homemade stir plate problems

[christopherrburns]

have a home made stir plate 12v pc fan, not variable speed connected to a adjustable voltage regulator. it consistently goes from not moving to full speed and throws my stir bar, stir bar does not have a ridge on it, dont know if the problem is my stir bar is too small and ridgeless or if it something else. ive seen other stir plates that are super fast without throwing the stir bar.

 

[stpug]

Speed control is very helpful. Aside from that, tweaking and more tweaking will help. Distance between bar and fan. Shielding the motor from you magnet.

 

[DonnieZ]

My homemade stir plate is very finicky. It seems it helps if I move the flask around on the surface of the stir plate. If I get it set just right, it will go for days. If its even a few millimeters off, the stir bar throws after a few seconds to a few minutes and rattles like a spray paint can.

Definitely invest in a potentiometer from radio shack. It's a $5 investment but well worth it. I found I needed it even n a 12V fan running off of a 7.5V power supply. Start it slow, get the stir bar lined up so it doesn't throw, then crank the speed a bit. You don't need a vortex that touches the bottom, just movement. Even no vortex is ok as long as your starter wort is moving.

 

[mikronmagic]

I've just gone through the same problem as you're talking about, here's some things to check:
1. Make 100% sure that the magnet(s) on the fan are centered correctly. This is extremely important
2. Try different distances between the bar and fan (like stpug said). It's odd that sometimes the bar is more stable when the magnet is a little bit away.
3. The biggest thing is to use a rehostat or potentiometer (like DonnieZ said). You don't need some crazy cyclone going in your starter. Just a good whirling to help exchange CO2 for O2 and to keep the yeast from falling out.

 

[christopherrburns]

The voltage regulator is suppose to be a fancier rheostat, i've used a rheostat with a rectifier with poor results and have put copy paper under the flask to give some distance between the magnet and the flask and have moved to fan lower in the box without any luck. Last night I moved it up so that the box is providing some drag on the fan and slowing it down. That seemed to do the trick for now. Will have to come up with a new plan once the contact point between the fan and the box starts to ware.

 

[stpug]

How are your magnets arranged on your fan? One or two magnets? Directly on fan or spaced/shielded? Distance between magnets?