Volt Amps = ??

[Franc Zabkar]

On Mon, 5 Jan 2004 11:06:34 +1100, "Phil Allison"
<philallison@optusnet.com.au> put finger to keyboard and composed:

"David" <no_way@hotmail.com

The angle in the power factor, as Kevin has stated. If the voltage and
current waveforms are in phase, then regardless of the waveform, the power
factor will be unity.


** Wrong - you are totally wrong.

There is no reference to phase angle in the general definition of PF.


There HAS to be a phase difference between the
voltage and current waveform for their to be reactive power,


** There is no reference to "'reactive power" in the general definition of
PF.

A non unity power factor exists whenever the current waveform does not
follow the voltage waveform - though they may be exactly in phase. This is
the case with typical electronic devices where current is drawn only at AC
voltage peaks.

In typical electronic devices current pulses are drawn *before* the
voltage peaks. They are not *exactly* in phase.

Such loads have PFs of around 0.5.

Computer PSUs are typically quoted as having a capacitive PF of 0.65
at full load, so your estimate of 0.5 may not be far off the mark.
Intuitively, however, I find it hard to correlate a 2ms current pulse
(as you state elsewhere) with an 0.5 PF. A duration of 2ms equates to
36 degrees at 50Hz, which would in the normal textbook "sinusoidal"
case result in a PF of 0.81. An 0.5 PF would normally suggest a phase
angle of 60 deg.

Having said that, here is an article that attempts to explain this
apparent anomaly:

http://www.st.com/stonline/books/pdf/docs/3711.pdf

It suggests that the actual PF is somewhat less than that which could
be expected by considering only the phase angle of the fundamental
component of the current pulse. Instead, the article shows that the
harmonic components of the current pulse tend to reduce the overall
PF.

How many times do I have to say it.

Not surprisingly, people prefer an independent, authoritative
reference.


- Franc Zabkar
--
Please remove one 's' from my address when replying by email.

 

[Phil Allison]

"Franc Zabkar" <
"Phil Allison"

** There is no reference to "'reactive power" in the general definition
of
PF.

A non unity power factor exists whenever the current waveform does not
follow the voltage waveform - though they may be exactly in phase. This
is
the case with typical electronic devices where current is drawn only at
AC
voltage peaks.

In typical electronic devices current pulses are drawn *before* the
voltage peaks. They are not *exactly* in phase.

** The current peak occurs *very close* to the voltage peak.

SMPS and transformer PSUs vary slightly.

Such loads have PFs of around 0.5.

Computer PSUs are typically quoted as having a capacitive PF of 0.65
at full load,

** The PF of a SMPS is not capacitive - it is due to waveform
distortion.

Also, the actual PF worsens at lower ie more typical loads as the charging
pulse gets narrower.

so your estimate of 0.5 may not be far off the mark.

** It was not an "estimate".

Intuitively, however, I find it hard to correlate a 2ms current pulse
(as you state elsewhere) with an 0.5 PF.

** Simple. Imagine the current pulse is rectangular and centred on the AC
voltage peak.

Then the power consumed in watts is V peak x I peak x 0.2

For 240 AC and a 1 amp pulse this is 335 x 1 x 0.2 = 67 watts.

***Now for the VA:

The rms current for a rectangular pulse train is I peak x sq rt duty
cycle.

So in the example 1 x sq rt 0.2 = 0.447 amps rms.

The AC supply is 240 V rms so the load = 107.3 VA.

Such a load has a PF of 67 / 107.3 = 0.62

Change the pulse duration to 1 mS ( ie when the supply is lightly loaded)
and do the same calculation.

The new PF = 0.44.

A duration of 2ms equates to
36 degrees at 50Hz, which would in the normal textbook "sinusoidal"
case result in a PF of 0.81. An 0.5 PF would normally suggest a phase
angle of 60 deg.

** The sub unity PF is not due to phase angle but wave shape and the
higher rms value of that wave shape.

How many times do I have to say it.

Not surprisingly, people prefer an independent, authoritative
reference.

** Shame those folk here have no brains to see the obvious nor can do a
simple Google on "active PFC".



............. Phil

 

[Franc Zabkar]

On Tue, 6 Jan 2004 16:49:52 +1100, "Phil Allison"
<philallison@optusnet.com.au> put finger to keyboard and composed:

"Franc Zabkar"
"Phil Allison"


** There is no reference to "'reactive power" in the general definition
of
PF.

A non unity power factor exists whenever the current waveform does not
follow the voltage waveform - though they may be exactly in phase. This
is
the case with typical electronic devices where current is drawn only at
AC
voltage peaks.

