Author Topic: Power consumption and economy.  (Read 2524 times)


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Power consumption and economy.
« on: May 11, 2006, 10:55:14 AM »
I was thinking about this last night, and want to share it with you.

A couple of times in the past I have been involved in projects where you had a wishlist of things to do or run, and a power budget to do it on, one example was a ruggedised computer that had to draw 11 watts.

My point is this, it is only when you really start to work on a problem like this, and need to tally every last individual item or component, that you realise how much power something draws, and where economies can be made.

Like I said, this occured to me last night, I was sat with the lights out having a last fag (cigarette) before bed, and looking at all the glowing LED's in my front room, two 21" computer monitors on standby, a cable router, an amplifier, and a total of 4 computers and one laptop all off but nevertheless drawing some power.

Add them all up, and I mean PROPERLY, and NOT "oh that will draw a few watts, but measure or look up the specs of EVERYTHING, and you will frighten yourself... in this house with everything "off" but not off at the wall socket and unplugged, I draw between 400 and 500 watts, that's a fair chunk.

Add it up, that's 12 KWh per day, or 4.38 MWh per year. If we assume a Lister will burn a gallon of fuel to produce 8 KWh, that totals an astonishing 547.5 Gallons of diesel per year, over ten gallons a week, WELL over a gallon a day, just to keep shit on "standby" and to run items like cable modems with "inconsequential" power drains, even though there were no running computers being fed by said cable modem. Don't forget fridges, any domestic white goods with a clock, clocks themselves, nightlights, central heating control systems, the list goes on, and it ALL adds up, and unless you have actually run the numbers it all adds up to a hell of a lot more than you would believe.

The projects that I have done, such as the 11 watt computer (and another 60 watts for a direct sunlight readable 12" touch screen TFT, really really really concentrate your mind on these factors, and until and unless you take this approach, you really are stabbing in the dark and pissing away energy at a rate that would frighten you, if only you realised it.

That 12 KWh per day is way too little to run a Lister for, unless you "buffer" the __efficient__ (eg 70% loaded) generation capacity of the lister with something like an inverter bank (but then you have to add conversion losses and the power consumed by the inverter itself running 24/7) which will take you up to say 15 KWh per day, or 6 hours per day running my 2.5 Kw Start-o-matic.

What is REALLY apalling is when you compare this with my "obvious" power uses.

Electric light from low energy bulbs. 1.5 KWh per day
Electric Fridge 2 KWh per day
Hot Drinks 2 KWh per day (I drink coffee like it is going out of fashion)
Vacuum cleaner etc 1 KWh per day
Cooker 2 KWh per day
No washing machine etc

So that lot adds up to 8.5 KWh per day.

Add in my computers when running 5 KWh per day


it's that "dripping tap" thing all over again.

Simply by turning shit off at the wall when not using it, I can cut my energy consumption in half, which means half my lister (if I was using it for that) running expenses, half the inverter and battery bank capital cost and running expenses.

Yes, I have more computers than most people, but I have less white goods and other electricals than most people, so while standby account for half of my daily consumption, I should suspect that if not half, it is at least one third for most of you.

But let's say it is half.

You can buy a 6/1 and 5 Kw head, instead of a 12/2 and 10 Kw head, how much WVO will that saving buy you?
Original Lister CS 6/1 Start-o-matic 2.5 Kw (radiator conversion)
3Kw 130 VDC Dynamo to be added. (compressor + hyd pump)
Original Lister D, megasquirt multifuel project, compressor and truck alternator.
Current status - project / standby, Fuel, good old pump diesel.


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Re: Power consumption and economy.
« Reply #1 on: May 11, 2006, 04:00:30 PM »
I agree, Lots of stuff on stand-by S**KS, and most of them "also" have clocks.
WHO decided EVERYTHING with a plug NEEDS a CLOCK!!! (I think someone else here mentioned this before).
BTW, clocks with the wrong time drive my wife nutts.... ::)
Alas.... :-[



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Re: Power consumption and economy.
« Reply #2 on: May 11, 2006, 04:08:07 PM »
Those are known as phantom loads. When I design my house electrical system, items like these will be on switched outlets so for example the entire home entertainment can be turned off with the flick of a switch.
2004 Ashwamegh 6/1 #217 - ST5 just over 3k hours.


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Re: Power consumption and economy.
« Reply #3 on: May 11, 2006, 06:32:18 PM »
Yes, phantom loads.

The nice folks out at (nice alt/renewable energy mag) I think coined the term a few years back.  Switched outlets are terrific.  Short of that, a powerbar can really tame the phantom loads.  The entertainment center and computing center are the two biggest offenders not counting refrigeration.  At least when the refer is "on" it's doing something. 

A "kill-a-watt" meter is invaluable for measuring actual phantom loads and a hundred other goodies.  They are about 35 US dollars.

That was the convincing factor for dumping our old desktop computers and switching to laptops, 1/4 of the energy use.  Plus I got a nice laptop out of the deal.

Finest regards,