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  • Author Author: shabaz
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Raspberry Pi 3 Cooling / Heat Sink Ideas

shabaz

Note: This is part 1 of a 2-part post. For part 2, click here: Raspberry Pi 3 Dynamic Current Consumption, Power and Temperature Tests

To see an implementation using a heat pipe, see the Outdoor Pi 3 Image Recognition Security Camera project (aka HAL-CAM 9001)

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Inspired by Christopher's   Raspberry Pi Operating Temperature report (with thermal photos from Gareth Halfacree) regarding the heat dissipated by the Broadcom chip on the Raspberry Pi 3, and the discussion with we started searching around for ways to keep the Pi cool.

Ceramic heat sinks have an innovative structure (vias or micro-pores) which allow a heightened thermal conductivity compared to traditional aluminium heat sinks. They also can have the advantage that they won't affect radio frequency (RF) communications as much, when positioned close to the wireless antenna that is present on the Pi 3.

Furthermore, ceramic heat sinks are not electrically conductive and therefore there is no risk of accidentally shorting something on the Pi.

Back-of-the-envelope calculations (we don't have all parameters since we don't have a copy of the Broadcom datasheet to examine the device operating conditions in detail, nor a copy of the schematic to examine if we can measure device power consumption isolated from the remainder circuitry) suggests that a heat sink with thermal resistance of around 10 degrees C/W might be effective to keep the Broadcom chip's internal temperature below 120 degrees C when the ambient temperature is below around 40 degrees C. These are guesstimates until practical measurements have been taken.

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Armed with this information, I searched for a suitable sized heat sink and I found a cheap aluminium one. However and suggested that there may be issues with the heatsink getting in the way of connected HAT boards on top of the Pi, and Brian suggested examining ceramic heatsinks.

In summary, I think these parts may be suitable although measurements still need to be done:

22x22x2.5mm MPC222225T22x22x2.5mm MPC222225T

15x15x2.5mm MPC151525T15x15x2.5mm MPC151525T

(Optional) 20x20x10mm 5V DC fan MC33873(Optional) 20x20x10mm 5V DC fan MC33873

(EDIT: after some discussions below, it looks like this Sunon 'DR-MagLev' design fanSunon 'DR-MagLev' design fan is a far better choice, it is 25x25x10mm, quieter, higher throughput, and more efficient with overall lower power consumption. There is also a 25x25mm finger guard25x25mm finger guard).

 

The Broadcom chip is about 14x14mm in size, and ceramic heat sinks do exist in approximately that size. However it is possible to attach a larger heat sink if desired.

The photo below shows the parts that were examined. All of these ceramic heat sinks come with adhesive tape on the underside; the protective tape is removed and the heat sink will stick to the top of the integrated circuit.

The photo at the top of the blog post shows the largest 22x22mm ceramic heatsink.

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The photo below shows a heat sink closer to the size of the Broadcom chip, 15x15mm. It also shows a 10x10mm heat sink on top of the USB hub/Ethernet controller chip, however this is really not needed. It doesn't get very hot according to the thermal photos in the previous blog post.

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The memory chip on the underside gets hot too. If desired, the 15x15mm heat sink could  be attached there too. The 22x22mm one is too large for that location due to nearby components (the memory chip has a lower height than the Broadcom chip on the top side).

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So, I plan to attach a 22x22mm part to the Broadcom chip on the top of the board, and possibly a 15x15mm heat sink to the memory chip on the underside. I don't think a fan will be needed unless a very small enclosure with no natural ventilation was used, or if the Pi was in a very warm environment.

In that case, a fan may be an option. I tried the MC33873 fanMC33873 fan and it generates a usable level of air that can be felt from a distance of 10cm or more. However it does generate a small amount of noise too (possibly inaudible if the Pi will be behind other items such as a TV, but I think there is still a risk it could be audible. The voltage could be reduced from 5V to lessen the noise). It could be mounted on the heat sink as shown here although I think a small gap would be good to allow forced air to hit the entire top face of the heat sink. (The red dot on the fan was placed by me so that I could see it spinning). The fan could be secured with epoxy adhesive. The overall height is less than the height of the USB connectors on the Pi 3. The problem with this is that a HAT board cannot be plugged on top if there is a fan in the way.

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A very nice solution would have been to put the fan on the side (to the left side of the photo above) so that the fan could blast air across the entire top face, and the underside of the board. However the display connector (the long white thing on the edge of the board in the photo above) is in the way and would block the flow of air which is extremely unfortunate. The Pi 3 wasn't designed with air flow in mind : ( However it might be possible with some 3D-printed duct design to achieve something that could work.

 

To summarize, some heat sinking ideas have been suggested however it is for further examination to see how well they perform. It will be good to see what solutions people come up with over time.

  • How did you mount the ceramic heatsink, did you use the included thermal tape, I would love to use thermal paste (i have some arctic alumina ceramic paste) for the superior thermal conductivity but how to hold the heatsink in place is the problem.

     

    I wish a manufacture would make a case that comes with a spring mounted heatsink so we can use thermal paste, instead of these low quality thermal pads, I use to make desktop computers and the heatsinks use to always come with a packet of white thermal grease, but nobody who knew better would use it, they would use AS5 or other good thermal paste.

     

    John.

