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Help with Fan Controller Math

#1bobsmith915Posted 12/20/2013 7:51:37 PM(edited)
I'm trying to run three 80mm fans in parallel off of an external 9v power supply. I'd like to use a single potentiometer to control the fan speeds, but I'm not sure how many ohms I need for the pot. Can someone help me figure it out? Thanks.
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#2jokujokujokuPosted 12/20/2013 10:05:30 PM(edited)
What's the current rating on the fans?

If I remember this correctly, you would add the current rating of the three fans, and divide your voltage by that to get your desired resistance. So 9V / [total current in amps] = the resistance in ohms you need for 100% fan speed across all three fans. That would be the minimum resistance you want for your potentiometer.