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Old Oct 02, 2012, 09:03 AM
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United States, AZ, Gilbert
Joined Jul 2010
514 Posts
OK, so I got the temperature control circuit working...almost, I still need to do the final tweaking and waiting on parts from Mouser...but I am pretty stoked about it. I have to give credit where credit is due to ronv at electro-tech-online for designing the circuit, I had the idea, but he made it work with just one op-amp, 4 resistors and a thermistor. We decided to simply use the PSUs built in fan control pin, pin #4 and control the speed of the fan based on temperature by changing the voltage on this pin. 4.6v to Vcc (Vcc=about 12v) is the range on pin 4 that will adjust the fan speed. The fan reaches a minimum speed at 4.6v and even if the voltage from the op-amp output drops below 4.6v (i.e. when the PSU first starts and it's cold) the fan will still not go below the minimum speed. We decided not to let the fan stall. The circuit ronv designed is excellent in my opinion because it doesn't generate any heat (the original design with a MOSFET would have wasted a lot of energy in the form of heat and required heat sinking the FET to the case with non-conductive thermal epoxy) and it doesn’t require any mods to the PSU's internal fan 555 timer and no splicing of the fan wires! So the built in protection is still intact where the PSU will shut down if the fan dies, meaning if it stops getting a tach reading from the fan, the PSU will still shut down to protect itself. My original design had to trick the PSU into thinking it had a tach pulse with a 555 timer because we disconnected the fan and allowed it to stall, but we dumped that idea. Thanks ronv! Once I get all the parts and get the circuit dialed in, I will post some pictures/youtube video showing it in action with the 1500+ watt water cooled (thanks to ()blivion!) dummy load we made as well.

If anyone is interested, you can find the schematic for the temperature controlled circuit, dummy load and all information about how we made the circuits in this thread:
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Last edited by jocanon; Oct 02, 2012 at 10:19 AM.
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