Some months ago new Raspberry Pi 4 was released. It is huge upgrade compared to previous version 3B+. One of major changes is completely new processor with four ARM Cortex-A72 cores. Now CPU work at 1500 Mhz speed, but it leads to some problems with overheat. In the Internet can find multiple articles and videos about cooling it with passive or active cooling. But I think that active cooling, using fan, is not required for this computer, otherwise it will become not so quite. Such relatively small amount of heat can take away with simple heat sink.
There are multiple options for choosing heat sink for Raspberry Pi 4. Some of them are tower like head sinks with heat pipes, that type is used in desktop computer. For example this model - ICE Tower CPU Cooling Fan
Of course this will cool Raspberry Pi to low temperatures, but it is rather big and makes noise. I think this can be too heavy for small computer and can find smaller heat sink that also will work well and cool processor. I have chosen this heat sink
It can be ordered for example from Gearbest. There is also version with two fans, but I think this version is enough for RPi cooling and later in this article I will show results of temperature testing.
This heat sink contains two thermal pads - for CPU and for memory. I have seen photos of Raspbery Pi where can see most hot places on this board. They are CPU and power controller. So I have decided that it is not required to cool memory, but instead should cool power controller.
This article has thermal benchmark photo where you can see that board has two most hot places marked in red. So I will try to cool board in these places. This heat sink like case supports only CPU and memory cooling, so I will have to modify it so it will be able to cool also power circuit.
I have prepared two copper plates. Larger one will be used for power circuit, smaller for CPU. I have used plate for CPU, because there is too large distance between heat sink and CPU - I will have to use two thermal pads, but thermal pads provides heat not so good as copper.
Then I have installed them to heat sink using thermal tape from Aliexpress. Between copper plates and CPU/power circuit Arctic thermal tape will be used.
After I have installed them, I had this result
One more piece of thermal tape I have put directly on power circuit, so it can contact heat sink. After that I have installed heat sink on Raspberry Pi it looks like this
Now it is time to test how effective heat sink is. I have tested it with sysbench and stress tests. I have run stress test for 10 minutes three times. Maximum temperature I could get was 65 degrees Celsius. So I think results are great! I have seen tests with small fans installed on board or with larger heat sinks without fan and temperature also was around 60-65 degrees. Only having large heat sink and fan can get temperature around 45 degrees. But as I have told this is not worth of it.
Then I have tried to overclock Raspberry Pi 4 and see temperatures and speed at maximum overclock. I did not tried extreme overclock, only maximum level 6, that is safe for Raspberry Pi. I have wrote raw result to file that can be seen on Github.
Maximum that I could get was 2125 Mhz CPU frequency. I have used these settings in /boot/config.txt file:
arm_freq=2125 gpu_freq=600 over_voltage=6
I have overclocked video card too, but I did not it. 600 Mhz is not much faster than base clock - 500 Mhz. So I think it will also work, but need to test later to be sure.
Then I decided to decrease over_voltage to level 5, because level 6 is not giving much boost compared to 5
arm_freq=2120 gpu_freq=600 over_voltage=5
At this speed computer was stable. Using stress test temperature at maximum was 82 degrees and sometimes throttling appears, but it lasts for small amount of time. In real applications temperature should not reach that limit. So I think this frequency can be used with heat sink.
About sysbench test result. Smaller time is better:
- Raspberry Pi 3 overclocked to 1300 Mhz - 93.6
- Raspbery Pi 4 base frequency 1500 Mhz - 62.7
- Raspberry Pi 4 overclocked to 1750 Mhz - 53.7
- Raspberry Pi 4 overclocked to 2000 Mhz - 47.0
- Raspberry Pi 4 overclocked to 2100 Mhz - 44.7
- Raspberry Pi 4 overclocked to 2120 Mhz - 44.4
I think Raspberry 4 overclocking potential is amazing. I could get 620 Mhz of frequency boost, it became 30% faster! Compared to Raspberry Pi 3 maximum that I could get was 1375 Mhz on one of three my Raspberry Pies. Other two worked stable only on ~1333 Mhz. So maximum that I could get overclocking Raspbery Pi 3 was 175 Mhz.
Compared to version 3, overclocked Raspberry 4 works more than 2 times faster!
Raspberry 4 has large performance boost compared to Raspberry Pi 3. It requires better cooling, but still active cooling is not required. Using case described in this article temperature can reach 65 degrees and overclocked to 2120 Mhz - 82 degrees with throttling small amount of time. So new board become much powerful and price for this power is larger heating. Raspberry Pi 4 now can be used for much larger scope of tasks: starting from Dreamcast console emulation and NAS storage creation - board has not only improved CPU, but also USB 3.0 for external drives to usage as desktop computer, especially if it has 4 Gb of RAM.