# Any Motor experts out there ?



## mind_the_goat (29 Dec 2013)

Non woodworking related motor question.

I have a bi-directional tumble dryer which has just developed a fault. The motor runs in one direction but not the other. pulling it apart has revealed the following:

It's a squirrel cage motor with 2 coils and a start/run capacitor, it has 3 wires, a common and 2 lives, rotation is reversed by applying power to one or the other live, with the cap between the 2 lives.
resistance between common and coil 1 is about 10ohms, common and coil2 is about 18ohms, suggesting either a fault different run and start coil windings.
No sign of burnout on the motor coils.
With the belt removed the motor appears to run fine in one direction but in the other direction it buzzes and kicks intermittently and irregularly, between the short kicks there is no detectable torque. it heats up fairly rapidly in this mode.
Not sure how much torque it has in the running direction, one test I missed.

Could this simply be a capacitor fault with the imbalance in the coils causing the different behavior? Can anyone explain this?

I have tried to Google this but not found anything matching these symptoms. Obviously there are more appropriate forums to ask this but I do believe there one or two people on this forum that might be able to give a proper explanation.


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## MMUK (29 Dec 2013)

Resistance appears OK but without knowing the actual spec of the motor it's not easy to give a 100% answer.

Make? Model? Wattage rating?


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## Racers (30 Dec 2013)

I think its the motor that's faulty, the difference in resistance and the heating up point to a shorted turn in one winding.

Pete


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## MMUK (30 Dec 2013)

Racers":2xnb5gz1 said:


> I think its the motor that's faulty, the difference in resistance and the heating up point to a shorted turn in one winding.
> 
> Pete




That's always a strong possibility but we need to know the full spec of the motor first. It may have different windings for forward and reverse rotation.


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## Deejay (30 Dec 2013)

Morning Rob

* I do believe there one or two people on this forum that might be able to give a proper explanation.*

Bob (9fingers) might be one of them. He can be found on The Wood Haven.

Cheers

Dave


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## mind_the_goat (30 Dec 2013)

Thanks for replies so far.

The motor label has the following information
Make: Creda Ltd
P.S.C. Motor Type 318
220 - 240V 50Hz 1.2A
Class F

I would expect a non rotating motor to get hot due to the high currents that would be flowing until it starts moving, combined with the lack of cooling as there is no air flowing round it. 

I'll plug it in again later and see it there is any usable torque in the functioning direction.

I have ordered a new cap for it just in case.


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## MMUK (30 Dec 2013)

OK, looks like both coils are the same so it looks like your coil #2 has a fused winding. There's a second hand unit on eBay at the moment, guaranteed working, for £40.


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## mind_the_goat (30 Dec 2013)

Wow, where did you find the info, I'm impressed.
Had spotted the Ebay motor (£50 inc postage) , but also found a new one with a capacitor for £70. Either way I may have trouble getting it past the boss who is is convinced it hasn't been drying things properly for months and is quite keen on replacing it.
Also I can see that if I fix it I will then be tempted to replace belts and bearings. I'll have to decide quick, recent weather makes it hard to do without  

Thanks for taking the time to investigate, much appreciated. I shall update later with the machines fate.

=D> =D> =D>


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## MMUK (30 Dec 2013)

Personally, I'd go with SWMBO but insist on a Bosch :mrgreen:


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## Racers (30 Dec 2013)

A bidirectional motor would have the same resistance on both windings.

Pete


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## maltrout512 (30 Dec 2013)

mind_the_goat":3jfwlpyv said:


> Wow, where did you find the info, I'm impressed.
> Had spotted the Ebay motor (£50 inc postage) , but also found a new one with a capacitor for £70. Either way I may have trouble getting it past the boss who is is convinced it hasn't been drying things properly for months and is quite keen on replacing it.
> Also I can see that if I fix it I will then be tempted to replace belts and bearings. I'll have to decide quick, recent weather makes it hard to do without
> 
> ...







:roll:


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## MMUK (30 Dec 2013)

mind_the_goat":1qk74n1y said:


> Wow, where did you find the info, I'm impressed.



