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Topic: Variable voltage (0-12V) using PWM from Arduino (Read 18185 times) previous topic - next topic

Grumpy_Mike

There is no need for any feedback, you should not get a voltage drop when you have a load that is what a regulator is for.

Why are you worried about short circuits on the FETs ? It is not normally an issue.

Wawa

PWM puts the full supply on the fans for a shorter or longer time.
e.g. when you set the PWM for 50%, the fans are getting full power half of the time, and are half of the time off.
Switching is done so fast that the fans see it as half power.

Your code needs a startup sequence, and a range with a minimum value that guarantees spinning fans.
Show us your code.
Leo..

TomGeorge

Hi,
Are your fans BLDC fans?
They may not like PWM as their supply because their speed is regulated by a built in switching system, speed is regulated by the system frequency not by the supply voltage.
That is why  they have 4 wire fans, the 3rdwire is tacho out and the 4th is speed in.
The fans will change speed with load from the air flow, all you can do with 2wire fans is keep their supply voltage constant.
Lowering supply voltage will lower speed but also make the speed unstable.

Tom.... :)
Everything runs on smoke, let the smoke out, it stops running....

simsoft

Quote
Why are you worried about short circuits on the FETs ? It is not normally an issue.
Short-circuiting can happen to someone who will connections to the fans, because they will not be permanently connected. Therefore, I would make sure that even when nothing short circuit burned.

Quote
Your code needs a startup sequence, and a range with a minimum value that guarantees spinning fans.
Show us your code.
Until now, PWM output steered manually using this code:
Code: [Select]
int R = 200;
byte value = map (R, 0, 1023, 0, 255);
analogWrite (9, value);

A value of 200 is an example ...
How do I know what the value may be the maximum, it will add security.
I wish it worked that way, that I set myself a specific voltage in uC and this value is specified for the load. This is important, that I associate with the speed voltage with generated wind.

Quote
Are your fans BLDC fans?
They may not like PWM as their supply because their speed is regulated by a built in switching system, speed is regulated by the system frequency not by the supply voltage.
That is why  they have 4 wire fans, the 3rdwire is tacho out and the 4th is speed in.
The fans will change speed with load from the air flow, all you can do with 2wire fans is keep their supply voltage constant.
Lowering supply voltage will lower speed but also make the speed unstable.
I have a 2-wire fans and can the control voltage.

Wawa

You might want to map to ~50-255
Fans need a minimum to keep spinning (~1-50 is useless).

You need fan bootup in your final code.
They need full power, or almost full power, for half a second to start spinning.
Leo..

raschemmel

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Short-circuiting can happen to someone who will connections to the fans, because they will not be permanently connected. Therefore, I would make sure that even when nothing short circuit burned.
 
In that case you might consider adding in-line fuses .

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