Sustainable Automatic Power Supply & Sockets Shutoff




About: I am a University of Edinburgh electronics engineering student.
Have you heard about standby power use?

This is when you turn your game console off from the remote control and think it does not consume any power from the grid ... this is wrong ... check this list below that shows the amount of standby power usage of some appliances:

        Appliance: (Range from Min to Max)(Average consumption of all sampled units)

  • DVD player:   0W to 10.5W;   1.5W
  • Subwoofer:   6W to 21W;   11W
  • Game console:    0W to 2W;   1W
  • Audio minisystem:   0.5W to 24W;   8W
  • LCD computer display:   0W to 4W;   1W
  • Notebook:   1W to 26W;   4.5W
  • Scanner / Printer Inkjet:   0W to 10W;  5 W
  • Set-top box Satellite:   7W to 33W;   16W
  • Power tool cordless:   0W to 4.5W;   2W
  • Microwave oven:   2W to 18W;   3W

Remember that these figures are true when the unit is off, but plugged into the grid i.e. you don't use your microwave oven or you pressed the off button on the TV remote control. If you work on the PC it could draw hundreds of watts from the grid. (Whole table here:

Lets say the average notebook draws 5W when it's not in use (it is turned off, but the battery charger remainss plugged) - i.e. the times when you are away from home or you sleep. Your audio system will consume 8W and the printer 5W standby power. This will roughly be during half or 2/3 of the day, so:

(5W+8W+5W) * 12 h/day * 365 days = 76 896 Watt-hours per year ... 

Now if you have 2 or 3 PCs the result multiplies by the corresponding factor.

And dependig on the local electricity price this equals to $7-10 per year per one PC set only. I am not trying to make a point about how you can save thousands here ... it is more about raising awareness around the standby power use.

A quote from Information and Electronic Technologies: Promises and Pitfall, 2004:

"Estimates of standby power consumption in the European Union (EU) range between 5 and 10 percent of total residential electricity consumption. Standby power is also consumed in commercial buildings (by office and building equipment and appliances, e.g., personal computers, copiers, phone systems, hot-water pumps, central computing devices) but is not yet well documented. A theoretical investigation (Menti 1999) suggested that standby consumption should account for less than 10 percent of total consumption in commercial buildings. However, actual measurements of 32 building appliances in Switzerland (Menti 1999) show that an average of 36 percent of total consumption is due to standby consumption at night (between 20:00 and 6:00) and during weekends."

Of course it is impossible to unplug everything that you don't use from the grid .... except from the frige apparently.

I am challenging you how you can design sustainable tools that fix these issues locally.

I designed a simple, very very simple circuit that detects when you turn your PC on or off and automatically turns the power supply on/off for you. Not only it does turn the power supply automatically on and off, but it can also do the same with the printer, speakers, your desk lamp ... or anything else that is powered from the socket  :)

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Step 1: How?

All  you have to do is plug a USB cable into your device - as simple as that.

If you lack free USB ports, you can use a USB hub, this is also fine.

The Sustainable Automatic Power Supply & Sockets system will be triggered by the +5V signal coming out of the USB cable when the PC is on.

Now it's only up to you whether you will plug your speakers, printer, desk lamp or maybe all of them into the Sustainable Automatic Power Supply & Sockets and start conserve power immediately.

I would like to hear if you like/dislike the design of my project. Do you think it adresses the sustainability theme or you wouldn't bother this much about the small things in life?

Step 2: Parts List

To do the Sustainable Automatic Power Supply & Sockets you will need:
  • Extension plug
  • USB cable
  • Prototyping board
  • 6VDC relay x 2 - relay must be rated for at least 2A at 120V AC for the US or 2A at 230V AC for the EU (depends on the grid standard in your country)
  • Diode - N4007 is ok
  • LED and a resistor above 2 KOhms (optional)

Step 3: Unplug. Open.



Now open the socket extender.

Step 4: Schematic

I have drawn the schematic for you.

The USB cable supplies 5V that switch the relays on. The LED is just to unform you that there actually are 5V on the USB cable and you have it plugged into the PC. Note that the diode across the +5V and 0V must be there! This is to do with energy "released" from the relays when the power supply is turned off. This excess energy will do through the diode, not through your PC.

Check the datasheet for the relays that you want to use.

There should be two terminals that power the coil, two terminals that are shorted and they become open circuit when the relay is powered, and two terminals that are open circuit and short when power is applied. We are interested in the last ones - they will connect the high voltages to the sockets when the relays are powered up.

Step 5: Power Sypply to the Relays

Cut small pieces of the prototyping board and solder the relays to it.

Attach the power supply cables to the relays. Polarity is not important at the relay terminals.

Step 6: Detach Metal Plates

Cut the cables leading to the metal plates for the Live and Neutral power lines.

Detach the metal plates off the plastic part.

Step 7: Solder Metal Stripes to the Relays

Solder the little piece of cable that you left on the metal stripes to one of the relay terminals referring to yhe schematic.

At this point it is good to note that soldering is not the best solution. Bigger relays have bigger contact plates and cables are not soldered, but crimped and then connected!

I took an image from google to show the crimping to you.

Step 8: Solder Power Lines to Relays

It is time to solder the power lines to the other terminal of the relays. Keep the colour the same.

Step 9: LED & Power Connection

Solder the rest of the circuit.

Step 10: Fit All In. Attach USB Cable.

I drilled a hole on the side of the socket box to fit the USB cable through it. Then a cable tie is used to restrain the cable from being pulled out.

