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12vdc fan controller

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Sceadwian said:
Make sure it's rated for the wattage it's going to be wasteing or it's going to get awful hot.
A 10k pot across the 12V supply will dissipate (12 squared)/10k= 14.4mW which is nothing.
The fan draws 0.5A at 12V. If the pot is set to halfway then fan's current is about 0.25A.
The TIP31 transistor has a typical current gain of 160 so its base current is 0.25A/160= 1.6mA. The 1.6mA in the pot with 6V produces a dissipation of only 1.6mA x 6V= 9.6mW which is nothing.

If the transistor has current gain near its allowed minimum then the pot might get slightly warm.


New Member
So how would i use the 10k pot?


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Forum Supporter
audioguru said:
Make the circuit like this:
It's too bad he doesn't have a 1K pot. The 10K pot will tend to cause the fan to only really start to work in the top 25% of the pots rotation. Using a darlington transistor will give better results at a sacrifice of 0.7V less at the max setting.


New Member
Thanks audioguru. It works great. Now i have to go find a TIP31(i am using a 2n2222, it doesn't like the heat...) How do the nice one's do it?, like the one i have pictured on the first post?


Active Member
how do the nice ones do what?

the expensive ( i dunno about nice ) fan controllers still have transistors, and they still get hot ... some of 'em saddle a poor rheostat with the burden instead, those don't often last too long.

or they cheat and use pwm, and then you're back to the beginning of this thread with pwm not being the optimal solution.


New Member
Screw it! The mod didn't turn out. The lucite cracked, and now the thing looks like crap.
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