PC Fan splitter with power input - Page 1
Forum section: electronics / general

author: JennySchubert
author_rank: Contributor
timestamp: September 16, 2015, 07:44:52 am
content: Hi guys (and gals), maybe you can help me out, pretty pleaseI don't know if general chat is the correct subforum for this, but I have no background in EE and don't want to get into too much theory in order to solve my problemThe problem:My mainboard in the PC has some fan connectors, two of which I can change voltage of, thus changing the speed of the connected fan.However, I want to control about 9 fans with a single connector (which I know I shouldn't do). The psu has some 12V/5V molex outputs which surely could handle 9 fans, but then I couldn't control their speeds.Can I somehow combine the voltage control of the mainboard with the power from the psu?Thanks for your responses!

author: Galenbo
author_rank: Super Contributor
timestamp: September 16, 2015, 10:54:58 am
content: Quote from: JennySchubert on September 16, 2015, 07:44:52 amA good start could be to look at those things decently, and discover there are 3-pin and 4-pin fans and connectors.Then look up what the differences are, see wich version you have, and somehow narrow down your question.Next step, even if everybody including you knows this will not work by just hooking together some cables, is to look up yourself in detail what the consumption of every fan is, and what the maximum output of the connector on your particular board is.What is your reason not to just buy a 3.5 or 5.25 fan controller?

author: JennySchubert
author_rank: Contributor
timestamp: September 16, 2015, 11:25:00 am
content: My fans all have only 3 pin -> no PWM. But I can control the voltage with software, so depending on the temperatures, I can speed up, or slow down the fans. In order to use this software, I need to have it all connected to the mainboard. If I got a fan controller, I would have to manually change the speeds (which I don't want). I COULD run all fans on that one 3 pin connector, but I'm scared I'll break the mobo, so I'd rather build something that can basically change the voltage of the 12V from the power supply to the voltage the mobo puts out.

author: canibalimao
author_rank: Regular Contributor
timestamp: September 16, 2015, 11:49:57 am
content: I don't understand one thing: your MB have 9 connectors for fans or you want to connect more than one fan to the same MB connector?If the case is the second, there are some 3 pin fan connectors splitters on ebay/aliexpress that cost only a few cents. The problem is that you should NEVER combine the two yellow wires from the 3 pin fans. That yellow wire is a feedback wire from the fan that tells the MB how fast it is spinning. So, you shouldn't combine the two yellow wires since all the fans spin at different speeds.However you can connect the two fans to the same connector with no problems at all. You just need to cut one of the yellow wires from the cable splitter.

author: JennySchubert
author_rank: Contributor
timestamp: September 16, 2015, 12:02:14 pm
content: no it has about 4. I want all 9 fans on one single connector whose voltage I can adjust with the software (I'll have to build a contraption for that) and this contraption should get power from the psu, so the 9 fans don't fry my mobo.

author: canibalimao
author_rank: Regular Contributor
timestamp: September 16, 2015, 12:23:02 pm
content: That way you can connect all the 9 fans in parallel and all of them run at same speed.Do you have thought about how you will control it? You'll use a microcontroller connected to a USB port so you can make a software to interact with it?

author: Chris C
author_rank: Frequent Contributor
timestamp: September 16, 2015, 01:20:58 pm
content: This is non-trivial.You won't be able to connect all 9 fans to a single 3-pin connector through a simple splitter, that would surely burn out the fan controller. Some people report burning out their controller with as few as two. There are no standards, or published specs, that can tell you how many can be safely connected.The most straightforward way to do this safely, would be to convert the variable voltage output from the fan connector to a PWM signal. That could be used to control 4-pin fans, which can gather their power separately from a Molex connector. Unfortunately, this seems to be an uncommon need, and I found no commercial product which does this. I did find a single reference to a homebrew converter. Pre-built units were supposed to be offered for sale, though I cannot find whether he ever actually made them available:http://www.overclockers.com/forums/showthread.php/746076-Fan-Controller-PWM-Booster-Regulator-Converter-Etc-Thread!The device you want is the "Voltage to PWM Converter, Stackable". If that doesn't work out:1) You could build a voltage-to-PWM converter yourself.2) Your motherboard's BIOS may have an option to switch your 3-pin fans to PWM control. Not all have this option, but if it does, it would simplify the converter greatly; as it would then just be little more than a level shifter.3) There are USB-controlled fan controllers, which would at least give you software control. But these appear to be so expensive that you might as well...4) Buy a new motherboard with 4-pin connectors, to which you can plug in commercially available splitters that handle up to 12 fans.

