So I built my own stir plate following one of the many instructions from online. Last night I made my first starter with it. The only problem is that the potentiometer doesn't really control the fan speed. I turn it very slow and the second it starts getting power to the fan, the fan just goes full speed and I adjusting the potentiometer doesn't seem to do anything; so the stir magnet just gets kicked off. I have a 12V fan, 12V DC Adaptor (output?), and the potentiometer is a 10ka...or something like that. Any suggestions or tips?