Raspberry Pi power consumption


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by K1lo » Mon Apr 30, 2012 10:49 am
Hi all! After being one of the lucky group to get a Pi a couple of weeks ago I"ve been fiddling around to see what this device is capable of. Today I had a chance to measure the power draw from the Pi at load and when idle and I"m really quite impressed. Short story – roughly two watts of draw at idle climbing to three and a bit at load. More details can be found here, but I"m very impressed, especially considering a SheevaPlug I tested against cleared five Watts easily. I"d be interested to hear what power draw figures others have been seeing. I"m using a Kindle wall charger as my power source.
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by plugwash » Mon Apr 30, 2012 11:46 am
With power efficiency and the Pi the PSU is key. A shitty PSU could easilly draw more power at idle than the Pi draws when running.
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by K1lo » Mon Apr 30, 2012 12:26 pm
With power efficiency and the Pi the PSU is key. A shitty PSU could easilly draw more power at idle than the Pi draws when running.

I can easily see that being the case. I can"t immediately think how to work out the efficiency (and thus impact) of the wall charger I"m using...
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by gjs » Mon Apr 30, 2012 12:26 pm
You are measuring the combined consumption of the power supply and the Raspberry Pi and using a plug-in "watt meter" which are notoriously inaccurate.

There are much more accurate and comprehensive power consumption figures posted on these forums.
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by K1lo » Mon Apr 30, 2012 12:33 pm
Agreed. I don"t have the spec sheet to hand for the watt meter, but I was assuming an accuracy of +/- 0.5W. There is also a distinction between technical specs for power consumption and their real world figures when you factor in (as you say) the power supply. Could you link the topics with more info?
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by jbeale » Mon Apr 30, 2012 2:29 pm
I believe 2-3 W is in the ballpark for what the Foundation claims about power consumption. The right way to measure the Pi's power use, though, is to look at DC voltage and current into the Pi. Although what you actually pay for is AC power, so the efficiency of your AC adaptor is not irrelevant. I have a "Watts Up? Pro" meter and I measured it to read about 3 W too low (!)  At work they have another of the same unit, which seems to be within about 1 W of correct.

Unless, I suppose you are off-grid and running the Pi directly from a 12V storage battery, for example... you'd probably have a 12V 1A USB car adaptor for that purpose.
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by abishur » Mon Apr 30, 2012 7:27 pm
I tend to consitently use 3.5-4.0 watts as measured by my kill-o-watt, but that is counting power loss through the AC->DC adapter.  But that's A) running at close to full tilt, B) Overclocking just a bit (I'm not tweaking the core voltages or anything, but I am forcing it to run a little hot), and C) using the full power available on both USB ports, using the Networking jack, the HDMI jack, and using the kernel that accesses the l2 cache.

All of which is to say, my numbers should be viewed as an upper power limit if you're really pushing your pi to the hilt.
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