Jump to content

Fan Controllers without a tach wire - in what way is that bad for PWM fans?

RevGAM

What is the disadvantage to such a hub or FC if the 3rd (tach) wire is missing? I know that a PWM fan can run without it, but at what cost?

It will negatively impact 3-pin fans as there will be no way to control the speed.聽

I've been using computers since around 1978, started learning programming in 1980 on Apple IIs, started learning about hardware in 1990, ran a BBS from 1990-95, built my first Windows PC around 2000, taught myself malware removal starting in 2005 (also learned on Bleeping Computer), learned web dev starting in 2017, and I think I can fill a thimble with all that knowledge. 馃槈 I'm not an expert, which is why I keep investigating the answers that others give to try and improve my knowledge, so feel free to double-check the advice I give.

My phone's auto-correct is named Otto Rong.馃お馃槀

Link to comment
Share on other sites

Link to post
Share on other sites

It shouldn't affect the fan speed control for PWM fans or non-PWM fans. The controller can change the speed without the RPM. Most controllers will change the PWM % of the fan, and not aim for a specific RPM.

The big issue is you don't know if a fan has failed, but in a PC this isn't the biggest issue.

Link to comment
Share on other sites

Link to post
Share on other sites

Just now, Electronics Wizardy said:

It shouldn't affect the fan speed control for PWM fans or non-PWM fans. The controller can change the speed without the RPM. Most controllers will change the PWM % of the fan, and not aim for a specific RPM.

The big issue is you don't know if a fan has failed, but in a PC this isn't the biggest issue.

I'm confused. If there is no tach wire, and the fan is a 3-pin, then the PWM cannot be used, nor can voltage regulation be accomplished because there is no tach signal, so how can this work for 3-pin fans? As far as I can tell, they'll behave like 2-pin fans - constantly at max speed.

I've been using computers since around 1978, started learning programming in 1980 on Apple IIs, started learning about hardware in 1990, ran a BBS from 1990-95, built my first Windows PC around 2000, taught myself malware removal starting in 2005 (also learned on Bleeping Computer), learned web dev starting in 2017, and I think I can fill a thimble with all that knowledge. 馃槈 I'm not an expert, which is why I keep investigating the answers that others give to try and improve my knowledge, so feel free to double-check the advice I give.

My phone's auto-correct is named Otto Rong.馃お馃槀

Link to comment
Share on other sites

Link to post
Share on other sites

Fan controllers, even the ones that have tach functionality, only operate on percents. You don't tell them "run at 1500RPM," you say "run at 50%" (assuming this is a 3000RPM fan). If you know the RPM range of the fan, you do the math ahead of time and know what percent lines with what RPM. The fan controller does not care what speed the fans are actually running at, the only reason to do so is if they have a dead fan alert or a display with the tach readout on it.聽

Link to comment
Share on other sites

Link to post
Share on other sites

1 minute ago, RevGAM said:

I'm confused. If there is no tach wire, and the fan is a 3-pin, then the PWM cannot be used, nor can voltage regulation be accomplished because there is no tach signal, so how can this work for 3-pin fans? As far as I can tell, they'll behave like 2-pin fans - constantly at max speed.

2 pin fans can be speed controlled, you just adjust the voltage. Same with DC fans without the speed sensor, the only disadvantage of that is you can't tell when the fans stall so you should keep an eye out for when that happens.聽

Link to comment
Share on other sites

Link to post
Share on other sites

1 minute ago, RevGAM said:

I'm confused. If there is no tach wire, and the fan is a 3-pin, then the PWM cannot be used, nor can voltage regulation be accomplished because there is no tach signal, so how can this work for 3-pin fans? As far as I can tell, they'll behave like 2-pin fans - constantly at max speed.

You can lower the speed of a 3pin fan the same way as a 2 pin fan, by lowering the voltage. Then the fan spins slower. From the boards Ive played with, they will do fan speed control on 2/3 pin fans without looking at the tach signal. Some use the tach signal to customize the curves if you want, but its not needed.

Link to comment
Share on other sites

Link to post
Share on other sites

2 minutes ago, RONOTHAN## said:

Fan controllers, even the ones that have tach functionality, only operate on percents. You don't tell them "run at 1500RPM," you say "run at 50%" (assuming this is a 3000RPM fan). If you know the RPM range of the fan, you do the math ahead of time and know what percent lines with what RPM. The fan controller does not care what speed the fans are actually running at, the only reason to do so is if they have a dead fan alert or a display with the tach readout on it.聽

Yes, I'm aware of that. But how can a 3-pin fan run with only 2 wires on varying voltage and no tach signal?

