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Phone chargers - the truth

How much is inside a phone charger?

One of the greatest dangers to society is the phone charger. The BBC news has been warning us of this since 2005:

'The nuclear power stations will all be switched off in a few years. How can we keep Britain's lights on? ... unplug your mobile-phone charger when it's not in use.'

Sadly, a year later, Britain hadn't got the message.

'Britain tops energy waste league'
  - and how did this come about? The BBC ram the message home:
'65% of UK consumers leave chargers on'
Charger Vader

From the way the BBC talks about these planet-destroying black objects, it's clear that they are roughly as evil as Darth Vader. But how evil, exactly? I had to find out.

How much power does a charger (left plugged-in) guzzle?

OneCharger0b I got a nice power-measuring meter and plugged in a Nokia charger. The power reading was Zero Watts. 0W.


I plugged in two Nokia chargers. Still Zero Watts.

ThreeChargers0b I plugged in a third charger (this one was for a Sony phone). Still Zero Watts.

FourChargers0b A fourth charger: this one was for a Toshiba pocket PC. Still Zero Watts!

FiveChargers00b I added a fifth charger: this one was for a Dell laptop computer. Still Zero Watts!

SixChargers200 I plugged in the three phone chargers, the laptop computer's power supply, the charger for a pocket PC, and a battery-charger for 4 AA batteries. Finally, the meter registered power! One Watt.

Hmm - to measure a charger accurately, a smaller meter is required!

But already we can make some interesting deductions. My measurements indicate that my phone chargers consume less than 0.5W when left plugged in. The total power consumption of the average Brit is 5000W. (Including car driving, home heating, and so forth, not just electricity.) So obeying the BBC's advice, always unplug the phone charger, could potentially reduce British energy consumption by one hundredth of one percent (if only people would do it).

Every little helps!

Can you think of any other things we could do that would reduce consumption by more than one hundredth of one percent?

titanic tea strainer Is there any chance that this emphasis on phone chargers is like bailing the Titanic with a tea-strainer?

Don't forget, the government's target is for a 60% reduction in carbon pollution...

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I've received a few comments about this webpage. One guy said I had done the experiment wrong because no phones were attached to the chargers. Yes, measuring consumption with fully-charged phones attached would be interesting too, but that doesn't mean I did anything wrong. I was measuring the consumption of chargers with no phones attached because the advice I wanted to assess was 'such idle chargers should be unplugged'.

Other people have said that the key assertion, 'phone chargers consume less than 0.5W when left plugged in', is incorrect. But it's true. Sven Weier and Richard McMahon of Cambridge Engineering Department did real experiments with accurate calorimeters and they found that a Standard Nokia charger (just like mine), not connected to the mobile, wastes 472 mW.

They also did the other experiment: the charger, connected to fully charged Nokia mobile, wastes 845 mW.

When the charger is charging a partly-charged Nokia mobile, it wastes 4.146 W as heat.

Finally, anyone who wants more detailed information about where the other 99.99% of our energy is going, and what we can do to make a difference, might like to read my book Sustainable Energy - Without the Hot Air.

David MacKay
Last modified: Fri Nov 14 12:09:39 2008