Electronics Controlling LEDs in a LED fan - what resistor

Discussion in 'Modding' started by MrWillyWonka, 8 May 2005.

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  1. MrWillyWonka

    MrWillyWonka Chocolate computers galore!

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    Not sure if this has been posted before - can't find anything, but:

    Can I controll the LEDs in my case fans without lowering the speed of the fan. My original thoughts were to desolder the black and red wires and connect them to a switch and resolder then back onto the fan pcb.

    However, would I be able to connect all LEDs on one fan to one switch, and would turning the LEDs off cause too much power to go to the fans alone?

    I am not an electronics person, the last time I did any electronics was in year 9, and I've forgotten all that now. So be gentle on me! :hehe:
     
    Last edited: 13 Oct 2005
    MrWillyWonka, 8 May 2005
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  2. bwgames

    bwgames Minimodder

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    That should be fine....

    Just put a switch on one of the wires (I don't think it matters, although I would say on the +ve side (red))

    I've done that, except put *all* my fans LEDS on one switch, and it worked fine...
     
    bwgames, 8 May 2005
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  3. MrWillyWonka

    MrWillyWonka Chocolate computers galore!

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    How would I go about putting LEDs on multiple fans onto one switch?
     
    MrWillyWonka, 8 May 2005
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  4. bwgames

    bwgames Minimodder

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    Am I correct in assuming you have a seperate black/red wire for the LED and the fan? So you can disable the LEDs without affecting the fan?

    In that case...
    de-solder the black wire from the power in side and connect all the black wires from the LEDs together, so that the LEDS +ve red wire is still taking power from the fan PCB, but route all the black wires together

    like

    [​IMG]
     
    bwgames, 8 May 2005
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  5. theshadow27

    theshadow27 What's a Dremel?

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    BWGAMES's idea will work, just make sure that the resistor is on the positive and not the ground. you can do this by mesuring the resitance from the last LED's black wire to the ground wire on the 3 pin fan connector.
     
    theshadow27, 8 May 2005
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  6. Ghlargh

    Ghlargh What's a Dremel?

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    Why would that matter? as long as the resistor is in the circuit, it doesn't matter where it is.
     
    Ghlargh, 8 May 2005
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  7. SteveyG

    SteveyG Electromodder

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    Correct.
     
    SteveyG, 8 May 2005
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  8. theshadow27

    theshadow27 What's a Dremel?

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    because if the resistor is located on the PC board of the fan, and the switch taps into ground at the molex connector (as per his diagram), then there is no resistor in the circut, and the LED fry!
     
    theshadow27, 9 May 2005
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  9. Firehed

    Firehed Why not? I own a domain to match.

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    I doubt that... they would probably have the resistor be the first thing if it were on the PCB, ie not have it going to the LED band to resistor to ground.
     
    Firehed, 9 May 2005
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  10. theshadow27

    theshadow27 What's a Dremel?

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    unless youve taken apart his brand and modle of fan, i wouldent make guesses like that unless you are willing to buy him a new one :thumb:
     
    theshadow27, 9 May 2005
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  11. Ghlargh

    Ghlargh What's a Dremel?

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    The resistor could just as well be on the other pole in the fan, there is no law that the resistor has to be on the positive side...

    Wouldn't it be better to tip someone to not cut out the LED resistor (check where it is) than to tell people to do something illogical that might not even work?
     
    Ghlargh, 9 May 2005
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  12. theshadow27

    theshadow27 What's a Dremel?

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    umm incase you didnt read my post:
    so how is that illogical? that might not even work? mesuring resistance is illogical? maybe for you...
     
    theshadow27, 9 May 2005
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  13. Ghlargh

    Ghlargh What's a Dremel?

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    What i mean is, you didn't suppy the reasoning for your tip.

    If the resistor had been on the tape around the fan along with the LEDs as with a lot of these i have seen, it doesn't matter if the resistor is on the positive or negative side, you wouldn't cut it off no matter on wich side you cut.
     
    Ghlargh, 10 May 2005
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  14. MrWillyWonka

    MrWillyWonka Chocolate computers galore!

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    So which wires do I cut and do I need a resistor or not, and if so, where? The fans are at home, so this weekend I will take them apart and give you the circuit diagrams.

    If I do connect both grounds to one ground, what happens to the cut off ground on the other fan, or it doesn't matter?
     
    MrWillyWonka, 10 May 2005
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  15. MrWillyWonka

    MrWillyWonka Chocolate computers galore!

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    So here I am with my 3 fans I wanna connect to one switch, I've done it sucessfully with one fan and one switch. Now, is there a way of me measuring resitstance for the resistor, without a multimeter? Its a 12V fan if its any help!
     
    MrWillyWonka, 30 Jun 2005
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  16. MrWillyWonka

    MrWillyWonka Chocolate computers galore!

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    After being very busy, I now have time to do this, and could one answer my question above!
     
    MrWillyWonka, 30 Aug 2005
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  17. SteveyG

    SteveyG Electromodder

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    We can estimate the resistor value by knowing how many LEDs there are in the fan and what colour.
     
    SteveyG, 30 Aug 2005
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  18. MrWillyWonka

    MrWillyWonka Chocolate computers galore!

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    The LEDs are red and there are 3 in each fan. I wish to connect 3 of these (120mm) fans together.

    As for the ground, could I connect all three grounds together and route them back into the ground of one fan?

    Fan specs:

    rated voltage: 12V
    started voltage: 6V
    rated current: 0.38A
    power input: 4.56W

    Thanks for the help!
     
    MrWillyWonka, 30 Aug 2005
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  19. SteveyG

    SteveyG Electromodder

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    Assuming the red LEDs are rated 2.2V@20mA and are connected in series the resistor you need for each set of LEDs is (12-6.6)/0.02 = 270 ohms. A 0.25W resistor should be fine to use.

    The grounds can be connected together, yes.
     
    SteveyG, 30 Aug 2005
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  20. MrWillyWonka

    MrWillyWonka Chocolate computers galore!

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    So I'm guessing I need this resistor, code G270R from Maplins here?

    And is my diagram correct?

    [​IMG]

    Where the thick lines are the original wires and the thin lines are the proposed one, switch and resistor are indicated. Hope it makes sense!

    Damn, I really need to learn about electronics don't I!
     
    MrWillyWonka, 30 Aug 2005
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