Rock 4C Plus - Fan is spinning after SBC power off

#1

Good day! Please help witth the following problem:

On my Rock Pi 4C Plus fan connector delivers full power when SBC is turned off.

At the same time - when SBC is turned on - official Debian distribution from Radxa (rock-4c-plus_debian_bullseye_xfce_b55.img.xz) has algorithms that adjust the fan speed when temperature increases.

So I connected separate PWM fan hardware controller to FAN pins so that cooler won’t work when 4C+ is shut down.

But at the same time, external PWM fan conroller won’t work when OS is booted, because software algorithm will interrupt hardware PWM controller functioning. I tried different thermal-governours - but this doesn’t help - OS is not running fan at full power therefore PWM fan controller has low voltage issues.

That’s why I need you help in either:

  1. Fully cut Fan pins power when SBC is not working

  2. If it’s impossible to do that - keep Fan pins power always at Max voltage so that I can connect seperate PWM fan controller.

Thank you!

#2

You may use USB to power up the fan and PWM pin for PWM control

#3

Thank you!

This could be a solution as workaround, but it either requires soldering wires or use of USB/GPIO port to connect.

Anyway it’s interesting to know if there are any software methods to regulate fan connector under Official OS images.

Also, I’d like to understand why fan is at full power when sbc is turned off - is it a hardware fault or this can be also fixed on software level as well?

#4

Because that how PWM works.
If it’s zero on 4 pin it’s 100% speed
The 5V gpio is always on if there power input if I remember correctly (need to test it)

#5

Yes 5v gpio is always on. 3.3v gpio and usb are on when sbc works.

If fan connector of Rock Pi 4C+ has 2 pins including pwm pin - how should I connect my 4 pin pwm cooler, that has plus, ground, rpm and pwm wires? So that it will shut down when sbc is off?

#6

Hm, if connector using pwm as ground then I’m unsure regarding how safe it will be to connect 5V to usb and pwm to GPIO

#7

So actually fan connector is useless if you cannot connect cooler just to fan connector?

Because somehow this fan connector should deliver 5v and PWM signal at the same time?
To my understanding PWM connector should have at least 3 contacts: +, - and PWM signal.

Not clear how it should work in Rock Pi 4C+ being honest.

Please help, because I don’t have enough knowledge about connecting PWM cooler to 2 pins on SBC.

#8

Can you check your 4C+ hw revision?

Because of a hardware limitation, the fan can not be turned off after power down.

#9

Hm, then I’m unsure how exactly it works.

In theory you are correct you need power, ground and control.

But it’s possible to use only 2 connector and control incoming voltage

#10

Rock Pi 4 C+ v1.41.
Understood about limitation.

#11

Soldered PWM conroller to USB 2.0.

Thank you everyone for help! I just wanted to be sure that there is no easier way before soldering wires to USB resulting in guarantee loss.

Not good for Radxa to add useless fan connector, while Rockchip RK3399T really needs active cooling.

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#12

To be fair - turning off rock pi 4c without turning off the power input is unusual case, since it’s impossible to turn it back on (with exception of RTC alarm) without replugging power

#13

On my Rock 4C+ and Debian from Radxa power button works both On and Off, so no need to plug in/unplug power.

I noticed that with certain Armbian distributions SBC doesn’t fully turns off and CPU continues staying warm even after shut down.