RE: [OT] Help with power usage calculation

["David Irwin" <david@xxxxxxxxxxxxxxxx>]

Hey all, new to the list, and know little about HA (but learning) and felt
=
I
could help here...

I can accept being told to go away and not butt in if required!!

> Alex Monaghan wrote:
>=20
> > As the electricity bill is in KW/h how would I convert=20
> usage when all=20
> > I have on the product specs is a single figure (for example=20
> my monitor=20
> > is rated at 150W and 5W on standby). If I can get to the same
unit=20
> > figure as the electricity bill, I can then work out actual=20
> =A3=A3=A3 cost of=20
> > having each device on.
>=20
>=20
> I suspect your bill is in kWh. Multiply the power consumption=20
> of your appliances by time to get the same units (ie 150W for=20
> an hour is 0.15kWh).
>=20

Just as a little more clarification 1kW/h means:
1 kilo	Watt			/hour
1 Thousand  (Units of Power)	per hour

So for a 150W device used for 1 hour it will consume 150W/h or 0.15kW/h

> >
> > For something like a PC where the PSU is rated at 300W (for=20
> example),=20
> > I guess it doesn't constantly draw 300W, could the usage be=20
> calculated=20
> > easily without actually plugging in a device to measure=20
> consumption ?
>=20
>=20
> Not really.

These are fairly cheap to purchase... for example "Plug-In Mains Power
&
Energy Monitor" =A325 from maplins:
http://www.maplin.co.uk/Module.aspx?ModuleNo=3D38343&TabID=3D1&source=3D15&=
WorldID
=3D&doy=3D16m3
And if you are really concerned, well worth the purchase - I found that one
of my device in my house was drawing 150W while in "sleep" mode
and 195W
when on, so now switch it off at the wall - that equates to a saving of
nearly =A3126 a year in electricity.
[calculation of before 150W x 23hrs + 195W x 1hr =A3133.04/year and after
1=
95W
x 1hr =A37.11/year (assuming that 1kW/h =3D 10p)]

Worth bearing in mind that these meters fail to read anything below about
2W, although this one can show total power usage in kW/h (upto 999KWh and
time period upto 9999 hours)

>=20
> > If I can do this, I can then work out how much cheaper it=20
> would be to=20
> > run an
> > LCD and provide full justification to SWMBO for replacement=20
> of monitors.
> > Maybe even justify some other new toys on this basis if I'm lucky
:)
>=20
>=20
> Unless you have a lot of very large CRTs which you intend to
replace=20
> with one LCD, I suspect you'll need another excuse :-)

Just to provide some numbers here, I am comparing to CTX products which are
equivalent in size:

EX700F - 17" CRT monitor:
Switched on:	75W
Suspend/Sleep:	4-5W (estimated)

S700B-1 - 17" LCD (TFT) monitor:
Switched on:	35W
Suspend/Sleep:	0W (or as close to... unable to measure with my meter)

That could be seen as a considerable saving when switched on, especially if
you have more than one computer.

>=20
> > How about calculating the use of things like power=20
> transformers (all they
> > say is the output voltage at X amps)
>=20
>=20
> Unless they are 100% efficient (Switch mode psus might manage=20
> 80-90%...), you'll need to at least measure the current going in...
>=20
> Jim
>=20

Again the best way to measure is by connecting a power meter.

Hope this has been of use!

Dave

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