FAN DC12V very slow

Hello folks,

I am trying to control a 12v fan Turn on/off with my arduino, the problem is if i put power suply on the arduino i can control the fan but it's very slow


I put power on the breadboard the fan spin but i can't cotnrol it

The shema i have done is this one: [

i am just switching the power supply between VIN or the breadboard](

Firstly move you free-wheel diode to across the fan where it should be, not across the anonymous switching device.

Secondly please give a diagram of your circuit with all the component values/part numbers, and a clearer explanation of the difference in the two setups.

The image you post suggests you are feeding 12V to the fan and to the Vin pin of the Arduino, which seems reasonable - no 5V is involved with the fan at all (which could explain the slow speed).

I send you everything this evening but I did no understand about the 5v? how can I use the 12v power and 5v from arduino?

For the shema it's only the + of the 12 supply that I change between VIN and the bread board .

But you don't explain each circuit clearly, such as with a circuit diagram, you could have done many things, each wrong for a different reason, which none of us has the patience to guess till you explain exactly what circuit you do have.

The fan needs 12V, that's a given isn't it?

The fan speed is slow you said. So what do you do with the arduino ? switch the arduino pin on and off, or are you pulse width modulating ? If you are pulse width modulating, some ranges in delayMicroseconds(0-1000) sometimes be quite messy, I just had the same problem and multiplied the value with 10 so I get 0-10000 time range. It was like:

" int time = 5000; int freq = 10000;

void loop(){ digitalWrite(3,HIGH); delayMicroseconds(time); digitalWrite(3,LOW); delayMicroseconds(freq - time); } " And it just worked out for me.

If you are not p.w. modulating there might be a problem with your setup, Check if all the hardware is correct. I used TIP120 OR TIP31 transistor. And It works with 12V DC fan. And I used 2.2K for the resistor. If you have the components try with this setup. If you still fail to do it text me and I can send the circuit of mine and the part list. Regards...

Are you trying to do PWM on the fan? Some fans are brushless and can't be controlled with PWM. Dwight

The shema i have done is this one:

Your "schema" is also wrong... the diode is on the wrong place, as noted by others... which places whoever you got this from in the "don't trust anything I do" list.


With grumpiness, I say, emphatically... NO. that is not a schematic. It is a horrible picture that has become the defacto standard to show people electronics pictorially. And while they may help someone build something who has no idea what they are doing, they are horrible at performing the task of a "schematic".

A schematic diagram, is a representation of the elements of a system using abstract, graphic symbols rather than realistic pictures. They are a means of communication and deliver relevant information about how a circuit is designed (not constructed), including component values, tolerances and part numbers, etc.

A picture, especially to other people who are to help you or understand what you are doing, is not as useful as you might imagine. Many details can be obscured or left out... and your case is a prime example.

rant off


Find a real schematic with part numbers and values and use the Attachment options of the forum to share it.