author: JennySchubert
author_rank: Contributor
timestamp: September 16, 2015, 01:32:47 pm
content: @canibalimao: There's a program calleds SpeedFan which I already use (I already ran about 6 fans on one output and 3 fans and a pump on the other one, and that worked quite well actually, but neither did I like running so many fans on one fan header, nor were 6 fans enough for me)@Chris C: I want to spend as little money as possible, and I have already spent quite a lot (for my taste) for the fans (which are beQuiet fans with only 3 pin headers). I had hoped to be able to somehow force the voltage of the fan header to a psu-output.

author: Chris C
author_rank: Frequent Contributor
timestamp: September 16, 2015, 01:59:24 pm
content: Quote from: JennySchubert on September 16, 2015, 01:32:47 pmAlready purchased 3-pin fans, that limits options.Check to see if your BIOS has that option to switch to PWM mode or not.If it does, I think we can use the PWM output to control a transistor for each fan. That will allow operating the 3-pin fans in PWM mode, by rapidly turning their power on and off.If it doesn't, the same technique could be used, if a voltage-to-PWM converter is added. So if that's the case, also check the availability of the one I linked.Then let us know what you find out.

author: Jeroen3
author_rank: Super Contributor
timestamp: September 16, 2015, 02:07:02 pm
content: Measure the output of the motherboard with your oscilliscope.Is it analog:-Connect 1 fan to the motherboard.-Tap off the feedback signal.-Convert signal (with mcu?) to multiple 4 pin pwm signals, or pwm'ed power mosfets (yes, you can pwm the power of these fans)Is is pwm:- Connect pwm to power mosfets with different supply branch.

author: AF6LJ
author_rank: Unknown
timestamp: September 16, 2015, 02:20:07 pm
content: Quote from: JennySchubert on September 16, 2015, 12:02:14 pmYou can get aftermarket fan controllers they are not so expensive.You could use the tachometer output from one fan to control the others provided you build a regular circuit that will handle the current of those other fans, then you would have a higher end version of what I mentioned above.The nagging question in the back of my mind;Do you really need nine fans?Being a gamer I know these computers can generate a lot of heat.This computer has four fans, counting the one on the CPU, and the one on the video card.The case seems to breathe just fine, the CPU never gets over 50C, 45C for the motherboard, and 60C for the video card. Generally speaking that is considered to be a cool running computer.

author: Galenbo
author_rank: Super Contributor
timestamp: September 16, 2015, 03:18:51 pm
content: I'm completely not interested in putting 9 fans in a PC, but some seconds google give me this:http://www.ebay.com/itm/Evercool-Model-EC-DF001-17-72-PWM-Fan-Splitter-Run-Multiple-4-pin-fans-/370642535130Some more seconds surely will give more results, suiting your needs.

author: JennySchubert
author_rank: Contributor
timestamp: September 16, 2015, 05:13:39 pm
content: Thanks to everyone who tries to help, I really appreciate it.@Jeroen3: Sadly I don't have an Oscilloscope, since I'm not an electrical engineer, just a computer scientist looking for help, sorry.@Chris C: SpeedFan actually lets me set the control mode (PWM or DC) and it's currently set to PWM. It also has a "reverse PWM logic" option. Sorry for thinking that it was voltage regulated and getting you running in a wrong direction. SpeedFan doesn't let my directly change "voltage" but instead lets me change the percentage of the fan speed. Reversing the PWM logic makes it so that 100% -> no fan spinning. So I guess we have PWM available even in 3 pin configurations. Good to know, sorry again for the inconvenience. I will look into the power mosfet solution.@AF6LJ and Galenbo: I want a low noise system. 9 (or in fact 12) fans can move a lot of air with a lot less noise than 3 or 4 fans can. But for that I need to be able to control their speed, so they're not insanely loud.@Galenbo: Those are for 4 pin fans, which I don't have

author: canibalimao
author_rank: Regular Contributor
timestamp: September 16, 2015, 05:26:05 pm
content: You can connect 3 pin fans to those connectors.However that doesn't seem very secure at all...

