

HN, can this be true? Charger that turns itself off when phone is not connected - pullor
https://www.kickstarter.com/projects/encompass/asmo-charger-the-worlds-first-truly-intelligent-ch

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FlyingAvatar
This can be mostly true already. If you look at Ken Shirriff's analysis of
chargers here:

[http://www.righto.com/2012/10/a-dozen-usb-chargers-in-lab-
ap...](http://www.righto.com/2012/10/a-dozen-usb-chargers-in-lab-apple-
is.html)

The best charger that he analyzed was a Samsung oblong charger that had a
vampire draw of 18mw. At 18mw, if it was plugged in all year without doing any
charging, it would consume a total of .12 kilowatt-hrs of electricity.
$0.01/yr is pretty close to zero power use. There's no theoretical reason that
figure could not be improved upon.

However, it is probably the wrong end to optimize on. From the same post,
you'll see that the BEST of these chargers was 80% efficient under load,
meaning when it's actually in use, it's only putting 80% of its draw into the
device. If it were charging only 1 hour per day, at its in-use draw of 2.4A,
21 kilowatt-hours are lost per year doing the actual charging, at a cost of
$2-3 per year (in the US).

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joosters
Note that 'dumb' USB chargers don't use anything close to their charging power
when idle. See Ken Sheriff's fantastic USB charger teardown -
[http://www.righto.com/2012/10/a-dozen-usb-chargers-in-lab-
ap...](http://www.righto.com/2012/10/a-dozen-usb-chargers-in-lab-apple-
is.html)

In that article, he measures the idle power usage of a bunch of chargers. Some
use as little as 19 milliwatts. The electricity cost of leaving that charger
plugged in all year is miniscule.

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baddox
I don't see any reason it couldn't be true. Just put a relay inside the
charger, and when the phone is plugged in, steal enough power from the phone
to set the relay. When the phone is unplugged, the charger's circuitry detects
that, and sets the relay. Of course this wouldn't work with a completely dead
phone battery. There's probably a clever way to get around this, maybe by
utilizing the resistance between pins when a phone is plugged in, but I doubt
that's worth it in practice (edit: I read the page more closely, and it turns
out they just have a manual button for this; clever indeed).

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zxcdw
What is the problem being solved which makes it possible to do this? Or, in
other words, why don't we have this as a standard way for chargers?

Is it cost? I understand nothing about electronics really, but I'd guess at
least one way to do this would be a microcontroller polling the wire and
controlling a relay to turn the device on/off, no? I repeat, I understand
nothing of these things. :)

~~~
baddox
I would guess cost and the fact that normal chargers use very little
electricity when in standby.

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raverbashing
Well, it can be true. It would be in fact not to difficult, but the issue is,
of course, cost (and maybe turning it on again when the device is plugged
again)

Also, a regular charger does not use the same amount of energy with the device
charging as it does with the device off, it's wasteful, surely, but not as
much as people think.

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quarterto
IANAEE, but regular switching power supplies use negligible power when
nothing's drawing current.

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incidence
At least ASMO charger is firesafe, unlike dumb chargers. And good to see Oulu
on the map too, backed this one.