Solder the final cables adhering to the circuit diagram.

Step 11: Glue & Close

Use glue to keep the parts tight.

Place the 5V circuitry far away from the high voltage. If needed, use some insulation material to isolate the low and high voltages.

Step 12: Finally!

Done! It actally looks so discrete that I like it. I think it is beautifull and most importantly, it works!

Now enjoy your PC day and night and don't forget to unplug the power supply socket after you switch the computer off .... or wait ... no, there is no need for that ... why would you bother unplugging it now ... your PC charger will use exactly 0W from the grid when the PC is off! It is the same with your music woofer and the printer! How cool! It is automated to do so!

Please share your comments and ideas. Thanks!

P.S. don't ask me why I decided to put the lams stickers on the pictures ... I am not sure ... I just wanted some colour.

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    68 Discussions


    2 years ago

    Nice idea. Same can be done wirelessly using the below instructable


    5 years ago on Introduction

    excellent! I guess this instructable's materials and supplies can be applied in 220V European plug....can you inform me if anything changes....(i guess the diode bridge must be for 220V) but what else....


    6 years ago on Introduction

    One final thing before you plug your TV, surround sound system, lamps, halogen heater, electric drill etc. into this: take the current rating of your relay (eg 1A), multiply it by your mains voltage (230 in Europe, 110 in USA) and that is the maximum safe wattage for the entire power strip. For a laptop charger and a small desk lamp it's probably fine but a desktop computer, LCD monitor and sound system together could well be over the maximum wattage.

    This is easily solved with higher rated relays, but make sure the combined current draw of the two relays isn't higher than the 500mA you can draw from one USB port.

    This is still a great idea and a very neat solution to the problem of phantom standby power usage.

    1 reply

    Reply 6 years ago on Introduction

    Yes, that is absolutely true! Thank you for the comment on my work :)


    6 years ago on Step 12

    Very nice man! Although the use of the kickback diode isn't necessarily required since the outlet is actually isolated from the 5V relay circuit, it is good habit. Only other thing is to maybe run spell check on your instructable and you're good to go! lol. Very easy and simple to do. :)

    2 replies

    Reply 6 years ago on Step 12

    If you don't fit the diode, you may find your usb port will fail, or worse your lap top. You should always install diodes across relays. Injecting several tens or even hundreds of volts worth of back EMF into equipment, is generally regarded as a bad idea.


    6 years ago on Introduction

    A couple of things bother me about this project: 1) The 5 volt lines come much too close to the mains inside the plugs unit. They could provide a certain amount of 'noise' to the d c circuits and, if shorted, could supply your USB +5 with totally uncontrolled line voltage. NOT A GOOD THING! 2) The extender outlet, probably marked at 10 or 15 amps, is now good for a maximum of 2 amps (the value of the two relays). (Two 2 amp relays in parallel or series still are adequate for only 2 amps) The load on the extender needs to be calculated as if everything plugged into it was on at the same time. It would be better to use a larger current relay (15 amp) to control a single outlet for this extender to plug into. Also, IMHO, soldering is always better than crimping if done properly!

    2 replies

    Reply 6 years ago on Introduction

    You are right about two relays in series. However, in parallel they are theoretically good to double the rating of a single relay. However, due to inconsistencies in manufacturing and uneven wear during use, the resistance across the two will undoubtedly be slightly different. Because of this, they are not actually good to 2x the amps of one, but are could easily be 1.95x


    Reply 6 years ago on Introduction

    This would be true in a current carrying capacity. However, due to imperfection in transfer, would not be true in a switching application. One relay or the other would invariably contact or release before the other (although only very slightly) and would result in only one carrying the whole load at the worst possible time, that of surge or spike.


    6 years ago on Introduction

    If it needs 2 relays for safety, there is a little snag - you have no idea if one relay has welded its contacts closed. Now you only have one relay and you don't know that the safety is compromised. I''ve even seen a sealed relay with a solder ball rolling around inside and shorting things. Yes, shorting things - meaning the mains and the 5V could get connected. It's already been pointed out the clearances between mains and 5V on the relay terminals are far too small for safety.

    However, the criticism of the possibility of overloading the relay contacts is very simply overcome in the UK version - just put a suitable fuse in the mains plug, preferably adding a label stating the correct fuse value.


    6 years ago on Step 12

    It looks like this will only work with a laptop that has a battery installed. Your comments indicate PC which would need a 5 volt source like a start button installed on the strip.

    1 reply

    Reply 6 years ago on Step 12

    Well yes, not a desktop PC but a laptop PC. And the laptop must have at least some charge in the battery in order to power up the USB ports.


    6 years ago on Introduction

    Hi there,
    I'm using this "gadget" for more than 7 years..... but it is built a little different.
    Because my computer case is always open, I use one free hdd power plug, from which I extract the +12 Vcc.
    This 12 Vcc energize an relay which consume less than 2 mA. This one interrupt the main 220 Vca which it's used for my monitor, auxiliary 12 Vcc, audio line, printer and router.
    All this time I use this "instalation" never fail, the USB socket in my computer it's always "ON" even the computer is off but connected to main 220 Vca.
    I don't have any schematic right now but if there is someone interested, I will publish it.
    Regards from Romania!!!

    3 replies

    Reply 6 years ago on Introduction

    Hi Florin,
    I am "almost" certain you are talking about a tower PC, therefore I for sure would be interested in looking at your wiring/schematic. It would be used for 110VAC in the USA.