Controlling multiple fans with a single potentiometer

Hi all, I have a project that involves several 120mm CPU case fans. They each come with a 10k potentiometer, however, I wanted to use a single potentiometer to control fan speed across all fans simultaneously. I tried a parallel circuit across two fans where the potentiometer input/output was hooked directly to both fans' potentiometer controls, and it burned out one of the fans... I had assumed it would work because the potentiometer would provide equivalent voltage drop across both inputs but apparently I was incorrect.

Would a series circuit work (ie, each fan's positive potentiometer input connected to the next one's negative and so on until the loop is closed at the pot)? I'm worried about burning out another fan.

Thanks for any help!

send your schematic to know your connection diagrm with motor specifications

SilverStone FM121 INTRODUCTION This is the type of fan. It has a 12v DC in power supply, along with a 2-pin JST connector for the B10K potentiometer input.

I currently have 3 of the fans connected in parallel to the 12v power supply:

S = Fan, 5v - 12v operating range, .5a max draw
p = B10k potentiometer hooked to fan potentiometer input with 2 pin JST connector

       _________(S)____
      |      |  ||     |
      |      |  (p)    |
      |      |         |
      |      |__(S)____|    
      |      |  ||     |
(12v)(±)     |  (p)    |
 dc   |      |         |
      |      |__(S)____|    
      |         ||     |
      |         (p)    |
      |________________|

I am wondering if something more like this would be possible:

       _________(S)____
      |      |  ||     |
      |      |  ||     |
      |      |  ||     |
      |      |__(S)____|    
      |      |  ||     |
(12v)(±)     |  ||     |
 dc   |      |  ||     |
      |      |__(S)____|    
      |         ||     |
      |         (p)    |
      |________________|

Please excuse the rudimentary diagrams, I don't know how to generate more precise ones.

I have never seen a combination of a 3-pin case fan and just a 10k pot.

The 3 fan pins are normally ground (black), +12volt (red), and tach out (yellow).

If it has a speed pot, it must also have some electronic circuitry.

Post pictures of the back of the controller/pot.
Leo..

The fans have both a CPU tach line (yellow), and an external pot line.


This shows the back of the pot, B10K


This shows the power in (12v, gnd) and the external pot line (2 pin JST)


This is toward the inside of the fan. You can see both the external pot and the CPU tach lines turn into yellow cables here, and there appears to be some sort of pcb.

I have considered just putting a linear 1k pot in serial between the 12v and the parallel fan input lines, but it’s hard to find a pot rated up to ~6 watts (12v * .5a max draw).

So this is a 5-wire fan.
Two extra wires for the speed control.

I have seen fans with an NTC sticking out.
They must have replaced the thermistor for a pot in this model.

You could use a stereo pot to control two fans.

I don't know the circuitry inside, so you're on your own.
You could start by measuring the voltages on the pot.
I would try an opto coupler and PWM the LED.
Leo..

Wawa:
You could use a stereo pot to control two fans.

Or a four gang pot for up to four fans. Past four they get pretty pricy.

Wawa:
I don't know the circuitry inside, so you're on your own.

...and the manufacturer provides zero documentation.

Chagrin:
Or a four gang pot for up to four fans. Past four they get pretty pricy.

...and the manufacturer provides zero documentation.

Awesome! I ordered a pair, hopefully they'll do the job without burning out any fans :slight_smile: Your electronics supply company site navigation is unparalleled!

Use digipots. You can have as many gangs as you like, just send the same code to each one and you're set. You can drive it with a ATMEGA328 IC and have a LED show the current speed, control it through a master pot or rotary encoder.

4 output digipot, http://www.analog.com/en/products/digital-to-analog-converters/precision-dac-lessthanequalto-12mhz/digital-potentiometers/ad5204.html
6 outputs: http://www.analog.com/en/products/digital-to-analog-converters/precision-dac-lessthanequalto-12mhz/digital-potentiometers/ad5206.html

Or use single-channel digipots, it doesn't really matter.

Both available in 10K, also 100K and 50K.

Now that would be a project you could be proud to share once you finished it.

Tossrock:
I have considered just putting a linear 1k pot in serial between the 12v and the parallel fan input lines, but it's hard to find a pot rated up to ~6 watts (12v * .5a max draw).

That little pot is a 6 watt pot? A 10K pot? At 12 volts it would be passing 6 watts or more only at 24 ohms or less. Anything more than 24 ohms, 25 ohms up to 10,000 ohms it is passing less than 6 watts, right? I am thinking it's just a voltage divider and is providing almost no current to the fan, the fan is using the voltage to create a PWM or something to chop the current at that point. Otherwise the waste is enormous, the pot needs to be huge, and it would never be a 10K pot, maybe a 100 ohm pot in the stupidest fan speed design ever.

If I am right about this you could probably just parallel that little pot and you will be set. You could shove an ammeter in there and see how much current it is really providing.