Farm Power (in Watts)

haysdb · Post by **haysdb** » Fri Jan 16, 2004 11:12 pm

I borrowed a Kill-A-Watt to measure the electricity usage of my folding "blade farm".

The five blades plus the Ethernet switch draw a total of 520 Watts.
The total watts would be less except for one odd board. Except for this one blade, the other four draw 75 to 91 watts each. The fifth blade draws 109 watts.

These are the numbers when the blades are measured alone, one at a time. When they are all running, the power usage goes up by about 50 watts, I don't know why. Perhaps it's just a "feature" of the Kill-A-Watt.

What's interesting to me is that this one odd board is my best board in terms of stability. Are these two factors related? Why would one motherboard use 18 watts more than another?

David

In addition to watts, the Kill-A-Watt also reports 6.5 amps, which didn't make sense. Watts=Volts*Amps, so 6.5 amps should equal 780 watts. In fact, the Kill-A-Watt can also report VA, which is reported as 780. So what's the difference between VA and Watts? This APC White Paper explains the difference.

lenny · Post by **lenny** » Fri Jan 16, 2004 11:35 pm

If I remember correctly the VA figure is what the power company is going to charge you with. So figure on burning 560 kW-Hours a month for your farm. Spare a thought for those poor folks out East facing rolling blackouts every time you finish another WU

Here in California that's going to set you back $78 or more per month if you run it at home (probably more since that alone goes above baseline). What are your rates in Kansas? You are one dedicated folder!

Edit: Just checked EOC to confirm my suspicion. Yup. It has to be you, my only threat currently

haysdb · Post by **haysdb** » Sat Jan 17, 2004 2:37 am

Lenny, fortunately the power company charges for watts rather than Volt-Amps, which I suppose is why electricity usage is expressed as Kilowatt hours rather than Volt-Amp hours.

I haven't seen an electric bill in awhile but I'm thinking we pay around 8 cents per kilowatt hour. 720 hours in a month times $.08 = $57 if the farm uses 1 killowatt, which is about what I expect the server and 7 blades to use.

I will keep it up as long as I can afford to, and as long as it remains fun.

David

Choy · Post by **Choy** » Sat Jan 17, 2004 1:36 pm

If you all can recall the electricity part of your physics courses, you can perhaps remember that there is active and reactive effect. Active effect (P) is the kind resistors uses and is counted in watt. Reactive (Q) is what inductors and condensators use and counted in volt ampere reactive. When you add them together (sqrt(P^2+Q^2)) you get the apparent effect (can remember the english word, so I direct translated it). This is measured in volt ampere. When you measure with a multimeter you get the volt and ampere and therefor get the apparent effect.

I think everyone pays for the active effect, since it is possible to compensate away the reactive effect.