Making a stir plate for $8
I’ve been planning to make one of these forever. I’ve known where all my parts were, what I was planning to do, etc…. Just never got around to it.
My original plan was to buy a switch, a potentiometer (Variable Resistor for controlling speed), and a project box from Radio Shack, then install those plus an old computer fan, magnet from a hard drive, and DC power supply from one of the many old and broken devices I own.
So, I went to Lowe’s to get some plumbing for my keg topper, and figured I’d pick up the potentiometer and switch.
My main concern was that most potentiometers have a power rating of 0.5 watts to 3 watts, then they get expensive. My fan is 12 volts, with .45 A, giving me a 5.2 Watt power rating. I didn’t want to have to keep replacing switches, so I wanted to get one rated for the power, or design a shunt resistor to wick away some of the current.
So Lowe’s only had 0.5 watt pots. Bummer ’cause I really wanted to make this. The guy there said I could use a dimmer switch because they are rated for 300 Watts. I got excited and bought one for $8. On the way home, my mind was racing on how to wire it up. I realized that the dimmer switch had such a high power rating because it is an AC device. I was planning on only having DC coming into the box….
So I rewired it for AC into the box, controlled by the dimmer switch, then that signal is converted to DC by the power supply hardware:
1) Computer cord
2) Dimmer Switch
3) Transformer, Full Wave Bridge circuit, and RC Pi Filter from a 12 volt, 1000 mA AC-to-DC power source
4) Fan (12 volt, 450 mA)
5) Rare Earth Magnet - Harvested from Maxtor 80 Gig HD - (Much nicer than the ones I got from 2 Western Digital drives.)
So, I cut the computer cord close to the female end and threw the female plug in the trash. Then I soldered together:
1) Ground wires of plug and dimmer switch (Green wires)
2) Black wires of plug and dimmer switch together
(NOTE: Both switch leads on dimmer switch are black. Polarity does not matter in this case.)
3) One of the Dimmer switch leads to the power IN leads on the step down transformer
4) White wire of plug to the other power IN lead on the step down transformer
5) Cut off connectors from RC filter and fan, and soldered DC wires together.
I tested that out and it worked! So here I have a functioning circuit to run my stir plate. For $8.
Now, other costs I will incur:
1) Project Box from Radio Shack: $7
2) Mountings (Tape or Screws): $2
3) Stir Bar: $7
So, $16 more dollars. I can live with that. Especially when these things cost upwards of $100.
I’ll post pictures soon. My camera is out of batteries…