# Electronics Would this be feasable?

Discussion in 'Modding' started by Yourmum366, 6 May 2009.

1. ### Yourmum366First-Time Modder

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Thoughts of this have been swilling around inside my brain for a while now, and i just wanted for someone to tell me whether or not i could actually do it, and if not, what to do to allow me to do it.

I was thinking of making a pcb with a 12V input from a 3-pin fan power connector (using one of these), then having a variable resistor (Potentiometer if you're in the US) and then going to several 3-pin outputs (these). I plan to use AC Ryan Blackfire4 fans, as it's more the lighting on them that I'm interested in, and they have a 3-pin for the LEDs and a 3-pin for fan power.

Also, would the same concept be applicable to a similar board, using 4-pin Molex connectors (for LED light strip control etc)

2. ### Yourmum366First-Time Modder

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Another thing - would i have to add any other resistors or ic's or anything other than what's listed above

(also, the outputs are to be in parallel)

3. ### sammo1999New Member

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You'll want to make a voltage divider using a fixed resistor and a variable resistor (Pot). The values of the resistors will depend on the load from the fan (but you can figure out what you need experimentally). Check out the example below:

Vout = [ R2 / (R1+R2) ] * 12

where 12 is your Vin

You should make R2 your variable resistor. I would use a proto-board to build the circuit and try different values for R1 and ranges for R2 to see how the fan load effects Vout.

For example if you use 10K for R1 and a 10K variable resistor for R2 you will be able to adjust Vout between 0 and 6 volts.

This should work fine for controlling the lights, however I think it will be more difficult to control the fan speed because the fan probably has a minimum voltage requirement before it will begin spinning, what you really need to do is control the current for the fans while keeping the voltage at the required 12v. If you want advice on how to do this let me know.

4. ### Yourmum366First-Time Modder

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I see what you're getting at, but could you show a complete schematic to avoid confusion?

And don't worry about controlling the fan speed, this is gonna go nowhere NEAR fan control!

5. ### ch424Design Warrior

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You can do it like this

R1 and R2 should be the same, and you should set them so that when the variable resistor is set to 0 ohms, the LED current is still limited to what it should be.

R1 = R2 = (12 - LED voltage drop) / (standard LED current)

Then you should make the variable resistor R3 about five times the value of R1 and R2.

Yourmum366 likes this.
6. ### Yourmum366First-Time Modder

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And I'm guessing to add more outputs, i would need to just metaphorically clone one of the other outputs and place it similarly in the circuit?

7. ### ch424Design Warrior

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Yeah Though if you add more outputs, you should probably make R3 smaller so that it's easier for you to adjust the brightness. It'll still work if you don't though!

8. ### Yourmum366First-Time Modder

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Ch424, what software did you use to make this schematic?

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