Selecting a Power Supply
In my original version of this article, I used the Carnetix
PNX-P5V linear regulator. The article goes in-depth on the installing the PNX-P5V in the Sheeva Plug's case. I later realized the PNX-P5V was a terrible idea. Heres why:
In the simplest terms, a linear regulator works by taking in a high-voltage and "burning off volts" to reach the desired voltage. What does this look like for efficiency? Terrible. The average power consumption of the plug is 5 watts. That means 5 volts at 1 amp. To produce this from a 12 volt input we need to burn off 7 volts at 1 amp. This brings the total power consumption to 12 volts at 1 amp. 12 watts in, 5 watts out. 41.7% efficiency.
Switching regulators do significantly better. They are able to achieve efficiencies of over 90%, however they require more components and thus take up more space. I now use and recommend the Mean Well SD-50A-5 which can pump out 5 volts at 10 amps and has a wide input range of 9.2 volts to 18 volts. Perfect for a car. 50 watts is far more power than neccessary but I chose to use it as a power supply for many other devices
as well. To cut down on cost and size I can also recommend the 15 watt SD-15A-5, which matches the AC adapter's output specs exactly or the 25 watt SD-25A-5 which gives you more room.
As a final note on power supplies, if you only intend to run the sheeva plug when the car is running, the PNX-5V is not a bad choice. Minus its terrible efficiency, it served me well for over a year. However, my Sheeva Plug runs off of my car battery 24/7 and in that situation, 43% efficiency just doesn't cut it.