After playing around with different fan speeds we found that a speed of 20% gave some air flow with very little noise so this was used as a base speed for when the power supply is cold. Once the heat sinks reach 30°C the speed is increased to 40% and then gradually increased at 5°C intervals until it is running at full speed at 65°C. We wrote the code for the Arduino and then tested the fan output by holding a soldering iron over one of the sensors to warm it up.
Once we were happy that the circuit was working properly we transferred it to a piece of strip board, added some insulation to the back and insulated the temperature sensors and went about installing it into the power supply. Each heat sink had a pair of spare M3 threaded holes in them so a clamping system was devised using some mechano and washers. Some thermal paste was used to make a good contact between the sensors and the heat sinks.
The control board was taped underneath a bar which runs across the top of the chassis and the power supply was reassembled. After some initial testing it all appears to be working well and the new addition hasn’t affected the output voltages in any way.
The workshop is now a lot quieter when we are working on our projects.
The circuit schematic and code can be downloaded from https://github.com/briandorey/PSU-Temperature-Monitor