power supply question

5 posts
by rjcarneymt » Tue Nov 06, 2012 3:39 am
Hello all,

I just got my R-Pi, and want to make sure I don't blow it up right off the bat. I'm self-admittedly electricity stupid.

From poking around online, I understand that I need a 5V / 700mA supply with a micro USB connector. However, the only ones I have laying around are 5.1V and 5.25V.

Can either of these be used safely? And if not, can anyone point me in the right direction as far as an appropriate one that I can order, preferably in the US?


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by stinos » Tue Nov 06, 2012 10:31 am
Both will do fine..
I doubt there is any 5V charger delivering exactly 5V, they normally will give you more instead to make up for losses in cabling etc and after all the USB spec is 4.75 - 5.25 V. Also the board has a fuse and a voltage clamper as protection against too much voltage (well, within a certain range though).
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by redhawk » Tue Nov 06, 2012 12:12 pm
The PI's SoC is powered by 3.3v from the RG2 regulator so the input voltage isn't critical except for attached USB devices.
In any case you'll find that once the PI is running with USB devices the output voltage would drop below 5v even if your PSU was pumping out 5.2v.

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by ski522 » Tue Nov 06, 2012 12:28 pm
Short answer is yes, you're okay with those.
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by redhawk » Tue Nov 06, 2012 12:41 pm
In theory these power supply should be fine however in practice may not perform as well as expected.

To check the PSU run your PI with some attached USB device and measure the voltage at TP1/TP2, if it drops very low i.e. 4.2v then you may want to consider changing it.

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