author: Jeroen3
author_rank: Super Contributor
timestamp: September 16, 2015, 08:17:32 pm
content: Since it seems you're not equipped to go diy.The alternative is to buy few high quality fans, instead of 9 cheapies. Noctua makes some high quality stuff.There is also no need at all to make the fans run at a dynamic speed. If they do well at 100% load, they do well at 10%. The benefit of single speed fans is a consistent noise level, instead of changing background noise.

author: Chris C
author_rank: Frequent Contributor
timestamp: September 16, 2015, 09:04:43 pm
content: Quote from: JennySchubert on September 16, 2015, 05:13:39 pmOk, this is good news! I believe it can be made to work simply with as little as two parts, like this:1) Connect a 1k, 1/4W resistor between red and black on the motherboard fan connector. (Common, through-hole, 5% tolerance resistors are fine.)2) The fans will be powered by the 12VDC/GND from a high-current Molex connector.3) There will be a single N-MOSFET between the fans and ground, of sufficient power rating for the combined total current of the fans, and with a Vgs of 18V or higher. If a large enough MOSFET isn't readily available, several can be used in parallel.4) The MOSFET gate(s) will be connected to either red or black on the motherboard fan connector. (This depends on whether the motherboard is switching the power or ground in PWM mode, of which I'm not certain. But one or the other will work, the parts remain the same either way, and hooking it up wrong should cause no harm.)5) And finally, connect one (and ONLY one) yellow lead from a fan to the motherboard connector. Speedfan will then register the speed of that fan. There will be no way to read the speed of the other fans, unless you add a switch.Experts please check this solution. I assume the fans won't be interfering with each other in any way that will require a separate MOSFET for each fan, but as I haven't done this in real life, I'm not 100% sure.

author: AF6LJ
author_rank: Unknown
timestamp: September 16, 2015, 09:18:23 pm
content: Quote from: Galenbo on September 16, 2015, 03:18:51 pmThat is generally not a good idea due to exceeding the maximum current on any one of the motherboard fan voltage sources.When I built the computer before this one, it was water cooled and the pump had a tach. output which went to the motherboard, I split off the power and ground leads and powered them directly from the power supply since the current required for the pump was over .2A.The motherboard knew there was something important spinning and would shut down if it ever stopped, and I didn't have to worry about the fan control IC / transistor getting fried.EDIT:I should have used my Good Eye, they did exactly what I was talking about, so that would work just fine.

author: AF6LJ
author_rank: Unknown
timestamp: September 16, 2015, 09:20:20 pm
content: Quote from: JennySchubert on September 16, 2015, 05:13:39 pmI get the noise issue; this computer sits behind this monitor and unless I turn off the sound and load up the CPU I can't hear the fans. Having a solid state drive goes a very long way to lower the noise level also.

author: JennySchubert
author_rank: Contributor
timestamp: September 16, 2015, 09:35:09 pm
content: @Jeroen3: My fans are already quite high quality. BeQuiet isn't a bad company. Still, I want to be able to control them, because when learing/working in silence, I want the fans to run as slowly as possible, but when gaming or rendering they can crank up a little. In my current configuration, it isn't possible to run all the fans at 10% anyway (which is the reason for this thread).@Chris C: That looks promising, Thank you!So my job now is basically finding out what beefy a mosfet I need and wire that up - sounds doable

author: AF6LJ
author_rank: Unknown
timestamp: September 16, 2015, 09:38:03 pm
content: That will be a fun project.

author: Galenbo
author_rank: Super Contributor
timestamp: September 17, 2015, 08:50:31 am
content: Quote from: JennySchubert on September 16, 2015, 05:13:39 pmNo they are not. Have a better look at the picture.Try to enlarge your attention span from 0.5s to 5s, a new world will open for you.

