to earth its immaterial

Shhhhh its a secret

[Ian Stirling]

If it measures 45K at 9V (more probably 3 IIRC), then if it was a perfect resistor, you'd see about 5.3mA at 240V. However, dirt generally does not form a good resistor, and will often have a much lower resistance at high voltage.

Yes, but don't get any on the bearings.

Motors can actually be quite reasonable, for some devices.

is worth a look.

Also, when you clean, if you find any burnt plastic where the current is running, you should scrape it off to clean plastic.

[T i m]

You could be right re the ohms test voltage. I used a little (Maplin) DMM. Just a minor point of detail. Assuming a resistance breakdown issue wouldn't 300V be a more realistic voltage for these issues. I mean the peak to peak being ~300 (240 RMS) and assuming a resister would react (as in conduct phase voltage / current to ground in this case) very fast the 300 could be more relevant (ie it might be ok at 250 but fail at 300?) .. after all .. we aren't looking at power here are we .. Just thinkig out loud .. ;-)

Ok. I can probably strip the whole lot down to it's core components .. clean bits as needed and re-assemble / lubricate etc.

Just had a look on the net .. a new Zanussi for ~ £200 (not that we have that 'spare' but potentially it would make more sense than spending say £100 on a new motor)

It looks like new on the outside The inside is very good. There is a little surface rust on the inside of the chassis base and that's about it? . No water splashing about, no leaky pipes, no corroded connectors or melted anything (if you took the pump out pump out it woud look like new). I fitted new bearings and inner drum seal a few years ago (bearing went) for about 30 quid the lot. A new 'spider' (with bearings / seal) was over 100 pounds!

The motor is a bit dusty (rubber / carbon mix) but the windings you can see are as new and there is no 'burnt shellac' smell at all?

I think this machine was designed when they were 'made to last' (and made in Germany' possibly unlike some of the lower end AEG models (made by Zanussi) at the time? (I have loads of Zanussi stuff and it's also fine)

All the best ..

T i m

[T i m]

Oh dear ;-( I gussed that with windings that size there was no way

45k could be a genuine windings resistance. But the brush holders are quite big and unburnt and made no difference to the readings even when removed (and underneath is's all clean and tidy) This motor is nearly the same size as the one on my Myford ML10 lathe!

I'm not sure if it's ever been wet in it's life (there is a pretty good cover round most of it) and I can't see much that could get 'burnt / tracked (not saying there isn't of course) ;-)

Just a little DMM?

A megger will show up these sort of

Nope, the motor is loose on the kitchin top as we speak and is 'just' the motor (stator, rotor, brushes and multipole connector).

Hmm, I feel I'd like to clean all the dust out of it first and then wash it with something 'solventy' but not too strong that might damage the insulation any further? Maybe 'Gunk' followed by some warm soapy water and a rest in front of the fan heater / oven etc (for both me and the motor ) ? I even wondered if it might be worth having it rewound?

Understood .. so little to loose by trying to clean it up either?

Doh! ;-)

Cheers John ..

T i m

[Tony]

the current on the neutral must be the same as the live

thats how an RCD works , if there is an inbalance it trips

-- Tony

[Ian Stirling]

I was talking about the calculations for an ideal resistor. The conventional way to measure current is RMS, 240VAC and 240VDC will cause the same RMS (root mean square) current, and the same heating in a resistor. The numbers work just the same for milliwatts, and gigawatts.

A usefull thing to do might be to keep measuring the resistance as you clean it.

[T i m]

Indeed .. but I was thinking more along the lines of something 'breaking down' where the peak voltage may be more relavent than the RMS? (I know it's just terms in this case .. an AC (sibe wave) having RMS value of 240V *will have* a peak of ~300v etc. I was thinking if you were to conduct a breakdown voltage test by applying a constant (not alternating) voltage and slowly raising it till breakdown point ocurred ... )

Good idea .. ;-)

I really can't see why something as substantial as this motor could 'break down' other than by:

1) The gradual deterioation of the insulation on the windings (vibration, expansion / contraction, heat, time). 2) Damage to the windings by intrusion by a foriegn object (loose screw, mouse etc) or pressure on a sharp object (motor laminations etc).

I can see how you could easily have option 1) and get 45k ohms but i would have thought 2) would give a short cct or intermittent low resistance?

Maybe I'll put the motor in a warm dry place tonight and measure it again in the morning ..?

All the best ..

T i m

[T i m]

No, ssshhh Tony ... !

T i m

[Tony]

what are you saying tim?

-- Tony

[T i m]

You may have missed the other trread and I didn't really want to start that up again (how RCD's do or don't work..) so my question was tounge-in-cheek .. ;-)

All the best ..

T i m