Outrageous Electricity Consumption

Electricity MeterMy electricity bills recently have been horrendous. My bills being high were not a surprise when I was running computers for a business; it was a business cost, and I had made a commercial decision to run them 24/7.

I have now added a page with the scans of the PM230 instructions

The commercial decision was based on the (admittedly rare) unreliability of our broadband connection… not particularly the start-up time of the machines. I wanted to be sure that we captured as many emails relating to orders overnight as possible, in case we could not access the internet the following morning. If we went without the internet for a whole day, we still would not have quite enough information to complete the orders, but if we had the emails we would at least be able to progress all the administrative tasks involved in sending out exciting things like – bottles of ink and paper. I know, my business was exciting!

Anyway, for quite a while I didn’t change my approach to switching the computers off each night, but as electricity prices crept up and up, it became far harder to ignore. Additionally, I’ve been feeling a little bit skint, so dealing with it moved right up the priority list.

There were going to be two main approaches to saving electricity, one was the ‘simple’ way of just start switching everything off (that was sane to) as a rule. But, I don’t like the vague approach, and I wanted a better idea of which items were going to be the key ones to concentrate on; after all, How Much Electricity Does My XXXXXXXXX Use? (insert whichever item you choose).

With the computers, I thought that the way to do this was to find out exactly what hardware I had in the box, find the tech specs for each part, and sum the power consumptions; but that would not tell me an ‘average’ consumption, and possibly an unrealistic one at that. I really wanted to find out how much my TV consumes on standby – I don’t tend to leave it on standby, but with all the stuff we hear these days about it, I was interested to find out.

I started a search for some sort of power-meter that I could plug into a standard wall socket, plug a device into it, and it would tell me how much power the device used over time. Let me save you some bother… the correct search term to use is ‘Power Meter’ (possibly with ‘residential’ added on. In the USA, it seems a particular brand name for this type of device is ‘Kill-a-watt’. No such thing in the UK, but a Google.co.uk or ebay search with the term will probably get you something appropriate. I went for a Brennenstuhl PM230 Electricity Meter (for UK sockets), and it cost about £20.

I won’t go into the detail of what this device is capable of, but suffice to say it can show the current power usage (in Watts) and it can also track electricity usage over time (in kilowatt hours – kWh). It should also be noted that whilst the technical specifications allow for an accuracy of “+/-5% of measured value +/-10 Watts” for the wattage display (which is particularly significant if the measurement is less than 10Watts!), I did find the measurements repeatable for the majority of appliances and devices I tried it with.

Hard and Soft Switched Devices… and Back-EMF

I’d best just point out that some devices have power switches that physically switch off the power. If the switch is ‘off’, electricity physically can not flow past the switch, I refer to these devices as ‘hard-switched’ – the switches act in an equivalent manner to switches on the wall socket, and are almost the equivalent of unplugging the device from the wall.

Then, there are ‘soft-switched’ devices. These devices have some-sort of power switch, but in truth that switch is not directly connected to the power cable, but indirectly via some other electronic switch mechanism. I have a small stereo in my kitchen which is like this; I can turn it on by remote control or pressing the power button. In general, anything which shows some kind of power light, even when ‘off’ will be soft-switched.

Finally, there are devices which do not have any kind of switch at all; phone chargers are classic examples of this. If I remember my physics rightly, looking at the wiring for a transformer would suggest that electricity would flow freely between the live and neutral power lines. However, when no power is consumed from the secondary turnings of the transformer, something called Back-EMF comes into play which actually chokes the flow of electrons through the primary windings. I guess the details are not important, the summary is, a transformer will waste energy if it is not switched off at the mains or with a hard-switch (but it is not so much as if Back-EMF did not exist).

Cut to the Chase

Over time, I’ve tested the basic device power consumption that we are told cost so much electricity; phone chargers, TV’s on standby, and so on. Perhaps I can save you some effort; my device could not measure any electricity consumption when my TV was on standby, or for any of my phone chargers (mobile, or cordless DECT handsets) *See Footnote*.

But I did find many devices that did have electricity readings… even when they were ‘off’ (though as defined above, they were obviously ‘soft-switched’ devices:

  • A Minidisk player component of a stereo system – nearly 10W when ‘off’ – all other components of the stereo system had proper power switches – this device has a soft-power-switch which leaves it consuming electricity when not in use;
  • Altec Lansing 3-speaker system – 21 Watts when switched off at the speaker. The feel of the power switch suggests it is a hard-switched device, but it obviously is not (just to prove the feel of the switch alone isn’t proof of anything);
  • External IoMega HDD – 7 Watts when off;
  • Microwave – 7 Watts when only the clock was on, essentially the default standby mode;
  • Shredder – 10 Watts when not in use, although there is no power switch as such for this device;
  • Computer – 37 Watts after powering down using Windows-controlled shutdown. 3 of my 4 computers have power consumption of 30 – 37 Watts when they were off.

I personally believe that the most significant of these figures are those for the computers; that 37 Watts equates to a running cost per year of around £23, for each of three computers… that’s before I’ve even switched them on! Now that is crap. Those Altec Lansing speakers are pretty poor too, costing about £13 a year, before even using them.


Well, I guess the most obvious lesson to learn is that, whilst you will almost certainly benefit personally (and benefit the environment), by unplugging your phone chargers and keeping your TV off standby, the savings you will make by doing this could be undone if you leave your computer plugged in (even if it is ‘off’). Or maybe your stereo system, or speakers.

