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I've been having trouble getting my Raspberry Pi to work, and I found out that the power supply I was using had only been supplying 4 volts (give or take half a volt). I bought this one from Adafruit, which is made specifically for the pi thinking it would do the trick, but when I plug in my Pi and use my multimeter on the test contacts I'm barely getting 4.5v. Here's an even clearer image of the multimeter. With my previous power cables I was lucky to get past the initial boot up sequence. With this new one I can at least get to a command line, but attempting anything more intensive than launching vi causes it to overdraw and shut down.

At this point I've tried a number of power supplies, and none of them work, not even the one made specifically for the Pi. I don't know what to try next. Is this power faulty? Could it be a faulty Pi? I've had such bad luck finding a power supply that will deliver enough power I'm starting to think there may be some other issue causing the voltage to drop.

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5 Answers

Do you have access to a regulated power supply? I am currently using a 5V DC 1A wall wart to power my Raspberry Pi. You might be using the incorrect power supply unit. I am using the one similar to what you had bought from Adafruit. Test your Raspberry Pi without connecting wireless adapter or a keyboard. Determine the current drawn with your multimeter. It cannot be a faulty Pi since you are able to use it.

I tested the voltage levels on my Pi and I measured 5V. If you do not want to experiment different power supplies, it is best to determine the current drawn by lab power supply (They call it the D.C regulated power supply).

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I'm certainly no expert, but I run my Pi using the plug socket part from a spare iPad charger with the USB cable off my camera going from the iPad bit to the micro usb on the Pi and it works fine.

If you know somebody with an iPad (charger) it might be an idea to see if that works with your Pi.

I've found it so easy to power the Pi I do wonder if yours might be faulty.

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Without looking at the power requirements of the Raspberry Pi, i got mine to work just fine with a powered USB hub. I bought it because i heared that the Raspi's power supply can become shaky if both mouse and keyboard are plugged into it's 2 USB sockets and also draw power from them.

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That "shakiness" will probably be more to do with the keyboard and mouse drawing too much current, rather than low input voltage –  Andrew Nov 26 '12 at 18:11
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There is a polyfuse in series with the power. This can have quite a large voltage drop, so perhaps that is what you are seeing. The more current you draw (including the usb ports) the higher the voltage drop will be. Eventually there is not enough to function properly

It's possible that all the power supplies you have tried so far are not up to spec, but that seems pretty unlikely.

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The RPi has a polyfuse located on the back of the Pi, right next to the micro USB port. It is a fuse designed to protect the Pi from too much power, however, if it is bad it can prevent the Pi from getting enough power.

Use the guide on this page to test the F3 polyfuse. There should not be more than a .3 volt difference. Make sure you're testing your Pi with all peripherals removed - this includes ethernet and SD card.

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