Bending fins in Active Cooler Pi5? PiNAS (Radax Penta SATA HAT + RaspberryPi5)

Comments

• frongt@lemmy.zip ⁨1⁩ ⁨week⁩ ago

  Just pop the heatsink off and do it.

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• Cyberflunk@lemmy.world ⁨1⁩ ⁨week⁩ ago

  A heatsink works by increasing surface area to dissipate heat through convection (air moving past it) and radiation (infrared energy). The key principle is:

  Heat dissipation ≈ Surface Area × Temperature Difference × Heat Transfer Coefficient

  but, for me, math is hard, so…

  Why You Can Cut Fins Off (Usually)

  1. Diminishing Returns: Each fin you add provides less cooling benefit than the previous one because:

  • Inner fins get less airflow (they’re shielded by outer fins)
  • Heat has to conduct through more material to reach outer fins
  • The temperature gradient decreases as you move away from the heat source

  1. The Rough Rule: A heatsink typically operates with 30-50% margin. So if it’s rated for 5W and your RPi CPU draws 3W, you have room to lose some fins.
  2. Fin Efficiency: There’s actually a mathematical concept called “fin efficiency” - fins that are too long or too closely spaced become ineffective. The last row of fins might only contribute 10-15% of total cooling.

  Napkin Math Example

  Say you have a heatsink with 8 fins:

  • First 4 fins: ~60% of cooling
  • Next 2 fins: ~25% of cooling
  • Last 2 fins: ~15% of cooling

  Cutting off one row (2 fins) loses maybe 10-12% of cooling capacity. If your CPU was running at 65°C with the full heatsink, it might now run at 68-70°C - usually fine since RPi CPUs throttle around 80-85°C.

  When You Can’t Cut Fins

  • If the heatsink was already barely adequate
  • If you’re overclocking
  • If ambient temps are already high
  • If there’s no airflow

  The real question to ask: “What’s my current CPU temp under load?” If it’s 60°C, cut away. If it’s 78°C, maybe find a different heatsink.​​​​​​​​​​​​​​​​

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  • edgyspazkid@lemmy.wtf ⁨1⁩ ⁨week⁩ ago

    Okay. Thanks for a napkin math example (I finds math hard…) I get it now!

    “What’s my current CPU temp under load?”

    I gotta check when I run full service. I use docker or podmans (I’ve heard Podman is less resource-hungry but fact check me if it’s not ture) for almost every service only Tailscale is installed via curl.

    So basically

    watch -n 1 vcgencmd measure_temp # To watch my temp and if it's above 78°C - 80°C buy new cooler and immediately stop using it t not overheat my Pi5!
    

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