# Power Consumption

Discussion in 'General Discussion' started by smoove, 24 Jul 2006.

1. smoove

# Posts: 5,392

How would i workout how much money my pc is costing us on our electricity bill per week?

Say it draws on 200w for 8 hours a day, for a week? How would I figure out how much im charged per 1 unit of electricity?

Thanks.

2. Jonny69

# Location: Kapitalist Republik of Surrey

You'll be charged about 9p per unit which is 1KW/hr

so you're drawing 1/5KW x 8hrs x 7days x £0.09 = approx £1 per week

Not exactly that simple because usually the first X number of units is charged higher so it's probably closer to £1.25

3. fatmas

# Location: Swindon

*Does calculations...*
No Idea.
Sorry.

4. Scott Salisbury

# Location: Newcastle, UK

If I have a 480w power supply, when the PC is switched on, is it constantly using 480w's ? Or does the power it uses vary on what components I have etc?

5. smoove

# Posts: 5,392

Is that all? I would have thought it would have been in the region of £5 per week.

6. Ricochet J

# Posts: 12,906

Q = IV
V = IR
R = (ρl)/a
therefore
Q = (I²ρl)/a (thats (current squared * resistivity * length) all divided by cross sectional area) (where Q equals 1 unit of charge)

7. fatmas

# Location: Swindon

Your not always using 480w's of power. It really does depend on the PC.
Well I think it does anyway :-S

8. Jonny69

# Location: Kapitalist Republik of Surrey

Yeah it depends on the PC. My laptop draws a lot less than a hulking Athlon dual core with two SLI graphics cards, a pair of Raptors and neons.

9. fatmas

# Location: Swindon

Yeah that makes sense. Have fun running a PC off a battery.
Even a lot of UPS's only last about 20-40 minutes...

10. Jonny69

# Location: Kapitalist Republik of Surrey

And don't forget it'll add about £3 to the bill each year by just being left plugged in and not switched on. The PSU draws about 5W when in standby. This is also the case for your phone charger, the little lights on the front of the video, DVD player, stereo, digibox, monitor, microwave oven etc etc. you can save over £50 a year by just unplugging stuff overnight.

11. Pho

# Location: Derbyshire

Best bet would be to buy one of these 'Energy Cost Meter' things for £20 or so (theirs some cheaper £10 ones too)

12. pinkacidbootson

# Location: Rhone-Alpes, France

This website allows you to calculate how much power your PC uses (peak usage). Even if your power supply is 600W, it won't use 600W all the time, if at all.

13. cobxx

# Posts: 276

Worked it out a while ago, it's really not as much as you would think. Sure people with pelts are slightly more conscious of price though

14. cyborg

# Location: Belfast

I was always interested in how much power my pc draws by being on at the wall but shutdown.

With powersupplys the wattage (which is voltage times the ampage) that is drawn is only what the device is drawing. This is why as long as you use the same voltage you can use a much larger powersupply to power something without blowing it to crap. (6A PSU for something that only needs 3A)

15. clv101

# Location: Bristol

I have one of those and this is what I measured with it: http://uk.theoildrum.com/story/2006/7/1/1033/23099

Regarding the PC:
System unit = 180-270 (idle-load). Call it 200W
Monitor = 85-95. Call it 90W

But also note the standby consumption:
System unit = 22W
Monitor = 27W

So, 8 hours on would be:
System unit = 8 x 200W = 1.6kWh
Monitor = 8 x 90W = 0.72kWh
Total = 2.32kWh, at 9 pence /kWh that's 20.9 pence per day.

Should also look at the 16 hours standby (off but not off at the wall).
System unit = 16 x 22W = 0.352kWh
Monitor = 16 x 27W = 0.432kWh
Total = 0.784kWh, at 9 pence /kWh that's 7.1 pence per day.

So in total that's 28 pence per day or £70 over 250 working days a year.

The system unit is an Intel Pentium 4 2.8C running at 3GHz with an ATI 9800PRO graphics card and four hard drives. The monitor is a 21" Sony Trinitron.

For my next system I'm looking at a Core 2 duo due to lower power consumption for the performance and the 7600GT which seems to hardly need any juice at all!

16. Jonny69

# Location: Kapitalist Republik of Surrey

That's really interesting to read clv, I was being conservative with a 5W figure for standby but it looks like it's a lot more than I thought. No wonder the bill was so high last time! I'm quite tempted to buy one of those power meters.

17. zetec452

# Posts: 9,454

Those power meters do indeed look good.

Its interesting how much more power a pc running seti would cost.

18. PeterNem

# Location: NJ/NY, USA

The power supply won't be 100% efficient... let's assume it's only 75% efficient.

Therefore to output 480watts it will need to use ((480/3)*4)watts = 640 watts

HOWEVER... it will only draw as much power as it needs.

If you're sat idling in windows, your CPU won't be working too hard and neither will your graphics card (two of the biggest users of power). Also your drives will most likely have spun down.

It'll only go near maximum useage when you're doing something really intensive like gaming. Even then though it'll only use what it needs, which could be 400 watts, it coud be 480 - it depends what you have in your system.

19. smoove

# Posts: 5,392

Another person in the hardware place just said this:
I take it thats incorrect?

20. clv101

# Location: Bristol

no, of course it's right - the PSU will draw what the components in the system require plus a bit due to inefficiency. Use a 300W or 600W (of the same efficiency) on a system whose components only draw 100W and the total system consumption will be identical.