Fan mod - 9v (what resistor to use) [Archive]

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aoch88

11-21-2007, 07:51 PM

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

11-22-2007, 03:29 PM

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

cirthix

11-22-2007, 03:39 PM

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

bassie

11-23-2007, 08:45 AM

U/I=R

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

aoch88

11-23-2007, 10:11 AM

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

11-24-2007, 05:29 AM

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

aoch88

11-25-2007, 02:57 AM

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

11-25-2007, 08:07 AM

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 ! :rolleyes:

aoch88

11-25-2007, 11:44 PM

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

11-26-2007, 03:08 AM

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 :yepp: .

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

aoch88

11-26-2007, 09:28 AM

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

11-26-2007, 10:19 AM

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 :D .

aoch88

11-26-2007, 10:35 AM

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

Prodigys

11-26-2007, 10:39 AM

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

11-26-2007, 10:52 AM

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

11-26-2007, 11:05 AM

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

http://www.emulatronia.com/reportajes/directpad/psx/images/esquema-alim.gif

Prodigys

11-26-2007, 12:19 PM

I gonna make it like this :

http://i18.tinypic.com/6u9peyu.jpg

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

aoch88

11-26-2007, 10:26 PM

What's a L7809CV regulator? Any pics?

Polizei

11-26-2007, 10:53 PM

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 (http://www.electronicplus.com/images/products/10W-.51.jpg).
What you bought probably looks something like this (http://www.solarbug.com/resistor.jpg).

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

11-27-2007, 02:51 PM

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 :D .

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

aoch88

11-27-2007, 08:42 PM

Prodigys

11-28-2007, 03:54 AM

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

11-28-2007, 07:07 AM

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

11-28-2007, 07:27 AM

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 :D .

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

aoch88

11-28-2007, 07:37 AM

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

Prodigys

11-28-2007, 02:47 PM

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

http://www.blackfiveservices.co.uk/fanspeedcalc.php

No problem ;).

aoch88

11-29-2007, 09:53 AM

Here's a dumb question. We have loud fans producing high cfm and we want to let it run at a lower voltage so it's less noisy.

At the same time, we can get fans that runs 12V but produces lesser cfm.

The thing is:
8V high cfm fan performs just as well or worse than a 12V normal cfm fan?

I mean, why are we modding our fans to run 8V when we can get silent ones from the stores :D

Boogerlad

11-29-2007, 07:44 PM

'cause they suck up different # of amps through the line.

aoch88

11-29-2007, 10:58 PM

Prodigys

11-30-2007, 07:58 AM

Sorry, maybe I should rephrase.
For instance:

120mm Panaflo which produces 104cfm, 41.5dba
120mm Vizo which produces 53cfm, 28dba

If both are running at 12V, the Panaflo would be much noisier. Now I mod it so that the Panaflo runs at 8V compared to the stock Vizo at 12V. Reducing Panaflo's voltage would also mean it'll run slower and produces less airflow.

So in conclusion, wouldn't both fans be performing about the same in the end?

Yes that is true, but when you need (overclock session or so...) the real 104CFM then your Vizo is already running on the MAX, and the Panaflo you can turn it up back to 9-10-12V or so ...

And there is a good chance that if you mod the Panaflo to 8V it produces 28dba like the Vizo but instead of 53CFM it produces 60CFM...

You know what i mean ?

aoch88

11-30-2007, 10:27 AM

Yes that is true, but when you need (overclock session or so...) the real 104CFM then your Vizo is already running on the MAX, and the Panaflo you can turn it up back to 9-10-12V or so ...

And there is a good chance that if you mod the Panaflo to 8V it produces 28dba like the Vizo but instead of 53CFM it produces 60CFM...

You know what i mean ?

Yep, there are chances it'll happen. Besides, we don't have the tools to measure cfm's :D

Prodigys

11-30-2007, 12:01 PM

Yep, there are chances it'll happen. Besides, we don't have the tools to measure cfm's :D

Jep that's correct.

And i always think like this :

Better a fan on 5V with 50CFM then a fan on 12V with 50CFM, because if you need more CFM then you can't do anything with your 12V/50CFM fan :).