The hotend fan is running even when the hotend is cold

General Discussion
1

Basic Information:

Printer Model: Creality Ender 6
MCU / Printerboard: Bigtreetech skr mini e3 V3.0
Host / SBC Raspberry py 4b
klippy.log

klippy.log (195.8 KB)
printer.cfg (8.2 KB)

The hotend fan is running as soon as I start the printer.
What can I do do start the fan when the hotend is 50 degres?

I have in my printer.cfg:
[heater_fan hotend_fan]
pin: PB15
heater: extruder
heater_temp: 50.0

I have a classic direct drive E3D hemera.

2

Maybe a broken MOSFET ?

3

What happens if you comment out your [heater_fan hotend_fan] statement like:

# [heater_fan hotend_fan]
# pin: PB15
# heater: extruder
# heater_temp: 50.0

If the fan still runs then you probably have a broken driver transistor.

4

Tryed to comment away as sugestion, but the fan still run.

5

The last thing you can try is to swap the fans (with the control pins) in your printer.cfg to see if the heatbreak_cooling_fan is now on continuously and you can control the hotend_fan:

[heater_fan hotend_fan]
pin: PC7 # <=== was PC15
heater: extruder
heater_temp: 50.0

[heater_fan heatbreak_cooling_fan]
pin: PC15 # <=== was PC7
heater_temp: 50.0

If the problem moves to the other fan than you’ve definitely got a bad main controller board.

6

Have read a bit about the problem and creality ender 6. Apparently the hot end fan is running constantly on this model. It has a small circuit board on the top right back of the printer, where stepper motors etc. are connected, then a wide cable runs down to the mcu at the bottom.
This small circuit board is feeding the fan power all the time.
Maybe you can disconnect it from that board and extend it down separately to the bigtreetech mcu “hot end heat sink fan” port.