Subject: Problems with DIY Temperature Control
By: ThomasA (IP: 85.228.244.*)
Written on: 31-05-2011 22:27
I just built the Temperature Control, and it works except for one thing: it's really sensitive to adjust.
If I turn the trimmer to 10kOhms the fan doesn't start, obviously, but I would think that turning it halfway would give the fan 6V, right? And all the way gives it 12V.
What happens is if I move the trimmer just a millimeter, it starts to pass voltage through fast, and just a millimeter more and it's at 12V. If I hold the thermistor between my fingers after managing to set it to like 3V, I can see the voltage climbing slowly, so it's indeed working.
What could be wrong? I didn't use the right transistor, as I already had one at home that I thought might work. I have one of these: http://parts.digikey.com/1/parts/1004777-transistor-power-npn-220-bul39d.html (a TO-220 NPN 100V 3A MOSFET). Could that be it, that it opens up (saturates, is that the word?) fully too fast?
Should I replace it with another MOSFET, or could I perhaps replace the trimmer with one with a higher value? Like 20K, or more?
Great guide btw, and great site!
Thanks in advance,