Can You Run PWM Fan Without PWM Input?

In summary: Most likely. I didn't look at the datasheet. Assuming the power supply voltage is the same as the logic voltage, then yes. I would pull it up with a 10k-100k resistor, also maybe a .1uF decoupling capacitor from the PWM lead to ground so it has a stable voltage if the supply has transients from the motor.
  • #1
gomerpyle
46
0
Excuse my lack of knowledge on PWM and fans, but can a fan configured with 4 wires (power, ground, tach. signal, and PWM input) be run off of a DC power supply without using the PWM to control its speed? As in, not using the PWM lead and just hooking up power/ground and controlling fan speed by adjusting voltage? Or is it required that the PWM be used if you wanted to be able to adjust the fan speed.

This is the fan I was looking at:

http://search.digikey.com/us/en/products/3122FT-D4W-B56-E50/P14778-ND/2647852

Don't have much of an electrical background so I was hoping someone with more knowledge could help me out.
 
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  • #2
Could you set the PWM lead to 100% duty cycle, and then vary the DC power supply voltage?
 
  • #3
DragonPetter said:
Could you set the PWM lead to 100% duty cycle, and then vary the DC power supply voltage?

Problem is I don't have a motor drive for PWM. All I have to work with is a DC psupply. That's what I'm wondering is if the lead wire for PWM just gives you the "option" to use that function if you want to, but otherwise you can just adjust fan speed directly with voltage if you hook up the other leads.
 
  • #4
gomerpyle said:
Problem is I don't have a motor drive for PWM. All I have to work with is a DC psupply. That's what I'm wondering is if the lead wire for PWM just gives you the "option" to use that function if you want to, but otherwise you can just adjust fan speed directly with voltage if you hook up the other leads.

PWM at 100% just means its pulled up to logic high. Its PWM would be 0% if you grounded the lead.
 
  • #5
gomerpyle said:
... run off of a DC power supply without using the PWM to control its speed? ...
Maybe. I remember reading a blog where the guy was experimenting with computer case fans. He found that the circuitry inside the fan varied by manufacturer. If I recall correctly, some fans will work without a PWM signal, others won't.

It might have been on Hack-a-Day or Instructables.
 
  • #6
DragonPetter said:
PWM at 100% just means its pulled up to logic high. Its PWM would be 0% if you grounded the lead.

so to run the fan at 100% pwm I would just connect the pwm lead to the + terminal on the power supply?
 
  • #7
gomerpyle said:
so to run the fan at 100% pwm I would just connect the pwm lead to the + terminal on the power supply?

Most likely. I didn't look at the datasheet. Assuming the power supply voltage is the same as the logic voltage, then yes. I would pull it up with a 10k-100k resistor, also maybe a .1uF decoupling capacitor from the PWM lead to ground so it has a stable voltage if the supply has transients from the motor.
 

Related to Can You Run PWM Fan Without PWM Input?

1. Can you run a PWM fan without a PWM input?

Yes, it is possible to run a PWM fan without a PWM input by connecting it to a constant 12V power source. However, this will result in the fan running at full speed constantly, without the ability to adjust the speed.

2. How can I control the speed of a PWM fan without a PWM input?

If you want to control the speed of a PWM fan without a PWM input, you can use a separate PWM controller or a fan speed controller. These devices can be connected between the fan and the power source to adjust the speed of the fan.

3. Is it safe to run a PWM fan without a PWM input?

Yes, it is safe to run a PWM fan without a PWM input as long as you are using a compatible power source and not exceeding the maximum voltage and current ratings of the fan. However, it is not recommended as it can lead to unnecessary wear and tear on the fan.

4. Can I damage my PWM fan by running it without a PWM input?

Running a PWM fan without a PWM input will not immediately damage the fan, but it can lead to premature wear and tear due to the constant full-speed operation. It is best to use a PWM input or a separate controller to properly regulate the fan speed and prolong its lifespan.

5. What are the advantages of using a PWM input for a PWM fan?

The main advantage of using a PWM input for a PWM fan is the ability to adjust the fan speed according to the system's needs. This can result in quieter operation, lower power consumption, and better cooling performance. Additionally, it can help extend the lifespan of the fan by reducing unnecessary wear and tear.

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