  • in reply to tinderbox(uk)

    Hi John,

     

    It's been a while since I checked the precise value, and the Pi people did modify the exact algorithm at some stage too, but when the Pi's SoC reports 80 or 85 degrees C then the CPU speed is decreased (i.e. throttled) in an attempt to get the CPU to cool down. If you're running the Pi without an enclosure then you're usually fine with no enclosure or heat sink. Some applications (e.g. some but not all video related applications) will use certain CPU resources that will push the temperature up and then a heat sink becomes useful. If it is inside a case then the heat sink alone isn't sufficient during those scenarios because eventually the CPU will heat up to the same temperatures and the CPU speed will decrease until it cools down a bit. This was observed by in his tests here: Raspberry Pi temperature and cooling testing Part 1 initial tests.

    Generally a heat sink and a fan will eliminate the throttling. Then the question is what heat sink and fan you want. Even a small fan and heat sink can eliminate throttling at normal room temperature. The ceramic heat sinks are nice because they are tiny and will not get in the way of any plug-on board attached to the Pi, and are electrical insulators unlike the aluminium ones, and are safer, and better for wireless. Small fans are nice because they can be mounted sideways for a low profile but the disadvantage is the noise they make (large fans can be quieter if run slower). The optimum situation is one where a fan is avoided because then you have a silent solution, but it isn't always possible.

    I sometimes use my Pi's without an enclosure and they are fine unless I run specific code that executes a portion of functionality known as NEON. When I run NEON code then a heat sink is definitely required, and if in an enclosure then additional measures need to be taken (which could include a fan).

    If you're just experimenting with a Pi you don't need to attach a heat sink or fan, and no hardware damage will result. The Pi protects itself by limiting the CPU speed if it gets too hot (of course the applications suffer meanwhile by running slower).

    You can type a command on the Pi at any time to see what temperature the SoC is reporting (the command is in Brian's post) and the CPU speed.

    I've not seen a need to apply a heat sink to the other chips on the top side of the Pi, perhaps others have, I'm not sure. However there is a memory chip on the underside, and under intense use I think it gets hot and that causes the Pi's SoC to stay hotter too. This is an extreme situation though, I've not investigated it in as much detail as I'd like. A sideways fan has the advantage that some air could be directed to the underside of the board too. This all requires experimentation by someone, my comments could be wrong.

    Cooling a Pi isn't the same as needing to cool a large desktop PC because for the Pi for most of the time it doesn't matter but for some use-cases it really helps performance. So, don't be afraid to power it up with no heat sinks or fan when it arrives. What can be important is to have a power supply capable of supplying a few amps, such as the 'official' Pi 3A power supply.

    Have fun with your Pi!

  • I just ordered an Raspberry Pi 3 Model B yesterday, and i should get it on monday.

     

    I watched an youtube video of a guy checking the Pi 3 SOC for throttling, he said it happens at around 80c and it does not take a lot to get to 80c, even with a heasink in a sealed case with no airflow the heatsink make very little difference, he recommends an heatsink and a fan, or an heatsink and an open case.

     

    I was looking for a ceramic heatsink and found a UK seller that sells all the heatsink mentioned in post 1, but he also has these ceramic heasinks with fins to improve the cooling effect

     

    The heatsink below is 25mmx25mmx5mm and is the smallest one the ebay seller does and was only £2.89 delivered

     

    I wonder what the weight this heatsink is as it`s 5mm high (i will weigh it when i receive it), compared to the 22mmx22mmx2.5mm heatsink (no weight given) from post 1 the more ceramic material should equal great heat dissipation?

     

    ceramic heatsink

     

    I ordered a case that can take a fan as it has the mounting holes, 2 of the 3 heasinks supplied can be used.

     

    case

     

    John.

  • in reply to Former Member

    Hi Gergo,

     

    Great points.

    As you say, it wouldn't help having a fan in operation like that, I should have marked on the photo that it is just to show the physical size of that fan and the various bits. Nothing was connected or powered.

     

    There were discussions on some topics that might be of interest in the comments, so it takes a while to go through but worth it.

    The discussion helped a lot, based on that some of us put a sideways mounted fan to not obstruct any boards plugged on top. A vertical mount configuration sound pretty interesting.

     

    did a lot of work to run the Pi 3 and record detailed measurements, it is also worth checking out his findings in the comments, and this location: Raspberry Pi temperature and cooling testing Part 1 initial tests.

  • ceramic heat sink- ok. actually a smart choice

    fan- ok

    but there are some major mistakes- fan on top of the heat sink is useless in this arrangement- the fan has to blow the air somewhere and to suck it from somewhere. putting it on top as in the photo blocks the airflow. possible solution would be to enter intermediate plate with cut off sections to allow airflow.

    simple solution would be to get turbine type fan from/for GPU and probably also the heat sink with keeping the ceramic plate as intermediate.

    the ceramic heat sink doubles the surface (may be even x4) but this is not big gain. aluminium heat sinks multiply the surface x10 and more

     

    best solution (in my opinion) would be to get a heat pipe and then there will be enough space to add extreme cooling without blocking the Pi ports.

     

    as I tested yesterday my Pi with YouTube and it overheated badly (once BSOD with dump and once did not get to the dump phase (Win IoT)) I will get some cooling also. the bad thing is that all the 3 chips get hot. the good- without cooling internet browsing and not very intensive tasks are ok.

     

    If you will 3D print case- then it is best first to consider passive aluminium heat sink and orientate the blades to be along the airflow. If I have enough time I will try aluminium heat sink with "chimney". 3 chimneys means that the Pi will have to be straight and not flat in the box, but then the chimneys can be longer. (probably the USBs will be facing up)

     

    p.s. I plan to use my Pi headless and not sure if I will use many IO pins.