It's easy to budget your VA requirements. Just take the max input
current listed on all your devices and multiple by wall voltage (~120V
in the US). That gives you max VA for that device. Do this for all
devices you plug in and add them up. Buy your UPS for that total.
You're guaranteed to be covered, but you will likely have some margin
too if you don't always draw max current.
If utilties start charging residential customers for additional VARs, it
will be because they are greedy bastards.
On 8/2/2011 12:28 PM, DSinc wrote:
Bino,
OK. You win! Yes the AC voltage you measure at the wall plug is 0.707
(rms) of the peak AC sinusoidal wave-form (169.731V) when viewed via
an o-scope. My comment was with regards to your concern about KWh and
KVA values. In your apartment you spend your dollars buying AC power
measured in Watts not KVA.
Yes, have read about these new digital 'smart' residential
watt-meters. I have one on my home now. And I fully expect that in the
future (as my AC Service provider completes it's 'Smart Grid'
technology) I may see my bill change based on 'time of day' power
usage during peak demand (system wide) situations.
Yes, it is confusing in the UPS calculation game. All of my UPS's are
rated at 1500KVA. Yet, they also will only supply a maximum output of
875 watts continuous.
I do not follow your points about 'VA' rating of a device. If it plugs
into your wall plug it is spec'd in watts.
My understanding about Power Factor and/or Power Factor Correction
technology is some form of quantifying electrical efficiency. IMHO. I
leave area to the those that understand. I do not. Yet I do agree that
our modern PSU's are very much more efficient AC to DC converters.
Sorry to interject skepticism into your search for truth.
Best,
Duncan
On 08/02/2011 00:31, Bino Gopal wrote:
Duncan, if you actually check my other post after this one, my share
is *not* useless; recapping the key point from there: "In some
regions utilities already installed digital power meters ("smart
meters") at the residential level, which compute W, VAR, and PF. They
may surcharge you for VAR." from
http://www.generatorguide.net/watt-acpower.html
so it's not a moot point. But in any case no commercial project or
anything-was just trying to understand a few things: First, I was
trying to understand the relationship b/w VA and watts and the peak
values for each vs the RMS (root mean square) for each, which I think
I do now-and what's interesting is that for AC power since it's
sinusoidal and thus it's the cos45, RMS is sq rt 2 or 70% of peak
values (which is why American power outlets which are labeled 120V
refers to 120V rms, whereas peak voltage can be up to 170V)...
Then:Q1) Do I need to worry about devices with low PF b/c then I
would be paying more for the VA vs watts if the power company was
keeping track of that?
A1) As per the link above, unless I have a digital power meter (smart
meter) I won't get charged for VA, I only get charged for watts, so
I'm cool Oh and you're completely missing the point at the end
too-sure we get *billed* in Wh or kWh, but as I also pointed out in
another email, it's very important to know the VA draw of devices as
when sizing UPS systems, as if anything plugged into the UPS has less
than a perfect VA, your UPS will not give you as much run-time as you
expect-or even be able to handle the load. See this link for more
details: http://www.power-solutions.com/watts-va.php I didn't
understand the whole VA vs watts distinction (and even peak values vs
rms values) and now that I do I can be more informed about UPS sizing
and power draw of my devices (and also better evaluate which PS to
get based on different PS ratings and their efficiencies under
different loads and at different temps)-that's at least all of what
I've learned from this exercise! ;) Hope it might've been helpful for
other folks though it seems like most people knew most of this
already!! BINO> Date: Mon, 1 Aug 2011 17:23:50 -0400
From: [email protected]
To: [email protected]
Subject: Re: [H] PFC (power factor corrected) PS for PCs?
Bino,
I know you are smarter than I am. But, your share of, (...*but they
definitely do charge industrial customers for VA since they probably
would have low PF otherwise.. ) while true is useless.*
*Are you doing something local behind you own apt's wattmeter; or, are
you trying to do a commercial project for somebody else? KVA is a
commercial measurement per Greg's last share.
In your apartment, you live in a KiloWatt/hour world (per your
supplier's installed WattMeter).
Your share is very confusing. Why is Power Factor so important to
you ATM?*
*Best,
Duncan*
On 08/01/2011 13:12, Bino Gopal wrote:
Well the confusion is that the utility *could* charge you for VA
instead of watts, but apparently they don't for residential
customers (since most residences only have older-style meters that
read only watts) but they definitely do charge industrial customers
for VA since they probably would have low PF otherwise...ahh, from
the PF wikipedia article:-Importance of power factor in
distribution systems-The significance of power factor lies in the
fact that utility companies supply customers with volt-amperes, but
bill them for watts. Power factors below 1.0 require a utility to
generate more than the minimum volt-amperes necessary to supply the
real power (watts). This increases generation and transmission
costs. For example, if the load power factor were as low as 0.7,
the apparent power would be 1.4 times the real power used by the
load. Line current in the circuit would also be 1.4 times the
current required at 1.0 power factor, so the losses in the circuit
would be doubled (since they are proportional to the square of the
current). Alternatively all components of the system such as
generators, conductors, transformers, and switchgear would be
increased in size (and cost) to carry the extra current.-Utilities
typically charge additional costs to customers who have a power
factor below some limit, which is typically 0.9 to 0.95. Engineers
are often interested in the power factor of a load as one of the
factors that affect the efficiency of power transmission.
-And I read somewhere (can't find the link now; it was one of like
30 I was reading yesterday before I read this one that clearly
states that utilities charge for watts, not VA ) that some
utilities are installing meters than can read VA instead, since
they have to pay to push VA and not watts...which actually makes
sense to me.-
BINO-> Date: Mon, 1 Aug 2011 05:55:00 -0400
From: [email protected]
To: [email protected]
Subject: Re: [H] PFC (power factor corrected) PS for PCs?
What's the confusion? You're paying for watts....you don't pay for
VA..that's a unit used for complex power, part if which includes
reactive power, which is not converted to useful work. Real power is,
which is measured in watts.
On 8/1/2011 5:29 AM, Bino Gopal wrote:
Lol that's exactly one of the links I found (among about the 20
or so I've been perusing all day), but it still isn't clear to me
from any of them whether I'm paying for VA or watts...anyone know
for sure or does it depend on your particular power company and
the kind of meters they use maybe...?
> Date: Mon, 1 Aug 2011 00:12:50 -0700
From: [email protected]
To: [email protected]
Subject: Re: [H] PFC (power factor corrected) PS for PCs?
"Capacitor Input supplies have the characteristic that the Watt
rating is in
the range of .55 to .75 times the VA rating (power factor of
0.55 to 0.75)."
http://www.power-solutions.com/watts-va.php
On Jul 31, 2011 11:50 PM, "Bino
Gopal"<[email protected]> wrote:
