Going to attempt to change the capacitor on my tumble dryer... Its a 8 micro-Farad one.
I think its dead anyway but I'm assuming I can check with a multimeter? What sort of voltage/current is one of these likely to have?
Assuming it is still ' live' how do I discharge it to make it safe?
Does your meter support capacitance? if not you're wasting you're time, these are only a few pence anyway in a maplins outlet.
-- Sir Benjamin Middlethwaite
Most likely it is discharged through the motor windings unless the switching is such that it gets disconnected, although relying on the motor windings being intact is not smart when the thing is known not to be working properly. Secondly, it probably has a bleed resistor built in, although those can fail too. I would probably just short it out with a screwdriver, although that can in theory damage the capacitor. Leave it for at least 5 minutes since last powered up, and then short out, and you'll be fine. Making up a proper resistive discharger for this one occasion just isn't worth it.
-- Andrew Gabriel
I was in the local Maplin shop the other day and saw that you can purchase 1 farad (huge) capacitors for power supply smoothing chav's in car audio systems.
Must be interesting when you accidently short one of these!
David
Does the motor have brushes and a commutator? If so, change the brushes before you start looking elsewhere, they're seldom expensive and are a consumable item. Capacitors may or may not last the life of an appliance but brushes are certain to wear from day one and are usually the first suspect in a misfiring/intermittant motor.
With brush type motors, the brushes wear down and consequently less pressure is applied by the spring, causing a higher resistance/poorer connection between brush and commutator. An arc is caused, which heats the brush and can deform the casing causing the brush to stick, making the problem increase exponentially. It also causes the commutator to become blackened which makes matters even worse.
I'd take out the brush carriers and check the brushes move freely and that there's plenty of length left on them. Also check the commutator is clean.
If the motor does not have a brush/commutator arrangement, I'd check all connections are secure and check the control board for dry/cracked solder joints before suspecting component failure.
Dave
Nah - that's nancy stuff for kids
.... real man stuff here!
Stick a big screwdriver across it. This is bad advice for capacitors in general, but for these motor capacitors used on 240V AC only it's OK. There is minimal likelihood of there being any charge left in there, you're only shorting it to make _sure_ before you touch it by hand. If it _had_ been charged up by the Workshop Pixies beforehand, then it just costs you a screwdriver and a pair of trousers.
If you're fooling with HT DC on capacitors, then fit proper bleed resistors before you start and make yourself a discharging stick with a resistor in it.
nonsense it is clearly an induction motor.
Or how about this :-
Probably, but I'm not at the OP's house to take a look and be certain this is the case, and as the symptoms are classic signs of worn brushes, I thought I'd mention it in case.
The rest of my advice about looking for bad connections before replacing components is perfectly valid as well.
Dave
A capacitor with a digital readout? Now they've gone over the top! :)
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Yep. It is.
I worked for many years in the domestic appliance repair trade. To discharge motor caps I just used a neon mains voltage tester, the type with a croc clip to complete the circuit. thatgets the voltage down to just a few volts almost instantly, whence you can safely short the cap if necessary with a screwy or spanner whatever. Shorting out a fully charged 8 or 10 muff cap with a screwdriver doesn`t do the cap, screwdriver or customer any good ;) In the absense of a neon device you could use a light bulb or a resistor of a suitable value.
btw, I`ve never seen a tumble dryer in the UK with a brush type motor, always induction motors with either capacitor or relay start.
Ron(UK)
-- Lune Valley Audio Public address system Hire, Sales, Repairs www.lunevalleyaudio.com
There is a TB regarding capacitors on White Knight TD's, the fault is caused by the capacitor being affixed too close to the motor, the spare part now includes a bracket to move it further away. Sometimes even when the part is replaced the motor subsequently burns out if the windings have been damaged by a stalled motor.
How many tumble driers use brushed motors?
How many brushed motors also have a capacitor?
Now this assumes that it _is_ a capacitor of course. If it does have a brushed motor, I wouldn't be surprised if it had a line filter instead and these can look very similar to capacitors.
The neon tester will only get you to around the 70 volt level. Still not a bad idea. That way you can see if it is charged to the full voltage. If you are going to use a light bulb, you may as well use the screwdriver as when the bulb is cold the resisitance is very low.
In theory, but a neon strikes around 70/90 volts, it maintains down to a much lower voltage and will drain much of the charge. try it. Using a bulb, you get a flash of light, using a screwdrive you get a big bang and a flash of hot metal - better watch your eyes.
Ron
-- www.lunevalleyaudio.com
Not sure how you'd get down to a few V if going through a neon tester. They typically drop out at around 50-60 V.
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Does anybody worry about the inrush current to these, and what that does to one's alternator?
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Indeed. And they draw so little current that it'll take forever to discharge a big capacitor using one.
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