0

I have a Noctua NF-12x25 5V fan, used in a custom Raspberry Pi case, that's a bit too loud for my taste. Noctua sells low-noise adaptor cables for 12V their fans that, from what I understand, are just cables with an in-line resistor. I know almost nothing about electronics. How would one size a resistor and make such a cable based on the 5V fan's specifications?

Aside: I'm checking with Noctua whether this particular fan will actually run/start at 3.3V but I'm assuming it will.

tibbe
  • 101
  • Try different value resistors. It's impossible to calculate which resistor value equals to which loudness. – Justme Mar 31 '21 at 18:17
  • "How would one size a resistor and make such a cable based on the 5V fan's specifications?" - Based on the specifications? You can't. They say the fan requires 5V and and it produces 1900 rpm, period. Nothing in the specs or description suggest that the speed can be reduced, so any method you use to do it is out of spec! – Bruce Abbott Mar 31 '21 at 18:27
  • If this doesn't work well enough and you really want fan silence, buy a fan specifically designed to run quiet, preferably a larger one if it will fit and run it at less than it's full rated speed. You may also be able to find for example a 9V or 12V fan that will run at a lower speed at 9V without wasting power in a resistor. If you know how to program a Pi, your skills are enough that you could consider a PWM fan controller with a temperature sensor. This will let you run the fan at a lower % of rated speed than a resistor, and make it auto adjust with temp. What appeals? – K H Apr 01 '21 at 03:53
  • Also, do you have any other fans available to experiment with? What is your power budget for the fan? If I'm reading Noctua's ultra quiet list correctly, your fan is on it and there is a 5V PWM 4 wire version available, although fans without actual PWM capability can often still be PWMmed for some increase in operating range. – K H Apr 01 '21 at 04:05
  • Off the top of my head most of the similar fans I've messed with will run at 60% of rated voltage, and many will run as low as 40% of rated voltage, so somewhere in there is the boundary of what can be achieved adding a resistor. If a fan will run but not start at a given voltage, you can also make a circuit to start it at 5V and then reduce to running power. Do you have a variable voltage source, a bunch of AA/AAA batteries or some resistors in the range of 25 to 500 Ohms available? Depending on what you have to use we should be able to establish an effective voltage. – K H Apr 01 '21 at 04:12

0 Answers0