Custom Fan resistor - Help needed

[JPBruwer]

Hi,

 

I have 3 Coolermaster SickleFlow fans in my case that make WAY to much noise... I am planning on modding the molex to 3pin connector to include a resistor in the cable leading to the 3 pin connector for the fan.

Would a   1/2 watt 47-ohm  resistor placed on the red wire do the trick? Reducing it to possibly 7V / half the noise? I know these things can be ordered. It just takes so long to get here, so I thought i'll just make my own. 

 

Thanks for the help!

 

 

[W-L]

3 minutes ago, JPBruwer said:

Hi,

I have 3 Coolermaster SickleFlow fans in my case that make WAY to much noise... I am planning on modding the molex to 3pin connector to include a resistor in the cable leading to the 3 pin connector for the fan.

Would a   1/2 watt 47-ohm  resistor placed on the red wire do the trick? Reducing it to possibly 7V / half the noise? I know these things can be ordered. It just takes so long to get here, so I thought i'll just make my own. 

Thanks for the help!

Why not just voltage control the fans if they are hooked up to the motherboard instead of using resistors since they would output heat. 

[JPBruwer]

I could, But I want all 3 controlled... So would need to custom a splitter, so they can all plug into the mobo.... See the thing is, my case does not have front bays for controllers, etc.. Thats why I am asking.. Any help would be appreciated.

[W-L]

1 minute ago, JPBruwer said:

I could, But I want all 3 controlled... So would need to custom a splitter, so they can all plug into the mobo.... See the thing is, my case does not have front bays for controllers, etc.. Thats why I am asking.. Any help would be appreciated.

If you wanted them to all be controlled you can just use a regular splitter and have them hooked up to the motherboard so they would work as a group. However if you wanted them to all be individually controllable you could just get something like the NZXT Grid+ V2. 

[JPBruwer]

2 minutes ago, W-L said:

If you wanted them to all be controlled you can just use a regular splitter and have them hooked up to the motherboard so they would work as a group. However if you wanted them to all be individually controllable you could just get something like the NZXT Grid+ V2. 

Cool, I didn't know about the NZXT Grid V2, but shipping that to Africa is always such a schlep. Could I mod a single wire to split from the mobo to all 3 fans? It would be an issue voltage wise, etc...? And then should I use speedfan to control the speeds, or from the BIOS?

[W-L]

1 minute ago, JPBruwer said:

Cool, I didn't know about the NZXT Grid V2, but shipping that to Africa is always such a schlep. Could I mod a single wire to split from the mobo to all 3 fans? It would be an issue voltage wise, etc...? And then should I use speedfan to control the speeds, or from the BIOS?

If you were to just make a splitter it would be controlled as a group via a single motherboard header which would work, just note that depending on the fan you shouldn't really put more than 3-4 fans per header or it will overload it. 

[JPBruwer]

Yeah, its the Coolermaster SickleFlow X fans...

[DragonTamer1]

W-L is right, it would be easier to just connect it to the motherboard. A fan spliter is just two wires that split the output. If you have any kind of connector to tear down you could just rewire them together to share an output.

 

However here is the math:

 

At 12V your fans pull 0.35A from the power source. This results in 34.29 ohms of effective resistance (this will change with the voltage applied but it is our maximum for now).

 

12V/0.35A=34.29 ohms

 

Inserting a 47 ohm resistor would result in a voltage found by the following equation:

 

[12V/(34.29+47)]*47

 

This results in roughly 7V maximum across the fans assuming the resistor is connected to the negative lead. It will be considerably lower if it is connected to the positive lead. This is only a rough calculation and I can't get more accurate without an actual current curve chart. In reality I would put the voltage with the 47 ohm resistor somewhere between 5 and 7 volts.

 

Your resistor needs to be rated for at least 5W since your fans can pull a maximum of 4.2W, even that is too low in my opinion.

[JPBruwer]

2 minutes ago, DragonTamer1 said:

W-L is right, it would be easier to just connect it to the motherboard. A fan spliter is just two wires that split the output. If you have any kind of connector to tear down you could just rewire them together to share an output.

 

However here is the math:

 

At 12V your fans pull 0.35A from the power source. This results in 34.29 ohms of effective resistance (this will change with the voltage applied but it is our maximum for now).

 

12V/0.35A=34.29 ohms

 

Inserting a 47 ohm resistor would result in a voltage found by the following equation:

 

[12V/(34.29+47)]*47

 

This results in roughly 7V maximum across the fans assuming the resistor is connected to the negative lead. It will be considerably lower if it is connected to the positive lead. This is only a rough calculation and I can't get more accurate without an actual current curve chart. In reality I would put the voltage with the 47 ohm resistor somewhere between 5 and 7 volts.

 

Your resistor needs to be rated for at least 5W since your fans can pull a maximum of 4.2W, even that is too low in my opinion.

It makes sense... Maybe I should see if I cant just connect them to the mobo and use speedfan or the bios to control them.

[JPBruwer]

I have this mobo, GA-890FXA-UD5 (rev. 2.1) , but can't find out what the system fan header wattage / amps is. Each coolermaster fan uses 4.2 watts and 0.35 amps. Would 3 on 1 header be safe?

[JPBruwer]

Any Ideas?

[W-L]

13 hours ago, JPBruwer said:

I have this mobo, GA-890FXA-UD5 (rev. 2.1) , but can't find out what the system fan header wattage / amps is. Each coolermaster fan uses 4.2 watts and 0.35 amps. Would 3 on 1 header be safe?

I really doubt the fans are that power hungry even with really inefficient motors since the Noctua industrials at 3K at max use less power (0.3Amps) than those fans. As for the headers I wouldn't put more than 3 per header as most have a 1Amp capacity but to be safe if you are going by their rating two per fan header. 

[JPBruwer]

Great! Thanks! I did ask Gigabyte for the header "amp" output, but no reply from them yet.

[JPBruwer]

Yeah, it seems that the e-support from Gigabyte is not very good. Does anyone know where I can get that info. Its NOT in the MB manual.

[asand1]

Rather than use a resistor, just move your fan negative from a black lead to the red lead. 12v+ minus 5v+ creates 7v.

 

 

[JPBruwer]

5 minutes ago, asand1 said:

Rather than use a resistor, just move your fan negative from a black lead to the red lead. 12v+ minus 5v+ creates 7v.

 

 

Is this safe though?

[asand1]

Its safe as long as you don't plug the other end of the adapter into a HDD or something. I would cut the output molex off so it could never be used. I usedx this in one of my ghetto PCs for ever. I would be more concerned about the extra heat a resistor would make, it would literally convert the 5v into heat.

[JPBruwer]

I read it could damage your PSU...

[asand1]

Maybe, I didn't experience this though. YMMV, be warned. Maybe more will post on the subject.

[JPBruwer]

Thanks... It would be nice yes

[JPBruwer]

I could be totally safe and wire it to the 5V and the ground... Which will run my 2000RPM CoolerMaster Sickleflow x fans at around 600RPM. The CFM should be around 21 "ish".... I am setting them up in my InWin 303 as exhaust at the top, and would put fans running at 1000RPM at bot for a slightly positive air pressure.