Controlling lots of Fans in parallel.

[Averydev]

Hi there!

I'm new here and am embarking on one of my first electronics projects and I could use some guidance before I proceed.*

The basics of the project is that I have 8 pc fans that I am trying to control with one on/off switch, and their speed with one knob. The power source is a regular 120 wall outlet.*

If I understand this correctly my 8 fans together will draw a max of 1.3 Amps and 16V aproximately

I've found on/off switches that are rated to handle that current but I feel like there is a right way to do the speed control. Potentiometers and Rheostats seem to be generally rated at low power capacities. Im guessing that you can use a small Potentiometer to electronically control another element that would actually attenuate the power going to the fans. But I can't figure out what that next element in the line is called or how to control it.

Thanks so much and thanks for creating such a remarkable community and wealth of knowledge!

Component details:

*I'm planning in connecting them in parallel through an adapter in groups of 4, and then those groups again into one molex 4 pin.*


The fans I'm planning on using are here: https://www.amazon.com/gp/aw/d/B000O8I474?m=A2EUTVCJXLAJ4K

Voltage 12VDC*
Current (Ampere) 0.15 + / - 10%*
Input (Watt) 1.8W + / - 10%*

12VDC / AC adapter:
100-240VAC 50/60Hz 2A*
Output: 12V +- 2A --- 5V+- 2A

 

[rohitkhanna]

The best way would be to use your pot to vary the duty-cycle of a PWM signal.

PWM with variable duty-ratios are easy circuits - many examples available on the net. Google for PWM, you'll come across '000's of simple circuits. The simplist would use a 555 timer chip + 2 diodes + R & C, and your Pot of course. Alternately you could use a CMOS schmitt inverter instead of the 555. I suggest CMOS b'cos you can run these directly off the +12v as well.
You feed the output to a BJT or MOSFET which then powers your fans.

 

[betwixt]

A cautionary word:

PC fans usually have a transistor oscillator inside them and this primariliy sets the speed. Limiting the power available to them will not give good speed control as the osxcillators will still try to run at the same frequency, The speed will drop with voltage of course but mostly because the fan no longer has sufficient 'push' to move the air efficiently and starts to stall. The current the fan draws will also vary according to air flow so this will not decrease linearly with applied voltage. You might find the current is maximum when the voltage is quite low and the fan has completely stalled. With several fans wired in parallel you will probably see interaction between them.

Brian.

 

[BradtheRad]

If the fans are the type with three wires then they probably need 12V supply to two wires, and the third wire is a control wire. You could control all the fans with one or two potentiometers this way.

On the other hand if they have two wires, this means you can vary the current through them to vary their speed. It may or may not be recommended for your fans, I can't be sure.

Anyway, if it's okay to do it via resistive drop, a transistor is handy. Per schematic:

You would either need 8 transistors for 8 fans, or you might try to use one transistor to control more than one fan, in parallel.

You ought to run tests to see if the fans slow down uniformly.