Delivering 16 V DC From A Solar Panel, Continued

When the solar-powered PC is idling, the special M2-ATX power supply achieves a stunning efficiency level of 92.37%. If we load up the CPU or the graphics subsystem, efficiency sinks to 88.4%. Internal power consumption in the PSU itself varies from 5 W at idle up to 14.2 W under load.

These measurements bolstered our decision to go with a 16-Volt DC solution. Using conventional A/C power, the best PSUs achieve efficiency values of 87% under optimal conditions. This approach not only does away with energy losses inherent in two-stage transformation of output, it also does better at dealing with DC input than the best conventional PSUs do with A/C input. This PSU is built in the USA, and costs $80-90 - well-known mini-ITX vendor Logic Supply and automobile PC vendor SolarPC are good sources for this part in North America.

PSU connectors

Back side of the PSU circuit board

Power Supply Connectors and Components

1. Power LED
2. To motherboard on/off switch
3. To external power on/off switch
4. ATX connector (20-pin)
5. P4-12V power connector
6. User jumper settings
7. Positive voltage input (battery)
8. Ignition (switched battery, positive)
9. Negative voltage input (battery)
10. Amplifier control via remote on/off
11. Configuration for on/off timer settings

In cases where the power supply has to work at peak output for any length of time, the manufacturer recommends installing a cooling fan. We chose the Papst 512 F/2 using a 5 V adapter, which caused the fan to draw only 160 mW.