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Watts vs VA

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Simon3359

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Nov 26, 2002, 5:27:36 PM11/26/02
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I have a Question I know that Watts equals Voltage x Amps to get the amount of
Power the unit consumes. I had always thought the VA rating was the same as the
Watts rating. However I have noticed that on the power rating what a UPS
(Uniterrupted Power Supply) can supply when the A.C. power goes off the specs
says like 500VA 270Watts. Can some one please clarify if there is any
difference betweem the two? If there is a difference I would like the formula
how to figure the VA rating of device.

Thanks You
Simon3359

Homer J. Simpson

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Nov 26, 2002, 5:44:54 PM11/26/02
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VA is the apparent power, or RMS AC voltage times the RMS AC amperage.
Watts is the Real power, which will be different if the load is not strictly
resistive. See this for more detail:
http://www.traceengineering.com/technical/tech_notes/tn11.html


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Paul Landregan

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Nov 27, 2002, 2:49:05 AM11/27/02
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"Simon3359" <simo...@aol.com> wrote in message
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VA = AC Volts X AC Amps.
AC Watts = VA X Power Factor (Typically 0.7 is used)

Hope this helps, and doesnt confuse you even more.


>


Martin VK2UMJ

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Nov 27, 2002, 7:16:27 AM11/27/02
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Just to help clarify a little:

> VA = AC Volts X AC Amps.

VA = Amps X AC Volts (RMS)

> AC Watts = VA X Power Factor (Typically 0.7 is used)

VA = Watts X 1.4 (power correction factor)

>
> Hope this helps, and doesnt confuse you even more.
>

--
Martin Howells, VK2UMJ
vk2...@REMOVEyahoo.com.au

**Delete "REMOVE" from e-mail address to reply**

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Peter Gottlieb

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Nov 27, 2002, 8:50:05 AM11/27/02
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Arrrrrggggghhhh! No!! Look at the previous post regarding reactive loads.


"Martin VK2UMJ" <vk2...@REMOVEyahoo.com.au> wrote in message
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CJT

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Nov 27, 2002, 10:40:17 AM11/27/02
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Peter Gottlieb wrote:
> Arrrrrggggghhhh! No!! Look at the previous post regarding reactive loads.

Which one specifically?

Martin VK2UMJ

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Nov 27, 2002, 3:57:49 PM11/27/02
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"Peter Gottlieb" <pe...@NewYorkNERD.com> wrote in message
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> Arrrrrggggghhhh! No!! Look at the previous post regarding reactive
loads.

Perhaps you have some info that the UPS manufacturers don't have??? And as
the original post related to a UPS rating, I (maybe wrongfully) presumed
that the info I had found many times in UPS calculation info from UPS
manufacturers may be of some use......

I'll try this again, copying EXACTLY as it is written in this here UPS
catalogue...

"Each device you list has an amperage or wattage requirement. Use the
following formulas to calculate the VA requirements of the UPS:
Amps x 240 (Voltage) = VA [in Australia where AC RMS = 240 V]
Watts x 1.4 (power correction factor) = VA"

> > Just to help clarify a little:
> >

> > VA = Amps X AC Volts (RMS)
> >

> > VA = Watts X 1.4 (power correction factor)
> >

Yep, that looks the same. If I have been misled by wrong information from
UPS manufacturers, then I am sorry and I apologise, but that is the
information that I have at hand....

Peter Gottlieb

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Nov 27, 2002, 5:39:35 PM11/27/02
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"Martin VK2UMJ" <vk2...@REMOVEyahoo.com.au> wrote in message
news:5daF9.85036$g9.2...@newsfeeds.bigpond.com...

> "Peter Gottlieb" <pe...@NewYorkNERD.com> wrote in message
> news:h44F9.5048$Sb....@nwrddc04.gnilink.net...
> > Arrrrrggggghhhh! No!! Look at the previous post regarding reactive
> loads.
>
> Perhaps you have some info that the UPS manufacturers don't have???

Depends on the department and the audience. In Engineering we had all the
info, but Marketing has to both simplify and to match specs with
competitors. Was that a wiseass question?


kip

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Nov 27, 2002, 6:20:36 PM11/27/02
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You cannot argue with Ohms Law.!!

kip
va3mm


Peter Gottlieb

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Nov 27, 2002, 6:49:36 PM11/27/02
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You can argue with it, but the consequences of breaking it are severe!


"kip" <k...@istop.com> wrote in message
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CJT

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Nov 27, 2002, 9:49:51 PM11/27/02
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I suppose, as long as you don't confine yourself to real numbers.

Jim Adney

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Nov 27, 2002, 11:32:23 PM11/27/02
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On Wed, 27 Nov 2002 18:20:36 -0500 "kip" <k...@istop.com> wrote:

>You cannot argue with Ohms Law.!!

Sure you can. It's just going to be hard to win! ;-)

-
-----------------------------------------------
Jim Adney jad...@vwtype3.org
Madison, Wisconsin USA
-----------------------------------------------

Martin VK2UMJ

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Nov 28, 2002, 4:14:37 AM11/28/02
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> Depends on the department and the audience. In Engineering we had all the
> info, but Marketing has to both simplify and to match specs with
> competitors. Was that a wiseass question?

