I had 3 different Case fans that I tried... No luck.Depend on the motor beneath the stirbar, mine is from a 120mm case fan and i mix 80/20 and it stirs even before the mix is on 30degrees
I then chopped up an old RC chopper and used the motor from that with a PWM regulator to adjust the speed. this worked a bit, but when I then started making batches of 300ml plus in a go (for one flavor) it no longer worked. not sufficiently anyway