Case Fans doesn't go full speed when connected to Molex (PSU) but when connected to motherboard they have full speed.

Toggle sidebar Toggle sidebar
Vlp3r

Vlp3r

Honorable
Nov 1, 2013
57
0
10,640
I have a Deepcool Kendomen case and it comes with 5 pre installed fans. 2 LED front Intake and 3 Exhaust (2 on top and 1 on rear)

My MOBO has 3 System fan inputs. So i connected the rear exhaust to the MOBO since it is very close.

And for the front two fans intake , one was connected to the MOBO (sys fan header) and the other one was connected to the MOLEX coming from the PSU.

Deepcool Kendomen has an option in the front panel for controlling fan speed to low , off and high. So i put it up high(where we gotta slide the button to extreme right).

Now when i turn on my system , I observed that the fan which was connected to the PSU rotates very slowly like it is 700-800 RPM where as the Motherboard one pushes out so much air which really feels like 1700-1800 RPM. i could feel keeping my hand infront of those two fans and there is so much difference.

The fan which is connected to the molex doesn't even match the speed of the fan which is connected to MOBO atleast when the fan controller speed (front panel option) is set to low.

Is there any way i could control the fan speed which was connected with the Molex?

P.S : I thought maybe the fan was a defect one , so now i connected my rear fan to the molex unplugging it from the mobo sys fan header and checked it. Now even the rear fan dropped the speed into half. so clearly the fan wasn't a defect.

Also can anyone suggest if this deepcool fan hub is worth purchasing so that all fans can remain at same speed?Also how does it work? I'm so worried because i stay in India and the idle temperatures are around 40-45c.

 
Solution
Windrunner
not really. if you connect fans to yellow+black wire (12v) on molex directly to psu,they should work on their max rpm. maybe you connected them to red+black wire on molex,in that case you're getting just 5v,so they will be kinda double slower. connecting them to mobo is also giving 12v,but can provide some control of fans through bios,speed fan,or similar software,including that fans are 3 or 4 wire type. or if you disable those control options in bios,they will again spin at their max rpm. fans with just two wires and two pins connector will also spin at max,only an external regulator (potentiometer) can control those type of fans. further more,4pin fans can regulate themselves through an temperature diagram (aka msi afterburner or...
Sort by date Sort by votes
Vlp3r

Vlp3r

Honorable
Nov 1, 2013
57
0
10,640


But the case fans wires are too short that they can't even reach the sys fan ports :( Only one could reach and it is running fine but the other one i had to plug it to the molex.
 
Upvote 0 Downvote
OfficialJJTech

OfficialJJTech

Commendable
Jan 28, 2017
34
0
1,560
I cant do anything about it. Its just the issues between the power supply and the motherboard. It need to go through the power supply then to the motherboard instead of going directly to the motherboard.
 
Upvote 0 Downvote
D

Dark Falz

Reputable
Mar 8, 2015
97
0
4,660
Unless it has some kind of weird built in control any fan connected to the PSU should run at its maximum speed. Variable fan speed on the motherboard works by the MB changing the voltage from 7V or something to the maximum of 12V, Molex should only be providing 12V. The current draw is pulled by the fan, not pushed by the MB or PSU.

I wonder if it's possible that you have plugged the Molex in the wrong way, supplying 5V rather than 12V to your case fan. Can you confirm the PSU wire that lines up with the fan connector is yellow (12V) not red (5V)?
 
Upvote 0 Downvote
Vlp3r

Vlp3r

Honorable
Nov 1, 2013
57
0
10,640


Yes it is Yellow!! Also i forgot to mention that , i have stacked up the top 2 fans and one front to the molex on the top of each other and connected to the PSU. Maybe is that the reason for slow spinning because one single molex from psu is giving power to all 3 at once?
 
