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Electronics Guys? Help for my fan control design?

Discussion in 'Modding' started by El_JimBob, 5 Jan 2004.

  1. El_JimBob

    El_JimBob What's a Dremel?

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    Ive finished planning out my design for a fan controller. I apologise in advance for the ghetto image :)
    [​IMG]
    [​IMG]

    The circuit is basically 6 Zalman Fan-mates in parallel.
    The Voltage Regulators are 7805s, with a ref. voltage of 5v.
    The resistors are rated @ 680 ohm
    The variable resistors (pots) are rated at B1K.
    The yellow line is voltage in, orange/voltage out.

    Can anyone suggest any precautions i should take with the circuit? Any components i could add to make it more reliable?
    The voltage regs. are rated at 0.5-2A. Is there any advantage in using a higher rated one depending on the fans i use?

    Lastly, ima wire in LEDs that will grow in brightness related to the voltage. What i would ideally like to do tho is wire a dual colour LED, say blue/red, that would glow blue at the highest voltage output, then change to red when the voltage moved down to, say, 7v. Anyone able to suggest how i might be able to do this?

    Look forward to any suggestions u guys might have. Pics and credits will be posted when im finished :)

    Take care :thumb:
    JimBob

    and maybe one day ill learn to draw circuits properly, sorry :blush:
     
    Last edited: 5 Jan 2004
  2. nleahcim

    nleahcim What's a Dremel?

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    I think you're confusing the 7805 with something else. The 7805 is a 1A 5V regulator. Were you perhaps thinking of a LM317?
     
  3. El_JimBob

    El_JimBob What's a Dremel?

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    nah, the 7805 is the v reg used in the zalman fan-mate - i removed the component and checked it with my boss whos an electronics engineer.

    It has a min (reference) voltage of 5v and the circuit itself can put out a max of around 11v which is fine for me.

    I wired one up on a piece of stripboard and it worked ok - its only that im putting 6 in parallel now and im just wondering if i need to make any modifications to the circuit :)
     
  4. nleahcim

    nleahcim What's a Dremel?

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    I'm sorry - believe me or not - but a 7805 will put out a maximum of about 5 volts at 1 amp. From what I can see from your drawing - it looks like you are attaching the positive lead of the fan to the output of the 7805 and the negative lead to a pot which is grounded. You'll get a maximum of 5V from that circuit - which is pretty slow for a fan.

    If you don't believe me - check out Fairchild's 78xx page: http://www.fairchildsemi.com/pf/LM/LM7805.html

    Wait - what exactly is "vr b1k" I was assuming it was a pot - but maybe it's something else? and what's the component below it?
     
  5. El_JimBob

    El_JimBob What's a Dremel?

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    VR is indeed a pot - a 1k linear
    the component underneath is a 680 ohm resistor.

    the component is a 7805 (its stamped on the chip) but im guessing but im guessing maybe it has a variable output like the LM317s

    any guesses anybody?
    does anybody know 100% what type of 7805 is in the fan-mate - its also in their fan controller model as far as i know.
    im just too tight to spend £30 on it.

    bsides, home made is best, right?
     
  6. El_JimBob

    El_JimBob What's a Dremel?

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    ok ima break my fan mate apart again and do some more tests on it.
    any more suggestions will be much appreciated
    thanx so far :)

    *edit*

    ok heres exactly whats on the chip -

    mc
    7805
    CT
    NLGA 047

    the fan mate gives out between 5 and 11 volts, so its gotta be a variable voltage regulator, right?
    agh, if i didnt waste so much time working in music shops i might have some decent knowledge :)
     
    Last edited: 5 Jan 2004
  7. El_JimBob

    El_JimBob What's a Dremel?

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    ok.......
    its been done at Toms Hardware Guide, but they conveniently forgot to post a guide :(

    [​IMG]

    also found a quote at a place called StorageForum:
    'I didn't buy a second fanmate, I made it myself with a 1k trimmer and a 7805 regulator...'

    so people are doing it - can anyone explain how :(
     
  8. Hazer

    Hazer In time,you too will be relixalated

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    To clarify: It is a 7805 and it is a 5V regulator. But look at the wiring. The 'ground' pin is connected to the pot to vary the ground reference. The output will be 5V higher than the ground. Get it?

