PWM Fan control?

[Chris230291]

Alright guys? I'm just looking for someone to help me work out how to control my fans.

I plan on getting all PWM fans for my Rad/s but i would like to run them all off the CPU fan header.

If PWM is pulse width modulation, then that means the fans are always running at the full 12V, they are just turned on and off real quick to achieve a desired RPM? So if i ran them all off the CPU header the computer can control them as it pleases... Sweet!

Now i doubt the one fan header has enough "umpf" to power all of the fans it needs to. So i'll need one, or several of these?...

Am i right in saying one, or several of these will not effect the operation of the fans (other than provide enough juice)?

Hopefully everything is right so far?

Now if i put a pot on the 12V input to the fans (from the splitter molex or w/e) am i right in saying the PC will manage the speed itself, but i can limit it further using the pot to decrease the voltage?

Hopefully that makes sense to someone haha.
Any help or advice is appreciated!

Chris.

 

[jamesriley94]

What fans will you be using? Controlling fans isn't really necessary - just whack on 5/7v resistors and you'll be better off.

I'd be concerned about running all the fans off the CPU fan header. The header will adjust fan speed based on CPU temperature, unless you can lock it down, which will mean your fans will rev up and down pretty frequently. Under any load at all really, your fans would be pumping out 12v, and it'll be really loud.

You'd be better running them all straight off molex at 5/7v. You may need to rewire the fan a little to fit a 3pin resistor.
I'm guessing Noctua NF-F12s or Akasa Venoms?

 

[Chris230291]

Alright mate thanks for the reply.

Fans... i think Sp120's - which i just noticed are not PWM. In which case ill need to add PWM to 3 pin convertor like this?...

http://forums.overclockers.co.uk/showthread.php?p=22644791

The idea is the fans DO change speed with load
Since i rarely max out my CPU, i figured it would stay at low RPM's for the most part anyways? If I'm way out let me know!

Once set up i would stress the CPU using prime or something, then when it's at full whack i'll tweak the pot to limit the top end?

I didn't like the idea of running all of the fans at a constant speed. It seemed unnecessary.

 

[jamesriley94]

PWM on the Corsair SP120s make an awful motor noise. and I really wouldn't be wanting to make one of those things anyway...

You don't need PWM, and you don't need your fans to change speed based on load. As long as you have good enough cooling anyway, you can afford to run all your fans really slowly all the time. For example, now on my loop, I run every fan at 5v, so the lowest speed they'll actually run on, and temps don't go above 65 degrees on the CPU under load, and it's quiet constantly. Same story on my old D14.

I didn't like the idea of running all of the fans at a constant speed. It seemed unnecessary.

Unnecessary because you think they might be running faster than you need them to when the rig isn't under load?
That's not really what I'm saying. Run them at the lowest speed so they're always quiet.

Actually - the SP120s come with voltage resistors for 7v already.

You should never be running fans at a full 12v tbh.

 

[Chris230291]

Hmm. Ok well maybe i should listen to you. I have NO water-cooling knowledge, i'm just trying to be clever.

I think i'll try running them all off the PSU like you suggested, but use a pot rather than a resistor so i can fine tune them to my liking. If i'm not happy with temps under load, i'll play around with PWM splitters.

Unnecessary because you think they might be running faster than you need them to when the rig isn't under load?

yes thats right.

Thanks for your advice,
Chris.

 

[S_I_N]

just get a fan controller if your looking to fine tune them. easiest simple way to do it. I have 13 yes I said 13 140mm spectre pro blue led fans in my case and have all 13 of them on my fan controller. Only during extremely heavy gaming sessions do i even think about turning them up a tad. Currently and 95% of the time I have them set to the lowest speed. When I need I reach over and slide the switch up to the middle. which is still ubar quiet.

 

[Chris230291]

Hello S_I_N. A pot is the same thing used in a fan controller to control the fan speed. Why would i need a fan controller if all i wanted to do is change the resistance? Are there any benefits? I won't really have room for a proper controller if i want it to look right.

 

[S_I_N]

if you have room to put a pot on each fan I'm sure you can find a spot for a fan controller. seeing as a pot would require some modding skills But another thing you may want to look at is the Swiftech 8-Way PWM Splitter Box at 10$ it may be the answer your looking for. I have 2 arriving today to switch my fans from my controller to this to free up the 5.25 bay for something else.

http://www.swiftech.com/8-waypwmsplitter.aspx

 

[alpenwasser]

Hello S_I_N. A pot is the same thing used in a fan controller to control the fan speed. Why would i need a fan controller if all i wanted to do is change the resistance? Are there any benefits? I won't really have room for a proper controller if i want it to look right.

You don't really, a fan controller just offers some more convenience for some people. But there
are fan controllers that don't work with adding resistance to the circuit but do their voltage
regulation differently, which means they don't waste power in an additional resistor (I think
Lamptron controllers belong to that group, but I'm not entirely sure tbh).

You don't actually need resistors though, you can reduce the voltage of your fans by changing the
cables in the plug like this article describes, or this one, or this forum thread.

If you never want to change fan speeds anyway, that would be pretty much the perfect way.
No additional tinkering with resistors, and no power losses in them either.

EDIT: One downside of this method: You can only reduce to 5 V or 7 V, respectively,
not so much possibility for fine tuning.

 

[NRG!]

If you don't have PWM fans then don't bother trying to use pwm with converters.

I have 3 fans in my rig running with the cable in the OP. the molex supplies the power (you could rejig it to supply 5v or 7v if you like experimenting), the link to the cpu fan head supplies them all with the on/off signal.

 

[Chris230291]

if you have room to put a pot on each fan I'm sure you can find a spot for a fan controller. seeing as a pot would require some modding skills But another thing you may want to look at is the Swiftech 8-Way PWM Splitter Box at 10$ it may be the answer your looking for. I have 2 arriving today to switch my fans from my controller to this to free up the 5.25 bay for something else.

http://www.swiftech.com/8-waypwmsplitter.aspx

Yes i have seen those. But because SP120's are not PWM, i would need to make a convertor anyways so that they are pulsed on and off at the 12V input.

I would use one pot to control all of my rad fans.

You don't really, a fan controller just offers some more convenience for some people. But there
are fan controllers that don't work with adding resistance to the circuit but do their voltage
regulation differently, which means they don't waste power in an additional resistor (I think
Lamptron controllers belong to that group, but I'm not entirely sure tbh).

You don't actually need resistors though, you can reduce the voltage of your fans by changing the
cables in the plug like this article describes, or this one, or this forum thread.

If you never want to change fan speeds anyway, that would be pretty much the perfect way.
No additional tinkering with resistors, and no power losses in them either.

EDIT: One downside of this method: You can only reduce to 5 V or 7 V, respectively,
not so much possibility for fine tuning.

Yes i have already thought of wiring them to 5,7 or 12V, but i would like to turn it up and down as i please.

Im not concerned about the wasted energy, it's nothing really :/

 

[Chris230291]

If you don't have PWM fans then don't bother trying to use pwm with converters.

I have 3 fans in my rig running with the cable in the OP. the molex supplies the power (you could rejig it to supply 5v or 7v if you like experimenting), the link to the cpu fan head supplies them all with the on/off signal.

Why not? That sounds exactly like what i wanted in my OP?

The on/off frequency sets the RPM. Then i can change the input voltage with a pot?

So essentially it auto adjusts, but i have a manual override.

Am i missing something?

Obviously because the fans i want to use don't have the PWM circuit built into them, i would have to use an external one like the (DIY) one i linked to earlier?