Upvote 0 Downvote
Vlp3r

Vlp3r

Honorable
Nov 1, 2013
57
0
10,640


Basically the fans which are connected to the MOBO system fan header are the ones which can be controlled by the front panel fan controller. So in my case only the rear fan and one front intake fan can be connected to the mobo which have really good rpm. (since only these fan wires could reach them)

For the front LED fan it has 4 pin and the top two exhaust have 3 pin. However i stacked up the top 2 fans with one front fan on one another through molex and connected it to the molex of the PSU.
 
Upvote 0 Downvote
Vlp3r

Vlp3r

Honorable
Nov 1, 2013
57
0
10,640


Hmm maybe i need to do trial and error with those fans with molex/mobo header or get a Deepcool fan hub. So that at least all the fans can give the same RPM.

Also is it safe to enable the high RPM in the bios for the case fan settings? it was normal i cranked it up to high xD
 
Upvote 0 Downvote
Windrunner

Windrunner

Distinguished
BANNED
Jul 11, 2016
101
1
18,695
not really. if you connect fans to yellow+black wire (12v) on molex directly to psu,they should work on their max rpm. maybe you connected them to red+black wire on molex,in that case you're getting just 5v,so they will be kinda double slower. connecting them to mobo is also giving 12v,but can provide some control of fans through bios,speed fan,or similar software,including that fans are 3 or 4 wire type. or if you disable those control options in bios,they will again spin at their max rpm. fans with just two wires and two pins connector will also spin at max,only an external regulator (potentiometer) can control those type of fans. further more,4pin fans can regulate themselves through an temperature diagram (aka msi afterburner or similar software),and the 3pin fans cannot control themselves automatically. at the end,there are types and types of fans. most of big 12cm case fans are really slow,like 1000-1800rpm. if you need an fast fan,you simply must search for it. there are some great 8 or 12cm fans which can operate at 3000-4000rpm or so...medium size cpu fans usually operate up to 2500rpm. gpu fans normally can go up to 4000rpm also.
 
Upvote 0 Downvote
Solution
P

Paperdoc

Polypheme
Ambassador
Oct 19, 2006
11,278
1,031
69,340
What I'm aiming for here is this. I suspect there is a flaw in the case's built-in fan control slider. The best solution probably is to connect all the fans to mobo fan headers and ignore the case control unit. But there are three issues to settle to get that to work.

1. The Kendomen website does not make it clear what fans are pre-installed, but they appear to be some variety of 3-pin fans. Is that correct - do ALL of those fans have three wires coming from them, ending in a female connector with 3 holes and small ridges along one side? Do the front ones with LED's in them also have an extra cable for the LED's, or do they have only the one 3-wore cable for all of the fan unit?

2. Now look especially at the two at the front with LED's in them. On their labels does it specify either a Watt (W) rating or an Amp (A) rating? If so, tell us that. Otherwise, tell us the model number on those fans. With that we can look up some required info.

3. Tell us the maker and exact model number of your mobo so we can look up the fan headers' capabilities. In general, you cannot use a fan HUB with 3-pin fans, you can only use Splitters. But that requires that the mobo headers can use the older Voltage Control Mode (aka DC Mode).

Your issue of not being able to reach the mobo fan headers can be solved with fan extension cables. But if you will use Splitters to connect five fans to three mobo headers, the Splitters themselves will provide enough cable length to do the job.
 
Upvote 0 Downvote
madmatt30

madmatt30

Titan
Ambassador
Jan 1, 2013
24,574
650
91,240
If you're plugging the fans to,molex then you are NOT using the case controller at all.

The built,in fan controller has a molex cable that plugs to the Psu for power & a pair of 3 pin female fan connectors to plug 2 fans into.

That will give you switching between 12v (full speed) & 7v (50% speed or thereabouts)
 
Upvote 0 Downvote
You must log in or register to reply here.

TRENDING THREADS

Latest posts

Moderators online

Share this page

COMPANY
RESOURCES
FOLLOW
Top Bottom