I wanted to include a chemistry-style magnetic stir plate function into my temperature controller. I thought that would be beneficial in circulating the water in different containers. Since I was designing my controller to be modular and be container-independent, I didn't want to have to rely on always using a submerged "fish tank" pump. Particularly, I was thinking about small coolers with closed lids for this application.
My original plan of using an 110-volt AC computer fan with Neodymium magnets is not working so well. The fan spins entirely too fast and doesn't grab the magnetic stir bar; it just causes it to dance around. I also don't have a good way to slow the fan down and understand that changing the speed of AC motors is none too easy.
Another big issue I had was that the magnets were actually strong enough to prevent the motor from starting. There was considerable attraction to the copper coils under the fan blade. I think that instead of attaching the magnets directly to the top of the fan, I should have put in a wood or cork spacer. I think that might decrease the attraction just enough to start the fan normally.
Then, I went on to Plan B. I use a 12v DC computer fan, attached to a 12v AC/DC adapter, inside the case attached to the power inlet. I would run a potentiometer across the circuit and control the voltage and visavis the fan speed that way. But, then I heard that controlling a DC motor that way is also not that simple and you can burn out the potentiometer. Hmmm.
The adventure continues...
My original plan of using an 110-volt AC computer fan with Neodymium magnets is not working so well. The fan spins entirely too fast and doesn't grab the magnetic stir bar; it just causes it to dance around. I also don't have a good way to slow the fan down and understand that changing the speed of AC motors is none too easy.
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| The Neodymium magnets superglued to the top of the fan with the stir bar attached. |
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| I attached a plastic cover around the magnets because I was concerned they would become loose while spinning and centrifugal force would send them into my eyes or TV screen. They are too strong for the motor to start spinning with a little push. |
Another big issue I had was that the magnets were actually strong enough to prevent the motor from starting. There was considerable attraction to the copper coils under the fan blade. I think that instead of attaching the magnets directly to the top of the fan, I should have put in a wood or cork spacer. I think that might decrease the attraction just enough to start the fan normally.
Then, I went on to Plan B. I use a 12v DC computer fan, attached to a 12v AC/DC adapter, inside the case attached to the power inlet. I would run a potentiometer across the circuit and control the voltage and visavis the fan speed that way. But, then I heard that controlling a DC motor that way is also not that simple and you can burn out the potentiometer. Hmmm.
The adventure continues...
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