Fan mod - 9v (what resistor to use)

[aoch88]

I know about the 5v and 7v mod but it's a bit too low for the fan to work in an optimum level. I understand that we can get it running at 9v but probably need to place a resistor in the "red wire" from the PSU to fan. If so, what is the resistance (ohm) I should put?

I don't need a fanbus or controller but having it running at 9V-10V is simply fine. Anyone can help? Also, If I mod and plug towards the motherboard, will the fan run at a lower voltage?

[2uantuM]

depends... how much current does the fan draw?

[cirthix]

you could use the +3.3v for ground and +12v for +12v, giving you 8.7v for the fan.

[bassie]

U/I=R

U=Volt
I=Ampere
R=resistance in ohm.

[aoch88]

Ok, I found some information and I can solder resistor onto it. My question is, do I solder the resistor on the red wire or the black wire?

[yngndrw]

Either would work, but technically you should put it on the Red. Putting it on the Black may effect the RPM Sensing.

[aoch88]

Thanks, I had a 5 ohm resistor which reduces the voltage to around 10v BUT it's still noisy. Hmm, maybe I need to get it to 8v?!

[Prodigys]

Hey guys, i need this information to.
I want to run every fan what i have on 7V.

But i have many fans that are different in W (Watts) and A (Amperes)

I dont know anything about electronic things, i only can solder some but thats all. So can someone give me the resistor valeu's that i need for the following to get them to 7V.

If you can say what resistors i need then you would help me a lot !

Here is the excel sheet for all details etc... : http://www.megaupload.com/?d=IRQJGF2C

Thanks for the help !

[aoch88]

My opinion is that 7v is a bit too low wouldn't it? I'd prefer to have them running at least 8.5v to 9v but the heat output from the resistor is relatively high

Plus, I can't seem to get a variable resistor or rheostat which is 0-50ohm

[Prodigys]

Yes, i have tought about it and i would like 8V. Still enough CFM and low noise.

I found this site for calculting the resistor, but everybody is telling me that i need to deal with the heat that the resistor is going to produce or else it is going to blow up .

And like you say, a variable resistor would be great. In mine case one from 0-100 Ohm...

[aoch88]

I did the mod with a resistor which is capable to handle the heat and when I touch it with my finger, it really feels hot.

[Prodigys]

I did the mod with a resistor which is capable to handle the heat and when I touch it with my finger, it really feels hot.

Well i went to the store today and got :

2 x 27 Ohm Resistor
2 x 33 Ohm Resistor
2 x 39 Ohm Resistor
2 x 47 Ohm Resistor
2 x 56 Ohm Resistor

And 5 little swithes like in planes used, this with 2 circuits. This that i can swith to a normal + wire to the fan, or the wire with the resistor.

So i can swith the fans to 8V for normal use, and 12V for a overclock/bench session .

[aoch88]

Yup, that should do the job but make sure you get those big ones so that they can handle the heat.

[Prodigys]

Yup, that should do the job but make sure you get those big ones so that they can handle the heat.

I have really little ones, the biggest (56 Ohm) is like 8mm long and 2-3mm diameter. The 27 Ohm is 5mm long and 1-1.5 mm diameter...

My dad says it gotta work, and the shop worker to, but they need ventilation he said, but i will see, if it doesnt work, then i try agina .

Do i need to make a drawing of my circuit for you ? Or can you do it yourself now ?

[aoch88]

I'm ok because I just solder a resistor onto the red wire (I didn't perform the switch method). Having a resistor that doesn't withstand the heat might just blow off? I'm not sure but was afraid of that happening.

[neo2005th]

With L7809CV regulator, it can convert 12v to 9v.

[Prodigys]

I gonna make it like this :



The swithes that i have are more smaller and are chrome finished .
Going to make them in a panel of my pc case.

[aoch88]

What's a L7809CV regulator? Any pics?

[Polizei]

Before I say anything, getting a fan controller will be infinitely easier. And...

Yellow = 12v
Red = 5v
Orange = 3.3v
Black = 0v (ground)

First off, you want the highest wattage resistors you can find, so they can easily cope with the heat output. 10w should be plenty. Chances are, the resistors you bought are rated for 1/4 watt. Resistance will be calculated in a second.

A 10 watt resistor looks something like this.
What you bought probably looks something like this.

Divide 3, which is the voltage drop from 12v to 9v, by the current drawn by the fan (amps), and that will give you the resistance of the resistor you need to solder in series with the fan to get it to run at 9v.

EDIT: To calculate the watt requirement of the resistor, multiply 3 by however many amps the fan draws. Power output (watts) is equal to the voltage across something (the resistor) multiplied by the current through it, P=VI. Now that I think about it, not many fans draw more than 1A, and since the voltage across the resistor is only 3v, you cant need more than a 5W resistor unless you want to run more than 1 fan per switch. Then you will need a higher wattage rated resistor. According to your diagram, you shouldnt need more than 5w.

[Prodigys]

I solderd a resistor today on a + wire of a 80mm fan.

It spinned @ 8.1V and the resistor didnt went anything of warm ...
So i dont know, but for me it's oke .

Resistor used was 56 Ohm (0.35watt) while it had to endure 0.36 watts...

[aoch88]

I have a multimeter but how do I measure the voltage? I have to turn the multimeter to "volt reading" and put the +/- to red/black wires in the molex connector?

Do I do this when the PC is on or off?

[Prodigys]

I have a multimeter but how do I measure the voltage? I have to turn the multimeter to "volt reading" and put the +/- to red/black wires in the molex connector?

Do I do this when the PC is on or off?

You need to put the mulitmeter on volt reading, then you take your 2 sticks of your meter with + on red wire of fan, and - on black fanwire.
But you need to look that you measure BEHIND the resistor. So the wire between the fan and the resistor is good. Otherwise you just measure 12V, and that's not what you want .

[aoch88]

You need to put the mulitmeter on volt reading, then you take your 2 sticks of your meter with + on red wire of fan, and - on black fanwire.
But you need to look that you measure BEHIND the resistor. So the wire between the fan and the resistor is good. Otherwise you just measure 12V, and that's not what you want .

Thanks but do I measure when the PC is running or I have to turn off the power? Btw, if I have a 12V fan with 0.5A, how many ohm do I need to reduce the voltage to 8V?

I'm poor when it comes to maths and even worse when it's physics.

[Prodigys]

Thanks but do I measure when the PC is running or I have to turn off the power? Btw, if I have a 12V fan with 0.5A, how many ohm do I need to reduce the voltage to 8V?

I'm poor when it comes to maths and even worse when it's physics.

Wait, need to think hard now .

12V 0.5A => 8V needs a 12 Ohm resistor that can handle 1.33 watt .

[aoch88]

Thanks dude. How does the math goes? Any site to do the calculation, etc?