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[SOLVED] 7v Fan Mod for Molex KK?

Netbug

By Netbug
in Hardware

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Netbug Contributor

Netbug

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Hi,

 

Does anybody know of a tutorial to do the 7v fan mod on a 4PIN Molex KK connector? All I can find are only on the larger Molex.

 

I got a SuperMicro CSE-M35T-1 and the fan was WAY too loud. So I went out and bought a well reviewed replacement (forgive me, I'm not at home at the moment so the name escapes me), however it is still running WAY to loud at 12V.

 

I know there are a number of tutorials on how to modify a fan on a standard molex from 12v to 7v, however the connector on the SuperMicro fan is a Molex KK (and must be attached or alarms go off).

 

Thanks.

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Netbug Contributor

Netbug

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No problem, ill see if I can locate a pinout for the connector. Worse case, if you have a volt meter you can get the pinout relatively easily.

 

No volt meter (still new to this, but learning).

 

The fan is a Nexus 92mm 700 to 2500 RPM Real Silent Case Fan.

 

Here are the specifications from CanadaComputers.com:

http://www.canadacomputers.com/product_info.php?cPath=8_130&item_id=040014

 

Model number: DF1209SL-3PWM

Dimensions: 92x92x25mm

Versions: Clear chassis and foggy rotor/blades

Fan mounts: 4 pieces purple ultra-soft silicone fan mounts

Fan speed: 700 ~ 2500 RPM (10%)

Noise level: From 15.8dB(A)*

Airflow: Up to 43.5 CFM

Static Pressure: 3.15mmH2O

Rating voltage: DC 12V

Voltage range: DC 7V ~ DC 13.8V

Starting voltage: 7V

Label current: 0.15A (Max.)

Working current: 0.17A 15%

Power consumption: 2.04W 15%

Operating temperature: -10C ~ 70C

 

EDIT: Here is a  (blurry) picture of the connector. It is connected to a three-pin male. The bottom wire (which I assume is for control functionality) is not connected to a pin.

Vx2TW.jpg

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Influencer Rising Star

Influencer

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Ok, from what I've gathered here is the pinout:

Black: Ground

Yellow: 12V+

Green: Sense

Blue: PWM

 

The Green wire is what makes the alarm go off, the blue wire is useless to you, so its the black and yellow that we're looking at.

 

There are two ways to do this, but let me start off by saying according to the specs you posted, the starting voltage is 7V, so you will want to do some tests starting up the server to make sure the fan starts reliably as you'll be right at the threshold(personally its been years since I've seen a fan that doesn't start reliably at 5V, but you never know).

 

Method #1, the resistor method:

 

Since your going from 12V to 7V, you have a target drop of 5V. The fans working current is .17A. Without going into the math involved, your target current is .099A, which is a resistance of 50.42 Ohms, which needs to safely dissipate .496W. This tells us we need at the very minimum 50 ohm 1/2W resistor. Being so close to the wattage, I'd feel safer going with a 1W resistor. Radioshack doesn't sell 1W 50 Ohm resistors but they do sell 1/2W 100 Ohm resistors. You can by a pack of these(5 come in a pack for $1.19), and wire two in parallel inline with the yellow wire to get your target voltage.

 

In case you don't understand what I mean:

                                                  ___1/2W 100 Ohm____

________________________ |                                |_____________

                                                |___1/2W 100 Ohm____|

 

Wiring them in parallel doubles the wattage, but halfs the resistance, giving you 1W 50 Ohm, which equates to just over 7V.

 

I really hope that image looks right on your screen, it looks right here atleast!

 

Method #2, Wire swap method:

 

Another way to get 7V is the way most popular with standard molex fans, by attaching the ground from your fan(black wire) to the 5V line on the molex. This gives you 7V. The red wire on the standard molex is 5V, and the yellow is 12V. You could simply snip the black wire from your fan and connect it to the red wire on the molex, and you have 7V.

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Netbug Contributor

Netbug

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Thanks, Influencer.

 

A couple of questions:

 

With method one, the resistors that you mention, I understand the principle, but it's getting a bit beyond me. Do you purchase them ready to be connected in-line to the existing connectors or is there some wire "splicing" involved? I'm looking at http://www.sayal.com (my local electronics store) but I'm not sure what I should be looking for here.

 

With method two, I would snip the black wire at the fan end, and then reconnect it to the red wire on the molex. So basically, the black wire (visually) is a loop; it's exiting and entering at the molex. How does one connect it to the molex after cutting it?

 

Thank you again. Sorry about the very uneducated questions.

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Influencer Rising Star

Influencer

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With method 1 they are bare resistors, you would have to splice them in line the yellow wire. This is best done with by soldering but can be accomplished by crimp connectors. Either way be sure to wrap with either electrical tape or heatshrink.

 

Method 2 you would snip the black wire about an 2 inches from the fan connector to leave room to put it back if you ever decide to do so. Strip the end about 1 inch, strip away about one inch on the red Molex wire, stick the stripped part of the black wire through the middle of the red wire, wrap it around and tape. I'll see if I can locate a website explaining the best way to do this

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Influencer Rising Star

Influencer

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It will split like that, the wire is made of many small wires.