Connections/relations in the trade :wink: :mrgreen:


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## mind_the_goat (31 Dec 2013)

maltrout512":2haercl9 said:


> :roll:



 
To be honest the tumble dryer is usually last on our list of drying options but there is only so much washing you hang around the house without it getting as wet inside as it out.


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## Myfordman (31 Dec 2013)

There is no obvious electrical reason why an induction motor should run in one direction and not the other.
The comments that the windings should be equal resistance - implying that one winding is used for one direction and the second one for the opposite direction is complete rubbish.
One winding - usually the lower resistance one, will be the running winding and the other used for starting.

On low power motors sometimes the starting winding is left in circuit usually with a series capacitor and this type is often referred to a permanent split phase or perhaps permanent split capacitor - note the motor is marked PSC type.

A relay or other switching device driven by the timer/controller will change the relative phase of the start winding to the run winding and it is this that will govern which way the motor will run from stationary.

I would suggest that this switch might be the source of the problem and certainly worth investigating.

My Creda drier is of mid 80's vintage and uses a current operated relay to control the starting (in either direction) and I don't think is has a capacitor (but is it years since I needed to investigate the internals). The spare motor that I keep in stock is marked 1.6 amps so is quite possibly a different model to yours. I got this from an identical model to mine and it sits in a box completer with starter switch ready for the day I might need it. There is no capacitor in my box of spares which reinforces my belief that mine does not use one.

Finally the suggestion that it is not drying as well as it used to is normally down to inadequate cleaning of the airways and filter and sometimes a build up of fluff on the fan blades and in the exhaust tubing. Fluff normally gets burned off on the element before is collects but that is always worth a check when you service the machine - you do service it of course? ;-)


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## mind_the_goat (31 Dec 2013)

Surely a PSC motor doesn't need a switch or relay, the capacitor provides the required phase shift and it stays in the circuit permanently? Measuring the input voltages showed that the power was switched to either one or the other coil wires. This way power is provided directly to one coil and the capacitor provides a phase shifted voltage to the other. Given that that there would some losses through the capacitor it makes sense to me that the coils would be identical, otherwise the power output and torque would be a little different in each direction. This may or may not make any significant difference to the operation, depending on the application.

As for not working as good as it used to, I struggle with that concept as it's such a simple machine, I suppose there could be a failed thermostatic switch, I would have checked those if I got it working.

Have to admit the actual behavior is strange but I'm pretty sure it's not down to the cam switch which seems to deliver a steady voltage to each alternate coil wire. There are a surprising number of parts available for what is now an old machine (17 years we think) but the cam switch seems to be one of few that I can't easily replace, so if it did turn out to be that then it's not really reparable anyway.

Repair decision has been taken out of my hands now anyway, we have a new condensing machine (B rated) arriving next week.

I've asked on Freecycle for a broken machine, If I can fix it for free then I will still do so (and maybe put it back on Freecycle), but otherwise does anyone have any ideas what I could make with a tumble dryer drum, other than a tumble dryer ?

Thanks again for all the input.


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## Myfordman (31 Dec 2013)

From your reply, you seem to have failed to grasp how an induction motor reverses.

The relative phase of the two windings need to be swapped. So the sequence is 
Running clockwise
Stop
Change the starting phase
apply power &run anti clockwise
stop 
Change the starting phase 
Apply power & run clockwise
etc
etc

A relay (or other electronic switches) will be used to reconfigure the start winding phase.


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## kostello (31 Dec 2013)

"
otherwise does anyone have any ideas what I could make with a tumble dryer drum, other than a tumble dryer ?

Thanks again for all the input."


I used or old one as a large patio planter it's full of herbs note

Or maybe a wood burning chimenea type thing?


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## Racers (2 Jan 2014)

Myfordman":3h6cbptx said:


> From your reply, you seem to have failed to grasp how an induction motor reverses.
> 
> The relative phase of the two windings need to be swapped. So the sequence is
> Running clockwise
> ...



The 2 pole synchronous motors I have worked on in the past have been wired in the way Mind-the-goat said with the capacitor permanently in circuit and the feed switched between the poles.
Thats why I said the windings should be the same resistance.

Pete


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