Hi there,
I'm new here and have an hardware-question.
Would be great if someone can tell me which amount of current (I in mA) do supply the motherboard-fan-header (PWM-signal only) and with which current work/expect (normally) the PWM-controller on the fan.
I cant find either the specifications of respective motherboards nor of the fan, only max PWM-current = 5mA, see specs 2004 Rev. 1.2
https://folk.uio.no/kyrrens/diverse/viftekontroller/developer-specs-REV1_2_Public.pdf
Thanks in advance and best regards.
P.S.1: If anybody is interested, I read a "read-only"-thread handling PWM (see link below), for your information: no PWM is working or taking effect if lower than 30% = 5V to the fan, any PWM-value under 30%=PWM-off=Fan not run, at least for PC-fans and pumps.
https://forum.arduino.cc/index.php?topic=18742.15
P.S.2: My actual project should be offer the possibility to drive up 125 to 500 fans with only 1 (one) PWM-fan-header no matter if PWM come from a motherboard or Arduino. Please tell me if the schemes are interesting for the community.
Arny006:
Would be great if someone can tell me which amount of current (I in mA) do supply the motherboard-fan-header (PWM-signal only) and with which current work/expect (normally) the PWM-controller on the fan.
You're probably better off finding out what usual voltage this fan will work at. Is it 5V DC?
If 5V DC, then just have a PWM system that puts out 5V DC at 100% PWM setting. You just have to make sure that your PWM circuit is able to supply the required amount of current. The rest is just a matter of applying the PWM waveform across the fan's terminals.
On page 9 of your document that you provided .... click here
.... it says "fan operating voltage shall be within the range 12 V ±1.2 V"
This means at maximum PWM level (100%) .... which will be DC conditions..... 12 volt may be applied. This means your PWM raw source can be up to 12 V. It can be less if you want.
You could measure the DC resistance of the pin. That will tell you how much current it will take with 100% PWM.
More important is the capacitance. You are basically charging and discharging a tiny capacitor thousands of times per second. Even with an unmeasurably-small capacitance in the low pico-Farad range, this may take a significant amount of current to do. At this low level, the capacitance of the wire bundle becomes significant.
Unless there's something weird about these fans, I expect the Arduino output could easily drive 100 of them. Probably more. 500? Maybe. It would really be better to test it yourself.
You can not connect an Arduino pin directly to a fan. It has to be boosted by sending it through a transistor first.
500 fans, that's a lot of wiring, even if the PWM wires are very efficiently done that's a couple hundred meters. Even at a modest 10 pF/m that's a few nF worth of wires. Each fan has it's own input capacitance as well, giving a total stray capacitance of easily 10 nF. It could be up to an order of magnitude higher depending on the actual fans, actual wire length, wire layout and length
Most MOSFETs have a smaller gate capacitance than this yet current limiting resistors are considered mandatory, and larger MOSFETs can't even be driven by an Arduino pin directly as the pin is too slow charging/discharging the gate... while those MOSFETs are typically driven at 500 Hz, while computer fans usually take 25 kHz PWM.
It takes some serious oomph to drive a clean PWM signal into a 10 nF capacitance at 25 kHz! Especially considering the massive electrical noise all those fans will be producing between them.
Hi,
Welcome to the forum.
Please read the first post in any forum entitled how to use this forum.
http://forum.arduino.cc/index.php/topic,148850.0.html .
What is the application that uses that many fans, cooling, work of art?
Where are you getting your fan power from?
Can you please post a copy of your concept in block form, in CAD or a picture of a hand drawn circuit in jpg, png?
A picture is worth a thousand words...
Tom... 