 

And not to sound like a smart ass, but you sound completely new to anything electrical like this, before you do anything unplug the power supply from the wall and then press and hold the power button on the pc for a few seconds, release, and press it again. Do this a few times to ensure all power has been drained from the power supply.

 

Also, since you are new to it, you might want to post a picture of the completed work to make sure it all looks good before firing it up.

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beckp Apprentice

beckp

Posted
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Netbug,

 

DO NOT ATTEMPT method two! It may be easier to just purchase this...

http://www.amazon.com/Gino-Noise-Reduction-Cable-Cooling/dp/B007PPHKO2/ref=pd_cp_e_0

 

Influencer,

 

Method two is not an option. There is no 5 Volt  (red wire) to swap (See reply with picture).

It is connected to a three-pin male.

The three male pins are +12V, GND and Tachometer. The four wires/contacts on the fan end are +12V(Vin), GND, Tachometer and PWM

Netbug can't directly power the fan from the power supply 4 pin connectors (Red, Black, Black, Yellow)

must be attached or alarms go off

The rack must use the tachometer lead to detect a stalled fan. Changing the ground refernce may fry some circuitry on the rack backplane.

 

PB

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Netbug Contributor

Netbug

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It will split like that, the wire is made of many small wires.

 

And not to sound like a smart ass, but you sound completely new to anything electrical like this, before you do anything unplug the power supply from the wall and then press and hold the power button on the pc for a few seconds, release, and press it again. Do this a few times to ensure all power has been drained from the power supply.

 

Also, since you are new to it, you might want to post a picture of the completed work to make sure it all looks good before firing it up.

 

Yeah, I'm pretty new to electrical stuff. The post below yours has me not doing this, so I think I'll abandon this way. :(

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Netbug Contributor

Netbug

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Netbug,

 

DO NOT ATTEMPT method two! It may be easier to just purchase this...

http://www.amazon.com/Gino-Noise-Reduction-Cable-Cooling/dp/B007PPHKO2/ref=pd_cp_e_0

 

Influencer,

 

Method two is not an option. There is no 5 Volt  (red wire) to swap (See reply with picture).

It is connected to a three-pin male.

The three male pins are +12V, GND and Tachometer. The four wires/contacts on the fan end are +12V(Vin), GND, Tachometer and PWM

Netbug can't directly power the fan from the power supply 4 pin connectors (Red, Black, Black, Yellow)

must be attached or alarms go off

The rack must use the tachometer lead to detect a stalled fan. Changing the ground refernce may fry some circuitry on the rack backplane.

 

PB

 

Doh. :(

 

Method one is way over my head with the resistors. And unfortunately the Amazon.com product is not really an option as I'm in Canada and it would end up being like $30 after shipping and duty (I've been bitten in the past).

 

I can't find anything comparable on Amazon.ca

 

Well this is very frustrating.  :-[

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Influencer Rising Star

Influencer

Posted
Posted

Changing the ground reference can add some load to the 5V line, but I was thinking it was connected via the motherboard, not the backplane.

 

Netbug, I agree with Beckp. Changing the ground is generally safe when connected to the motherboard as the load from the rest of the motherboard plus other components soak up the added load from changing the ground to the 5V line. But with it being connected via the backplane, as beckp said, it may do damage.

 

Method 1 is pretty straight forward. Two resistors, connected together(so each end connects with each other). Cut the 12V line, and connect each end of the 12V line to each end of the resistors.

 

If you don't feel comfortable, do you have a friend or co-worker who may have more experience?

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Netbug Contributor

Netbug

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Method 1 is pretty straight forward. Two resistors, connected together(so each end connects with each other). Cut the 12V line, and connect each end of the 12V line to each end of the resistors.

 

If you don't feel comfortable, do you have a friend or co-worker who may have more experience?

 

I'm not uncomfortable with doing the actual mod, it's just buying the correct items that always confuses me.

 

I'm going to head up to the electronics store this afternoon. The place is http://sayal.com. What exactly am I looking to get?

 

1x 1 watt 50 Ohm resistor

or

2x 1/2 watt 100 Ohm Resistor

 

Not seeing anything like that in the search results. :/

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Netbug Contributor

Netbug

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2 x 1/2 watt 100 Ohm resistor: SAYAL STK#: RAC-100R-6

 

1x 1 Watt 50 Ohm resistor: SAYAL STK#: RAD-51R-4

 

You can get either, it would be marginally easier to use the 1Watt 50 ohm resistor, but if you can't get that, then 2x 1/2 watt 100 ohm resistors wired in parallel will work.

 

Got em! Attempting the mod now. Gonna try it on the fan that came with the SuperMicro first, then do it on the newer fan if it works.

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Netbug Contributor

Netbug

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Success!

 

I modified the original fan as shown above and it's running about 33-50% quieter. It's not at the level I'd really like, but it's FAR better than it was before. I may purchase a lower RPM 12V fan (maybe 1000-1200) and attempt the mod again.

 

Thank you so much for all of your help, guys.

 

;D

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S80_UK Collaborator

S80_UK

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The reason it may not go as slow as you hoped is possibly due to the fact that it's a PWM fan - the fourth (blue) wire controls the speed from the motherboard.  While you can reduce the voltage and current as you did with the resistor, the motherboard may adjust the PWM control to try to compensate.  Series resistors work much better with the older 3-pin fan types many of which are intended to be voltage controlled.

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