The thing I find most puzzling is that whilst 3 of 4 of my computers are using over 30 Watts when off, the other one shows no power consumption most of the time, and occasionally flicks up to about 7 Watts for about a second. Over an extended period of time, it seems like the average power usage is 0.007 Watts. Why can one transformer (granted, one for a laptop) need so much less power than another?

In the meantime, I am switching off (at the plug) all of my computers and screens when not in use, my microwave and oven, that minidisk player… and a good few other devices.


* Remember that just because the power meter did not show any power consumption when the TV was on standby (or phones were being charged) did not mean that they were not using power, they were. It was just that the power being consumed by those devices was too low for this particular power meter to measure.

New page for the Manual Scans

I have now added a page with the scans of the PM230 instructions.

24 thoughts on “Outrageous Electricity Consumption

  1. hi
    i wonder if you could help me i am in need of a popy of the instructions for the brennenstuhl Wattage and current meter PM 230 as i lost mine and i am having a hell of a job working it out

    thank you v much

    darren rhodes

  2. Hi,
    I found your blog via google by accident and have to admit that youve a really interesting blog 🙂
    Just saved your feed in my reader, have a nice day 🙂

  3. Hi Darren,

    I’ve sent you a separate email with some scans of the manual; watch out though, as it is not from ‘kebabShopBlues’ but another email domain…


  4. Hi, just been trawling the net to try and find some instructions for a PM230 and came across your blog, which makes for very interesting reading. I’m just about to embark on the same sort of study you’ve been doing and have the same problem as Darren (can’t find the instructions anywhere!). Just wondering whether you’d mind sending me a copy of the same file? Many thanks Tim

  5. Many thanks for the email, that’s really appreciated. The meter makes a whole lot more sense now. Thanks for all your help.

  6. Hi there. Enjoyed your article. I too am trying to find instructions for the Pm230. Could I also have a copy of the file? I would be eternally greatfull!



  7. Hi – I was looking for the instructions for my PM 230 and came across your site. Bought it years ago and I’ve found the gizmo but not the paperwork. Apologies – but if you could send me your scans – it would be much appreciated !! Don’t fancy reprogramming it without them.

    Thanks !

  8. Like the above found this site while trying to locate instructions for the PM 230. Did anyone find them? Would someone be kind enough to send me a copy? MalvernBry@yahoo.com

    Many thanks

  9. To kick-start the savings we are setting the thermostat at 78 or higher. I read that for every single degree one adjusts the thermostat, one saves 10% on electrical billing. We shall see.

  10. Hi

    same as all the others..looking for instructions for my Bennenstuhl meter. Again if someone can email me that would be great. Basically wattmeter has stopped working and I’m wondering if it just needs new batteries.

    If anyone’s interested I’ve set up a spreadsheet to record gas, electricity, motoring and flying and convert to Kg of CO2. You can enter readings whenever you remember or whenever you fly and the spreadsheet calculates period and cumulative daily averages and estimates annual CO2 consumption.

    I’ve been doing it for just over a year so now have a real annual measurement of our domestic energy use.

    Our average daily CO2 emission is 28.2 kg and annual is 12.8 tonnes.
    Electricity usage is just over 9 units a day.

    My daughter was serving in Gibraltar until recently so we made more than the usual number of flights last year making 6 person-flights to Malaga. We also did 19000 miles in a diesel Peugeot 306 (55mpg).

    Of the total CO2 emissions we are directly responsible for 19% was for electricity, 25% was for gas (CH/cooking), 36% was for motoring, and 19% was from flying.

    These estimates use conversion factors available from various websites and one of the carbon offset websites for flying.

    If anyone else has similar analysis it would be good to compare.


  11. Hi

    just found your download for the manual..so thanks for that.


  12. I am yet another person who has lost the manual for the PM230 and would much appreciate it if you could email me a copy

  13. What is it with these instructions? I lost mine within hours (perhaps minutes) of unpacking the meter … are they printed on self-destruct paper? Many thanks for being out there with a solution

  14. Excellent…
    I have just looked through the instructions, and it appears that if the consumption is under 0.02A, which is equivalent to 5 Watt, then it shows a zero, because it realises it is not accurate enough to measure such low values.

    I would hope and expect that phone chargers and similar are under this, but not by much, so the cumulative effect of a lot of these around the house could be as significant as your Altec Lansing speakers.

    My PC has a mains output which is turned off when the PC is turned off (hard or soft turn off). I am going to recable my PC peripherals (including my Altec Lansing speakers) so they are all wired in through this, so that they all turn off fully when the PC is turned off.

  15. How much brennenstuhl pm230 electricity meter?
    May I buy it from?

  16. Which way round do the batteries go?
    (The battery carrier and socket on the PM230 have no markings.)

  17. Used a powerbar years ago to shut off my computer, monitor, printer, etc. each time I wasn’t using it. Ultimately, the small internal battery failed, causing the computer’s clock to cease. It was an expensive repair that probably negated all the electricity costs I save. Don’t know about latest and greatest computers out today but food for thought. Really enjoyed the reading!

  18. Hi Bob,

    Yes – the battery on a computer can run-down and it seems that it would be more likely for it to do so when the mains power is off. The battery is, mostly, considered to be a user-serviceable part and can normally be replaced easily once the computer-case-cover is off. Having said that – I appreciate a lot of peopleget quite worried with these sorts of issues of technical computer support!

    Best wishes, and thank you for your comment,

  19. Thanks for these instructions. A life saver!

    Thought I had held down the set button for 5 seconds to wipe the accumilated price but obviously hadn’t

Leave a Reply

Your email address will not be published. Required fields are marked *