I've been using computers since around 1978, started learning programming in 1980 on Apple IIs, started learning about hardware in 1990, ran a BBS from 1990-95, built my first Windows PC around 2000, taught myself malware removal starting in 2005 (also learned on Bleeping Computer), learned web dev starting in 2017, and I think I can fill a thimble with all that knowledge. 馃槈 I'm not an expert, which is why I keep investigating the answers that others give to try and improve my knowledge, so feel free to double-check the advice I give.

My phone's auto-correct is named Otto Rong.馃お馃槀

Link to comment
Share on other sites

Link to post
Share on other sites

Just now, RevGAM said:

Yes, I'm aware of that. But how can a 3-pin fan run with only 2 wires on varying voltage and no tach signal?

The Tach signal isn't needed by the fan. It doesn't affect the operation of the fan. It will spin at the same speed if the tach pin is plugged in or not.

Link to comment
Share on other sites

Link to post
Share on other sites

2 minutes ago, RevGAM said:

Yes, I'm aware of that. But how can a 3-pin fan run with only 2 wires on varying voltage and no tach signal?

Just to be clear, the tach signal is only to report to the controller what RPM the fan is currently running at. Whether or not the controller cares what RPM the fan is currently operating at is irrelevant, changing the voltage will vary the fan speed either way.聽

For context, a common hack to get those 2 pin molex fans to run at a lower speed is to just plug the molex header in upside down. It doesn't like to go in backwards, but it will do it with a bit of force. That will change the voltage going to the fans from 12V to 5V, meaning they'll run at a little under half speed in theory (in practice, fan speeds aren't linear with voltage a lot of the time, so it's going to vary a bit). The same theory applies here, if it doesn't see the tach wire it will just run at whatever voltage you set it to with the rpm changing with the voltage, just hopefully with finer voltage control than just 12V and 5V.聽

Link to comment
Share on other sites

Link to post
Share on other sites

@RONOTHAN##@Electronics Wizardy

Ok, so if you're manually controlling the fans, the lack of a tach wire is not a big deal. However, I've seen suggestions that some fans are sensitive to having the voltage changed. Is that nonsense?

I've been using computers since around 1978, started learning programming in 1980 on Apple IIs, started learning about hardware in 1990, ran a BBS from 1990-95, built my first Windows PC around 2000, taught myself malware removal starting in 2005 (also learned on Bleeping Computer), learned web dev starting in 2017, and I think I can fill a thimble with all that knowledge. 馃槈 I'm not an expert, which is why I keep investigating the answers that others give to try and improve my knowledge, so feel free to double-check the advice I give.

My phone's auto-correct is named Otto Rong.馃お馃槀

Link to comment
Share on other sites

Link to post
Share on other sites

Just now, RevGAM said:

@RONOTHAN##@Electronics Wizardy

Ok, so if you're manually controlling the fans, the lack of a tach wire is not a big deal. However, I've seen suggestions that some fans are sensitive to having the voltage changed. Is that nonsense?

PWM fans, sure, some of them don't like operating in DC mode (not all though, just a couple). DC based fans do not care, it's what they're designed to do.聽

Link to comment
Share on other sites

Link to post
Share on other sites

I guess that the lack of a tach wire poses a problem because a fan controller on auto can't determine if the RPMs are appropriate.

I've been using computers since around 1978, started learning programming in 1980 on Apple IIs, started learning about hardware in 1990, ran a BBS from 1990-95, built my first Windows PC around 2000, taught myself malware removal starting in 2005 (also learned on Bleeping Computer), learned web dev starting in 2017, and I think I can fill a thimble with all that knowledge. 馃槈 I'm not an expert, which is why I keep investigating the answers that others give to try and improve my knowledge, so feel free to double-check the advice I give.

My phone's auto-correct is named Otto Rong.馃お馃槀

Link to comment
Share on other sites

Link to post
Share on other sites

1 minute ago, RevGAM said:

@RONOTHAN##@Electronics Wizardy

Ok, so if you're manually controlling the fans, the lack of a tach wire is not a big deal. However, I've seen suggestions that some fans are sensitive to having the voltage changed. Is that nonsense?

I have a lot of fans Ive played with changing voltage on, and they almost all work just fine with pretty big voltage cuts.聽

Some fans will cut out earlier, but typically motherboards and fan controllers don't let you lower the voltage to a point where this is a issue. 7v is a typically low point for a board or controller, but many fans will work down to about 4-5v.

Link to comment
Share on other sites

Link to post
Share on other sites

Just now, RevGAM said:

I guess that the lack of a tach wire poses a problem because a fan controller on auto can't determine if the RPMs are appropriate.

Since RPM varies between fan model, typically controllers don't aim for a specific speed on something like a desktop where the fan used is unknown. And if fan speed

Also typically fan controllers seem to be used for case fans mostly. Typically a a single case fan failing will have smallish(depending on the layout) impact.

