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[Reply #15 on:]

I manage to remove the ground from arduino to the FET (IRFZ44N). I also generated a schematic. I hope we can avoid the + from psu to optocoupler.

[Reply #16 on:]

Yes it is all wrong on the fan side.

Don't connect anything to the base of the opto transistor. Connect the emitter to the gate and the collector to the +12V, then a pull down from the gate to ground.
The fan should be connected to the +12v with the other end to the FET drain. Finally the gate pull down and the -12V to the FET source.

[Reply #17 on:]

Finally the gate pull down and the -12V to the FET source.

This part I don't understand.

Can the +12 to optocoupler collector be avoided? Because +12 has 30 A.

[Reply #18 on:]

By the way, is it save to solder the 4n35. Does the high temp destory the IC?

[Reply #19 on:]

Yes that new circuit is what I meant.
The gate pull down resistor (the resistor's end not connected to the gate) and the source and the -12V all to the same point just like you have.

Can the +12 to optocoupler collector be avoided? Because +12 has 30 A.

The fact that the 12V supply can provide 30A should be of no concern to you nor the transistor. The current drawn will only be in accordance with Ohm's law, and if that doesn't dictate 30A then 30A will not flow. The important thing is that the 12V supply is totally isolated from the arduino circuit.

is it save to solder the 4n35.

Yes

Does the high temp destory the IC?

Only if you take more than ten minutes with the soldering iron on it.

[Reply #20 on:]

The fact that the 12V supply can provide 30A should be of no concern to you nor the transistor. The current drawn will only be in accordance with Ohm's law, and if that doesn't dictate 30A then 30A will not flow. The important thing is that the 12V supply is totally isolated from the arduino circuit.

Maybe this sounds stupid. But what is the use of the FET at this setup? The voltage of the fet and the optocoupler is same right?

[Reply #21 on:]

Do I need Inductors? Because the AlphaCool Heatmaster has a fan controller, with fet's and Inductors.

http://www.aquatuning.nl/product_info.php/info/p6747_Alphacool-Heatmaster.html

[Reply #22 on:]

Ok, I went for it and connected to the psu 12 volt. And it worked !!! No failure or damage. The fet doesn't get hot nor the optocoupler. I can read the rpm and I'm now working on the tempreader. Soon more updates and pics.

[Reply #23 on:]

But what is the use of the FET at this setup?

It has the current capability that the opto transistor on it's own lacks. You would fry the opto if you tried to pass that amount of current through it.

Do I need Inductors?

No. They are probably supply decoupling.

[Reply #24 on:]

When swapping low high, the fan makes alot of noise. I have read other forums, but I saw no solution. Does PWM fan make the same noise? delay in miliseconds doesn't work eather. But the motherboard can handle the RPM without noise. I think mobo sends variable voltage. Do I have this option?

[Reply #25 on:]

Woo! Very hot topic!