In the 3-wire fan, the tach is not PWM. It is a two-pulse per revelation TTL level signal. I actually build a fan controller once using a "dead bug" 50 cent, 8-pin AVR microcontroller, and an external transistor switch. So I had to look into this.
I think the real reason for the 4th wire is that with BLDC motors you can no longer control the fan speed simply by putting PWM on the power. The fan motor speed is determined by firmware inside the fan, not by voltage control. Ging to a BLDC motor forced us of a separate control signal. What happens if you fail to but PWM on the control wire? Hard to say because it is controlled by firmware inside the fan. Likely you get zero RPM on the fan. On Tue, Dec 10, 2019 at 12:29 PM N <[email protected]> wrote: > The PWM tachometer signal most probably have really good noise immunity as > timing is robust against noise. Might also have really good accuracy if > derived from a clock with low jitter and slow enough clock drift. However > very unlikely to make any noticeable difference on a fan. > > Once asked for external availability of PWM signal on measurement > instrument as I could see it was used internally in datasheet/manual for > data transmission over an isolation barrier and they might have listened as > I have seen it is available in some now though I did not yet have any use > of it, have used the analog signal with more or less noise. > > > > > With a 3-wire fan there are two power wires and the third is a > tachometer. > > Fan speed is controlled by varying the volts (or duty cycle) on the > > power wires. > > > > With a 4-wire fan all thee above wires do the same thing but wire #4 is a > > speed control signal that is PWM. This saves the need to PWM the > power. > > > > On Tue, Dec 10, 2019 at 4:16 AM Gene Heskett <[email protected]> > wrote: > > > > > Greetings all; > > > > > > I am running the stretch iso install here on this big house box, but > > > since the fire destroyed the old Asus board, I now have a new Prime > > > Z370-A ll, with a 9nth gen 6 core i5 running at 3.7GHz and 32G of ddr4 > > > memory. Much quicker than the old 2.1GHz 4 core phenom. Pretty quick > > > now. > > > > > > But the cpu fan I put in, a monster cooler-master, has the new 4 wire > > > control, and is working very well, but is not reporting its speed. > > > A run of sensors-detect only found coretemp and once modprobed, thats > > > working well. Showing the max temps in the 29C range. Its a BIG cooler > > > and I can't feel any heat at its base, so big I can't put the towers > > > side panel on as it (the coolers heat pipes and radiator) is about 1/2" > > > too tall. Shrug, its been off for 12 years now ;-) > > > > > > Does anyone else have any experience with these newer 4 wire fans? > > > > > > Thanks all. > > > > > > Cheers, Gene Heskett > > > -- > > > "There are four boxes to be used in defense of liberty: > > > soap, ballot, jury, and ammo. Please use in that order." > > > -Ed Howdershelt (Author) > > > If we desire respect for the law, we must first make the law > respectable. > > > - Louis D. Brandeis > > > Genes Web page <http://geneslinuxbox.net:6309/gene> > > > > > > > > > _______________________________________________ > > > Emc-users mailing list > > > [email protected] > > > https://lists.sourceforge.net/lists/listinfo/emc-users > > > > > > > > > -- > > > > Chris Albertson > > Redondo Beach, California > > > > _______________________________________________ > > Emc-users mailing list > > [email protected] > > https://lists.sourceforge.net/lists/listinfo/emc-users > > > _______________________________________________ > Emc-users mailing list > [email protected] > https://lists.sourceforge.net/lists/listinfo/emc-users > -- Chris Albertson Redondo Beach, California _______________________________________________ Emc-users mailing list [email protected] https://lists.sourceforge.net/lists/listinfo/emc-users