Link to comment
Share on other sites

Link to post
Share on other sites

1 minute ago, RevGAM said:

I guess that the lack of a tach wire poses a problem because a fan controller on auto can't determine if the RPMs are appropriate.

Again, even the smartest fan controllers aren't all that smart, and it's not like the actual RPMs of a fan matter all that much. An 80mm fan running at 3000 RPM is going to be moving a heck of a lot less air than a 140mm fan running at that same speed. The only situation where it would matter is if it were to alert you that a fan had died, and I'm not aware of any fan controllers that actually do that. This just isn't an issue.聽

Link to comment
Share on other sites

Link to post
Share on other sites

5 minutes ago, RevGAM said:

I guess that the lack of a tach wire poses a problem because a fan controller on auto can't determine if the RPMs are appropriate.

Not necessarily. Some may not even use that feedback loop, they'll just vary the PWM % on a set curve based on some other input, such as temperature of a component.聽

That Tach cable is mostly for user feedback in software.聽

Link to comment
Share on other sites

Link to post
Share on other sites

5 minutes ago, Electronics Wizardy said:

I have a lot of fans Ive played with changing voltage on, and they almost all work just fine with pretty big voltage cuts.聽

Some fans will cut out earlier, but typically motherboards and fan controllers don't let you lower the voltage to a point where this is a issue. 7v is a typically low point for a board or controller, but many fans will work down to about 4-5v.

I've played with a lot, too, and I've only had one cut out - it's my most powerful fan, a Delta, and I think the controller just couldn't handle the power requirement at high speeds. I've also noticed that the low end for when fans will start spinning is a wide range. Using Fan Control is frustrating because it doesn't have the ability to do what I can do manually with a fan controller.

I've been using computers since around 1978, started learning programming in 1980 on Apple IIs, started learning about hardware in 1990, ran a BBS from 1990-95, built my first Windows PC around 2000, taught myself malware removal starting in 2005 (also learned on Bleeping Computer), learned web dev starting in 2017, and I think I can fill a thimble with all that knowledge. 馃槈 I'm not an expert, which is why I keep investigating the answers that others give to try and improve my knowledge, so feel free to double-check the advice I give.

My phone's auto-correct is named Otto Rong.馃お馃槀

Link to comment
Share on other sites

Link to post
Share on other sites

2 minutes ago, RONOTHAN## said:

The only situation where it would matter is if it were to alert you that a fan had died, and I'm not aware of any fan controllers that actually do that. This just isn't an issue.聽

The Akasa FC.Trio, admittedly a poor quality device, actually has such a function and it worked. I've also seen other FCs with that alarm feature.

I've been using computers since around 1978, started learning programming in 1980 on Apple IIs, started learning about hardware in 1990, ran a BBS from 1990-95, built my first Windows PC around 2000, taught myself malware removal starting in 2005 (also learned on Bleeping Computer), learned web dev starting in 2017, and I think I can fill a thimble with all that knowledge. 馃槈 I'm not an expert, which is why I keep investigating the answers that others give to try and improve my knowledge, so feel free to double-check the advice I give.

My phone's auto-correct is named Otto Rong.馃お馃槀

Link to comment
Share on other sites

Link to post
Share on other sites

3 minutes ago, GuiltySpark_ said:

Not necessarily. Some may not even use that feedback loop, they'll just vary the PWM % on a set curve based on some other input, such as temperature of a component.聽

That Tach cable is mostly for user feedback in software.聽

I understand now, and that temperature can be used instead, which is a better solution than RPM. Unfortunately, I need a fan controller that actually gives that feedback, so if it's missing the tach wire it's a deal-breaker for me.

I've been using computers since around 1978, started learning programming in 1980 on Apple IIs, started learning about hardware in 1990, ran a BBS from 1990-95, built my first Windows PC around 2000, taught myself malware removal starting in 2005 (also learned on Bleeping Computer), learned web dev starting in 2017, and I think I can fill a thimble with all that knowledge. 馃槈 I'm not an expert, which is why I keep investigating the answers that others give to try and improve my knowledge, so feel free to double-check the advice I give.

My phone's auto-correct is named Otto Rong.馃お馃槀

Link to comment
Share on other sites

Link to post
Share on other sites

afaik there isnt any fan controller that cares about the tach signal, other than maybe some motherboard BIOSes that have 'constant RPM' modes, or have a low fan speed warning (this last one is common for servers, but it's not related to the fan controller itself)

in other words, the 3rd pin can as far as i am aware *always* be omitted if you dont care about getting a readout for the exact speed the fan is spinning at, for monitoring purposes. the only thing that doesnt work if the tach is disconnected, is RPM readout.

case in point... i have the tach pin detached on the fans in my server, so that it doesnt trigger low fan speed errors on the big-ass noctua fans, on a board designed for 80mm screamers. PWM works just fine on the PWM fans, DC control works just fine on the DC control fans.. the motherboard just has no idea how fast they're spinning.

