Control a 12V dc fan via PWM and a level shifter

Question

I wish to control a 4 pin 12V dc pc fan (https://www.arctic.ac/en/F9-PWM/AFACO-090P2-GBA01) with my raspberry pie. After reading several threads I came up with the following:

First problem is that the PWM signal must be 5V but the GPIOs only give 3.3V. So I decided to use a level shifter from 3.3V to 5V (https://www.amazon.com/-/de/dp/B07LG646VS/ref=sr_1_3?dchild=1&keywords=level+shifter&qid=1605728038&sr=8-3) to feed a 5V PWM signal to the fan. Other than that I connected an external 12V dc power supply to the fan (first two pins on the fan connector).

The only thing left to do is to connect the GPIO pin which I use for the PWM signal to the 4th pin of the fan. In the end my circuit looks like the one from this tutorial: https://www.raspberrypi-spy.co.uk/2018/09/using-a-level-shifter-with-the-raspberry-pi-gpio/ except that I don´t use a 5V sensor but the 5V PWM input of the fan. So the PWM signal wire is the only connection between the pie and the fan.

Good thing is that the fan is running (at full speed) when I connect the power supply. I use the following code to vary the duty cycle.

import RPi.GPIO as GPIO
import time

GPIO.setwarnings(False)

GPIO.setmode(GPIO.BCM)
GPIO.setup(12, GPIO.OUT)

p = GPIO.PWM(12, 25000)
p.start(0)

time.sleep(2)

try:
    while True:
        p.ChangeDutyCycle(100)
        print('100')
        time.sleep(5)
        p.ChangeDutyCycle(50)
        print('50')
        time.sleep(5)
        p.ChangeDutyCycle(0)
        print('0')
        time.sleep(5)
            
except KeyboardInterrupt:
    pass

p.ChangeDutyCycle(0)
p.stop()
GPIO.cleanup()

When I connect the fan to the dc power supply, connect the 5V PWM signal and start the script the fan will continue to run at full speed, no matter what.

To test if my circuit is wrong I installed a LED which gets the 5V PWM signal as the positive voltage. The LED changes from 100% brightness to 50% and then switches off as expected.

I tested every connection line of the four from the level shifter. I tested another fan. I switched to other GPIOs. Unfortuntely it´s always the same result. LED works perfectly. Fan runs at full speed all the time.

I really like the idea of using a level shifter. It´s a compact and simple solution for me. So my question is if somebody has an idea where the problem is and how to solve it.

A second question related to this is if it would be beneficial to use a L298n motor driver for fan control.

Answer 1

You need to connect a ground wire between the Pi and the fan. Otherwise the PWM signal will have no effect as the fan will not know when the signal is high or low.

I doubt that software timed PWM will actually manage 25 kHz. I don't know how the fan will react at the likely frequency of about 10 kHz (depending on the Pi model being used).

Answer 2

Since everything is working now I want to post a summary of how I am controlling a 12V fan with my Pi.

My Hardware for this is:

• 1x KeeYees 4-channel IIC I2C level shifter from 3.3V to 5V
• 1x Artic F9 PWM fan
• 1x 12V dc power supply

This is how my circuit looks like:

^{simulate this circuit – Schematic created using CircuitLab}

I figured that you could skip the level shifter and feed the 3.3V PWM signal from the GPIO directly to the fan. But it is less stable from my experience. Sometimes the fan will go to full speed as if no PWM signal is present while controlling the fan. So I recommend using a level shifter.

I wrote the following script for testing (you may have to change the GPIO pin number):

import RPi.GPIO as GPIO
import time

GPIO.setwarnings(False)

GPIO.setmode(GPIO.BCM)
GPIO.setup(12, GPIO.OUT)

p = GPIO.PWM(12, 1000)
p.start(0)

time.sleep(2)

try:
    while True:
        p.ChangeDutyCycle(100)
        print('100')
        time.sleep(5)
        p.ChangeDutyCycle(50)
        print('50')
        time.sleep(5)
        p.ChangeDutyCycle(0)
        print('0')
        time.sleep(5)
            
except KeyboardInterrupt:
    pass

p.ChangeDutyCycle(0)
p.stop()
GPIO.cleanup()

If everything is working fine the fan should turn on after 2 seconds at full speed. After 5 seconds it should throttle down to 50% and after another 5s it sould stop. Until the script is interrupted this loop will stay active.

I hope this helps anybody who is new to this stuff and wants to start up an easy PWM fan control for his project.

Answer 3

In addition to @Kai 's answer, I'm sharing my experience using PWM fan but with Super6C with CM4 modules.

My configuration:

• 1x Super6C with 5 CM4
• 1x KeeYees 4-channel IIC I2C level shifter from 3.3V to 5V
• 1x ARCTIC P12 Slim PWM PST (12v)

For PWM signal, I'm using the first CM4's GPIO18 (the only port available in Super6C per each CM4 module). I've updated Kai's script from the answer to use GPIO18 instead of GPIO12.

Below is the Super6C first CM4 module and level shifter configuration:

Super6C CM4 $1	Level Shifter
5V_CM4	HV
3V3_CM4	LV
GND	GND
GPIO18	LV1

PWM fan	Level Shifter
GND	GND
12v	not connected!!!, leave it as is
Tach	not connected!!!, leave it as is
PWM	HV1

Notes:

• you can use any LVx-HVx combo (e.g. LV4-HV4 instead of LV1-HV1)
• Level shifter has two GND (upper and lower rows) but it doesn't matter which one you connect FAN GND or CM4 GND to - upper and lower level shifter's GND are the same GND.
• you can use any CM4 module (1-6) to control PWM FAN. I used $1.
• you could potentially connect FAN TACH to other module's GPIO18 to get FAN speed via GPIO18 to LV3 and HV3 to TACH. It's not required for PWM to work and is out of the scope of my answer :).

The major caveat I had is not every PWM fan stops when p.ChangeDutyCycleis called with 0. For instance, ARCTIC P12 Slim PWM spins at 200 RPM for when p.ChangeDutyCycle(0). Apparently, stop mode was removed since many customers thought that they fan was defective because it didn't spin :D. I spent quite a bit of time debugging since I expected my fan to stop at some point using Kai's script.

I'd highly recommend to use 5v LED with 330Om resistor to troubleshoot any issues:

• run the script
• connect wire #1 to GPIO18 and wire #2 to GND on Super6c.
• the LED should be on, dimmed and then off in cycles.

Note: to determine polarity and test your configuration, connect LED + resistor to 3V3_CM4 and GND.

I hope it helps.