I agree - of course you can go into the calculations fully and take into
consideration all values, but I think for general use so the average Joe
Bloggs can figure out if he needs a 1000VA or 3000VA UPS, the calculations
given are adequate.

Sam Goldwasser

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Nov 28, 2002, 12:00:10 PM11/28/02
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"Martin VK2UMJ" <vk2...@REMOVEyahoo.com.au> writes:

> > Depends on the department and the audience. In Engineering we had all the
> > info, but Marketing has to both simplify and to match specs with
> > competitors. Was that a wiseass question?
>
> I agree - of course you can go into the calculations fully and take into
> consideration all values, but I think for general use so the average Joe
> Bloggs can figure out if he needs a 1000VA or 3000VA UPS, the calculations
> given are adequate.

Well, last time I checked, this was not a Marketing forum. Therefore,
simply stating a claim originating from a marketing brochure isn't really
helpful. To state that VA=W*1.4 or whatever the silly result was is
misinformation, period. :)

--- sam | Sci.Electronics.Repair FAQ Home Page: http://www.repairfaq.org/
Repair | Main Table of Contents: http://www.repairfaq.org/REPAIR/
+Lasers | Sam's Laser FAQ: http://www.repairfaq.org/sam/lasersam.htm
| Mirror Site Info: http://www.repairfaq.org/REPAIR/F_mirror.html

Martin VK2UMJ

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Nov 29, 2002, 3:23:29 PM11/29/02
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> Well, last time I checked, this was not a Marketing forum. Therefore,
> simply stating a claim originating from a marketing brochure isn't really
> helpful. To state that VA=W*1.4 or whatever the silly result was is
> misinformation, period. :)
>

What the hell is your problem, Professor??

The ORIGINAL question was:

>I have a Question I know that Watts equals Voltage x Amps to get the
amount of
>Power the unit consumes. I had always thought the VA rating was the same as
the
>Watts rating. However I have noticed that on the power rating what a UPS
>(Uniterrupted Power Supply) can supply when the A.C. power goes off the
specs
>says like 500VA 270Watts. Can some one please clarify if there is any
>difference betweem the two? If there is a difference I would like the
formula
>how to figure the VA rating of device.

Now, all the info provided to consumers when purchasing a UPS tells them to
calculate the total VA used as specifies the formula VA = W x 1.4, so I do
NOT consider this as misinformation.

The original poster did NOT specify that he wanted to accurately calculate
the exact VA of a reactive, or capacitive, or any other specific type of
load, nor did it specify a particular type of load, just a general reference
to a UPS and if there is a difference between Watts and VA My response
provided the information that there IS a difference, and the simple method
used by MILLIONS of people (sales, and others) to calculate what size (i.e.
VA rating) UPS to connect....

So, Professor, misinformation??? Not helpful?? WANKER.. Go play with your
damn engineering notebooks. Why post a response to a question that would
most likely shoot over the heads of most readers? If you're technically
minded enough to understand the in-depth answer, then you probably already
know the damn answer and wouldn't be posting such a question in the first
place, now would you? "Highly technical" people like you, the ones that
MUST have the exact correct response right down to the last decimal place
and Nth degree, really annoy the crap out of me. If the question asks for
such a response, then fine, but my interpretation of this question was that
a basic answer was all that was needed (sorry if I was wrong), so why
confuse everyone with information that's really not wanted??? Sorry if we
aren't all as smart or technically correct as you, Sir Professor.....

My warmest and kindest regards

--
Martin Howells
*Electronics Technician
*Australian Amateur Station VK2UMJ
*Australian Scientific Station AX2NAG
*ACBRO Member #470

Peter Gottlieb

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Nov 29, 2002, 4:03:54 PM11/29/02
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PFC supplies do complicate things, though.


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Chris

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Nov 29, 2002, 5:05:15 PM11/29/02
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Only when it's a mobile ohm in an AC sort of way?

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Engineer

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Dec 2, 2002, 1:35:37 AM12/2/02
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I've just read this thread (or what I can get of it) and notice that no one
seems to have answered the question of how "watts" differ from "volt.amps"
(VA)

Watts = volts x IN PHASE current. They are the "real power", the stuff you
pay for at the electric meter.

Volt.amps = volts x current, regardless of the phase. Thus, VA ratings are
always higher than watt ratings because they contain what is called
"imaginary power" in addition to the real power.

There's also Power Factor (PF) = cosine of the angle between voltage and
current, generally lagging, i.e. the current lags voltage in inductive
circuits (the majority of loads.) BTW, current leads voltage in
capacitative loads.

One could go one about real and imaginary power, PF correction, vector
diagrams, etc, but I'll leave that others (got to finish dinner!)

Cheers,

Roger
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Peter Gottlieb

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Dec 1, 2002, 11:30:42 PM12/1/02
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For a purely resistive load (i.e., electric heaters, incandescent bulbs)
there is no "imaginary" power and Watts are equal to VA. Ideally, PF
corrected power supplies act the same way.

Meterology wise, instantaneous V multiplied by instantaneous I and converted
to RMS over a cycle will give Watts; Instantaneous V converted to RMS over a
cycle multiplied by instantaneous I converted to RMS over a cycle will give
VA.

Clear as the Charles now, right?


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