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Odd question.. but does this exist?

C

Copyright

Supreme [H]ardness
Joined
Nov 17, 2000
Messages
6,004
So I love the fan control on my Asus mobo but the 200mm fan i want to run pulls like 3.36 amps which is a lot of a fan header port. Is there any type of adapter that will use external power but still let the mobo control the fan speed? Basically I want to mobo to say I want X watts and whatever power source I use to supply X watts... if hte mobo supplies more.. I need the external power supply to supply more to the fan.
 
3.36 amps?! That's like 40 watts. Sure it wan't watts or perhaps 0.33 amps? Or have you nicked the fan off a small airplane?
 
I dont know if they exist readily on commercial market... but it wouldn't be a hard circuit to design and build ;-) (really just a simple mosfet circuit)
 
It looks like the Cooler Master MegaFlow uses 3.36 watts, so if that is the fan you will be using, you have no problem hooking it up to the mobo directly.
 
The only fans I've seen rated for that much amperage are extreme high speed ones (4000+ RPM for 120's). A 1000 RPM 200mm fan (the fastest I've seen) is roughly equivalent to a 2000 RPM 120 fan at best.
 
For the uneducated...

Voltage x Amperage = Watts

I really doubt that the fan is pulling that much. Unless it's a small box fan...
 
Yeah, sorry.. I misread Watts for Amps LOL.. was trying to do some quick surfing at work and that back fired. Thanks for the replies guys.
 
Oh yeah, another thing.

Motherboards typically control the fan by varying the amount of voltage it gets, which is the case in any non-PWM fan. As far as I recall, there are no 200mm PWM fans at the moment. If your fan was getting its power from an external source, how would your motherboard vary the voltage?

There are some (expensive) fan controllers that use a PWM signal from your motherboard to control your fan speed. I don't know any off the top of my head, but that would be your best bet if you wanted to go that route. Of course, your motherboard would need a free PWM header.
 
Well, as I mentioned earlier... it would be REALLY easy for my to build a simple MOSFET driver that would connect to the motherboard header, PSU, and the fan. But we have already established that the OP doesn't actually NEED one, lol.

I have been thinking of building this circuit for myself, to control several case fans off the typical only (1) aux. speed controlled MB header. Sick of builds that have speed control on CPU fan, and only 1 case fan... while any other fans just run balls out. :-p

EDIT... side thought... would this circuit be any different than the bulk of bay-mounted fan controllers available?? No sense in my re-inventing the wheel, lol.
I'm thinking one pigtail to connect to the motherboard header, maybe a bay-mount panel, and the MOSFET circuit could drive 3 or 4 fans in tandem... with maybe speed control on the panel as well.
 
Tsumi said:
Oh yeah, another thing.

Motherboards typically control the fan by varying the amount of voltage it gets, which is the case in any non-PWM fan. As far as I recall, there are no 200mm PWM fans at the moment. If your fan was getting its power from an external source, how would your motherboard vary the voltage?

There are some (expensive) fan controllers that use a PWM signal from your motherboard to control your fan speed. I don't know any off the top of my head, but that would be your best bet if you wanted to go that route. Of course, your motherboard would need a free PWM header.
Click to expand...

My 3 pin fan header varries voltage just fine on my Asus board. I can build the fan curve however I want it relative to the CPU temp with the Asus software. All is good!
 
Copyright said:
My 3 pin fan header varries voltage just fine on my Asus board. I can build the fan curve however I want it relative to the CPU temp with the Asus software. All is good!
Click to expand...

My point was if you had an external source, how does your motherboard control the voltage of that external source?

On another note, most manual bay fan controllers use rheostats to directly control the voltage. I think it is the LCD display ones that use MOSFETS. The rheostat design usually can handle more wattage, so they're the preferred ones for ultra-high speed fans. Most LCD ones I've seen can only handle about 10 watts per channel, while rheostats can go up to 30 watts or more.
 
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