Safely discharging a capacitor

[powerstation]

But its NOT a washing machine he's fixing ! its a tumble drier

[powerstation]

All the ones I have ever seen are, because they revolve the drum slowly, a washing machine needs to spin at high speed

[The Natural Philosopher]

Thats because youy get a really good one bult nto any car that chavs don't buy.

[Andrew Gabriel]

A European washing machine operates its motor at a large number of different speeds (and even gradually vary the speed in some cases) throughout various stages of the wash cycle, and depending on the wash program selected. This is most easily done with a universal motor combined with an electronic speed control board and servo feedback. (It used to be done with an induction motor and solenoid operated gearbox 40 years ago, but that's more expensive and a lot less flexible.)

Tumble driers only have to be able to reverse the drum, but don't need to change the speed. For this simpler requirement, an induction motor tends to win.

[The Natural Philosopher]

its nowhere as bad as what a statrter motor does...alternators are limited anyway.

[James Sweet]

Yeah somehow I missed that we were discussing a dryer. The matching Creda dryer does in fact have an induction motor in it, weird to see a clothes dryer that will plug into a 15A 240v receptacle, US dryers are almost universally 4KW.

[James Sweet]

Why do they have to be able to reverse the drum? I've never seen a dryer that did that, obviously they must exist but I'm not sure of the benefits.

[James Sweet]

Would be nice, but I'm afraid back in '84, '87 and '88 respectively, cars didn't come with CD players of any sort, hence my need to install aftermarket units in mine.

Not to mention I'm still not aware of any OEM units that will play MP3 discs, an essential feature to me that made all earlier CD players virtually obsolete. 10 hours of music on one disc, no more fumbling with CD's in traffic.

[Bob Eager]

Loads of them do it[1]...helps to untangle the clothes.

[1] except in the backwards USA?

[news07]

In message , Slurp writes

'DISCLAIMER: the experiments described below are fantastically dangerous, and they are described without reference to the many precautions needed to guarantee the experimenter's safety. Accidentally discharging these capacitor banks through your body can not only kill, but can explode flesh and bone.'

Followed by

'PARENTS: I supply no detailed plans for reproducing these experiments. Also, these experiments require large and expensive lab equipment which is not obtainable by children. (And the plans for an atomic bomb are safe for children too, because kids can't afford to buy kilograms of Plutonium!) If your kids have access to 5,000 volt high-current power supplies, then they are already in great danger, whether or not they read about my capacitor discharge experiments below.'

Has my respect!

[usenet]

According to my Electrical Engineering professor at university *all* electrical machines (including transoformers) are really induction motors.

[powerstation]

Motors with squirrel-cage rotors can be used on single-phase alternating current by means of various arrangements of inductance and capacitance that alter the characteristics of the single-phase voltage and make it resemble a two-phase voltage. Such motors are called split-phase motors or condenser motors (or capacitor motors), depending on the arrangement used. Single-phase squirrel-cage motors do not have a large starting torque, and for applications where such torque is required, repulsion-induction motors are used. A repulsion-induction motor may be of the split-phase or condenser type, but has a manual or automatic switch that allows current to flow between brushes on the commutator when the motor is starting, and short-circuits all commutator segments after the motor reaches a critical speed. Repulsion-induction motors are so named because their starting torque depends on the repulsion between the rotor and the stator, and their torque while running depends on induction. Series-wound motors with commutators, which will operate on direct or alternating current, are called universal motors. They are usually made only in small sizes and are commonly used in household appliances.

[<me9]

They tangle then untangle the washing. Our first one did that, Our current one only goes one way, It's much less efficient, and is more work separating at the end.

[david lang]

I don't know, never had one apart, but I assumed they all did. Every washing machine I've ever repaired had a brush motor, why would they use induction on a tumble fryer as a matter of interest?

Dave

[paulfoel]

Nope. Definitely an 8 micro-Farad capacitor.

[paulfoel]

TB ? (Technical Brief?)

Where can I see this info?

[powerstation]

Sent to your email if it genuine Peter

[Andy Dingley]

You use induction motors whenever you can - they're quieter (this is a domestic appliance after all) and they're cheaper. The advantage of the brushed motor is that they have much higher torque at low speeds or when stalled (why they appear on power tools) and they're also more easily controllable for variable speeds etc. There's a lot of things a washing machine does that a tumble drier just doesn't need.

[Tony Williams]

Relatively constant speed operation under variable load, without the expense of speed-sensor and controller?

[david lang]

Odd. The only experience I have is with high pressure cleaners. The el cheapo DIY jobbys have brush motors which make a terrible screaming noise - but they use them to reduce costs.

I can see the logic in that, but I've always assumed (from my HPC experiences) that induction motors were much more expensive.

Dave