Ender 3 Pro Hotend Fan is not controllable

General Discussion
1

Basic Information:

Printer Model: Ender 3 Pro
MCU / Printerboard: Ender 4.2.7 Silent Board
Host / SBC: Raspberry Pi 4B
klippy.log
klippy.log (1.0 MB)

Describe your issue:

In Klipper the bigger fan on the hotend is not controllable, but the smaller one on the side, which I’m pretty sure is for the extruder is controllable in Klipper. I would like to have the hotend fan go to 0% when not actively printing. Is this possible?
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2

This board has this fan hardwired to be always on and is not controllable by any firmware. You would need to do a hardware adaptation to be able to control it (extending the board, for example).

4

That’s interesting, I wonder why it was built that way-

Anyway, is there a guide online for how to do that? Thanks!

5

I can think of a number of reasons why the engineers have an always on fan:

  1. Safety. If the fan is always on then if you have a runaway extruder heater, the fan is always on making sure the heat doesn’t extend into the structure.
  2. Cost. No MOSFET Transistor.
  3. Don’t use a MCU IO pin if they are in short supply.
  4. Software simplification. You don’t have to put in the code to determine whether or not the fan needs to go on.

If you want to have the ability to turn it on and off then I suggest that you buy a new motherboard - I don’t know the schematic for the board but you’ll have to find either an unused pin or change an already allocated pin to this function (which means the previously allocated function will be lost).

If you want a printer that has control over the heat sink fan, then buy a new main controller board.

6

This board has unused extension ports that can be used to plug another cheap simple board for the purpose of extending its capabilities. Obviously it’s not for everyone, but investing on whole new board (and all the rest that comes with that choice) is not strictly necessary.

Unfortunately I don’t know of any guides for this board specifically…

7

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