In typical electronic devices current pulses are drawn *before* the
voltage peaks. They are not *exactly* in phase.


** The current peak occurs *very close* to the voltage peak.

SMPS and transformer PSUs vary slightly.



Such loads have PFs of around 0.5.

Computer PSUs are typically quoted as having a capacitive PF of 0.65
at full load,


** The PF of a SMPS is not capacitive - it is due to waveform
distortion.

OK, substitute "leading" for "capacitive".

Also, the actual PF worsens at lower ie more typical loads as the charging
pulse gets narrower.



so your estimate of 0.5 may not be far off the mark.


** It was not an "estimate".



Intuitively, however, I find it hard to correlate a 2ms current pulse
(as you state elsewhere) with an 0.5 PF.


** Simple. Imagine the current pulse is rectangular and centred on the AC
voltage peak.

Then the power consumed in watts is V peak x I peak x 0.2

For 240 AC and a 1 amp pulse this is 335 x 1 x 0.2 = 67 watts.

***Now for the VA:

The rms current for a rectangular pulse train is I peak x sq rt duty
cycle.

So in the example 1 x sq rt 0.2 = 0.447 amps rms.

The AC supply is 240 V rms so the load = 107.3 VA.

Such a load has a PF of 67 / 107.3 = 0.62

Change the pulse duration to 1 mS ( ie when the supply is lightly loaded)
and do the same calculation.

The new PF = 0.44.

I guess that one could argue, from an intuitive standpoint, that the
filter capacitor is now representing a greater component of the load,
and hence the PF falls as a consequence of this.

A duration of 2ms equates to
36 degrees at 50Hz, which would in the normal textbook "sinusoidal"
case result in a PF of 0.81. An 0.5 PF would normally suggest a phase
angle of 60 deg.


** The sub unity PF is not due to phase angle but wave shape and the
higher rms value of that wave shape.



How many times do I have to say it.

Not surprisingly, people prefer an independent, authoritative
reference.


** Shame those folk here have no brains to see the obvious nor can do a
simple Google on "active PFC".

Some may not be as conversant with this subject as you, and that
includes me, but that does not make us stupid. If you had illustrated
your case with your example early in this thread, there would have
been no need for a protracted slanging match. I wager that most people
would agree that the PF concept presented in your example is
counter-intuitive, and therefore not obvious, but the maths
nevertheless makes sense. The only thing that bothers me is that you
have used an artificial, unrepresentative pulse shape. If instead you
use a triangular pulse of 2A amplitude, then the wattage remains the
same, but the VA increases somewhat, ie by a factor of 1.16. This
would bring your 0.62 PF figure closer to 0.53, which is what you
stated from the outset.


- Franc Zabkar
--
Please remove one 's' from my address when replying by email.

 

[Phil Allison]

"Franc Zabkar"

"Phil Allison"

** The PF of a SMPS is not capacitive - it is due to waveform
distortion.

OK, substitute "leading" for "capacitive".

** It is not leading either - it is due to waveshape distortion.

I guess that one could argue, from an intuitive standpoint, that the
filter capacitor is now representing a greater component of the load,
and hence the PF falls as a consequence of this.

** The issue is the distorted waveshape and rms current values thereof.

It has NOTHING to do with angles, reactances, leading, lagging etc.

How many times do I have to say it.

Not surprisingly, people prefer an independent, authoritative
reference.


** Shame those folk here have no brains to see the obvious nor can do a
simple Google on "active PFC".


Some may not be as conversant with this subject as you, and that
includes me, but that does not make us stupid.

** When you stubbornly ignore the facts that are posted you are being
stupid.

When you stubbornly and mindlessly repeat a basic error in face of the
correct answer your are being stupid.

When you publicly insult the person presenting the truth - then you are
an utter arsehole.

If you had illustrated your case with your example early in this thread,
there would have
been no need for a protracted slanging match.

** You were the first here to even hint that you wanted to see one.

The other two morons were hell bent on ignoring my case and burying the
truth in order to protect their pathetic egos.

I wager that most people would agree that the PF concept presented in your
example is
counter-intuitive, and therefore not obvious, but the maths nevertheless
makes sense.

** Most people associate PF only with reactive phase angles, but that is an
error. People who have engineering backgrounds and qualifications should
not make that error, or at least when it is pointed out realise it and not
persecute the person saying the truth.

