Measuring PC power usage?

[anon418600J5]

Is there a way to measure how much electricity a computer is using? It
doesn't need to be exact, just a guide.

Is it as simple as saying "if it has a 400W power supply then it uses 400W
per hour"? Or is that just the maximum? is it per hour?

Basically, I just want to know roughly what % of my electricity bill is due
to the computer, what % is wide screen tv etc etc.

Sorry if this seems like a really obvious/stupid question...

Thanks.

 

[Andrew Gabriel]

Is there a way to measure how much electricity a computer is using? It
doesn't need to be exact, just a guide.

You can buy (at least in the UK) plug in power meters.

Is it as simple as saying "if it has a 400W power supply then it uses 400W

Definately not.

per hour"? Or is that just the maximum? is it per hour?

Watts (power) is already a rate of energy use (Joules/second).
Hence watts/hour doesn't make any sense (unless you are
referring to rate of change of power usage, which you aren't).

Basically, I just want to know roughly what % of my electricity bill is due
to the computer, what % is wide screen tv etc etc.

If you said what spec these items are, someone who has measured
similar spec items can probably give you a ball-park figure.

 

[TimPerry]

Is there a way to measure how much electricity a computer is using?
It doesn't need to be exact, just a guide.

search for "kill a watt" meter

Is it as simple as saying "if it has a 400W power supply then it uses
400W per hour"? Or is that just the maximum? is it per hour?

that's the max rating of the supply.


if your load is 1W and operated for one hour that would be 1 W-H
(watt-hour)
if the 1 watt load operated for 1000 hours is then 1 kW-H (killowatt-hour)
if a 1000 watt load operates for one hour it's 1 kW-H

 

[anon418600J5]

Cool, I googled for them and found one for £16.50 - that'll do nicely!

 

[Andrew Gabriel]

Cool, I googled for them and found one for £16.50 - that'll do nicely!

BTW, don't buy the Brennenstuhl one -- it's horribly inaccurate
for loads like PC power supplies. I also have a no-name Taiwan one
from Maplin, and that's OK. (Maplin used to sell the Brennenstuhl
one, but stopped some time ago.)

 

[anon418600J5]

it's a PM230, but not sure of make...?

 

[Andrew Gabriel]

it's a PM230, but not sure of make...?

Oh dear, that's the model number of the Brennenstuhl one.
Test it with a compact fluorescent lamp, and if it reads 2 - 3 times
the power rating of the lamp, then it's as crap as my one.

I'm not entirely sure what's wrong with it. I did play with it for a
while when I first got it, and my impression is that it measures some
type of average current, some type of average voltage, and the phase
shift, and works out power as I x V x cosØ. It is failing to realise
that low power factor can be caused by things other than phase shift,
as is indeed the case with many PC power supplies (and integral
electronic ballast compact fluorescent lamps), which have low power
factor, but cosØ = 1 (almost).

 

[[email protected]]

Oh dear, that's the model number of the Brennenstuhl one.
Test it with a compact fluorescent lamp, and if it reads 2 - 3 times
the power rating of the lamp, then it's as crap as my one.

I'm not entirely sure what's wrong with it. I did play with it for a
while when I first got it, and my impression is that it measures some
type of average current, some type of average voltage, and the phase
shift, and works out power as I x V x cosØ. It is failing to realise
that low power factor can be caused by things other than phase shift,
as is indeed the case with many PC power supplies (and integral
electronic ballast compact fluorescent lamps), which have low power
factor, but cosØ = 1 (almost).

You can find true RMS clamp on multi-meter in the used market for
$20-30US. That is also going to be good for lots of other things.

If it is a name brand the manufacturer will usually swap it out for a
rebuilt one for about $20-30 too so buying a broken one in a garage
sale for a buck is a bargain. I got one out of the trash and sent in
in.

 

[Jon D]

BTW, don't buy the Brennenstuhl one -- it's horribly inaccurate
for loads like PC power supplies. I also have a no-name Taiwan one
from Maplin, and that's OK. (Maplin used to sell the Brennenstuhl
one, but stopped some time ago.)

Um, I bought the Maplin Brennenstuhl. :-(

ISTR Maplins sold it in two versions: one with the mains plug above the
buttons and powered by two button cells. The other with the mains plug
below the button and powered by AA cells.

 

[Jon D]

BTW, don't buy the Brennenstuhl one -- it's horribly inaccurate

Oh dear, that's the model number of the Brennenstuhl one. Test it
with a compact fluorescent lamp, and if it reads 2 - 3 times the
power rating of the lamp, then it's as crap as my one.

I have an 18W fluorescent lamp and my PM230 reads just under 16W. Don't
know exactly what's in a fluorescent lamp but I would expect the
transformer and other things to need power in addition to the bulb so I
would expect a reading of 18+ watts.

I'm not entirely sure what's wrong with it. I did play with it for
a while when I first got it, and my impression is that it measures
some type of average current, some type of average voltage, and the
phase shift, and works out power as I x V x cos. It is failing to
realise that low power factor can be caused by things other than
phase shift, as is indeed the case with many PC power supplies (and
integral electronic ballast compact fluorescent lamps), which have
low power factor, but cos = 1 (almost).

I notice that the cells must be in the unit or the readings will be very
different.

I had thought the button cells on the unit merely kept the clock and
pricing data and that it was ok to power the display from just plugging
the unit into the mains. However I find there is a big difference in
readings (about x2) with and without the cells.



[also to sci.engr.lighting group]

 

[Victor Roberts]

I have an 18W fluorescent lamp and my PM230 reads just under 16W. Don't
know exactly what's in a fluorescent lamp but I would expect the
transformer and other things to need power in addition to the bulb so I
would expect a reading of 18+ watts.

If the CFL does not have proper Hg pressure control then the
power will drop when the system is fully warmed up.

--
Vic Roberts
http://www.RobertsResearchInc.com
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[Roy L. Fuchs]

I have an 18W fluorescent lamp and my PM230 reads just under 16W. Don't
know exactly what's in a fluorescent lamp but I would expect the
transformer and other things to need power in addition to the bulb so I
would expect a reading of 18+ watts.

A lamp does not have to be fully driven to light. It may be being
pumped at 12 Watts with 3 Watts of losses. The power module would get
a bit warm at that level, however.

 

[repatch]

Is there a way to measure how much electricity a computer is using? It
doesn't need to be exact, just a guide.

Is it as simple as saying "if it has a 400W power supply then it uses 400W
per hour"? Or is that just the maximum? is it per hour?

Basically, I just want to know roughly what % of my electricity bill is
due to the computer, what % is wide screen tv etc etc.

Sorry if this seems like a really obvious/stupid question...

Thanks.

Buy a meter. They are around $20-$30 at the local hardware store.

TTYL