power factor

[Jim GM4DHJ ...]

Can anybody explain power factor when it comes to 3w and 5w led bulbs and why a smart meter will charge you the same for both of them...keep it simple I'm not very bright....get it ...bright...tee hee

[JNugent]

Is this a leading question?

Or a lagging one?

[Jim GM4DHJ ...]

don't get that

[sid]

Perhaps the smartmeter has a minimum resolution greater than the current difference for the two led lamps.

[John Rumm]

Domestic meters should record just the instantaneous power, and so should not be fooled by a poor power factor loads. They should only bill for the real power being used, and not the reactive power.

A domestic meter's accuracy and resolution might not be good enough to reliably see a 2W difference though. (They tend to be better on higher loads rather than lower ones).

How many lamps are you comparing, and do you know if the lamps actually draw the current that their wattage would indicate?

Just to complicated it, different types of LED can present different electrical loads. Some LED "filament" lamps can have very simple PSUs that just rectify the mains and slap it across long strings of LEDs in series to allow them to match the mains voltage. Others using far fewer LED chips will have more sophisticated SMPSUs that have the more characteristic pulsed current waveform - just taking a glug of current close to the peak of the mains cycle.

Some more general stuff on power factors:

[newshound]

Mr Nugent is a lawyer

[Brian]

You shown brush up on basic AC theory, it was included in your RAE.

[JNugent]

...or perhaps a qualified electrical engineer.

"Power Factor" is a concept used in electrical supply. AC circuits - especially those involved in the supply for highly inductive loads such as motors - suffer from the current and voltage peaks being out of phase with each other. This causes the power requirement to be higher than it would be if the to were in phase with each other. At domestic levels of usage, this is hardly important, but at industrial levels, the difference is a major one and can cause the supply bill to be significantly more than necessary. The remedy is to use a highly capacitive load connected in parallel. This brings the phase difference down and the power factor more nearly back into balance.

I hope I have remembered that something like correctly. It's been a

*long* time since I learned it (or did any electrical work).

For a more learned explanation, see:

[Chris Green]

It's not the *power* that is higher, it's the current. So, if the power factor is 1.0 and the current (at 240 volts) is 10 amps, then you're consuming 2.4kw. However if the power factor is 0.5 then a current of 20 amps at 240 volts will be 2.4kw. Thus, if the power factor is poor you have to supply more current at the same voltage which means you need heavier current carrying capability.

[JNugent]

I said "power requirement", meaning the power consumption as measured.

But I did learn all this a long time ago and haven't dealt with it for a living in nearly fifty years.

I also provided a link to a better explanation than I am able to give without undue revision and research.

I believe that I more or less said that, though perhaps not with your elegance of language.

[Chris Green]

The power measured won't increase if it's a proper WattHour meter, that's the whole point of the meter!

[JNugent]

I don't doubt what you say.

My experience of the matter is limited to two or three one-hour lectures at a technical college, more than fifty years ago!

Given that, I don't think I was far out. And I did issue an inaccuracy warning.

[Andy Bennet]

I wuz taught the old whirring disc thingy measured V*I*cos(phi). I would assume the new smart meters would do the same for consistency.

[Brian Gaff (Sofa]

I also wonder how the voltage for the leds is derived. Some asymmetrical loads can also confuse meters. Brian

[Brian Gaff (Sofa]

When I worked in an old tv factory, the fact that most tvs had autotransformers and often cheap half wave rectifiers brought us some attention from the electricity supply folk, as significant numbers of these sets left on to soak test put a dent in the mains every other half cycle.

Brian

[Jim GM4DHJ ...]

you mean the three hour written exam I sat in 1973?....then the 12wpm cw test ...unlike you class BM3 ?...

[Jim GM4DHJ ...]

you tell me

[alan_m]

A 5W LED bulb will cost you approx 0.1p an hour to run and approx 0.06p for a 3W LED bulb. How are you determining that your smart meter is charging the same for each of the bulbs? To see the difference you would probably have to turn off every electrical equipment in your house and ONLY run each bulb for a couple of weeks or so to determine the energy consumption on a smart meter.

[alan_m]

Big Clive on his Youtube channel usually measures the power taken by LED lighting and finds that a lot of Chines export (CE marking) takes significantly lower power than what is written on the side of the box or on the bulb/fitting.

[Robin]

I don't know where SMETS2 meters ended up but early specs required measurement of both active and reactive, in and out, but consumption was based on active in. Though given the costs of dealing with poor power factors I can see the case for switching. With that in mind I did find it a bit worrying that the last GU10s I bought promised only that the power factor was >0.5 :(