The only thing that bothers me is that you
have used an artificial, unrepresentative pulse shape.

** The pulse can be modelled as a simple rectangle - just square off the
top of the pulse and sharpen up the sides and you have it.

If instead you use a triangular pulse of 2A amplitude,

** But it is NOT a triangle - the pulse shape resembles the last 1.5
cm of your little finger.

then the wattage remains the same, but the VA increases somewhat, ie by a
factor of 1.16. This
would bring your 0.62 PF figure closer to 0.53, which is what you stated
from the outset.

** The was no debate over the actual PF figure - you maliciously
misrepresent things.

The issue was the inability of two posturing fools to concede the existence
sub unity PF with NO PHASE ANGLE at all.

Something that nearly all mains powered electronic devices ever made present
as a load, something which is a recognised problem in electricity supply and
for which there is a modern solution - ie active PFC.




.......... Phil

 

[Phil Allison]

"Peter_purple" <purple@203.0.178.192> wrote in message
news:3FFBAA77.342119D6@203.0.178.192...

Phil Allison wrote:> > If you have electronic loads with whatever PF then
the
VAs just add.


** There is no PFC in the vast majority of electronic items -
including
some that draw up to 4000 VA from a single phase circuit. Also there is
virtually no phase angle, peak current draw co-insides exactly with
peak
voltage. The PF of such loads is about 0.5.

........ Phil

Wrong, if there is no phase angle the pf = 1

thats its definition.

** Go drop dead Moron.



.......... Phil

 

[Peter_purple]

Phil Allison wrote:> > If you have electronic loads with whatever PF then the
VAs just add.

** There is no PFC in the vast majority of electronic items - including
some that draw up to 4000 VA from a single phase circuit. Also there is
virtually no phase angle, peak current draw co-insides exactly with peak
voltage. The PF of such loads is about 0.5.

........ Phil

Wrong, if there is no phase angle the pf = 1

thats its definition.


--
that is because,

peter purple proclaims

The infamous big dollar scam list of email addresses, growing,
appended here for those nice news bots to collect their email addresses...

benjamin_cole2000@yahoo.com, williams_adebayo@hotmail.com, frpierrejr@yahoo.fr,

"fprohanp" <fprohanp@libero.it>, "mariam seseseko" <maseko01@yahoo.ca>,
"GEORGE JOHN" <george_500@tiscali.co.uk>, "gerald abam"
<geraldabam@fsmail.net>,
<geraldabam@yahoo.co.uk>, <tariqani_2@gawab.com>, <romesmith@freesurf.fr>,
"tariq ani" <tariqani_2001@fsmail.net>, "Dr. Isa Gambo"
<gamboisa@zwallet.com>,
Rebeka Abubakar <rebekaluv@fsmail.net>, abanigo@justice.com,
abanigo72@swissmail.net
From: "Dr. Ahmed Banigo" <ahmedb@aol.com>, "Dr. Ahmed Banigo"
<abanigo@justice.com>,
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akuwilly@fsmail.net, "kwanta douglas" <douglaskwan@mail.com.fr>,
douglaskwan@mail.com.fr,
"TEMBA BAKO NGANBA" <tawandanganba@netscape.net>, "mariam abacha"
<mariam_6666_abacha@fsmail.net>
mariam_6666_abacha@fsmail.net, adetaylor73@yahoo.com.au,
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"ddlucian" <ddlucian@libero.it>, tonyagha1@fsmail.net, tonyagha2@maktoob.com,
jerry brown <jerrybrown@fsmail.net>, "DR HARRISON OHALE......."
<aceohale@hotmail.com>
haohale@hotmail.com, "Dr.Alex.alex" <alex.alex@alex4all.com>,
Mr A.Manfred <vanmannfred@fsmail.net>, "FROM WILLIAM SANKOH."
<william.sankoh@voila.fr>
"michael adekunle" <michael_adekunle90@fsmail.net>,
webmaster_michael2002@yahoo.co.uk
"ray famous" <rayfam3@fsmail.net>, rayfamo@yahoo.com, Ali_yusufu@yahoo.com,
"NIEUWENHUYS ALBERT S." <a.nieuwenhuys@702mail.co.za>,
<nieuwenhuys@tech4peace.org>,
bulusmohammed@excite.com

 

[Peter_purple]

Kevin Ettery wrote:

In vector terms both the current and voltage are vectors rotating in space.

No, they are not rotating in space, there are no coordinates, cartesian or
otherwise !full stop.

