Is a dimmer and incandescent light efficient?

Wit respect - Cobblers!

I'm not defining power factor - the definition already exists.

Varying the resistance doesn't alter the phase - as soon as the resistance changes the current does so as well.

Phase relationships are the same at whatever level they are studied. The more complex the circuit the more effects have to be taken into account but these are interactions of the basic building blocks, not completely new concepts.

As you said earlier, RUBBISH!

If the dimmer delays the conduction of the lamp, then the current is delayed. the voltage is not delayed, so the supply sees an out of phase current component. thus a less than unity power factor. The load at the output of the dimmer may be unity power factor, but the dimmer can (and usually does) affect the power factor seen by the supply.

I'd think that's pretty unlikely. For one, power meters of the spinning-wheel type do deal with the common on garden reactive loads very well and accurately over a long time. And for another, ISTR that power meters can't ever run backwards, 'cause they have a mechanical widget to prevent just that. A fully qualified electrician, breaking the seals and making an honest mistake wiring up a three-phase power meter, which then runs backwards for a few months before the mistake is corrected is a common story:-)

Or run their own large banks of capacitors switched to keep the reactive component within limits...

Thomas Prufer

The voltage to the load is delayed and it is that causes the current to flow.

A purely reactive load won't turn the meter at all as it's not using any energy. In practice, most reactive loads are lossy, so the meter will record those losses.

Indeed, which is why I said _Domestic_ meters neither know, nor care. That's inherent in the way they work.

You are misunderstanding the load.

Correct. However, we're talking about a resistance in series with a dimmer (chopper), and this pair doesn't look remotely like a resistive load.

OK, define it for non-sinusoidal voltage and current then.

Ian

There was at one time - ah, kids these days - a common fiddle on the spinning wheel meters. If you attached the appropriate reactive load, you could get 'em to go backwards. The electricity board used to get awful cross if you did this.

They don't know about power factor, don't care about power factor and ... in some cases at least ... don't take account of power factor.

I spent a couple of years of my life developing power dissipation measrement techniques for highly reactive loads (AC loss testing of low temperature superconducting coils) and using off-the-shelf power meters was /never/ an option. In case you're interested, the answer was accurate calorimetry, calibrated with a resistive load supplied with DC.

Ian

Whats is the angle between a rubber band wound round a stick, and a blob of plasticene?

Its the phase angle innit? har har.

What is the color of 2.4Ghz? its the powerfactor innit?

I know you could stop them with pin stuck in a hole drilled through the perspex, bu me and my engineering chums tried all sorts of tricks with capacitors, and they wouldnt go backwards.

Oh dear. They are DESIGNED to take care of power factor.

Oh dear.

Yes, it was quite complicated. Measuring gaseous helium production rates of a few ml / second is non trivial!

Ian

It's exactly the same regardless of waveform...

Power factor = power / (V[rms] * I[rms])

Over what time period are you calculating the rms values? I have a torch here. It's switched on for about 1 minute per week. When it's on, it draws 0.3A from its 3V supply. Resistive load. Power factor?

Ian

I assume the torch is powered by a battery (=DC)?

Is this a joke? I hope so . Otherwise where on earth does RMS, power factor and, by implication ,Phase come into your example?

Yup.

Ian

Ah. You see the problem with the definition offered, then?

Ian

Now how do you calculate RMS for a totally non sinusoidal waveform?

NOT easy.

If it's periodic it's dead easy : sum of the rms values of the fourier components (easily proved using the orthogonality of sinusoids).

But that's not the issue here.

Ian