Subject: Temp Control
By: rockman20 (IP: 24.119.247.*)
Written on: 17-02-2008 15:55

I built your device and it worked wonderfully. I tested it with an old computer power supply and an old processor fan. I could get it to turn on and off perfectly.

Then I went to put it in the actual application. I am inserting it in my entertainment center to keep my components cool. Currently I am running 2 fans Approximately 4 Watts and .3Amps.

I have this powered by a 12 volt AC/DC adapter. I plugged everything in and the fans were already on. I tried to turn the potentiometer down but it wouldn\'t turn off. It\'s like the two fans blew something and I\'m not sure what.

I am not sure what to do. I wired the two fans in parallel.

This is what I used:

IRF510 Power MOSFET Transistor. N-channel 60Volt. (Radio Shack 276-2072)
10K-Ohm 15 turn Cermet Potentiometer .75Watts (Rado Shack 271-0343)
Thermistor 10K OHM +/- 0.20C (Digi-Key 615-1010-ND)

I know that the pot is only rated at .75 Watts. Could this be my problem? Perhaps it blew the pot?

I was thinking about adding another 2 fans to my setup so there would be 4 total. I was thinking about perhaps inserting a relay into the circuit? What do you think? Please take it easy on me! I have dabbled with electronic circuits, but am still very wet behind the ears. Thanks!!!!!

By: rockman20 (IP: 165.234.180.*)
Written on: 18-02-2008 16:13

Never mind. I feel so sheepish for even admitting this! I found my problem.

The problem wasn\'t the fans. The problem was me. I am using a Radio Shack transformer to go from houshold current to a 12 volt DC current. Well, when I disconnected my previous setup (an automotive switch to turn the fans on and off manually) I made a mental note on what wire was what.

I have learned now that mental notes are no good and that I should of wrote it down. The wire with the grey strip on it WAS NOT the negative but rather the positive. So I had reversed the polarity on my circuit.

This blew the POT. I took my original circuit and put a new POT on the board and now it works wonderfully! I also added a heat sink to the transistor.

I would like to know a little more about adding capacitors to the system to keep the fans from humming before they turn on.
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