Turning on and off 12V fans using arduino

Projects General Guidance
1

Hello,

I would like to ask what is a general approach to use an arduino (or any other microcontroller for that matter) to turn on and off a bunch of 12V fans? I am using 7 12V fans, and they draw around 1A of current when all of them are on. i have a 12V rail that i cen get the required current from, so thats not a problem.

Should i use a n channel mosfet? The arduino pins can only provide 5V so that wont open the mosfet completely right?
Any ideas would be greatly appreciated.

2

You can buy relays that will operate on the Arduino 5V pin output and switch anything between 12V and 250V - normally open or normally closed. You can but a bank of eight of the relays side-by-side.

Something like this:

Cheers

Catweazle NZ

3

You get a "Logic" MOSFET. These turn completely ON at 5V. Look at the spec sheet for Vgs(on) being 5V or less. here is a typical example: http://www.sparkfun.com/datasheets/Components/General/RFP30N06LE.pdf

4

As i understand this mosfet would be fine: Lemona ?

Should i connect a small resistor to the gate?
And also should i add a pulldown resistor? What value?

5

If you want to be sure, post a simple question in "General Electronics" asking if that is a "logic MOSFET". I do not think so - the Gate Threshold is not the same as the voltage for fully on. They cite 10V gatevoltage for the fill on and besides, 0.15 Ohm for fully on is not mindboggling low, but sufficient for your purpose. Otherwise you can use "any" MOSFET, and a small signal pnp transistor to pull the gate voltage up to the 10+V.

The in series resistor kan be 1K or so it is to avoid the current pulse when going from 0V to 5V damaging (stressing, quickened wear out) you Arduino output pin. The pulldown resistor (typically 10K to 56K is there to ensure that the gate is OFF when you apply power until the Arduino has set the pinMode to OUTPUT. If there is no problem if the fans start turning a little just at power up, you can leave it out. But it is almost to cheap to leave it out.

This circuit with these values can have all fans in parallel activated by one digital pin, or repeat the circuit for any number of pins to have them inidvidually connected. (Are you measuring temperature or something and the fans are there to compensate?)