Link to comment
Share on other sites

Link to post
Share on other sites

3 minutes ago, manikyath said:

afaik there isnt any fan controller that cares about the tach signal, other than maybe some motherboard BIOSes that have 'constant RPM' modes, or have a low fan speed warning (this last one is common for servers, but it's not related to the fan controller itself)

in other words, the 3rd pin can as far as i am aware *always* be omitted if you dont care about getting a readout for the exact speed the fan is spinning at, for monitoring purposes. the only thing that doesnt work if the tach is disconnected, is RPM readout.

case in point... i have the tach pin detached on the fans in my server, so that it doesnt trigger low fan speed errors on the big-ass noctua fans, on a board designed for 80mm screamers. PWM works just fine on the PWM fans, DC control works just fine on the DC control fans.. the motherboard just has no idea how fast they're spinning.

I get it. Too bad I need that wire. Sigh. It's sooo hard to find one that has that, a display and manual control (e.g. dial or slider).

I've been using computers since around 1978, started learning programming in 1980 on Apple IIs, started learning about hardware in 1990, ran a BBS from 1990-95, built my first Windows PC around 2000, taught myself malware removal starting in 2005 (also learned on Bleeping Computer), learned web dev starting in 2017, and I think I can fill a thimble with all that knowledge. 馃槈 I'm not an expert, which is why I keep investigating the answers that others give to try and improve my knowledge, so feel free to double-check the advice I give.

My phone's auto-correct is named Otto Rong.馃お馃槀

Link to comment
Share on other sites

Link to post
Share on other sites

5 minutes ago, RevGAM said:

Unfortunately, I need a fan controller that actually gives that feedback, so if it's missing the tach wire it's a deal-breaker for me.

Why? I legitimately can't think of a use case outside of failed fan alarm, and even them it's not usually that hard to just look at the fans and see one is dead.聽

Link to comment
Share on other sites

Link to post
Share on other sites

1 minute ago, RONOTHAN## said:

Why? I legitimately can't think of a use case outside of failed fan alarm, and even them it's not usually that hard to just look at the fans and see one is dead.聽

I'm testing fans and some of my tests require that I reach a specific RPM.

I've been using computers since around 1978, started learning programming in 1980 on Apple IIs, started learning about hardware in 1990, ran a BBS from 1990-95, built my first Windows PC around 2000, taught myself malware removal starting in 2005 (also learned on Bleeping Computer), learned web dev starting in 2017, and I think I can fill a thimble with all that knowledge. 馃槈 I'm not an expert, which is why I keep investigating the answers that others give to try and improve my knowledge, so feel free to double-check the advice I give.

My phone's auto-correct is named Otto Rong.馃お馃槀

Link to comment
Share on other sites

Link to post
Share on other sites

1 minute ago, RevGAM said:

I get it. Too bad I need that wire. Sigh. It's sooo hard to find one that has that, a display and manual control (e.g. dial or slider).

arduino, a potentiometer, and either an LCD module or 7 segment display module.

potentiometer goes on analog input, tach signal goes on an interrupt pin, PWM signal goes to a PWM output, LCD module goes to I2C interface.

it is extremely trivial to make your own fan controller to do this, given your rather specific needs... and given the scale of your testing you mentioned last time i've seen you around... spending an afternoon to figure out an arduino and some libraries should be trivial if you can then make a device that can do your fan controlling.聽

Link to comment
Share on other sites

Link to post
Share on other sites

@RONOTHAN##BTW, the Zalman ZM-MFC3 also has an alarm.

It's looking more and more like the first FC that I find that has even ONE 4-wire with manual control and a display is going to have to be what I get.

I've been using computers since around 1978, started learning programming in 1980 on Apple IIs, started learning about hardware in 1990, ran a BBS from 1990-95, built my first Windows PC around 2000, taught myself malware removal starting in 2005 (also learned on Bleeping Computer), learned web dev starting in 2017, and I think I can fill a thimble with all that knowledge. 馃槈 I'm not an expert, which is why I keep investigating the answers that others give to try and improve my knowledge, so feel free to double-check the advice I give.

My phone's auto-correct is named Otto Rong.馃お馃槀

Link to comment
Share on other sites

Link to post
Share on other sites

Create an account or sign in to comment

You need to be a member in order to leave a comment

Create an account

Sign up for a new account in our community. It's easy!

Register a new account

Sign in

Already have an account? Sign in here.

Sign In Now