Slow down three fans but keep motherboard rpm reading

mgiammarco · Post by **mgiammarco** » Tue Apr 27, 2004 2:04 am

Hello,
I have three 120 mm fans connected to my motherboard with rpm monitor.
I need to slow down them but I want to continue reading rpm with motherboard.
Please suggest me the simplest thing to buy (no soldering!).

Thanks in advance!

Bluefront · Post by **Bluefront** » Tue Apr 27, 2004 2:11 am

An Antec Fanmate will do it.....it just connects between the fan and the MB. Not all motherboards can read low rpms though, so you might have a problem there.

MGP · Post by **MGP** » Tue Apr 27, 2004 4:15 am

Fanmates may also be purchased online under the Zalman brand...either way, you'll get a useful product with the same quality.

Post by **Rusty075** » Tue Apr 27, 2004 4:58 am

EDIT: I wrote this post, and then re-read your original question. The simplest thing to buy would be exactly what Bluefront and MGP suggested, Fanmates. There may also be some baybus' available that maintain RPM reporting, but I can't think of any off the top of my head. My 2 alternatives both require a little re-wiring (not necessarily soldering though) so they may not be what you're looking for. But they would be free. I'll leave them here in case they be of use to you, or some future forum surfer .

A couple of other methods besides the Fanmates:

1. Add resistors in series to the fan, reducing the voltage its receiving from the motherboard.

2. Cut the positive and negative wires off the existing connector, leaving the third wire (the RPM wire) connected. You can then connect the power wires directly to a PSU molex to get 12, 7, or 5 volts, or to a baybus.

silvervarg · Post by **silvervarg** » Wed Apr 28, 2004 5:54 am

As a rule of thumb, most motherboards can't read a good RPM signal if your fan is spinning too slow. Usually somewhere in the region 800-1500 RPM is the lowest that works fine. Exactly what value depends on your motherboard.

If you lower voltage to reduce fan speed you will also degrade the RPM (TACH) signal. It usually works fine at around 6V with most motherboards. Lower voltages may result in unreliable reading or no reading at all regardless of fanspeed. This also depends on what circuits your motherboard is using.

mgiammarco · Post by **mgiammarco** » Sun May 02, 2004 11:30 am

I have just received the case with the fans.
The fans have 12volt and 0.80 ampère which seems to much for zalman fanmate or I am wrong?

Thanks again!

macklin01 · Post by **macklin01** » Mon May 03, 2004 4:32 am

Any fanspeed control that leaves the ground lead fixed (i.e., varies fan speed by varying the voltage of the positive lead) should maintain the RPM readings, down to a certain voltage. I designed a fanbus like this a few years ago ...

Here's a screeny of RPM readings taken at different voltages with such a fanbus (one that worked by varying the + voltage by means of an NPN transistor with variable resistor):

-- Paul

Slow down three fans but keep motherboard rpm reading

Slow down three fans but keep motherboard rpm reading

My fans suck a lot of watt