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.
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! :)
--- sam | Sci.Electronics.Repair FAQ:
Yep. It is.
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.
Does anybody worry about the inrush current to these, and what that does to one's alternator?
No.
Car wiring is radial from the battery to alternator and from the battery to load. The impedance of the battery is much lower than that of the alternator radial circuit - thus transient currents will be met almost entirely by the battery.
You may like to think what effect the starter motor has on the alternator.
Also, the energy stored in a capacitor depends on the capacitance and on the square of the voltage. Rather than have a 1F capacitor on the 12v line, it would be much better to go to the higher voltage power rails of the amplifier and stick beefy capacitors there.
Why do you say that? Most European washing machines use series wound universal motors with carbon brushes. I've got a Creda washer sitting in my basement right now awaiting arrival of a set of brushes amoung other things, no idea how it ended up on this side of the pond but it's a cool little machine.
They went over the top years ago, those capacitors have been available for a while.
Just try to find a car CD player anymore that looks at home in anything but a gaudy racer boy Japenese compact. Seems like they're all fugly and bubbly, loaded with useless distracting blinky lights and buttons so small and jumbled it's impossible to operate them safely while driving.
While this is true, don't forget that the starter motor will never be operating under load while the alternator is producing any current unless you're jump starting another car.
But we were talking about a dryer. They seem to use induction motors (well, mine does).
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