Chaps,
I need to slow down a cooling fan speed, it is a Noctua NF-S12B Redux 700. How do I calculate resistors values?
Cheers,
Horacio
I need to slow down a cooling fan speed, it is a Noctua NF-S12B Redux 700. How do I calculate resistors values?
Cheers,
Horacio
This is a PWM controlled model. You can either buy the NA-FC1 controller that permits lossless speed control, or just connect a series resistor. I would start with 100 ohms 1W, and see if it is too high or low.
Thank you for the info. The NA-FC1 is a 4 pin PWM and my NF-S12B is a 3 pin fan. I will have to buy a 4 pin fan but it is a redux 1200RPM not 700.
Horacio
Horacio
Find specs. Do math.
Max. input current 0,05 A
Operating voltage 12 V
It "acts like" a resistor of 12V/0.05A or 240 Ohms.
It is not any kind of Ideal Resistor, but may follow the same trends for small changes.
If you have one 240r resistor at 12V, and add a 240r series resistor, each gets half. That will not be exact for a fan, but half-voltage is MUCH less air flow, almost useless. (There is also trouble with starting on low voltage.) Use something smaller. Pencil 120r series. That's a 1/3rd:2/3rd split, 8V on the fan, significant drop of noise and airflow.
Which is pretty near lcsaszar's suggestion of 100r.
The full-voltage fan power is 12C*0.05A or 0.6W. When you split the power with a resistor you can only get less power. lcsaszar's "1W" power rating seems fine. It may turn out to be 0.16W, but always pick resistor power generously. Smoke stinks.
Max. input current 0,05 A
Operating voltage 12 V
It "acts like" a resistor of 12V/0.05A or 240 Ohms.
It is not any kind of Ideal Resistor, but may follow the same trends for small changes.
If you have one 240r resistor at 12V, and add a 240r series resistor, each gets half. That will not be exact for a fan, but half-voltage is MUCH less air flow, almost useless. (There is also trouble with starting on low voltage.) Use something smaller. Pencil 120r series. That's a 1/3rd:2/3rd split, 8V on the fan, significant drop of noise and airflow.
Which is pretty near lcsaszar's suggestion of 100r.
The full-voltage fan power is 12C*0.05A or 0.6W. When you split the power with a resistor you can only get less power. lcsaszar's "1W" power rating seems fine. It may turn out to be 0.16W, but always pick resistor power generously. Smoke stinks.
+1 
PRR is right on the nose.
I did a lot of work on this 20 years ago fixing the stupidly crude cooling on early PCs.
I found some fans had trouble starting at < 7v. Adding a 100uF cap across the series R would give a reliable starting kick to allow running at 5V ish, for almost zero noise.
PRR is right on the nose.
I did a lot of work on this 20 years ago fixing the stupidly crude cooling on early PCs.
I found some fans had trouble starting at < 7v. Adding a 100uF cap across the series R would give a reliable starting kick to allow running at 5V ish, for almost zero noise.
Chiming in to confirm the "starting cap" bit.
Motor coils pull current in bursts so a source cap caters to that.
Motor coils pull current in bursts so a source cap caters to that.
I hate fan noise, for my computers I put 12V fans on 7V. If you slow down the fan, you sacrifice cooling capacity.
Amazon (and I am sure Ali Express) offer tiny PCB's containing a 2.5A voltage regulator for less than $2 each. Then you can adjust your fan speed as desired.
Granted, a switching regulator might not be what you want in audio equipment. Use the good ol' LM 317 to make an adjustable voltage. It takes a LM317 and 2 resistors. Drawings abundantly available in Google.
Amazon (and I am sure Ali Express) offer tiny PCB's containing a 2.5A voltage regulator for less than $2 each. Then you can adjust your fan speed as desired.
Granted, a switching regulator might not be what you want in audio equipment. Use the good ol' LM 317 to make an adjustable voltage. It takes a LM317 and 2 resistors. Drawings abundantly available in Google.
- Status
- Not open for further replies.