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More than you cared to know about PC fans

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Re: More than you cared to know about PC fans

#51

Post by exmadscientist »

axiolite wrote: post #34

> "there is no readily-available 24V source from an ATX power supply," This is false. ATX provides both +12V and -12V: * https://pinoutguide.com/Power/atxpower_pinout.shtml Hooking them together would provide 24VDC. On a 350W PSU, I see -12V rated to supply 0.3A, which would allow for 24V fans drawing up to 7.2W of power, if desirable. I don't see any reason to prefer 24V fans, however. The current losses over such s…

Do not use 24V fans for anything, if you have any control over it.

24V fans in general are poorly stocked. 24V 4-wire PWM fans are, these days, more or less special order items. There are thousands of 12V 4-wire PWM fans in stock at Mouser and Digi-Key. There are less than a dozen 24V 4W fans in stock, and most of those are sizes you probably don't want.

I'm a consulting EE these days. One of the jobs I get to do is clean up designs that aren't working. We always flag these fans when we see them... then nothing gets done because they're "available enough"... then when build time comes we can't source the fans because the "stock item" is completely out of stock and all possible substitutes are out of stock. But 12V versions are available.

So, yeah, stick to 12V fans whenever possible (or 5V for the little guys). Also genuinely never use AC fans, but that's a different story.

Re: More than you cared to know about PC fans

#53

Post by nicolaslem »

antifa wrote: post #20

I wish noctua would sell aftermarket replacement CPU fans for laptops. I thought there was something wrong with the loudness of my Dell laptop's fan (with low confidence), but I couldn't gauge that any replacement product wound actually be quieter or cared about noise levels.

Most laptop parts are specifically designed for a particular laptop model. This is very different from the highly standardized desktop parts. Noctua would be sure to lose money selling laptop fans.

Re: More than you cared to know about PC fans

#54

Post by exmadscientist »

amelius wrote: post #36

How does a fan get power to drive the tach output, if the only power it gets is a pwm signal (which might be low when it needs to switch)?

It doesn't. They're almost always open collector/open drain signals, with the pull-up on the host (PC) side. No power needed, if you've got mechanical switches doing the commutating!

(Of course those aren't so reliable over the long term, so transistors are usually used. But swinging a base or gate around is all that's needed, and that is easy to do with almost any available power source. Like the main power for the fan!)

Re: More than you cared to know about PC fans

#55

Post by amelius »

robotguy wrote: post #43
amelius wrote: post #40

Earlier quoted context omitted.

Well, PC fans come in 3-wire and 4-wire forms, where the 3-wire type has only pwm,tach and GND connections (no DC power).

3-wire is: TACH, DC, GND 4-wire is: PWM, TACH, DC, GND https://noctua.at/en/what-pin-configuration-do-noctua-produc...

In practice pwm is used instead of DC.

Re: More than you cared to know about PC fans

#56

Post by fnordpiglet »

jenscow wrote: post #15
owenversteeg wrote: post #11

Does anyone know if there are high-heat-resistant PC fans (and at what temperatures normal PC fans will melt)? The only fans I can find that claim to be heat-resistant are the Noctua Industrial PPC series which, aside from not being cheap at $33/piece are "only" heat-resistant up to 140C and the airflow isn't crazy high - subjectively the ones I've got feel like they move substantially less air than a standard diesel…

I prefer fans that are not heat-resistant. That way, it has more motivation to do its job properly.

The melting will stop when cooling improves.

Re: More than you cared to know about PC fans

#57

Post by post_break »

rietta wrote: post #10
azalemeth wrote: post #3

Honestly this isn't more than I cared to know about PC fans. I've worked extensively with industrial appliances and fans are bloody important and underlooked: fan failure is often the step that precedes component failure. The one part of the spec I wasn't aware of was just how insanely high the maximum current draw is; I'm glad that we've made more efficient, longer-lasting, effectively silent air-movers that can fit…

Adding fans to consumer devices that don't have them but should, such as a cable modem, certainly improves its reliability in my experience!

Slow big fans on my home receiver kept it going much longer than it probably would have lasted passively cooled.

Re: More than you cared to know about PC fans

#58

Post by tristor »

This was a great read, I have always had a love of PC fans, and the technology behind them. It'd quite a complicated engineering challenge to produce a high static pressure, high rate of airflow, and minimize noise while maintaining high reliability. I'm one of those folks that has no problem dropping significant money on fans every time I do a PC build, and so far I have very very rarely ever had a fan fail on me, even after decades of running at high duty cycles. The thing I always marvel at is how high the draw is for some of these fans. At one point I even retrofitted a system with an external radiator for water cooling that used 120V 120mm Panaflos and was separately powered from the computer.

I wish folks took cooling more seriously. There are so many devices that benefit from active cooling but rarely get it, or even being strategic around placement, positioning, and mounting to make convective cooling more effective. Thermal limiting is such a common occurrence on modern electronics if you don't give due consideration to cooling, as we've moved towards more passively cooled devices, including PCs (laptop especially).

Re: More than you cared to know about PC fans

#59

Post by balfirevic »

exmadscientist wrote: post #51
axiolite wrote: post #34

> "there is no readily-available 24V source from an ATX power supply," This is false. ATX provides both +12V and -12V: * https://pinoutguide.com/Power/atxpower_pinout.shtml Hooking them together would provide 24VDC. On a 350W PSU, I see -12V rated to supply 0.3A, which would allow for 24V fans drawing up to 7.2W of power, if desirable. I don't see any reason to prefer 24V fans, however. The current losses over such s…

Do not use 24V fans for anything, if you have any control over it. 24V fans in general are poorly stocked. 24V 4-wire PWM fans are, these days, more or less special order items. There are thousands of 12V 4-wire PWM fans in stock at Mouser and Digi-Key. There are less than a dozen 24V 4W fans in stock, and most of those are sizes you probably don't want. I'm a consulting EE these days. One of the jobs I get to do is…

> 24V fans in general are poorly stocked.

I'm guessing the same holds for 48V fans?

Re: More than you cared to know about PC fans

#60

Post by deathanatos »

MaulingMonkey wrote: post #48
deathanatos wrote: post #46

Also, one thing I've always wondered: why do people want to use hwmon to set fan RPMs? (Or really, why do this from userspace at all?) It seems inherently dangerous to me, as you're asking a process who might not receive CPU time for whatever reasons from the very much not realtime OS to control a fan; if the current RPM is too low, and the system starts generating heat, but the fan controlling process doesn't get CP…

> It seems inherently dangerous to me In the old days, it kinda was - at least to your hardware. Then people realized that blowing up components because a fan failed, or became unplugged, or a filter clogged with dust, maybe wasn't a great user experience and/or caused more in-warranty returns that required replacing hardware ($$expensive$$!), and implemented thermal throttling and thermal cutoffs. Nearly two decades…

> and maybe your crappy motherboard vendor shouldn't be writing a ton of code running in kernel space - with all the potential stability and security issues that might entail

This wasn't the suggestion I was making. I was suggesting that the motherboard, itself, should be controlling the fan RPMs (or should at least provide such a mode). I don't feel like taking a temperature input, and mapping that to an RPM output should take much circuitry at all, but it that (somehow) required a full-blown CPU, I was thinking a (very small) auxiliary chip, dedicated to the task.

But yes, if you're going to do it on the main CPU, then in userspace. But now you incur all the problems I mentioned in the original comment, some of which can exhibit death spirals: CPU has to throttle due to heat, meaning less CPU time, meaning it will take longer to get to the code responsible for alleviating the problem of heat by notching the RPM up!

In the worse case, you hit the CPU's critical trip point before the problem can be brought under control.

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