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Mac mini 2018 Hexa Core Cooling Analysis

Fixing the stock cooling in a 2018 Mac mini

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The cooling solution Apple designed for the Late 2018 Mac Mini wasn’t properly validated before shipping their product. Yes, the TIM they use isn’t great, but that is hardly the issue. A detailed analysis at the thermal performance, a greater understanding of the thermodynamic properties at play, and creating a replacement cooling solution is what I’m attempting to do through the course of this project.

Publicly, the following is known:

  • 8th & 9th "generation" processors marketed TDP is not a fixed, maximum TDP
    • TDP for these "generations" have two, separate parts: PL1 & PL2.
    • PL1 is the marketing TDP that ranges from 35 W to 95 W for desktop-class processors.
    • PL 2 is PL1 * 1.25, or 25% above the marketed target.
  • Apple's stock thermal paste is dried crap.
    • Not literally, but figuratively
    • If it was literally, you'd have an awful stink when you used the computer under any moderate or heavy workload.
  • Replacing a base model's, on with an i3-8100B, TIM with Arctic's MX-2 prevents sitting at 98-100 °C load temps on the i3 quad core.
  • What will happen with an i7-8700B? I plan on finding out
  • Since I will be attempting to correct a design flaw and restoring the performance of the machine, I have a legitimate defense under Right to Repair legislation if Apple gives me grief in the future.

Mac mini (Late 2018) Cold Plate - EHP Mod.scad

Modified for aftermarket heat pipes with 3 pairs listed. Will update when material reduction is present to lower cost of manufacturing.

scad - 4.78 kB - 01/15/2019 at 23:08

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Mac mini (Late 2018) Cold Plate - SA Mod - Sine Wave.scad

Modified cold plate for thicker and louvered cold plate for greater surface area and all copper construction. Code cleanup & heat pipes added.

- 5.90 kB - 01/10/2019 at 04:15

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Mac mini (Late 2018) Cold Plate - Clearance.scad

Stock cold plate with EMI cage clearance added.

- 2.31 kB - 01/10/2019 at 04:14

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PwrData_2018-12-25_17-30-00 - MM i7-8700B MX-2 & Lapping.csv.bz2

Lapped Heatsink & MX-2 TIM Hardware Thermals, bzip2 compression

Bzip2 Archive - 23.30 MB - 12/26/2018 at 03:40

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PwrData_2018-12-25_17-30-00 - MM i7-8700B MX-2 & Lapping.csv.xz

Lapped Heatsink & MX-2 TIM Hardware Thermals, xz compression

xz - 17.83 MB - 12/26/2018 at 03:40

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  • Brief Update

    Michael O'Brien6 days ago 1 comment

    It's been about 6 months since I've updated this project and I've been busy with many things, but nothing practical to show for it:

    • I just did a quick update of the tags a little bit ago but didn't spam the feed with it.
    • I've been tracking down a deeper understanding of various thermodynamic properties and what role they play in what I'm trying to accomplish
    • Doing various additional 3D modeling to minimize cost of producing new parts. I also produced a clear resin print for case tolerance testing and fitment, which I'll post when I get around to using it.
    • Attempting to understanding various material properties and how they influence thermal performance has been where my focus exists, which means trolling a lot of research PDFs.
    • I still need to write up some Arduino code to take some thermal readings of the cooling solution since I'm polling 4 thermocouples that have been attached to very specific points on the cooling solution. It doesn't help that I'm not in the same thermal environment when I did my original testing.
    • After taking those readings, I also need to characterize the thermocouples to reduce their error and refine the data. From there, I can reasonably determine which of the 3 parts of the cooling solution has the greatest thermal resistance to prove or disprove my previously stated hypothesis.
    • Located/purchased a near-identical, full copper, zipper fin stack on AliExpress for under $15.

    Work is ongoing. I'm not done with this project by any reasonable measure.

  • Detailed Analysis of the i7-8700B & i5-8500B - Part 2

    Michael O'Brien02/08/2019 at 23:38 2 comments

    Due to the physical length of the previous log, I have written this one for a more detailed analysis and to posit a few ideas to keep performance along around longer despite the thermal limitations.

    Read more »

  • Detailed Analysis of the i7-8700B & i5-8500B - Part 1

    Michael O'Brien02/08/2019 at 08:53 0 comments

    After a bit of voodoo with Excel, I was able to make some dynamic graphs and simultaneously extract temperature, wattage (power), and absolute thermal resistance from the logs I created. I reached out to a YouTuber, PixelPoison, and asked him to run the same cooling test I did and pass me the data. He was nice enough to do so. I wanted data for the i3 variant, but didn't get a response, though after stepping through the i5 data, I'm not terribly concerned about it.

    The 'B' designation of the CPUs is insignificant in this testing, but is included for accuracy.

