Add Fan to Router - Power Question

[vidarr]

I am adding a fan to a router and want to get opinions on how to power it. I have watched a bunch of videos and all different methods work, but the one I like best is to sold right to the power jack pins. This fan doesn't need any special driver, just power. But, will this effect the power going to the router? Should I really make a little "driver board" with a resistor and capacitor? Or is that too much?

Thanks!

[nctnico]

Stick the fan on the outside and power it from a wall-wart. When the next router arrives, pull the fan off and stick it on the new router.

[vidarr]

That would be my First Option! But....

There is no housing. It is just the router board and the plastic back plate (bottom), like the pic. Also, where it is going, the 12v psu is hardwired inside a junction box (so it the router plugs into a jack, like a common receptacle, but a jack ---male to male jacks on a "patch" wire.). I don't want to touch any mains power. Also, this is Brazil, so everything is not right.

Thanks!

[Nominal Animal]

If you can keep the board vertical, I would recommend a large passive aluminium heatsink instead of a fan, shaped into an L, so it'd reach the three mounting holes, with heatsink fins also vertical.  I don't know the exact dimensions between the three holes, but I can find 100mm × 100mm × 18mm heatsinks on eBay for under 5€.  Drill the mounting holes for the heatsink, create board standoffs (cylindrical parts the same height as the processor IC [plus 80% of the thermal pad] is from the board) using a 3D printer or from suitable silicone or PVC tubing (hose), and use a ~1mm thick thermal pad between the heatsink and the fan to allow for slight misalignment between the two.

For even better results, lap the surface of the heatsink using 120 to 360 grit sandpaper on top of a mirror (so it'll be dead flat), and use a grain of rice -sized dollop of thermal compound between the IC and the heatsink, and plastic washers, springs, whatever to make the three standoffs perfect height.  The thermal compound is not intended to form a layer per se, just fill in any microscopic voids between the two to maximize the thermal contact surface.  (It will look like a continuous layer, though, when taken off.)

If you can take a picture from straight above (perpendicular to the surface), with a ruler in the same view (so I can see approximate dimensions), and measure the distances between the three or four mounting holes, I can make a more detailed suggested design for you.

Disclaimer: I'm not an EE, I'm just a hobbyist myself, but I do this kind of stuff regularly with my own SBCs (single board computers running Linux).

[David Hess]

Soldering to the power input should work fine, and no extra parts are required.  Keep in mind that even a tiny bit of airflow makes a huge difference in junction-to-ambient thermal resistance so the slowest and lowest power fan should be completely sufficient.

[mariush]

The fan will be mostly useless if there's no heatsink under it.  The fan moves air through heatsink fins and that air warms up and carries away heat, and the fins cool down a bit. So a fan improves the performance of a plain heatsink (without a fan, natural convection will do the job somewhat - warm air rises, so air will naturally flow through the fins)

My advice would be to get some heatsink that's big enough to cover the chip but not so big as to hit tall components around.
If you want free you could probably get one from a broken motherboard or a bad tv.
Use some double sided thermally conductive tape to hold the heatsink on the chip, or use regular thermal paste
You could use the holes in the corners to put a bar of metal or something over the heatsink and use some screws or something to tighten the metal bar, which in turn will keep the heatsink pressed down on the chip.

As for fans .. that fan is probably 5v ... Id suggest just getting a cheap 80mm / 92mm case fan and connect it directly to the barrel jack input, which is probably 7.5v--12v ... any fan will run at 7.5v but at slower speed.

[David Hess]

The fan will be mostly useless if there's no heatsink under it.  The fan moves air through heatsink fins and that air warms up and carries away heat, and the fins cool down a bit. So a fan improves the performance of a plain heatsink (without a fan, natural convection will do the job somewhat - warm air rises, so air will naturally flow through the fins)

Moving air has the same effect whether a dedicated heat sink is used or not.  For parts where the junction-to-ambient thermal resistance through the package is high, the lead frame conducts heat into the printed circuit board which becomes the heat sink.  Surface mount power devices rely on this almost exclusively.  In practice the junction-to-ambient thermal resistance is halved or even better with small amounts of forced air cooling even without dedicated heat sinks, and small heat sinks can halve this or better again, but not for power devices unless directly attached to the lead frame or a ceramic package.