Huxley 12cm outer-edge fan mount
by drdpj, published
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To add a little, I looked up a heatsink very similar to yours, That would have a thermal resistance of 6,5°C/W
The TO-220 package (from the lm7812 datasheet) has a 5°C/W, that would then add up to a 11,5°C/W instead of the 65°C/W junction to air.
This time setting ambient to 50°C, probably the highest it would ever see, that would leave you at 78,175°C with a 350mA load. So yeah, heatsinks are fucking magic :P.
I'd say that you'd probably want to have that sink on there. Assuming worst case here. Running the highest current 120mm fan that I could find in my stash, it ran 350ma at 12v/2600 rpm. With the huxley, that has a 19v PSU so the linear reg would need to drop 7 volts. 7v * 0,35A = 2.45W
Looking at the datasheet of an LM7812 (I happened to read up on the one from fairchild) the thermal resistance, junction to air is 65°C/W
With a generously low ambient of 25°C the junction temperature would end up at 2.45*65+25 = 184,25°C way way over the 125°C max.
Changing the fan to a 200mA fan, would leave us at 116°C, just 9°C short of the absolute max rating.
tl:dr; Keep that sink on ;)
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After a bit of use, I recommend sticking a big heatsink on the voltage regulator (2nd picture). This not only stops the fan slowing down as things heat up but also makes it look a bit more badass. If a fan can look badass, which it probably can't.
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