PROJECT: Prusa i3 MK3S Extruder Heatsink

It may come as a surprise but some 3D printer extruder stepper motors tend to run quite hot, like +25°C above ambient hot. This is not too bad when your ambient/room temp is ~20°C, but boy do the summers in Australia get toasty... and if things get toasty enough the heat can creep through the shaft/driver gears and warm up the filament surface, making it that much harder to feed in controllably

Now as far as I am aware I have not run into this issue with my Prusa i3 MK3S + MMU2S, however I was curious to see:

  1. What is the typical temperature rise of the extruder stepper motor
  2. If installing a passive (no fans) heatsink could help lower the above temperature

The Setup

I tested the extruder stepper motor of my Prusa i3 MK3S under 3 scenarios:
  1. Original (no heatsink)
  2. Dense fin pattern heatsink (ATS-FPX040040025-05-C1-R0)
    • Single fin dimensions are 0.8 x 8.5 x 22.2mm and there are 50 of them
    • Weight 29.6g
    • Thermal resistance 8.7°C/W (unducted flow)
  3. Light fin pattern heatsink (ATS-CPX040040025-116-C1-R0)
    • Single fin dimensions are 0.9 x 8.5 x 22.2mm and there are 32 of them
    • Weight 21.4g
    • Thermal resistance 4.1°C/W (unducted flow)
    • Suspect this will be the winner due to the spread fins 

In each case I logged the stepper motor & room temperature, from which the temperature rise (above ambient) value was calculated. I should point out that comparing the Δ/change in temperature is more suitable here instead of say comparing the absolute peak temperature in each scenario 

Also to make sure I was testing the heatsink performance (and not how well it coupled to the stepper motor) I used a crazy high thermal conductivity pad. The EYG-A091202DM, which is graphite based and has a thermal conductivity of 1850W/m·K! (two orders of magnitude higher than your typical thermal pad)
NOTE: To mount the heatsinks I had to change the M3 screws from 30mm to 35mm

Finally, for those curious this is the model I was printing for the test:

The Results

As I suspected the lighter fin pattern heatsink (ATS-CPX040040025-116-C1-R0) gave the lowest temperature rise, reducing it by a cool 7°C compared to no heatsink

On paper this may sound surprising, as this heatsink has a lower thermal resistance (4.1°C/W vs 8.7°C/W) which in theory should mean worse performance. BUT what one must realise is that we are extracting/exchanging the heat from the heatsink via convection currents (not forced air flow), and in this case it's easier for the air to couple into a less dense fin pattern

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