Looked all around to find the answer and can't find it so I'm posting it here? Built and wired the stir plat everything works but my fan speed pulses. Fan speeds up and slows down. It creates a vortex and then goes away and cycles like that when its on. Material used transformer 120/12v dc, 12v 30 amp rocker switch, 25 ohm rheostat 3 w. Used brushless 12v dc fan. Whats causing the issue? Would this still work as a stir plate if it pulses like this creating vortex half the time?