What exactly is PWM? Plus basic fan question

LePhuronn said:
That'll be because the voltage required for 600 rpm is too low to even get the fan spinning. The PWM version has the same voltage going into the motor to spin it, but the PWM signal can ensure the "pulses" are infrequent/short enough to only juice up the fan for 600rpm rotation. So PWM or not, you won't be able to get that fan down to 600rpm on voltage regulation, even if you use the PWM version on a 3pin plug.
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Very helpful, thank you!! Why is there not something like voltage based PWM, then? Can you use something like speedfan on PWM as opposed to having to use mobo software?
 
Speedfan is only an interface onto your mothrboards/other's sensors and control.

Speedfan will usually expose some level of control depending on your motherboard.
 
But does speedfan only "read" PWM or does it read any fan header?

Also, it turns out I have 2 pwm fan headers. If I want 2 fans, presumably this means I will only have pwm control in pairs of 2 when I use a splitter from the header?
 
Speedfan will read whatever the motherboard is capable of doing. Generally yes it's 4-pin PWM headers, but if you motherboard has the correct features and BIOS, you can override PWM and do voltage control through a 4-pin header. Speedfan will then be able to read that too.


As far as splitting fans goes, check out this bad boy:
http://www.overclockers.co.uk/showproduct.php?prodid=CB-031-AK&tool=3

Runs 3 PWM fans off a molex connector so you're not stressing the motherboard header for power, yet you still get PWM control from the 4-pin connector.

And as power comes directly from the power supply, I reckon you could use 3 PWM Y-splitters to get a whopping 6 fans all controlled by a single motherboard header.
 
"yet you still get PWM control from the 4-pin connector."

Does that mean, presumably that all fans would fun at the same speed, right? Speedfan would only be able to control.

Shivvy - does Speedfan allow you to turn fans off?

To be honest, for what I want, I think I only want 3 things.

1. Off
2. Setting for 600rpm
3. Setting for Full 1200 rpm
 
Chimp Paradox said:
So fans don't need to be PWM to run on speedfan?
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No, Speedfan can only talk to PWM headers unless your motherboard has some extra fancy bits.

So in order to use Speedfan you need PWM fans connected to PWM headers on your motherboard.

Chimp Paradox said:
Ive emailed Phantek to ask whether their PWM fan can run on 600rpm through voltage regulation or whether it needs PWM to do so.
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You're getting yourself confused now. If you have PWM headers on your motherboard then use PWM - there is no need to bother with voltage regulation if you have PWM, and voltage regulation just produces excess heat. Plus if you're buying PWM fans then plug them into 4-pin PWM headers, because I doubt very much the fan will even spin at the low voltages required to run at such a low 600rpm.

3-pin fans are really only used now for constant-speed fans like case exhausts.
 
Chimp Paradox said:
"yet you still get PWM control from the 4-pin connector."

Does that mean, presumably that all fans would fun at the same speed, right?
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Yes, that's the whole idea. The 4-pin connector will use the PWM signal to control the speed of all the fans at once, so they will all run at the same speed as each other. However the fans get their power directly from a molex so you don't risk drawing too much power from a motherboard header and burning it out.

Chimp Paradox said:
Speedfan would only be able to control.
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I don't understand what you're asking. Speedfan is only used to control fans, what else do you think it does?
 
"Speedfan would only be able to control." - that's a typo, I meant speedfan would only be able to control the speed of all of them at once and not individually.

So the long and short of it is, get the PWM fans, and control them using speedfan, which allows me to:

1. Turn them off
2. Turn on full

Who is it I need to ask if I can get them running as slow as 600rpm, then? My understanding from silentpcreview is that everyone over there runs slow fans.
 
Using that splitter I linked to will enable all the fans connected to the PWM motherboard header to spin up and down in unison, so they will all be controlled together as a single unit. 2 different PWM headers will allow you to control 2 sets of fans independantly.

From what I gather of your build I don't think you'd need to have different case fans running at different speeds, so in theory you'd only need to link off 1 PWM header and you're all good. Link that to Speedfan and you're all set.

As far as the fans running at 600rpm, you've already linked to fans that will do it, but if you're looking at different fans then just look at the spec sheet for them. You will find that they will be PWM fans.

Don't get hung up on the speed of the fans though. I know you want silence, so look at decibel ratings. I've had 120mm Gentle Typhoons that run at 1300rpm and are silent. I've also had cheapo 140mm fans that ran slowly but were still noisy. Also bear in mind that slower fans mean moving less air. Yes, the bigger the fan then the more air they can shift at lower speeds, but it isn't as easy as just getting a low RPM fan and be done with it. Especially if you're looking to use lots of fans at once. You need to move the air through your passive coolers, so check that your choice of fan can actually move enough at low RPM.
 
Thanks LePhuronn - in that case I was misunderstanding you earlier.

Can I therefore assume you mean that if a PWM says you can go down as low as 600rpm, then it can, provided you use PWM. You wont be able to do it with voltage (at least until you figure out how to modd the fan somehow).

Can I also assume that, for speedfan to work correctly, you need to disable all fan control in the BIOS, which is presumably where the mobo based PWM is set?

Finally on the fan point, I am using the phanteks simply because they are currently the quietest as rated by silentpcreview, but understand what you are saying.

According to them, the result of the thyphoon is

Scythe GT120-12 is 24 and 27 degrees at 12 and 11db @ 1m

The Phantek are 22 and 25 degrees at 12 and 11db @ 1m.

Not a lot in it. Full results here

http://www.silentpcreview.com/article1345-page7.html
 
I was just in the middle of tweaking my heatsink fan and noticed this forum popped up.

I'm usually one of the lazy ones who cranks up the fan to max rpm and leaves it. You know the guy you can never near on Vent/Teamspeak because his PC Fans are too loud. Anyway I've been busted because my guild master won't stand for it anymore.
 
You're correct about the low fan speed because the very low voltage required to spin the fan at 600 RPM will probably not be enough to even get the fan started, so PWM will be the only way to do it. So double-check the spec sheet (as you have done) for the fans to make sure they can do what you want them to do.

As far as controlling the fans goes, you don't need to change anything in the BIOS. The motherboard controls the fan speed, always has and always will. All Speedfan does is tell the motherboard what you want to do, and the motherboard then controls the fans accordingly. If Speedfan doesn't work properly then you can try turning off any fan control in the BIOS.
 
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