Thinkcat
Posts: 28
Joined: Wed Mar 14, 2018 10:50 pm
Location: Finland

Cooling compatibility between 3B, 3B+ and 4B

Tue Jun 25, 2019 12:32 am

Hello

I bought a heatsink + fan combination from Amazon for my model 3B. The title said that it's for 3B+, 2B and 3B. Now that I tried to install it, I saw that there is no way it will work on a 3B. The same thing was described as "3B+ only" in Aliexpress.

Now I could a) return it for a refund or b) buy a 3B+ for it. But since model 4 is here, I started wondering, will it work with model 4?

Am I correct that model 4 has the RAM between the CPU and the network chip? And since there is a bump in the cooler for the network chip, then I assume the RAM would be left without cooling. Is that a serious disadvantage?

I am talking about this: GeeekPi Raspberry Pi Fan Kit Aluminium Heatsink with Fan for Raspberry Pi 3B + and Raspberry Pi 3/2 Model B

Edit:

Yeah, the chip there (D9WHV) is the RAM. And the networking chip (BCM54213PE) has moved, but only slightly. As long as the RAM chip sits lower than the CPU, it should be possible. And if the RAM and CPU are on the same level, then it will cool the RAM also.

Another edit:

No. The RAM chip would require its own bump. Saw a picture that was three-dimensional enough to see that.

Yet another edit:

Here is the link to Aliexpress: GeeekPi Original CNC Extreme Cooling Fan Heatsink Kit For Raspberry Pi 3B+ / 3B Plus, Not suit 3B Board

LTolledo
Posts: 2165
Joined: Sat Mar 17, 2018 7:29 am
Location: Anime Heartland

Re: Cooling compatibility between 3B, 3B+ and 4B

Wed Jun 26, 2019 12:22 pm

might not fit the RPi4B board as is, as the LAN and 2 USB ports exchanged locations.

however, with a bit of machining or patient filing (but will loose the protective paint on the modified part) you may be able to fit the heatsink to the RPi4B. You might loose on warranty for the heatsink-fan combo.

or just wait for a newer version specifically designed for the RPi4B....
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Come to me with 'problems' and I'll help you find solutions"

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Thinkcat
Posts: 28
Joined: Wed Mar 14, 2018 10:50 pm
Location: Finland

Re: Cooling compatibility between 3B, 3B+ and 4B

Wed Jun 26, 2019 1:04 pm

Some general musings about cooling.

I think on a personal level that my Pis should be able to run sysbench or cpuburn and not throttle. Or at least I am interested in what do I need to accomplish exactly that level of cooling.

The cooling solutions can be divided into several camps. I am only here concerned about the CPU:
  1. Nothing. Just let the Pi get along with what it has. Variations of this are if the Pi is in a case or in open air.
  2. A random aftermarket heatsink attached to the CPU by some sticky thermal paste or thermal tape. Pi in a case or in open air. These can be as small as 14 x 14 x 6 mm or as big as 28 x 28 x 15 mm. I think the latter one is the biggest that can be safely fitted. Or 25 x 25 x 15 mm.
  3. The Pi inside a case that has a fan, but nothing attached to the CPU.
  4. The Pi inside a case that has a fan and a random heatsink stickied on top of the CPU.
  5. A heatsink with a fan or two fans, stickied on top of the CPU.
  6. A big heatsink that covers most of the surface of the circuit board and is attached using screws.
  7. The previous one and a fan added on top.
  8. A case, usually machined out of aluminium, with extrusions that touch the CPU and conduct heat away.
General notes:
  1. This way the Pi will inevitably throttle if you do a stress test or compress a big file or something. This is what I wish to avoid.
  2. Good thermal pastes used with big CPU coolers, like ones from Noctua, are not sticky but depend on some other fixing mechanism. Thermal tapes come in wide variety of qualities, and it's probable that the Amazon and eBay stuff is among the worst. The efficiency is measured as Watts per surface area per Kelvin or a variation of that (Kelvins per Watt for a certain surface area is another). There is a point of diminishing returns somewhere when the size of the heatsink is increased. One should also watch for air circulation around the heatsink. This might favor 10 mm high heatsinks intstead of 15 mm high ones.
  3. A bad heatsink is generally slightly better than no heatsink at all.
  4. I'd be very interested in whether this solution avoids throttling.
  5. This is interesting, except that one is usually dependent on thermal tape.
  6. This is a good, technically pure solution, since this allows one to use real thermal paste and the heatsink is fixed in place safely.
  7. If the previous one is not good enough, then this, preferably with a thermally controlled fan, should guarantee success.
  8. I only have model 3B. So I have already run into a situation where I have a cooling solution (type 5) that was sold for 3B but only fits 3B+. This same problem exists with many machined aluminium cases, since the extrusions that land on top of the CPU are made either according to the 3B or 3B+, which in latter case implies more unnecessary thermal interfaces with model 3B. Sometimes even some thick and horribly inefficient "thermal tapes".
There are some good ideas. Some ideas good but not good enough. And some ideas that would be good if some of the stuff in eBay would not be subpar or barely workable.

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