controlling multiple fans with single fan header?

[timje]

My K7 Master has one fan header for the CPU fan and one for a case fan. Is there any way to control the fan with the motherboard but power it from the power supply? I'd like for ALL my fans to go to sleep when the system is suspended...

 

[Generalen]

Don't blame me if i'm wrong here but one idea came to me when I was reading your question how about connect all ground(-, right?) wires to the ground(-) on mb and all + wires to a + wire from the PSU. This will power of the fans or? Will this work ?? I haven't a clue??? just a thought.

 

[Generalen]

mayby this will burn your single fan header but it's just a thought. why not make a fanbus that connects to a standard wire running out of your PSU and then buy a
off/on-swich and put it on the ground cable from the fanbus then place the off/on swich on a front plate on your case front side. Just another thought.

 

[timje]

Generalen,

Thanks for the ideas. Using your external switch idea, The fans could be on an isolated circuit completely, but with no monitoring, but could be turned off. I'd rather have it all automatic, of course! I'm very hesitant to wire both external fans together onto a single fan header, as I am to apply an external current source to a motherboard pin. I wonder if there's an isolator circuit I could build? Hmmm..

 

[Jhhnn]

You just need a 12v coil automotive-type relay. Have the board power the coil, run power from a psu plug to the fans thru the normally open points, provide ground thru a psu plug. You can maintain rpm monitoring on one fan by plugging the monitoring lead into the appropriate place on the board. Don't exceed the current handling capacity of the relay.

Bosch makes them, widely available, but the Potter&Brumfield (Siemens) VF4-45F11 is a better relay. I use them and their 24v cousins in the mass transit business all the time.

 

[timje]

Thanks, Jhhnn! Hopefully I can pick one up locally (Austin, TX) and play around with it and my voltmeter. Looks like a $5 part.

 

[GundamF91]

make sure you don't overload the fanheader.

 

[davidsnot]

The bosch will work, and it's such a good idea, I'm doing it tomorrow.

If you can't find one at the parts house, head for any car audio shop. Preferably one that does installs. They will have them for alarms, and such.

 

[timje]

Dave,

Since you're on top of this already, would you mind giving us an update when it's done
and let us know how it went? Any trickyness to getting it work? Any little problems
you had to solve? Thanks!

Had a full day, and didn't get to call around for the part. Gotta get more free time!

 

[timje]

Dave -- did you find the time to do this yet?

 

[davidsnot]

sorry, haven't done it yet. chasing other details... still on my list, though.

 

[Mday]

bzzzzzz poooooof...

--

time to wire the fans to the powersupply...

 

[davidsnot]

We're only talking about using the fan header as a turn-on, should be less draw than a fan. Of course, it's a valid point, the only time the fans should turn is when the computer is on.

Still gonna do it, though.