Silencing a 5V Fan on 6V: Recommended Resistor Value for Optimal Noise Reduction

  • Thread starter Thread starter jiggleswiggly
  • Start date Start date
  • Tags Tags
    Fan
Click For Summary

Discussion Overview

The discussion revolves around the challenge of reducing the noise of a 5V fan powered by a 6V supply. Participants explore methods to achieve quieter operation, particularly through the use of resistors to drop voltage, while considering the implications of back EMF generated by the fan motor.

Discussion Character

  • Technical explanation
  • Debate/contested
  • Exploratory

Main Points Raised

  • One participant seeks advice on the appropriate resistor value to reduce the noise of a 5V fan running on a 6V supply.
  • Another participant calculates that a resistor value of approximately 6.66 ohms would be needed to drop the voltage from 6V to 5V, suggesting a standard 6.8 ohm resistor as a practical option.
  • It is noted that using a 15 ohm resistor would reduce the voltage further to about 4.125V, which may quiet the fan but could risk stalling it.
  • Concerns are raised about the fan's current draw at lower voltages and the potential for back EMF to affect performance, indicating that the fan does not behave purely as a resistor.
  • A suggestion is made for a novel approach involving a mini duct muffler, though details are limited due to potential associations with illegal activities.

Areas of Agreement / Disagreement

Participants express differing views on the implications of using various resistor values and the effects of back EMF on the fan's operation. There is no consensus on the optimal resistor value or the best approach to achieve the desired noise reduction.

Contextual Notes

The discussion includes assumptions about the fan's behavior under different voltage conditions and the impact of back EMF, which may not be fully resolved. The calculations presented rely on specific current ratings and may vary based on actual fan performance.

jiggleswiggly
Messages
4
Reaction score
0
amazon.com/gp/product/B000XTFYSQ/ref=oh_details_o01_s00_i00So I bought this fan. My modem zoom 5341 kept overheating. So I stuck this in there, and soldered it to the 6v incoming.

Now, it's a bit too loud. I've never run it off 5v to see how loud it would be, but I imagine it would still be a bit loud. I want to make it near silent.

So what value resistor should I use to make it silientish?
Thx guys

Something like dis?
(6-4)/.15 (.15 is the amps the fan uses)
thats 13 ohms.
sound reasonable?
 
Last edited:
Engineering news on Phys.org
In normal use it draws 150 mA at 5 volts.

So, if you had 6 volts and wanted to run the fan off 5 volts, you would drop 1 volt in a series resistor.

The value of this resistor would be (1 volt / 0.15 amps) or 6.66 ohms. It would dissipate 150 mW, so a half or quarter watt resistor would be OK. The nearest standard value would be 6.8 ohms.

15 ohms would drop the voltage to about 4.125 volts which should be quieter, but may stall the fan.EDIT, just saw your calculation. The fan would draw less than 150 mA on 4 volts. To do the calculation, you work out the resistance of the fan (5 volts / 0.15 amps) or 33 ohms.
Then you work out the voltage from this.
It is still a bit of a guess because the fan may be generating back EMF.
 
Thx
what do you mean by generating back emf though?
 
A novel idea would be to make a mini duct muffler. Its hard to link you because its highly associated with an illegal activity.
 
jiggleswiggly said:
Thx
what do you mean by generating back emf though?

I mentioned that because a motor does not behave exactly like a resistor, so its current cannot be accurately predicted if the supply voltage is not the rated voltage. 5 volts in your case.

What happens is that the battery makes the motor turn, but a turning coil in a magnetic field is also a generator, so the motor generates a voltage which opposes the supply voltage.

This means the current is less than you might expect from just measuring the resistance of the motor.

So, you can find that a stalled motor draws a lot more current than a turning one, even if it has a lower supply voltage on it.

If you study motors you will find this is a very important effect. So, you learned something you didn't ask for.