Kill-o-watt meter used on computer UPS - bad readings?

[Bob F]

I just unplugged the Belkin 1200 VA UPS powering my computer, and plugged it
into my Kill-o-watt meter. After the UPS quit beeping after power was restored,
the meter shows 7-11 watts being consumed by the UPS feeding the computer, which
is way less than the computer (quad core core-duo processor) uses.

Does the killowatt have a problem reading accurately with UPS units?

[Dave Platt]

What does the meter read, if you connect the computer to it directly,
and entirely bypass the UPS?

Most of these consumer-grade "UPS" systems are *not*. That is, they
aren't "uninterruptable" - they are "standby power supply" devices.
During normal operation, when the AC mains are up normally, they
actually connect the load (PC) directly to the mains... their own
output circuitry is switched off. All they have running, internally,
is monitoring circuitry, and a trickle-charger for the battery. The
"UPS" only disconnects the load from the mains, turns on its inverter,
and begins generating AC power to feed to the load.

So, if the Belkin isn't beeping, it's probably just routing the AC
mains power through to the PC, and you'd find the meter reading almost
the same as if you plugged the PC directly into the meter...

... and this might not be a terribly accurate figure. My recollection
is that some of these "power consumption meters" don't do a very
accurate job of measuring power usage being drawn in pulses (i.e. by
a non-resistive load). Your computer's power supply may be presenting
a load that the Kill-a-watt is having trouble analyzing.

--
Dave Platt <dpl...@radagast.org> AE6EO
Friends of Jade Warrior home page: http://www.radagast.org/jade-warrior
I do _not_ wish to receive unsolicited commercial email, and I will
boycott any company which has the gall to send me such ads!

[Sylvia Else]

The reading seems strange (typically one would expect it to show a
higher than true figure), but cheap power meters often have difficulty
with anything other than appliances that behave like resistive loads.
Neither the UPS itself nor the PC is likely to do so.

Sylvia.

[Bob F]

Dave Platt wrote:
> In article <j58nff$bjn$1...@dont-email.me>, Bob F <bobn...@gmail.com>
> wrote:
>
>> I just unplugged the Belkin 1200 VA UPS powering my computer, and
>> plugged it into my Kill-o-watt meter. After the UPS quit beeping
>> after power was restored, the meter shows 7-11 watts being consumed
>> by the UPS feeding the computer, which is way less than the computer
>> (quad core core-duo processor) uses.
>>
>> Does the killowatt have a problem reading accurately with UPS units?
>
> What does the meter read, if you connect the computer to it directly,
> and entirely bypass the UPS?
>
> Most of these consumer-grade "UPS" systems are *not*. That is, they
> aren't "uninterruptable" - they are "standby power supply" devices.
> During normal operation, when the AC mains are up normally, they
> actually connect the load (PC) directly to the mains... their own
> output circuitry is switched off. All they have running, internally,
> is monitoring circuitry, and a trickle-charger for the battery. The
> "UPS" only disconnects the load from the mains, turns on its inverter,
> and begins generating AC power to feed to the load.
>
> So, if the Belkin isn't beeping, it's probably just routing the AC
> mains power through to the PC, and you'd find the meter reading almost
> the same as if you plugged the PC directly into the meter...
>

I'll try bypassing the UPS when my computer is not busy and report the results
later.

[Jeff Liebermann]

On Mon, 19 Sep 2011 17:41:18 -0700, "Bob F" <bobn...@gmail.com>
wrote:

>I just unplugged the Belkin 1200 VA UPS powering my computer, and plugged it
>into my Kill-o-watt meter.

What model Belkin UPS?
<http://www.belkin.com/IWCatSectionView.process?Section_Id=206698>
What model kill-o-watt meter?
<http://www.p3international.com/products/>

>After the UPS quit beeping after power was restored,

Some UPS power supplies will stop beeping BEFORE they switch from
internally generated power back to wall plug power. It's not clear
from your description if the attached computah is running on UPS
power, or wall plug power.

>the meter shows 7-11 watts being consumed by the UPS feeding the computer, which
>is way less than the computer (quad core core-duo processor) uses.

Make and model of the computer? Anything else plugged into the UPS
such as a monitor, printer, modem, etc?

>Does the killowatt have a problem reading accurately with UPS units?

Yes, sorta. If it's an old UPS, that doesn't have PF (power factor)
correction, the kill-a-watt will show a difference between VA
(volt-amps) and the real part of the power (watts). You can measure
the PF with the kill-a-watt (depending on model) and see if this is a
problem. However, the error is usually not very large and does not
account for a ridiculously low reading of 7-11 watts. The computah
should draw about 100 watts. The LCD monitor about the same
(depending on size). Add whatever for unspecified accessories. Take
the UPS out of the circuit and measure just the active loads plugged
into the UPS.

--
Jeff Liebermann je...@cruzio.com
150 Felker St #D http://www.LearnByDestroying.com
Santa Cruz CA 95060 http://802.11junk.com
Skype: JeffLiebermann AE6KS 831-336-2558

[Bob F]

I just tried plugging the computer directly into the Killowatt meter, and get
the same results. It shows 6 watts with the computer connected, and 9 with it
on. The killowatt just doesn't see the computer.

[mike]

I tried a Killawatt P4400 on my old dell.
Reads 100W/140VA.

Do you know if your Killawatt is working?
Try it on an incandescent light bulb.

It's possible to exceed the crest factor capability
of the meter, but your computer shouldn't do it.

You can work around that problem by measuring
a light bulb then adding the computer and subtract
the light bulb watts.