Its sheer imagination to say they are rotating in space, they are only
ever rotating with respect to each other, i have ben abstract maths
expert so I know this to be a mental construct.

Hope it cleared a few things up.

with the exception of your appreciation of space,

--
that is because,

peter purple proclaims

The infamous big dollar scam list of email addresses, growing,
appended here for those nice news bots to collect their email addresses...

benjamin_cole2000@yahoo.com, williams_adebayo@hotmail.com, frpierrejr@yahoo.fr,
"fprohanp" <fprohanp@libero.it>, "mariam seseseko" <maseko01@yahoo.ca>,
"GEORGE JOHN" <george_500@tiscali.co.uk>, "gerald abam" <geraldabam@fsmail.net>,

<geraldabam@yahoo.co.uk>, <tariqani_2@gawab.com>, <romesmith@freesurf.fr>,
"tariq ani" <tariqani_2001@fsmail.net>, "Dr. Isa Gambo" <gamboisa@zwallet.com>,

Rebeka Abubakar <rebekaluv@fsmail.net>, abanigo@justice.com,
abanigo72@swissmail.net
From: "Dr. Ahmed Banigo" <ahmedb@aol.com>, "Dr. Ahmed Banigo"
<abanigo@justice.com>,
"yusuf.mamman" <yusuf.mamman@telstra.com>, yusufmamman@fsmail.net,
akuwilly@fsmail.net, "kwanta douglas" <douglaskwan@mail.com.fr>,
douglaskwan@mail.com.fr,
"TEMBA BAKO NGANBA" <tawandanganba@netscape.net>, "mariam abacha"
<mariam_6666_abacha@fsmail.net>
mariam_6666_abacha@fsmail.net, adetaylor73@yahoo.com.au,
abraham_ojo_chambers@moldova.com
"ddlucian" <ddlucian@libero.it>, tonyagha1@fsmail.net, tonyagha2@maktoob.com,
jerry brown <jerrybrown@fsmail.net>, "DR HARRISON OHALE......."
<aceohale@hotmail.com>
haohale@hotmail.com, "Dr.Alex.alex" <alex.alex@alex4all.com>,
Mr A.Manfred <vanmannfred@fsmail.net>, "FROM WILLIAM SANKOH."
<william.sankoh@voila.fr>
"michael adekunle" <michael_adekunle90@fsmail.net>,
webmaster_michael2002@yahoo.co.uk
"ray famous" <rayfam3@fsmail.net>, rayfamo@yahoo.com, Ali_yusufu@yahoo.com,
"NIEUWENHUYS ALBERT S." <a.nieuwenhuys@702mail.co.za>,
<nieuwenhuys@tech4peace.org>,
bulusmohammed@excite.com

 

[Franc Zabkar]

On Tue, 6 Jan 2004 22:23:51 +1100, "Phil Allison"
<philallison@optusnet.com.au> put finger to keyboard and composed:

"Franc Zabkar"

"Phil Allison"



** The PF of a SMPS is not capacitive - it is due to waveform
distortion.

OK, substitute "leading" for "capacitive".


** It is not leading either - it is due to waveshape distortion.



I guess that one could argue, from an intuitive standpoint, that the
filter capacitor is now representing a greater component of the load,
and hence the PF falls as a consequence of this.


** The issue is the distorted waveshape and rms current values thereof.

It has NOTHING to do with angles, reactances, leading, lagging etc.

OK, I see that now.

How many times do I have to say it.

Not surprisingly, people prefer an independent, authoritative
reference.


** Shame those folk here have no brains to see the obvious nor can do a
simple Google on "active PFC".


Some may not be as conversant with this subject as you, and that
includes me, but that does not make us stupid.



** When you stubbornly ignore the facts that are posted you are being
stupid.

When you stubbornly and mindlessly repeat a basic error in face of the
correct answer your are being stupid.

When you publicly insult the person presenting the truth - then you are
an utter arsehole.




If you had illustrated your case with your example early in this thread,
there would have
been no need for a protracted slanging match.


** You were the first here to even hint that you wanted to see one.

The other two morons were hell bent on ignoring my case and burying the
truth in order to protect their pathetic egos.




I wager that most people would agree that the PF concept presented in your
example is
counter-intuitive, and therefore not obvious, but the maths nevertheless
makes sense.


** Most people associate PF only with reactive phase angles, but that is an
error. People who have engineering backgrounds and qualifications should
not make that error, or at least when it is pointed out realise it and not
persecute the person saying the truth.

The idea that PF is related to phase angles is a consequence of the
way the concept is taught. If students were instead taught that
lagging and leading PFs were merely special cases of a more general
principle, then such ingrained misconceptions would not arise. You are
the first person to challenge my understanding (sic!) of PF, and to
demonstrate to my satisfaction that there need not be any phase angle
between current and voltage peaks for a sub-unity PF to exist.

I may not like you, but that does not prevent me from acknowledging
you when you are right. I have no ego to protect, and I in no way feel
diminished when I confess my ignorance, especially if I can learn
something in the process.

The only thing that bothers me is that you
have used an artificial, unrepresentative pulse shape.


** The pulse can be modelled as a simple rectangle - just square off the
top of the pulse and sharpen up the sides and you have it.


If instead you use a triangular pulse of 2A amplitude,


** But it is NOT a triangle - the pulse shape resembles the last 1.5
cm of your little finger.

Once again I am basing my statement on the ideas presented in basic
engineering texts. Apparently reality is different (no sarcasm
implied).

then the wattage remains the same, but the VA increases somewhat, ie by a
factor of 1.16. This
would bring your 0.62 PF figure closer to 0.53, which is what you stated
from the outset.


** The was no debate over the actual PF figure - you maliciously
misrepresent things.

You are paranoid. There was no malice in any of my statements. In fact
I was conceding that your originally quoted figure of 0.5 sounded
reasonable after I had initially doubted it.

The issue was the inability of two posturing fools to concede the existence
sub unity PF with NO PHASE ANGLE at all.

The difficulty with this concept is that it bears no relation to
actual electronic loads. All common PSUs have a phase angle, however
small, between voltage and current peaks. The existence of such a
phase angle tends to reinforce the misconception that it alone is
responsible for the PF. That is why your statement appears
counterintuitive. In fact it is only now that I can understand why a
PSU with a PF of 0.65 need not necessarily have a massive ripple
voltage on the mains filter cap.

Something that nearly all mains powered electronic devices ever made present
as a load, something which is a recognised problem in electricity supply and
for which there is a modern solution - ie active PFC.

- Franc Zabkar
--
Please remove one 's' from my address when replying by email.

 

[Phil Allison]

"Franc Zabkar" <fzabkar@optussnet.com.au>

The issue was the inability of two posturing fools to concede the
existence
sub unity PF with NO PHASE ANGLE at all.

The difficulty with this concept is that it bears no relation to
actual electronic loads. All common PSUs have a phase angle, however
small, between voltage and current peaks.

** A small amount of asymmetry in the charging pulse shape about the AC
supply voltage peak has no effect on the wattage or PF. In a sine wave
system even a small phase angle immediately creates a situation were the
voltage and current are of opposing polarity for part of the cycle - this
is not so for the electronic load case.

The existence of such a phase angle tends to reinforce the misconception
that it alone is
responsible for the PF.

** There are cases where is is exact - does this make the PF drop to zero
?

The power factor of even a 10 degree phase angle is 0.99.

You are clutching at straws.

That is why your statement appears counterintuitive. In fact it is only
now that I can understand why a
PSU with a PF of 0.65 need not necessarily have a massive ripple
voltage on the mains filter cap.

** Oh no !! Not the filter capacitor value affects the rms draw debate
again !!!!!



BTW There is a simple way to measure the true watts consumed of a
typical electronic load - armed with the knowledge that phase angle is not
relevant.

The duration of the current pulse matches the nearly flat top of the AC
supply wave - so you can take the supply voltage as being fixed at a value
like 330 volts. All you need is the average rectified value of the current
pulses - easily measured with a standard meter ( not true rms) and then
multiply the reading by 0.9 to remove the sine wave rms calibration factor.

The *average* current value times a fixed voltage gives true watts -
same as from a DC supply.




......... Phil

 

[Brian Goldsmith]

"Franc Zabkar" wrote about Phil Allison:-

The idea that PF is related to phase angles is a consequence of the
way the concept is taught. If students were instead taught that
lagging and leading PFs were merely special cases of a more general
principle, then such ingrained misconceptions would not arise. You are
the first person to challenge my understanding (sic!) of PF, and to
demonstrate to my satisfaction that there need not be any phase angle
between current and voltage peaks for a sub-unity PF to exist.

I may not like you, but that does not prevent me from acknowledging
you when you are right. I have no ego to protect, and I in no way feel
diminished when I confess my ignorance, especially if I can learn
something in the process.


***** Took a big man to write the above! More power to him!!!!!

Brian Goldsmith.