Test to decide your bill saving priorites

  • wizzo227's Avatar
    Level 21
    I did something that as energy savers we're not meant to. I left an assortment of mobile phone chargers, camera small battery charger, and something ugly meant for small 5 Volt USB into a NiCd battery charger, all left plugged in at the wall for a whole week.

    They went through a UK mains multisocket extension from a plug-in energy monitor, so now I report on the total kiloWatt.hours (kWh) used by this group of things, plugged in all week and used occasionally, to charge the phone and the various batteries and for most of the week just doing nothing.

    0.004 kWh.

    That's right. I could run a 1kW fan heater for one hour with as much electricity as that lot would use in five years. We are all used to reading the energy saving advice to disconnect unused things such as phone chargers. This is Preliminary Spot Test Only: we should ask someone with a test group like Octopus Slough to try testing what they get. What do others who test find with their small chargers ?
    Last edited by DebF_EONNext; 24-07-23 at 20:00. Reason: remove featured thread
  • 9 Replies

  • Best Answer

    wizzo227's Avatar
    Level 21
    Best Answer
    self to self to do list: check calibration of plug in energy monitor at very low power. Use alternative contraptions to look for any background current at all into modern mobile phone charger while unused.

    Suppose that a million people all used 1kWh less of heating tomorrow. What I'm after is the comparison number. A million people saving a kWh tomorrow from less heating is worth the same as a million people switching off their 41.7 Watt large set top box of 2009 vintage. I don't have a newer one to test what the latest ones use. My assortment of small chargers though uses "too small to trust the measurement" less than the 41 Watt comparison figure; possibly more than two orders of magnitude less. Hence we might ask moderators here for more emphasis of "off-by-default" heating policy now that weather is warm enough to ask that of the mainstream households.

    I really would like to see it here; what does a professional test and measurement laboratory think of modern small battery chargers ?
  • retrotecchie's Avatar
    Level 92

    I don't think your power monitor is particularly accurate at low power consumptions, in the same way that your domestic electricity meter is also wildly inaccurate for loads less than 2A.

    That said, it's a pretty low figure.

    Most of the advice for pulling chargers or power supplies out of the wall to save money relates to the days when 'wall warts' were more often transformer/rectifier/regulator (linear) devices rather than the more modern SMPSUs we have today.

    However. a million people all saving those few watt hours soon adds up to much bigger numbers
    Don't shoot me, I'm only the piano player. I DON'T work for or on behalf of EON.Next, but am willing to try and help if I can. Not on mains gas, mobile network or mains drainage. House heated almost entirely by baby dragons.
  • wizzo227's Avatar
    Level 21
    No fault yet found in validation test of plug in energy monitor being used with a small ac/dc adapter. Here I describe a test underway:

    Some Ohms Law formulae and results are intentionally omitted because this test is well suited to secondary school science problems and disclosure might lose an opportunity for Learning By Doing. Safety-critical calculations are mentioned though answers are not given.

    The other various small battery chargers were unplugged from this plug-in energy monitor at a uk three pin socket.
    A 40 Ohm large ceramic power resistor on a brick was connected with screw terminals to the two wire output of a 12 Volt ac/dc adapter kept from a scrapped home broadband router of a previous year. The ac/dc is marked "240V ac" and "12Volts 1Amp" and after snipping off the nonstandard concentric barrel connector and stripping wires back to the copper, the positive wire was identified with a multimeter and marked red for future reference.

    The resistance of the power resistor was measured with a multimeter. This one measured at 40 Ohms where its label indicates 39.
    The resistance was connected to the small screw terminals and all four screws were checked for tightness.

    Theoretic power IV (Watts) expected at 12 Volts was checked by calculation against the maximum Watts power rating of the resistor and also checked to be well within the design maximum Amps of the ac/dc adapter. A factor of safety of more than two was calculated.

    The ac/dc adapter was plugged in. This one has a button "function" to be pressed a number of times to select what is shown from a number of things mentioned in its instruction manual. A multimeter to two of the screw terminals tested dc Volts and found about 12.03 to 12.07 Volts. The IV calculations of Watts and Amps at 40 Ohms were revised and it is of course still safe. The plug in power monitor at "kW" for power showed 4.6 Watts ac power used. By comparison to the calculated dc power used at measured Voltage, that was a bit more and was consistent with the ac/dc adapter having an efficiency approaching 80% at this modest power.

    By the way, this resistor gets too hot to touch. If you don't have a spare brick then you'd either need a rock or something else to leave hot things on. You might prefer to use a different resistor chosen to get less hot, because large ceramic resistors can be expensive, unless like me you take the lid off scrap appliances, at home and from other peoples' skips, and snip out anything recognisable which looks useful.

    Now for preliminary testing result, about which I can only say that nothing looks too wrong yet.
    Again pressing the "function" button on the plug in energy monitor to look at kWh and looking at a clock to get four hours,
    0.017 kWh was used in 4 hours.

