Testing Raspberry Pi's Power Supply

Raspberry Pi requires a good power supply to function properly under full load conditions.It uses a micro B USB socket for drawing power which are used by many mobile phone chargers.It requires a DC power supply of 5V with a tolerance of +/- 0.25V and is capable of delivering atleast 0.7 Amps. Many of us get tempted to use the USB port on out PC, but that's not a good idea as USB ports can provide a maximum of 500 mA. Also you risk blowing the fuse of the USB port in your PC.(PC's and laptops uses a solid state poly-fuse which automatically resets after 2-3 hours of rest).To find out the best possible power supply for Pi, I performed a few tests:-

Testing at Full Power:-

testing raspberry pi with full power
For testing at full power I connected 1A power supply from my HTC mobile charger. In order to measure the voltage across the Raspberry Pi, two probing terminals- TP1 and TP2 are provided on the device.Next I used my DMM to get the readings without connecting any external load.As expected the reading was 5.12 V which is considered within the specified range.I was quite confident that using the same power supply the Pi could be powered with full load, seeing how as I have already done so to use the device.I got a reading of 4.96 V after attaching all the loads via USB Hub.

Testing at Low Power:-

testing raspberry pi with low power
For testing at low power I used a 5 V 450 mA USB supply from my MP3 player charger.This is well below the specified 700 mA that Raspberry Pi requires to function properly.Still I went forward with the test and results were a little shocking to say the least.Without any external load the reading from DMM was 5.02!. As the voltage was within the specified tolerance of 0.25 V, I tested the voltage with full load, and the reading came out to be 4.88 V!. As anticipated,even with all the peripherals under full load the Pi booted successfully.But the joy lasted only for a brief moment.When I tried to use my keyboard and mouse they were not responding.

The final verdict? Well if you are planning to run the Raspberry Pi headless, you might be able to skimp on the current, but if you are planning on running a full fledged Linux box you should consider getting a decent power supply with a rating of 1A or greater.