author: Chris C
author_rank: Frequent Contributor
timestamp: September 17, 2015, 10:04:00 am
content: Quote from: Galenbo on September 17, 2015, 08:50:31 amJenny is right. Look at the text description, "5 x 4pin PWM". Also the picture that shows the actual connector ends, which are all 4-pin profile. Most do have a pin removed, the one for feedback, because you can't combine the feedback from multiple fans back into a single motherboard fan connector. That does NOT make it compatible with 3-pin fans.The picture that has labels declaring "3 pin" connectors is therefore right in a manner, since a pin is removed. But ultimately misleading if you stop looking there. Takes at least a 30 second attention span to catch that one.

author: Galenbo
author_rank: Super Contributor
timestamp: September 17, 2015, 10:11:16 am
content: Quote from: Chris C on September 17, 2015, 10:04:00 amI think no one here wanted to short these return signals together...Quote from: Chris C on September 17, 2015, 10:04:00 amI had a look of 31 seconds at it :-) I see 3-pin ventilators in the picture. Do you mean they will not work?They indeed used 4-pin male connectors for it. A 3-pin female fits in it, no?

author: Chris C
author_rank: Frequent Contributor
timestamp: September 17, 2015, 10:23:23 am
content: Quote from: Galenbo on September 17, 2015, 10:11:16 amLooking at it closer, I see they drew 3 wires from the fans to their attached connectors. That's just plain wrong. Didn't catch that the first time, I should have looked for 32 seconds.3-pin fans use a power line that's PWM'ed by the motherboard. 4-pin fans use constantly on power lines, adding a separate low-current PWM signal pin attached to a switching transistor built into the fan. Even if you could physically plug a 3-pin fan into the 4-pin connector, the lack of separate power and PWM in the 3-pin fan would mean that all the fans would be drawing their power from the motherboard's PWM'ed power, which is really only designed to handle one fan.

author: Galenbo
author_rank: Super Contributor
timestamp: September 17, 2015, 11:27:09 am
content: Yes, indeed strange things going on in those ebay pictures schematics.It must somehow include an amplifier/transistor/fet/... to work.It's beyond my 33 seconds free-attention span.Longer than that, my performances are followed by an invoice :-)

author: canibalimao
author_rank: Regular Contributor
timestamp: September 17, 2015, 05:58:44 pm
content: Quote from: Galenbo on September 17, 2015, 11:27:09 amAs far as I know chinese sellers on ebay, that doesn't seem to have more than a few cables soldered to some connectors. I think it only serves to fry the MB :lol:

author: JennySchubert
author_rank: Contributor
timestamp: September 22, 2015, 01:25:22 am
content: @Chris C: Okay I'd really appreciate it if you could look over this again:http://www.amazon.de/registry/wishlist/1HY216LA47FDLI'd buy 3 of those Molex splitters, which I would take apart for the 3pin connectors (and one Molex).Is that Mosfet okay or should I use a smaller one? According to the datasheet of the fans, they only take 0.09A.Because I'm a cheap bastardI'd use a small cardboard box to assemble the whole thing and have it not flying about my system (I know, cringe for most of you guys, but that's how I roll)Cardboard is non conductive and should do the job okay, right?

author: Jeroen3
author_rank: Super Contributor
timestamp: September 22, 2015, 05:54:55 am
content: Cardboard is flammable.

author: JennySchubert
author_rank: Contributor
timestamp: September 23, 2015, 02:28:48 am
content: Ok, I will find a plastic housing then. Is the hardware okay otherwise?

author: JennySchubert
author_rank: Contributor
timestamp: October 07, 2015, 04:45:13 pm
content: can anybody please tell me if these parts will work?http://www.amazon.de/registry/wishlist/1HY216LA47FDL

author: JennySchubert
author_rank: Contributor
timestamp: October 14, 2015, 08:48:28 pm
content: Okay I have made a sketch of what I think might work. If somebody could look over that, I'd be thrilled. Thank you in advance!