Portsdown 4 and Breakout board - a cooling solution

[radiogareth]

Having read that the RPI4 tends to run a bit hotter than its predecessor I did add fan cooling to my first build. Now, contemplating another build, this time as more of an 'accessories mule' and with the smaller (cheaper) 5" touchscreen I gave some thought to cooling. The Fan Hat did not inspire me (reports of early fan failure) and anything that costs £'s gets a 'think-around' which in this case cost zilch, at least at the point of construction -it came from my 'might come in useful one day' box and had been originally purchased to use as Power LED cooling solutions. I think they were something like this, but back then 50p each! https://www.ebay.co.uk/itm/113390019639 ... SwM6Fb9dgf
Removal of the fan from its heatsink reduced its footprint to the point it would fit onto the underside of the breakout board. By a fortuitous coincidence two holes could be drilled that cleared any tracks (just) and basically went through the PCB ground plane. Adding a pair of 3mm standoffs 6mm high allowed air into the back of the fan and clearance above a set of RPis stick-on heatsinks.
On 5 volts it dropped the reported temperatures from 50+C down to a 33C, on 3.3 volts (fan noise is less obtrusive at that voltage - tapped off the RPI 3.3V rail) but it still kept the CPUs down to 37. If desired, the unused fan support legs could be snipped off.
All this measured when transmitting testcard via a Pluto on 437MHz.
Pictures shows it all...
Gareth

RPi_Fan.jpg (145.55 KiB) Viewed 1205 times

RPI_fan_assy.jpg (82.49 KiB) Viewed 1204 times