2

I got my RPI3 cooled by a 5v dc fan and it only activates when it reaches 55°C so everything is fine i control it with PWM.

Now i want to cool it with a bigger 12V DC fan the problem is i need 12V, either from external source or from the PI itself and in this case i need a dc-dc converter which i found here

the thing is i can't find on the internet a similar project and how to cable it that's why i'm asking for help.

tried to do it myself on fritzing but i really dont think its good.

update : assuming the fan is a 4 wires (12v/grd/pwm/rpm) i did this on fritzing:

enter image description here

yellow wire is connected to PWM gpio.

Corn
  • 23
  • 1
  • 5
  • Are you not concerned about overloading the Pi? – Mohammad Ali Jul 09 '17 at 17:21
  • @MohammadAli how come ? The fan runs at 12v 0.20A – Corn Jul 09 '17 at 17:25
  • that's like 2.4 watts you sure your power supply is capable of that plus the spike in power required normally around 4-6 watts to start the fan? – Mohammad Ali Jul 09 '17 at 18:00
  • @MohammadAli What should i do to know how much my Pi consumes ? Is the limit the same for all PIs ? Or does it depend of my power supply ? – Corn Jul 09 '17 at 18:11
  • It's more about the power supply as the pis 5v line is just a pass through of the USB power – Mohammad Ali Jul 09 '17 at 18:12
  • It might be better to have a 12v power supply and then convert it down to 5v, eg with a car usb charger of suitable quality. (Check the 0v is common). – meuh Jul 09 '17 at 19:30
  • I got a normal power supply 5V 2.5A, so 12.5W, quite enough no ? – Corn Jul 09 '17 at 19:33
  • @meuh why go from 12v to 5v when the fan needs 12v to work properly ? – Corn Jul 09 '17 at 19:34
  • @MohammadAli i did not undestand the usb splitter part, do you mean i should use a power bank to power the fan ? I'm looking for a solution where everything is done via the PI so i could have total control of the fan, could you explain your idea again please. – Corn Jul 11 '17 at 06:20
  • @MohammadAli i understand. Still if i power the fan through the usb hub it will only get 5V which it's all about. Do dc-dc converters with usb input exists ? If they do i could use one to go 5v to 12v from the pi's usb then power the fan and control it with the pwm gpio. If that doesn't work i will for an external power to power it like a power bank or batteries. – Corn Jul 11 '17 at 06:26
  • @MohammadAli yes ! But shouldn't it be a male usb so i can put it in the pi ? Or do i need a male-male usb converter between them? – Corn Jul 11 '17 at 06:30
  • @MohammadAli that's right, my bad , so pi's usb gives 5v to that dc dc converter which output gives 12v to the fan and i control it with its pwm output directly via the pwm gpio. I will try that and keep this thread updated, thanks ! – Corn Jul 11 '17 at 06:35
  • @MohammadAli you really did help me, feel yourself free to do so. – Corn Jul 14 '17 at 05:02

2 Answers2

0

"the thing is i can't find on the internet a similar project" This is for the simple reason that it will NOT work.

You are likely to blow up the Pi.

On top of that you don't actually need a fan.

Milliways
  • 59,890
  • 31
  • 101
  • 209
  • I'm getting mixed answers here, could you explain me why it would not work please ? Would it work through a relay with 12v battery powering the fan ? – Corn Jul 11 '17 at 06:17
  • @Corn Poorly asked questions with no supporting information tend to attract speculation. Realistically no one can answer. Connecting an (unspecified) 12V powered device (presumably intended for a desktop PC) to a 3.3V GPIO is unlikely to work, and risks damage. My "answer" was more intended to warn of the risk. This in addition to the fact that the (unspecified) Pi is unlikely to be able to supply sufficient current from your (unspecified) power supply. – Milliways Jul 12 '17 at 01:23
0

I would personally recommend that you use either a dedicated power supply or a usb to 12v dc-dc boost converter like this. Furthermore do check whether or not your fan is capable of detecting a 3.3v pwm signal as that is the max and only voltage the pi's gpio operates on. which means that you will likely also need a dc-dc boost converter on your pwm signal as well.

Mohammad Ali
  • 2,383
  • 1
  • 11
  • 18