I am using a Raspberry Pi 4 (daenerys) as my desktop personal computer during the work day, which I access from my work provided computer using VNC. By using this Pi 4 I can access the Internet from my desk without going through the corporate Internet proxy.
I built daenerys in a Flirc case, which looks really nice and provides passive cooling, and it boots from a SSD in an Inateck case. The SSD gets power from the Pi and so under normal load I would see temperatures hover around 55 degrees celcius, which is well below the 85 degree threshold that causes the CPU to throttle down.
Over the holiday I built another Raspberry Pi 4 (arya) in a MazerPi case that has a fan. The fan draws power from the GPIO pins and has two modes, high speed if plugged in to the 5v pin (PIN 2) and low speed if plugged in to the 3.3v pin (PIN1). To complete the picture, ground is plugged in th PIN 6.
The MazerPi fan just stays on all the time, I am not aware of a way to control the fan so that it only comes on when a certain temperature threshold is past. I first plugged the fan in to one of the 5v pins and found it loud enough to be heard, although not terribly loud. When using high speed mode the CPU temperatures were in the mid to high 30 degree range under normal load. When I ran Octane 2 it then crossed 40 degrees.
I decided to try the low speed mode, which is quiet enough to not hear unless one concentrates. Temperatures where in the 40 to 45 degree range, which is plenty good.
At this point the thought occurred to me that it probably makes sense to use the case with the fan for the Pi that I am going to use every day rather than in one I am going to use as an accessory and thus I removed the SD card from arya and plugged in the SSD from daenerys and it booted right up. (BTW, note that in reality a computer host name is associated with the boot drive and not the actual computer, so daenerys is really the 250 GB SSD drive while arya is a 256 GB SD card.)
Finally, I decided I wanted to try overclocking daenerys, which given the fan should be safe. Normal speed for this Pi4 board is 1.5 GHz, so I decided to overclock it to 2 GHz. Performance is noticably faster. At 1.5 Ghz daenery’s Octane 2 score is 8098 and at 2.0 Ghz the score is 9777. Neither score is fantastic, but good enough for the type of web browsing that I do.
When you overclock a CPU it will run hotter and that can cause failures. In the MazerPi, with the fan in low speed mode, and the Pi 4 booting from a SSD and overclocked to a max frequency of 2 GHz and a minimum frequency of 1 GHz I am seeing temperatures ranging from 46 degrees to 55 degress, which is about the same as well using the Pi in the Flirc case but not overclocked.
The net result is that have “upgraded” daenerys to a faster processing speed that provides better performance while maintaining a good CPU temperature and so far after one full working day it has been stable. The MazerPi case cost only $8 and is easy to assemble with help from a video I found on YouTube.