First, for background, I've tried building a stir plate before. I used a simple circuit to control a DC computer fan. That seemed to work fine, but I could never get the stir bar to stir properly. I had used one of the curved hard drive magnets, and it was a pain to really get that thing centered properly. It's not balanced, so it makes it difficult to center without spinning the magnet out of place. And so, the stir plate always threw the stir bar if I went faster than a tortoise.
This time, I went with something a little different. I had heard that the magnets could interfere with the fan's operation, so putting some distance between them would help performance or prevent fan failure. It sounds plausible, so I went with it.
I picked up some round neodymium magnets from the local hardware store and mounted them with Gorilla Glue to a PVC coupling. I cut a couple of notches opposite each other and applied the glue. Then I just set the magnets into the notches. I tried to make the notches snug so the magnets fit in there tightly and wouldn't move. I used a piece of wood to keep the magnets separated while the glue dried. And to space them apart, I snapped them onto the stir bar to get an idea for placement before gluing. After the magnets were secured, I then glued the coupling to the fan hub and gently centered it while the glue was still tacky and the fan spun at a moderate speed with my fingertips until it was balanced.
The platform is pretty basic. Just some square dowel pieces and wood screws to attach thin oak plywood. I did countersink the screws on top so they wouldn't interfere with the flask. One key here is to get the platform as close as you can to the magnets. The closer they are, the stronger the magnetic field will be holding the stir bar in place. (The relationship is exponential, so small changes in distance make quite a difference in magnetic force.) My platform was farther than this and it kept throwing the bar. After cutting the supports shorter, I can now get a decent vortex going in the flask. I don't plan to leave everything open like this, though. That could be hazardous. This was mostly a proof-of-concept for me, and the supporting structure will be redone.
For the fan, I chose a 110V fan. I didn't want to deal with weak fans or power supplies. This was a simpler solution. To control fan speed, I wired in a fan speed control knob meant for ceiling fans. Works perfectly. This fan came out of a space heater that no longer produced heat, so it had a sort of shroud on it. This shroud had mounting holes that work really well for attaching the platform. I'll continue using these as I build a better enclosure. Your fan may not have these, or may have different mounting holes, such as in the four corners. That works, too.
I still need to make a proper enclosure for everything so I don't have exposed wiring and for better aesthetics, but for now it works well to test the concept. If you want a simple stir plate build and you can find a 110V fan to do this with, I'd highly recommend trying this method. No circuits to build, no soldering. Easy-peasy.
This time, I went with something a little different. I had heard that the magnets could interfere with the fan's operation, so putting some distance between them would help performance or prevent fan failure. It sounds plausible, so I went with it.
I picked up some round neodymium magnets from the local hardware store and mounted them with Gorilla Glue to a PVC coupling. I cut a couple of notches opposite each other and applied the glue. Then I just set the magnets into the notches. I tried to make the notches snug so the magnets fit in there tightly and wouldn't move. I used a piece of wood to keep the magnets separated while the glue dried. And to space them apart, I snapped them onto the stir bar to get an idea for placement before gluing. After the magnets were secured, I then glued the coupling to the fan hub and gently centered it while the glue was still tacky and the fan spun at a moderate speed with my fingertips until it was balanced.
The platform is pretty basic. Just some square dowel pieces and wood screws to attach thin oak plywood. I did countersink the screws on top so they wouldn't interfere with the flask. One key here is to get the platform as close as you can to the magnets. The closer they are, the stronger the magnetic field will be holding the stir bar in place. (The relationship is exponential, so small changes in distance make quite a difference in magnetic force.) My platform was farther than this and it kept throwing the bar. After cutting the supports shorter, I can now get a decent vortex going in the flask. I don't plan to leave everything open like this, though. That could be hazardous. This was mostly a proof-of-concept for me, and the supporting structure will be redone.
For the fan, I chose a 110V fan. I didn't want to deal with weak fans or power supplies. This was a simpler solution. To control fan speed, I wired in a fan speed control knob meant for ceiling fans. Works perfectly. This fan came out of a space heater that no longer produced heat, so it had a sort of shroud on it. This shroud had mounting holes that work really well for attaching the platform. I'll continue using these as I build a better enclosure. Your fan may not have these, or may have different mounting holes, such as in the four corners. That works, too.
I still need to make a proper enclosure for everything so I don't have exposed wiring and for better aesthetics, but for now it works well to test the concept. If you want a simple stir plate build and you can find a 110V fan to do this with, I'd highly recommend trying this method. No circuits to build, no soldering. Easy-peasy.
