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Old 03-17-2012, 07:45 PM   #1
brewvic
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Default Two stir plates, one power source?

I'm hoping someone can help me out with some dumbed down instructions...

I tracked down a beautiful whiskey bottle box (wooden on three sides with a slide-out plastic cover on the fourth). It's the perfect size to support two computer fan stir plates, but I'd like to have just one power supply to plug in, and switches to turn on/off the stirrers individually.

I've made single stir plates before following instructions found on the web, but I really know nothing about electronics. Is there a way I can split a single power supply to drive two stirrers? Will I need a power supply with greater amps out than I'd use if powering just one?

Thanks!

DS

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Old 03-18-2012, 06:13 AM   #2
SomeKindOfOctopus
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Hey there.

Using one supply for two fans is no problem. The easy way would be to make two identical fan and speed controls, as if you were making two completely separate stir plates, and then connect them both to your power supply in parallel.

Did you use the LM317 (or similar regulator), like on the page you linked? If so, that means you'll assemble two of those circuits, then connect the "12 v in" wire of each to the positive side of your power supply, and the 0v wire to the negative side of your supply. You may want to put a switch on each section, but you can also just leave the speed knob turned all the way down on the side you aren't using.

As far as supply current, you will be drawing twice as much, so you'd need to get one of appropriate size. I just tested a fan on my bench supply, and it drew about 250mA (0.25A) at 12v, so for two of these fans you'd be drawing 500mA (your fans may be different, it's best to check with a meter), and you'll generally want to oversize your supply. For 2 of my fans, I'd probably go with at least an 800mA supply. If you don't have a multimeter to check with, you'll probably be ok with something that big or bigger.

If you need clarification on any of that, let me know and I can draw out a diagram for you.

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Old 03-19-2012, 03:53 PM   #3
brewvic
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Default Got it!

Thanks Octopus. Those were just the tips I needed. I really appreciate the thoughtful response.

I got some free time yesterday and finished off the project:


Bourbon box with on/off switches and speed control knobs.


Box from the top showing plastic sliding top and hardware inside. Notice the notch with the power cord. For storage I can slide out the top, coil up the power cord, and store the adapter right in the box (my old homemade stir plates had the power run through a hole in the side of the container which meant the power adapter was swinging free and getting tangled up with everything when not in use).


The guts of the system. I found a 2.2amp output adapter. As directed above, I simple connected all the black power wires and all the red return(??) wires and otherwise setup the system as in the instructions from my first post.


With the 2.2amp adapter, I get enough speed that I get a good dimple at the surface when both are turned on.

Thanks again for the kick in the right direction on this project!

DS

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Old 03-20-2012, 02:15 PM   #4
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Wow, that looks great! I'm glad I could help.

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