i set out to build a stir plate about a month ago with things i already had laying around, so i didnt spend a penny. i use this with a 2L erlenmeyer.
1 - gun cleaning kit box 12’’ x 7 1/2’’ x 1 5/8’’ thick
1 - computer fan
1 - cell phone charger
1 - hard drive magnet
2 - 7 in. lengths of 1 3/8 x 1/2 wood ( box is flimsy, needed support for full flask)
plexi-glass (spacers for fan)
sticky things for wires lol
so i built this without a potentiometer...the original plans incorporated 2 separate fans with their own plug ins, for different speeds ( hence the sharpie outlines), but just this one worked regardless of how much fluid was in my flask. i had 3 different computer fans, and about 7 old cell phone chargers to choose from. all different voltages of course. it was just a matter of linking the right fan to the right power source to get a stir that wasnt too strong and wasnt too weak. for my needs this works perfectly. doesnt throw the stir bar after 24 hours (longest ive run it constant) just set my flask on there with stir bar in place, plug it in and leave it. with a full flask there is a slight vortex at the top maybe an inch long...with 4-6 oz of water for rehydrating my dry yeast its still perfect.