So i recently bought a server to put in my home, the fans in it were stupid loud, and due to a hardware issue they run at 100% all the time, so i decided to replace them with some silent fans that do about 60% of the air flow, (im not worried about over-heating this thing will never be over 20% of max capacity).

Anyway I wired them in, wired it all together after looking at some pin-outs, fired it up, critical fan failure.. WHAT??

So the wiring is pretty straight forward, 12v to 12v, ground to ground, pwm to pmw, but the last wire, that last wire,

On my fans the last wire is the tach, sends a signal its a signal generated by the motor itself indicating the rpm's.

The fans I pulled out however use that wire for something else entirely, something called an Open Collector. Documentation says : "Open-Collector, low-pass high-fail, trip-point alarm circuit terminated in a third lead wire; non-latching alarm is activated at specified low-speed threshold (70 percent of fan's nominal operating speed, standard)."

Link to fan documentation. (I'm working with option -04)
http://www.nidecpg.com/fanpdfs/c2008_0203.pdf

This is the diagram for the old fan function I'm trying to emulate.

So how would I emulate this signal. I could probably figure it out if i could read electrical diagrams. Any help is appreciated, I am too buried $$$ into this project now to abandon it.

 

I never played with this, but I guess you could use a 555 timer to generate the signal, google fan tacho signal emulator or something.
Also, have you tried to disable the fan speed check in bios? that might be the easiest route...

 

I'm not trying to emulate the tach, my fans have tachs, im trying to emulate the trip point alarm.

And there is no bios control for fans, its all hardware managed server-class equipment.

So if i need to somehow modify the current fan tach signal, so it works that might be an option, my biggest issue is I don't know what signal it is looking for.

 

Hi,
Since your server is new ,possibly you can claim a warranty for the Fan.
Next ,return back the previous Fan and see bios adjustment if any for the speed

 

Looks to me as though the original fan open-collector arrangement is intended to produce a signal whose average voltage reduces as the rpm increases. If so, and if the new fan's tacho signal increases with increasing rpm, then simply inverting your new fan's tach signal may do the trick.

 

Hi,
Since your server is new ,possibly you can claim a warranty for the Fan.
Next ,return back the previous Fan and see bios adjustment if any for the speed

Its actually a used server from 2013, I got it for next to nothing. The bios allows absolutely no control of the fans, the hardware takes complete control of the fan system, and if it doesn't like what it reads it shuts down the system, also since the Hard disk drives I'm using aren't hp branded they don't have the proper S.M.A.R.T settings, so the hardware controller runs the fans at 100% all the time, which isn't a big deal, I replaced the fans that were making about 50 db of sound with ones that make about 19 db.

Looks to me as though the original fan open-collector arrangement is intended to produce a signal whose average voltage reduces as the rpm increases. If so, and if the new fan's tacho signal increases with increasing rpm, then simply inverting your new fan's tach signal may do the trick.

I think you may be on to something here, because regular fans tach ranges from 0 - 12v, increasing with RPM, but how would I reverse this with circuitry? I know little about electric circuitry, I mean i'm all for doing whatever needs to be done, i already soldiered adapters from the proprietary plugs so circuitry could be added there.

I also had another thought, if what you said is true, couldn't i just cut the wire and have 0v and it should work? or should just reduce the voltage to 1v or something then try that?

 

couldn't i just cut the wire and have 0v and it should work?

Worth a try.
Just not using the tach output and instead connecting Signal to Ground (via a 1k or so resistor, to avoid a direct short-circuit) might well work. You would, of course, lose the Trip-point Alarm function.

 

Worth a try.
Just not using the tach output and instead connecting Signal to Ground (via a 1k or so resistor, to avoid a direct short-circuit) might well work. You would, of course, lose the Trip-point Alarm function.

I'll try that first when I get home, I really appreciate your help Alec_t!

Okay so if disconnecting it don't work, 1k resistor to ground. Alright, sounds easy enough.

 

Hello,

Keep in mind that when you bypass the speed security by using the resistors, the server won't know if there is a fan failure.
This might give overheat problems.

Bertus

 

Eh it will shutdown when it reaches 68c no matter what, and it will only be an issue if the fans fail. I'm quite okay with that.

 

You could use a 555 as a frequency to voltage converter, and use that with a comparator to shutdown the system.