====== Power supplies ======

Power supplies tend to be noisy, inefficient and heat producing. All these are bad in a low cost educational environment, which is why the Locolab started to investigate in the wonderful world of power supplies. This proved to be more difficult than we thought at first. The issue came up, since we made our own computers, with our own [[hardware:casings|computer casings]]. These needed power supplies. The power supply we wanted had to meet the following criteria((we did not consider external power supplies, since these can be stolen too easy)):
  - High effiency (higher than 80%)
  - Small size (to fit in the box)
  - Low power (all our motherboards consume less than 30 Watts)

Until so far, we have been unable to get power supplies which meet those simple criteria! All three criteria are described here  and their difficulties:

  * High efficiency: There are power supplies available which have the [[http://www.80plus.org|80plus]] certificate which means that they have an efficiency of more than 80%. However, these are expensive and not for sale in Cambodia. All other power supplies have an efficiency of around 60% only, meaning that 40% is wasted on heat. Switching on a normal ATX powersupply with no computer parts attached to it results in a 9 Watt power consumption already!  
  * Small size: There are some power supplies which are smaller than normal ATX power supplies, but they tend to be non standard. This is not acceptable for the Open Schools Program, since we want all the parts to be available on the market, for easy maintenance and replacement. There is one exception, which is the FLEX-ATX standard (used in 1U rackmountable servers).
  * Low power: There are no AC/DC power supplies in the market below 100 Watts. The one you can see on the picture in the [[hardware:casings|casing section]] is a ten year old second hand 90 Watt power supply which came in a Compaq computer. Obviously these are not generally available

The local made Cambodian computers are now equipped with a 150 Watt Flex ATX power supply. Detailed measurements have yet to be performed, but the hypothesis is that the efficiency will be around 60%.