kwh

[srp]

Has anyone else used the pluging power and energy monitor from maplins ? Does it measure the same as on the electricity meter ? ( Ive just got one for my pc..)

Simon

[BigWallop]

Both types of meter only measure the current (Amps) and the Voltage to give a rough idea of the power (Watts) the appliance uses. These little individual ones can sometimes be useful if you want to argue with the Leccy Co. about a bill. :-P

Voltage (V) multiplied by Amps (A) = Power (Watts)

[Dave Plowman (News)]

To measure how much the PC is using? It will tell you its power consumption in watts on the back. Although this is likely to be a maximum, I doubt it's that far out as an average. Especially if you include a CRT monitor.

[Set Square]

I've got one which I bought at MachineMart - but is probably similar, if not identical, to the Maplins device.

Mine gives believable readings when items of known power consumption are plugged in. I haven't compared it with the electricity meter. This would be very difficult in practice, because you'd have to ensure that *nothing* else was on at the same time. In our house, there are always freezers and power supplies for DC devices running.

[Stefek Zaba]

Well... PC mfrs have little incentive to put an accurate, representative, normal-case power consumption figure on their machines. OTOH, they have one incentive for putting a Big number on (Big = Better: This One Has A 400W PSU, This One Is Only 250W, So The 400W Must Be Better - More Powerful, More Room For Expansion, More To Boast About), and a contrary reason for putting a Small number reflecting Green Credentials - in which case they'll put a "takes as little as 20W in standby on a good day with a following wind" label.

The more likely of the above is seeing the max power rating of the PSU. In reality, a "domestic" PC with one or two hard drives and an "ordinary" CPU will take sthg in the 150W-250W range, with another

30-50W for an LCD screen and maybe double that for a CRT.

The Maplin box won't give especially accurate figures for a PC, because of the "weirdness" of the switched-mode PSU - unlike a nice resistive load like a lightbulb, you can argue for hours about how far the "real" power consumption of a PC with a SMPSU is compared to its supp-voltage x measured-current taken, and go on for longer still about peaks versus idling (are you running Prime95 while MP3-encoding a 100GB collection of music, striped across 5 10,000rpm HDs, or just doing Usenet?). Measuring the heat produced over an hour of representative running would be just about the most accurate way of measuring the power consumed, if you were really deeply interested!

Stefek

[Andrew Chesters]

Interesting idea! I might just drop my PC into a bucket and see how long it takes to boil 10l of water. HeHe :-)

[srp]

Thanks for the replies, my PC is a home brewed thing , it was only one of the things i wanted the monitor for anyway. Currently it's measuring the KWH of my electric blanket.. ( 0.06 kwh for 1 night!) It seems to give reasonable readings. With a kettle/ heater it was the same as on the lable of the appliance more or less. It's quite useful for checking how much an overnight heater is using as well.

I don't know how accurate the power factor measurment is on somthing like this though, I was wandering since this is important to the KWH accuracy isn't it ?

[Stefek Zaba]

Not that accurate, hence my wibbling on about the power factor of SWMPSUs. If what you want to know is the effect on your electricity bill of leaving the PC on, then what's important is how your meter reacts to your PC as a load, and that's most directly measured by running the rest of the house load constant (e.g. off, as far as practicable - fridges and freezers stay cold for several hours with their power off, btw) and having the PC (a) on in representative use, and (b) off. If you're happy watching the disc on the meter (assuming it's not an all-digital one!) go round manually, and doing sthg with the moral equivalent of a stopwatch, you can get an accurate reading in a couple of minutes. If you want to use only the figures on the dial, you need to use up enough juice to reduce the effect of the limited resolution of the digits.

[srp]

hmm that going to be a test for when I'm *really* bored then, because of the amount of devices plugged in on standby . not to mention my sky

• .. Do some electricity meters behave differently then ?

[Stefek Zaba]

You only need the difference between base-load and base-load+PC. It's worth turning off things with thermostats in 'em, as they'd produce unwanted variability - but all those things on Standby can just stay there while you take the "PC On" and "PC Off" readings.

As for different meters reacting differently to different power-factor loads - I'd expect variability between the older electromechanical style and various models of all-digital meter. But if what matters to you is what your PC running costs are, you're interested only in the response of your domestic meter, since that's what you're being charged for.