Power factor

[The Medway Handyman]

I was thinking more Janet & John .....

[The Medway Handyman]

I spose it depends on who the article is written for.

If its numpty level I'm an ideal test pilot :-)

I think I understand the difference between DC & AC current, but would anyone perhaps considering the purchase of a Savaplug know?

[The Wanderer]

Umm, don't re-invent the wheel. I'd keep your comments fairly brief and simple so anyone who wants a fairly simple explanation gets just that.

You might consider posting a link to this site

I came across. Seems to give a good explanation from the bottom up so to speak. It's American, but the theory's the same - I think! :-)

[John Rumm]

You have obviously not seen a handbook aimed at the US military ;-)

(instructions like "Push button A" will typically be accompanied by three diagrams showing a finger looming near a button, another showing it being depressed, and a third showing the finger withdrawing).

[John Rumm]

Tis kind of where I was aiming, since the question comes up here reasonably regularly,

Yup good call, a first rate site. (I certainly don't want to go to that level of detail here!)

[John Rumm]

You raise a good point, that perhaps there ought to be a bit more details on PF related gizmos that are promoted to home users, and why some of the claims are going to be doubtful in domestic situations.

[John Rumm]

Thanks, that saves some work!

(will stick those in next draft).

[The Medway Handyman]

Absolutely excellent site, thanks for posting the link. I'm going to read all of it.

Agreed, maybe a link on the Wiki?

[John Rumm]

Yup, done.

Andy's pictures are now included as well as a bit more narrative on how this relates to real world stuff.

[robgraham]

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Thanks John - it was too long ago now for me to remember the fine details, but it always struck me as gobsmacking.

[Bob Minchin]

John, I've been following this with interest but not contributing so far. The concept of PF is now well covered but may be slightly muddied by the introduction of SMPSU effects.

I'm genuinely unsure of the correct definition of PF . It could be thought of as purely the cos phi related issues with a second, different set of issues caused by SMPSUs that cause a similar problem to power distributors in having to supply peak current and maintain voltages. These might have a different name - non sinusoidal loads perhaps.

Moving on to Daves point (TMH) of debunking the quackery of Savaplugs and issues such as the much less than advertised energy saving of CFLs, these might well be best written up separately to save confusing the beginner who might still be just starting to understand PF.

Just my 2p

Bob

[<me9]

It was called harmonic current when I dealt with high power rectifiers 40 years ago. Steps had to be taken to reduce it by phase changing 3 phase supplies to multiple rectifiers.

[Andrew Gabriel]

I can probably make better images (those ones where straight out of ghostscript and not anti-aliased).

However, I played around with making a dynamic one where you can play with the phase angle yourself and see what effect it has...

[robgraham]

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=A0 =A0 =A0 =A0|

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John I don't know how much feedback you had on other contributions to the Wiki that you have kindly made, but do the statistics show that this somewhat low relevence topic to the average household has in fact generated more post than any other !!!

Why ?

Rob

[Andrew Gabriel]

People are interested in the power they consume, and are measuring power in various ways. Some loads, when measured using certain techniques which are only approximations, show wildly incorrect results. This is down to (amongst other things) power factor. I think it's not unreasonable that people want to understand this. Without that understanding, you see claims here that some device (often a CFL) is costing twice as much to run as it really is.

Power factor is not taught in school, and probably not anywhere other than an electrical engineering degree (although any mathematician or physicist would also easily pick it up, as its basically just maths). So I guess the object (or challenge) here is to cover it off, without going into half the first year electrical engineering degree syllabus or deep mathematical proofs, and yet have people understand what this effect is.

I found this area sufficiently interesting some ~30 years ago that I built my own true power meter. You can buy them (much smaller than my home made one) for a fiver now, so lots more people are investigating power usage. In some cases, you need a basic understanding of power factor, at least in so far as Volts x Amps doesn't allways equal Watts, unlike what you were taught at school.

[Owain]

Janet saw a tank with a flag on it. "Look, John," said Janet. "There is a tank." John looked at the tank. It did not have an American flag on it. "I shall shoot the tank," said John. John shot the tank. The tank and all the soldiers in it died. "Waytogo!" said John. "Waytogo!" said Janet. "A deeply embarrassing error in identification," said Janet and John's commanding officer. "Next time, let me have the bloddy gun," said Janet.

Owain

[John Rumm]

LOL! (sad but true alas)

[The Wanderer]

Funny how the obvious is sometimes so obvious it sails straight over the top of your head! I was looking through JR's wiki article, and thought that something was missing, but I just couldn't put my finger on it, so to speak. He hasn't mentioned true power anywhere.

[John Rumm]

wiki if you want?

(I must have a play with some client side java - I have done loads of back end server side in the past, but nothing pretty!)

[John Rumm]

Indeed...

This started as an exercise in "take a previous short group posting that answered a basic FAQ and wikify it" - hopefully without getting too bogged down in reproducing a whole years electrical principles syllabus.

The difficulty with doing "simple" explanations is what to leave out. The moment you get too much detail, the omissions become more glaring. I think we passed that point some time ago!

(not a complaint - I am happy to keep improving it until it sort of escapes (it will obviously never be "complete"!) although I expect its target audience may have shifted)

Andy raises a good point about measurement etc. Perhaps our intro ought to start off with that, explain that what you are seeing may be distorted by PF, and here is why etc.

(in fact electrical measurement could actually be an article on its own

- given the number of times not PF, but also inductive/capacitive coupling and high impedance test devices seem to trip up many DIYers)