So my stir plate project started out with finding this crazy-ass UV lamp power supply at the local e-recycler for $5. I liked the footprint, and the steel construction was sturdy.
The unit had a built-in lighted rocker for power and a 1/10 hour timer on the front. They were fed power through a 125V/250V fusable link. Great way to start. (I added the push button and potentiometer, you'll see why later.)
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The power originally went from the fuseable link to this sweet power rail. Just repurposed it with hot, neutral, and ground connections.
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Off of the 120V rail, I wired in a 24VDC adaptor.
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From the 24V adaptor, I hooked up this crazy power supply I ripped out of an old printer I had lying around. I couldn't figure out how to get it to work at first, but then I discovered that it needed to be turned on with an intermittent switch (just like your standard PC), so I added that button on the front. This little power supply has two 24V rails and a dual 12V rail. It also has USB ports, which I intend on finding a purpose for at some point.
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From the 12V rail on the power supply, I soldered the hot lead out to the adjustable lead on a potentiometer from an old guitar. I terminated the hot and neutral leads to an old HDD 4-PIN connector so, if I ever needed to, I could simply remove the fan from the bottom assembly.
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I had some PVC pipe lying around, so I cut a small chunk and glued it to a 12V fan. I created a little cradle/cross member for mounting the magnets. For the magnets, I had a rare earth magnet on my fridge, but it wasn't enough, so I added some magnets I had from some name badges that I got working some dead-end job years and years ago.
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And here it is! Not totally finished (need to fix that gaping hole on the top that I had to cut because magnets don't like to magnetize through solid steel plate). Total out of pocket cost: $10 ($5 for the case, $2 for a fan, and $3 in random connectors).
Video 1