What is the point of PWM?

[thekeemo]

3 pin fans have a tachometer wire to monitor speeds. Motherboards can vary the voltage.

A 5 second test can plot out voltage to RPM.

So why do we need PWM?

[nipppppyyyyyyy]

because for older machines that use analog you cant use that method can you

 

also its easier

[W-L]

1 minute ago, thekeemo said:

3 pin fans have a tachometer wire to monitor speeds. Motherboards can vary the voltage.

A 5 second test can plot out voltage to RPM.

So why do we need PWM?

One of the main benefits of PWM is the ability to do group control of a large number of fans, where 3 pin headers can only supply a certain amperage or number of fans, in general a good rule of thumb is 3-4 fans to not overload a header, where a PWM splitter that is power from the PSU only takes a PWM control signal to change the speeds of many fans. 

 

That being said PWM also has the advantage or lower starting speeds giving it a wider controllable range for silence. 

[thekeemo]

1 minute ago, W-L said:

One of the main benefits of PWM is the ability to do group control of a large number of fans, where 3 pin headers can only supply a certain amperage or number of fans, in general a good rule of thumb is 3-4 fans to not overload a header, where a PWM splitter that is power from the PSU only takes a PWM control signal to change the speeds of many fans. 

 

That being said PWM also has the advantage or lower starting speeds giving it a wider controllable range for silence. 

Wouldnt a normal fan hub do the same?

Take the RPM of a "control fan" and assume it is the same for the rest?

The start speed ofr my 3 pin fans is ~20% what is it for most PWMs?

1 minute ago, nipppppyyyyyyy said:

because for older machines that use analog you cant use that method can you

 

also its easier

Ive been able to do it since the P4 days..

[Sakkura]

8 minutes ago, thekeemo said:

The start speed ofr my 3 pin fans is ~20% what is it for most PWMs?

I sincerely doubt that.

[W-L]

8 minutes ago, thekeemo said:

Wouldnt a normal fan hub do the same?

Take the RPM of a "control fan" and assume it is the same for the rest?

The start speed ofr my 3 pin fans is ~20% what is it for most PWMs?

Ive been able to do it since the P4 days..

Well if your talking about fan hubs like the NZXT Grid+ units then yes those do let you control them thorough software though and not via the motherboard headers or using splitters per say. For PWM's they are usually a a root based curve to them so they start off at the very beginning but will mostly stay at the same speed until 20-30% and ramp up higher from there on but that can depend on the fan since some 3 pins can also go very low.

[Enderman]

most 3 pin fans can only go to about 40-60% before they stall

 

PWM allows fans to run at like 10, or 20% or even less

[thekeemo]

4 minutes ago, Sakkura said:

I sincerely doubt that.

https://goo.gl/photos/5KkXDzQsRKnu9ZgE6

3 minutes ago, W-L said:

Well if your talking about fan hubs like the NZXT Grid+ units then yes those do let you control them thorough software though and not via the motherboard headers or using splitters per say. For PWM's they are usually a a root based curve to them so they start off at the very beginning but will mostly stay at the same speed until 20-30% and ramp up higher from there on but that can depend on the fan since some 3 pins can also go very low.

No. A fan hub that doesnt exist yet. One that passes the tach signal from a primary fan to the motherboard and gets a voltage reading from the motherboard. It then amplifies that signal.

 

1 minute ago, Enderman said:

most 3 pin fans can only go to about 40-60% before they stall

 

PWM allows fans to run at like 10, or 20% or even less

All my 3 pin fans start at 20% thought that was standard..

[Enderman]

1 minute ago, thekeemo said:

All my 3 pin fans start at 20% thought that was standard..

what are you using to control them

i highly doubt its "real" 20%

20% means 20% voltage aka 2.4v

go ahead and try powering a fan with 2 AA batteries and you will see how it does not work

[WoodenMarker]

Fans usually need some amount of voltage to start up. 

By pulsing 12v, lower speeds can be achieved. My noctuas for example go down to 7%.

[W-L]

2 minutes ago, thekeemo said:

https://goo.gl/photos/5KkXDzQsRKnu9ZgE6

No. A fan hub that doesnt exist yet. One that passes the tach signal from a primary fan to the motherboard and gets a voltage reading from the motherboard. It then amplifies that signal.

All my 3 pin fans start at 20% thought that was standard..

20% is really low for 3 pins fans most aren't that low as mentioned. For a new type of fan hub that take the voltage as a sense from the motherboard and is able to take external power to then voltage control the fans that are connected to it would work but as of right now I don't know of any that is capable of that. 

 

Personally I use PWM fans but in my case I just use a swiftech splitter and wire up all my rad fans to it so they work as a group control in push/pull, unless I had that kind of a hub or got something else like those 3 pin fan hubs it would need to be split amount two headers ideally. 

[thekeemo]

Just now, Enderman said:

what are you using to control them

i highly doubt its "real" 20%

20% means 20% voltage aka 2.4v

go ahead and try powering a fan with 2 AA batteries and you will see how it does not work

2.68 according to my (rather sketchy) multi meter.

[thekeemo]

7 minutes ago, WoodenMarker said:

Fans usually need some amount of voltage to start up. 

By pulsing 12v, lower speeds can be achieved. My noctuas for example go down to 7%.

I guess in uber silent places you could tell the difference between 7 and 20%

4 minutes ago, W-L said:

20% is really low for 3 pins fans most aren't that low as mentioned. For a new type of fan hub that take the voltage as a sense from the motherboard and is able to take external power to then voltage control the fans that are connected to it would work but as of right now I don't know of any that is capable of that. 

 

Personally I use PWM fans but in my case I just use a swiftech splitter and wire up all my rad fans to it so they work as a group control in push/pull, unless I had that kind of a hub or got something else like those 3 pin fan hubs it would need to be split amount two headers ideally. 

Multimeter says it is actually 20%

I know which I find strange.

[WoodenMarker]

1 minute ago, thekeemo said:

I guess in uber silent places you could tell the difference between 7 and 20%

I stop hearing the difference below 11%.

[Deli]

Put a air filter in front of a voltage controlled fan. You will see the fan speed(rpm) reduces. So if the air filter/heatsink/radiator starts to have dust build-up, fan speed will be affected. While a PWM controlled fan will maintain its speed.

 

Many DC fans need 4.5-5v to start spinning.

[thekeemo]

2 minutes ago, Deli said:

Put a air filter in front of a voltage controlled fan. You will see the fan speed(rpm) reduces. So if the air filter/heatsink/radiator starts to have dust build-up, fan speed will be affected. While a PWM controlled fan will maintain its speed.

True, do you change your fan locations often/not clean it often enough to make a difference? Anyway I kind of see the point now.

[Enderman]

15 minutes ago, thekeemo said:

2.68 according to my (rather sketchy) multi meter.

and youre using a motherboard for this?

 

how old are the fans?

some fans can run at very low voltages if theyre like 5 years old

[thekeemo]

10 minutes ago, Enderman said:

and youre using a motherboard for this?

 

how old are the fans?

some fans can run at very low voltages if theyre like 5 years old

Correct

varying ages

one from 08ish one from 13 and the ones in my h440.

[ThomasD]

Better speed control across the entire range of operation.  

 

The pulse of pulse width modulation is always full voltage.  The two benefits of this are 1) the fan does not stall at very low RPMs, and 2) they always operate at maximum torque -meaning they provide the quickest response to any adjustment in speed setting.

 

IMO this makes them essential for any sort of CPU cooling operation - where rapid and full response improves cooling characteristics.  And also makes them useful in other applications where you might want to slow them waaay down.

 

Outside of those two settings they are something of an unnecessary expense.