John Rumm wrote:
The Natural Philosopher wrote:

Phase angles and power factors are for people who cant do calculus.
Fortunately, due to being designed by cleverer people than yu, and
electricity meter is a crude form of analogue computer that can.

more milk tibbles?

sausage roll withdrawal symptoms.

Kevin wrote:

ahhhhhhhhhhhhhhhhhhhhhhhhh a peak voltage of 240v and a peak amps of 10A
is 2400VA if the current leads the voltage by any ammount,at the time
the voltage reaches its peak then the current is all ready falling so it
might be say 9 amp then the meter will read 240X9=2160VA

Yup, I think you have it...

Imagine you sample the voltage and current 50 times (or whatever) a
second. Each reading you multiply together to get the instantaneous
power reading. The result you can sum over time (in effect integrating
the area under the power curve). So the meter gets the right answer for
the real power consumed regardless of any phase shift between current
and voltage waveforms (or any non sinusoidal components in either). The
thing it can't do easily is tell you what the power factor[1] is.

[1] And even if it could, knowing the power factor does not tell you the
full story, since it assumes sinusoidal voltage and current waveforms.




--
Cheers,

John.

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John Rumm wrote:


[1] And even if it could, knowing the power factor does not tell you the
full story, since it assumes sinusoidal voltage and current waveforms.


Hmm. Strictly I THOUGHT it was the ratio of the actual power to the RMS
volts times RMS amps...

which has some sort of meaning off sinusoid.

But hey, lets not split hairs.

The saasage rolls are almost cooked...

The Natural Philosopher wrote:
John Rumm wrote:
The Natural Philosopher wrote:

Phase angles and power factors are for people who cant do calculus.
Fortunately, due to being designed by cleverer people than yu, and
electricity meter is a crude form of analogue computer that can.

more milk tibbles?

sausage roll withdrawal symptoms.

Hmmm, you just reminded me what I forgot to buy the other day!

Oh well never mind, Happy Christmas everyone!

--
Cheers,

John.

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| John Rumm - john(at)internode(dot)co(dot)uk |
\================================================= ================/

"Kevin" wrote in message
...
pete wrote:
On Tue, 23 Dec 2008 18:42:12 -0800 (PST), wrote:
pete wrote:

Recently I picked up some energy saver bulbs from Wickes.
They are "advertised" as being 18 Watt (100W equivalent, but that's
not relevant to this).
However, on the top of the box, wher eit says 1100 lumen, it
also says 130mA. Now, my current mains voltage is about 235V, so
at that voltage, 130mA is just over 30 Watts, not the 18 W claimed.

Now this is my simplfied thinking - I haven't (and don't intend to)
looked into the power factor of these puppies, but does anyone have
any insights into the discrepancy between the figures offered?

Some interesting analogies, but no-one's yet hit on what's happening.
There is more than one way to get a non-unity power factor, and what
goes on in CFLs is that the mains input goes through a diode rectifier
bridge and to a reservoir capacitor. This draws current around the
voltage peaks, and nothing for the rest of the cycle. Thus what's
happening is quite different to the waveform you get with a basic
inductor ballast.

FWIW the phase shift occurring with an old fashioned switch start
inductor ballast (linear fls) is only an approximation to what's
happening there, as an electromagnetic fl circuit has 2 things in
series, ballast and tube. The ballast operates at near 90 degrees out
of phase, but the tube has a weird waveform specific to discharge
tubes. The resulting mains current waveform is a hybrid of the 2,
which is why its not possible to get such fittings to a power fator of
1 by adding capacitance.


NT

Thank you.
I suppose this is about average for usenet:
1 question asked, 38 replies. 37 talking complete ******** and one
that's informative.
Keep up the good work!
yup bolloxs rules OK

--
Kevin R
Reply address works

For goodness sake, why doesn't one of you switch everything off but one CFL
lamp and take a look at their meter reading for a few minutes; or an hour
if you are not very good at maths.
Michael

wrote:
On 24 Dec,
Andy Champ wrote:

The links I am seeing suggest that VAr and VA are the same. The
Wanderer implies that they are not.

They are not. VAr is from the out of phase component. W is the in phase
component. THe 'power' (VA) seen by the transmission medium is the vector sum
of the W and VAr.

At some places we had metering for all three. Usually we were charged for KW,
but also had a maximum demand charge for the maximum KVA over any half hour
within the charging period.


Ah! All is clear. Thanks!

I don't suppose you feel like fixing the Wikipedia article for the rest
of us...

Andy