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Best way to make an external fan controller?

38034580
By 38034580
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It will be 3 speeds (off/lo/med/hi). Is the best way to do it is to use a 54 ohm resistor on the low contact, a 27 ohm resistor on the medium contact, and a direct connection for high (and no connection for off)? I attempted this once and it was humming. How do I reengineer this to make it better? The power source is a 12v power adapter. It is a 4 wire fan.

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37 minutes ago, James Evens said:

The simplest DIY solution would be a voltage divider. Not perfect but good enough for fans.

You probably need to wire some of them in parallel to get enough heat dissipation (through hole are typically 1/4 W).

 

It is 4 wires.

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6 hours ago, 38034580 said:

It will be 3 speeds (off/lo/med/hi). Is the best way to do it is to use a 54 ohm resistor on the low contact, a 27 ohm resistor on the medium contact, and a direct connection for high (and no connection for off)? I attempted this once and it was humming. How do I reengineer this to make it better? The power source is a 12v power adapter.

 

Easiest for someone would be using resistors to limit the current going to the fan. The only thing you have to worry about is the power rating of the resistor - you must use a resistor rated for more power than what would be dissipated in the resistor.

The downside with this method is that the resistor values depend on the fan used, and it's power consumption. 

 

Next easiest method would be to use an adjustable linear regulator. At the very least, you would need two resistors or a resistor and a potentiometer, to configure the output voltage.  Optional (but nice to add) would be a couple capacitors, one on the input and one on the output of the linear regulator. 

 

Some very cheap and very popular and common regulators are  LM317  and *1117  (1117 with some letters in front, the code of various companies that make it)  but I do have to note that 1117 regulators sometimes have the order of the pins different so you have to pay attention and, some must have a small electrolytic capacitor on the output (ex 10-100uF) otherwise they can work erratically. 

 

LM317 even has a Wikipedia page : https://en.wikipedia.org/wiki/LM317

The first example circuit there is all you need ... use 100-120 ohm for RH  and then use either a resistor or a potentiometer for RL ... the output voltage will be V out  = Vref (1 + RL/RH)

 

Same story for the 1117 chips , see example circuit at page 9 in datasheet : http://www.soloelectronica.net/PDF/LM1117.pdf

 

image.png.c14273a2db9a066d4d70c8977ec45f5f.png

 

Like the previous regulator, use around 100 ohm for R1 , and R2 can be resistor or potentiometer ... the output will be  Vref value  x  (1 + R2/R1)   ... Vref is 1.25 for these regulators, your R1 will be 100-150 ohm , so by adjusting R2 you can adjust the output voltage.  Iadj is so small that you can basically ignore that IadjR2 in the formula.

 

( but note that you don't need Tantalum capacitors as the notes recommend...  when the datasheet was written 10-20 years ago, tantalum capacitors were the only ones that had reasonable good specifications at that low capacitance value of 10uF, nowadays you can find 10uF electrolytic capacitors that the designers of the chip and writers of datasheet didn't have ... so you can use a regular 10uF or better electrolytic capacitor on the input) 

 

The only downside of these linear regulators is that  they have a dropout voltage, a minimum voltage they use ... LM317 has around 1v..1.5v and 1117 chips have around 0.8..1.2v ... there's other newer linear regulators with as little as 0.1...0.3v 

Basically, if you give it 12v, the linear regulators maximum output voltage will be  12v - dropout voltage , so you'd be able to give fans  1.25v....10.5-11v  which means the maximum speed of the fans will be a bit lower. 

The plus size is you can finely control voltage from something like 5v all the way to 11v+ and you can connect more than 1 fan to the regulators, up to their maximum current of around 0.8A..1A for 1117 chips and around 1.5A for the LM317 chips  (but note a heatsink may be required for more than 1 fan)

 

 

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Maybe this isnt an issue with new fans anymore, but they might not be able to start up with lower voltages, so without feedback from the fan you have to be a little careful.

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