    Suggestions for further test:
    Hot resistors sometimes differ from their room temperature resistance. This being a ceramic R at less than 100C, I'm not expecting much change, but it might have been better to have measured dc Volts and Amps. I'll just leave it as it is until tomorrow when I can look at the kWh at 24 hours.
  • wizzo227's Avatar
    Level 21
    No fault yet found in validation test of plug in energy monitor being used with a small ac/dc adapter. Here I continue a test underway:

    After 24 hours running a 12 Volt mains adapter (scavenged from a home broadband router wifi thingy) into a suitable resistor and using 4.6Watts from the wall, the energy monitor shows 0.096 kWh used. Whilst that is a bit off from 4.6 Watts x 24 hours, that is in my opinion indicative.

    I have disconnected the resistor to next test what it uses when left plugged in for a day with no load.
  • retrotecchie's Avatar
    Level 92

    Very thorough and I certainly appreciate the methodical approach and detailed investigation. Interestingly, I did some tests recently on some older equipment to compare differences between 'standby' and 'operational' and to find out whether unplugging at the wall made much of a difference or not.

    It turned out that the worst culprits for parasitic draw were devices with linear power supplies. My Kenwood hifi (1987 vintage) has a 'standby mode' which physically disconnects power to most of the components (you can hear the relays) but the tuner/control unit has a vacuum display clock and the ability to switch the tuner and cassette decks for timer recordings means that the beast is drawing around 11W continuously in 'standby'. The USB charger for my newer phone barely registers when not actually charging the phone, but the linear charger for my old Ericsson GA628 consumes half a Wh just plugged in with no load. The primary of a transformer is a fairly high impedance at mains frequency, but is still a direct connection between Live and Neutral and there will always be some quiescent current flowing in the primary circuit, even if no load on the output.

    But oddly enough, it was a switched mode 'brick' for an old Toshiba LCD TV that really surprised me. That drew almost 1W when not connected to the TV and almost 5W with the TV in standby. It also completely wipes out my ability to receive LW radio anywhere in the building if it is plugged in, so not only is it generating radiating harmonics in the 100kHz to 400kHz frequencies but it is back feeding those harmonics into the house wiring. A newer power supply...problems solved straight away.

    So always good to hear others report their investigations into these things 👍
  • DebF_EONNext's Avatar
    Community Team
    As always @wizzo227 your experiments reel me in, I've been going through so much more energy in the last week but haven't been using anything differently so I believe I have a faulty appliance (possibly the washing machine) I've been testing EVERYTHING in my home for the past few days and let me tell you it has been surprising! It cost me an extra 19p having the TV on standby overnight this doesn't seem like much but over the course of a year that's almost £70 now if you are like me and have more than 1 TV in the house (teenagers bedrooms etc) then it adds up, that is a massive amount of money for the sake of getting up to turn off a switch!
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  • wizzo227's Avatar
    Level 21
    How big is that 0.6(ish) kWh overnight TV, how old is it, and were you including set top boxes and the usual group of TV-related things ?
    Please note: many smart meters can optionally report in kiloWatt.hours (kWh) instead of in £ and pence, if you press the button to select that. £ and pence may be more familiar but introduce uncertainty from the different electricity prices in different regions and won't be right next year. I always prefer kWh.

    I'm lucky having no TV. I watched the countdown at spaceX Texas on YouTube on a Raspberry Pi to hdmi 24" screen, and those don't use much power.
    Last edited by wizzo227; 19-04-23 at 19:39. Reason: typo in kWh
  • wizzo227's Avatar
    Level 21
    A little more testing later, my ten year old Benq 24" 1920x1080 pixels monitor draws 45 Watts while on and bright, and less than 1 Watt while 'off' but plugged in and on standby. That is, for the 0.6kWh used by your TV overnight, mine can be switched on and in use for more than 13 hours, or on standby for many hundreds of hours.

    I've been looking at the total used by the screen and computers group, and six Watts to the home broadband is the most uneccessary part which I should switch off. That would only save me 0.07 kWh per night.
  • wizzo227's Avatar
    Level 21
    Springtime and there is more sun on the solar panels and more free electricity to test appliances with.
    Today I unboxed a brand new ,,, ....
    plain old electric cooker ring
    It is rated 1.5 kW and this one is nothing special.
    My first try cooking rice for with lunch in an ordinary saucepan used 0.122 kWh according to the plug in energy monitor.
    It might be possible to cook that with less than half as much energy used.
    Does anyone have a purpose built rice cooker to compare ?

    It is only 4p worth of electricity, but given how much of the rainforests are going to be left to clean up for us after 2050, we now ought to be careful with the small daily tasks like this one.
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    Last edited by wizzo227; 11-03-24 at 14:43.