    Read more »

  • Plans A1/A2, Plan B, & Plan C Details

    Michael O'Brien01/19/2019 at 09:20 0 comments

    As I've been working on the project, I've been able to figure out what needs to be done and what I can do in order to try and achieve it. As such, I've been developing backup plans concurrently to each other. What I'll be discussing here is the figurative fleshing out of the said ideas and bringing up the rationalization of that has cause me to pump over to the "next level" of cooling, thus the next plan. Most of what I've already written thus far is regarding Plan A. What I'd like to achieve is a solution that fits inside the mini if at all possible.

    Note: I'm not providing many links in this log right now due to the WIP-state a lot of the research I'm conducting. With whichever plan(s) I execute, I will have full documentation.

    Read more »

  • Models Updated & Further Development

    Michael O'Brien01/14/2019 at 12:06 0 comments

    Adjusted a couple little parameters of the CAD files based on inaccuracies of the model that printed. Just widening the space between the threaded posts and adjusting the cutout for the heat pipes.

    To do list:

    • Place general markers in the CAD files for the fin stack and tie down points and some other clearance objects.
    • Develop a 5 pipe setup to provide a thermal capacity of over 200 W via the heat pipes and a copper interconnect.
    • Develop a larger cold plate with integrated barbs for possible water cooling.

    While spending more time reading up and playing with variables, it appears that the fin stack may also be insufficient. If that proves to be the case, then I will escalated things. In order to prove it, using two, short heat pipes to conduct up to 200 W of heat off the cold plate into a remote copper slug will be used. This will be right next to the speaker. 3 heat pipes will connect the slug to the fin stack. Despite the thermal resistance of the additional slug, it'll be modeled for all 5 pipes and in a way such that they can touch and be soldered to each other. If that doesn't provide my 50 °C temperature delta, then I have a last resort.

    Not practical on the machining side, but great for DIY, I will then enlarge and create a cavity in the cold plate. Enough room for a 1.5-2 mm thick copper foam sheet. After bolting and sandwiching, a cold plate with a larger thermally conductive surface area will have been made. Trim a few fins on the fin stack and you can create a custom, rather mini, water cooling loop.

  • Test Print Ordered (Updated)

    Michael O'Brien01/10/2019 at 04:57 0 comments

    STL files don't translate well over to a machine shop for making prototypes. In my travels, I came across https://print.all3dp.com/. There are probably other, better sites, but this works well enough for what I seem to need. I took the OpenSCAD model, outputted a STL model with angles aliased to every 10 degrees, and have an SLS print in nylon on the way and it will be here Friday. I'm serious about "fixing" the cooling solution.

    Read more »

  • Preliminary Results, Notes, & Conclusion

    Michael O'Brien12/30/2018 at 05:41 0 comments

    It has taken a few days to look at the data I've collected and tried to figure out what is going on. Why did I not see a notable increase in performance via reduced temperatures or faster clock speeds? Why did the quad core version have its thermals mostly sorted, albeit they are still high? Why do I have a 8-10 ˚C delta between half of my cores? What is my power consumption of the CPU more than 1.5 times that of the rated TDP? Did Apple fsck up or did Intel? Yes, Intel.

    Read more »

  • Mac mini i7-8700B Lapped CSV Files

    Michael O'Brien12/27/2018 at 04:07 0 comments

    Here are the CSV files of the thermal results from lapping the heatsink and using MX-2 TIM, compressed with 7-zip & bzip2, for others to look at on their own.

    Mac mini i7-8700B Lapped Thermals (bzip, ~23 MB)

    Mac mini i7-8700B Lapped Thermals (xz, ~18 MB)

  • Stock Thermal Solution

    Michael O'Brien12/26/2018 at 10:32 0 comments

    The following dimensions will be on the cold plate only, and not including the solderd-on heat pipes. The bottom side of the cold plate is recessed - maybe due to shielding - but anyhow, if you assume the corners are not radiused, this cavity is 1.25" by 1.8", or 31.5 mm by 100 mm. The depth of the cavity is 0.03655" or ~0.9284 mm. The external thickness of the cold plate is 0.11585" or 2.9426 mm, including paint.

    Read more »

  • TDP, Cooling, & Thermals

    Michael O'Brien12/26/2018 at 05:57 0 comments

    TDP, Thermal Design Power

    Very recently, the enthusiast community has dug into Intel's TDP ratings and performance. Even since Multicore Enhancement, aka MCE, the performance of Intel's CPUs has varied depending on the motherboard manufacturer. The frequency at which a CPU operates is dependent upon a number of factors and even some limitations like T-Junction, which is 100 ˚C for all three CPUs in this configuration.

    If you want to dive into the discussion of Intel's TDP ratings and how they fluctuate, you can read a number of articles such as this on over on Anandtech.com. More or less, TDP is allowed to be fairly high for some time frame before throttling down for thermal reasons inside the die. This upper limit is called the PL2 state, which is 125% the rating of the listed, marketed TDP, which is called PL1. For all three CPUs in the Mac mini 2018, the PL1 TDP is 65 W, thus PL2 is 81.25 W.

    Read more »

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