White Knight tumble dryer - drum not turning

[paulfoel]

Heater comes on no problem (so its not the thermal switch).

When I take belt off the motor does not turn until I give it a slight nudge. If I put the belt back on I still cant get the drum to turn (probably because I cant turn it fast enough to start the motor up).

Could this be the capacitor? I've heard that this type of motor uses the capacitor to kick start the motor.

To be honest, it started happening but if you left it for 30 mins it would then work OK (capacitor charging?). Now thought theres nothing.

My wife insists though that occasionally the dryer stopped half way through. I know its a reverse action so I was wondering if this could be explained by the motor needing to stop and then restart in the opposite direction (using the capacitor).

Any ideas ?

[J B]

None at all ..... but the drum's knackered in ours (makes one hell of a clunk on each revolution)) So if you're scrapping it .......

;-)

[Palindr☻me]

You might want to ask on a.e.electrical - as it is more an electrical problem than electronics or diy.

I'm not sure what type of motor this machine has - but would go looking for brush-holders and worn brushes. BICBW

[Andrew Gabriel]

The capacitor is easy to test. What rating is written on it? Assuming it's a mains one, connect it in series with a mains light bulb (something between 40W and 100W), and the light should come on, but not as bright running directly off the mains. Beware in case the capacitor case has become live in some internal failure.

However, the nature of the fault you describe sounds to me more like a broken motor winding. Capacitors don't usually fail intermitently.

[paulfoel]

If I can't fix ours, you're quite welcome to the drum out of mine (if you pay for the postage!)

[paulfoel]

8 micro Farrad

[J B]

Where are you?

[paulfoel]

Newport, S. Wales

[sPoNiX]

Dunno what type of motor would be fitted.

It could be the capacitor (If it has one). They dry out over a period of time and go open/short circuit. You should be able to get a new one for £3 to £4.

If the motor has brushes these could be worn, or the corresponding commutator dirty.

sponix

[Andrew Gabriel]

So that's an impedance of 398 ohms at 50Hz, so a 60W 240V lamp in series should be around half brightness if the capacitor is working. If it's not working, lamp will be fully on or fully off (depending on the capacitor's failure mode).

If you need a new capacitor, one source would be an electrical wholesaler, who will stock them as power factor correction capacitors for fluorscent fittings and HID lamps.

Actually, just checked CPC catalogue, and there are a few designated as motor run capacitors... CA00003 @ £3.95 (metal case, 1/4" tabs), CA00010 @ £3.35 (plastic case, 1/4" tabs), CA00019 @ £3.65 (plastic case, flying leads). All these are 8µF, 440VAC (which is fine for mains), with a mounting stud on the base.

[paulfoel]

Whats the difference between a motor run and a motor start capacitor ?

[powerstation]

Whats the difference between a motor run and a motor start capacitor ?

None... the difference is the motor the capacitors are the same.

[<me9]

Yes, the capacitor failed in ours. You could tell by the smell, though. I'm not sure if it was our current machine (white knight) or the previous.

Spares for our white night were readily available by phone from the manufacturer last time I needed any.

[paulfoel]

Bugger. Just paid =A312 inc delivery of =A36 for a motor start capacitor online. Could have got a motor run capacitor of the same for =A34 in maplins.

[powerstation]

Bugger. Just paid £12 inc delivery of £6 for a motor start capacitor online. Could have got a motor run capacitor of the same for £4 in maplins.

The White Knight is a run capacitor system i.e. the start and run windings are both energized when the motor is running. A capacitor start motor is usually much bigger and has a means of disconnecting the start winding and capacitor once the motor is running, either by the starter or a centrifugal switch.

[James Sweet]

It's either the capacitor itself, the starting switch if present, or a fault in the motor. I'd check the switch first, if that works then replace the capacitor, if it still won't start then it's probably the start winding in the motor.

[James Sweet]

No it's not, while you can use an oil filled run capacitor as a start capacitor, you *cannot* use an electrolytic start capacitor as a run capacitor. Start capacitors are rated only for momentary use.

[James Sweet]

Ah, that's a PSC (permanent split capacitor) motor. Low starting torque but simple, cheap, and generally reliable.

[powerstation]

using an electrolytic capacitor

[James Sweet]

If it uses an electrolytic capacitor that would explain why the capacitor fails. Most of the dryers I've dealt with have oil filled run capacitors, as does my drill press and the fan motors in my furnace and heat pump, those are are all the PSC motors I have I can think of other than the refrigerator compressor, dunno what sort of cap is in that, I've never looked.