    Example: When the pot is turned all the way down to ground, you get 5V out. As you turn the pot up, there will be [(5V)/(680 Ohms)] = 7.3mAmps going through the resistor. This current has to go through the pot, so the current going through the resistance of the pot raises the voltage on the 7805 'ground' pin higher than actual ground, thus the output is this voltage plus 5V for the regulator.

    Oh, PS: As for the wiring, having it wired in parallel is what you want. You should have no problems, just make sure that the wire going to your circuit board is as thick as the molex/ATX wires.

    PPS: They dont make fans much higher than 1.5Amps. If you find one, its gonna sound like a jet engine in your case. Most fans are 140mA to 330mA. The regulators should work fine as long as they are rated for a minimum of 1A.
     
  9. cpemma

    cpemma Ecky thump

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    The 7805 works exactly as Hazer says, I've a similar version shown here with fixed resistors, El_JimBob has made R2 a variable.

    [​IMG]

    Same snags as a 317T, the max output from 12v in will be around 10.5v, so there are better ways.

    Zalman have built it as cheaply as possible, the 7805 datasheet recommends some capacitors as shown for stability, but if it works without... :cooldude:

    A fan isn't as fussy a load as say some logic circuitry or a pre-amp.
     
  10. El_JimBob

    El_JimBob What's a Dremel?

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    Thanx for the help guys:)
    Gave the diagram to my dad to look at - he added a cap at V out, just like cpemma mentioned:
    [​IMG]
    so the circuit is ok (thanx guys)

    now all i wanna do is wire up 2 LEDs to each channel so that one is on at the highest voltage, dims when the voltage goes down, then changes to another colour LED when the voltage reaches 7v or so - could this be done simply, maybe with dual-colour LEDs?
    thanx for the help so far :)
     
  11. cpemma

    cpemma Ecky thump

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    Dimming leds just by going from around 11v down to say 5v is hard, I got decent results with a string of diodes as shown here. Be worth trying with a series zener diode (cathode to positive) around 5.1v instead of all the rectifier diodes to mop up the spare volts, and a resistor to give about 10mA at 12v, so

    Resistor = (12 - Zener voltage - LED forward voltage)/.01 ohms.

    Changing the colour needs a few more parts... [​IMG]
     
  12. El_JimBob

    El_JimBob What's a Dremel?

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    thanx for the help
    yeh, i kinda anticipated that dimming/changing LED colours would involve lots more parts, so i might just skip that idea.
    The whole point of this project is to make a dead simple circuit that is reliable (hence my use of the fanmate design)
    Ive spent the last two weeks devising an active 3 band eq with parametric mid for my bass guitar and ended up with something so complicated that im now sick of the sight of my soldering iron :)
    So the pc mods have to be as simple as poss, naturally :)
    i might just use a simple LED+resistor as i have the parts lying around - and see how i get on with that.
    Ill report back in a few days or so when Maplin delivers the parts and i have the basic circuit made....
    Thanks for the help so far guys - its all been really useful.
    take care now....

    *update - 7 Jan*
    Jeez when did LEDs become so expensive!!!!!!!!!!
    No decent affordable blue LEDs at all. Oh well, the 12v ones are cheap (£0.29) and dim nicely so ima go for a few of those for my FC - how comes they dont make these in blue (god only knows)??
    So its gonna be a mix of red and yellows just to keep things lookin nice, i guess. Ordering all parts today, including a sheet of alu to make a nice front grille for my pc :)
     
    Last edited: 7 Jan 2004
  13. quitchat

    quitchat What's a Dremel?

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    anybody uses the LM317?
    who can tell me the difference between LM317 and 7805?
    thanx
     
  14. El_JimBob

    El_JimBob What's a Dremel?

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    im prolly not the best qualified to answer this, but the LM317 can regulate voltage between around 2 to 30 odd volts, and the 7805, the one im using, has a fixed output of 5 volts.
    Thats all muggins knows.......now, over to the experts..........
    :)

    *heh, thats quite profound for a natalie imbruglia lyric :)*
     
  15. El_JimBob

    El_JimBob What's a Dremel?

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    .........and im still waiting to build the bloody thing :(

    ordered the parts from Maplin over 2 weeks ago - nothing for a week - rang them - they said they couldnt understand why the order had been ignored and would post it immediately - another week goes by and still nothing - rang them again - they say it was posted so it must have gone missing in the post - this sounds to me like a heck of a lot of bull****.
    Anyone know a good alternative to Maplin ????

    anyhoos, here is my current roll call of reliable suppliers:
    The Cooling Shop (for fans, blowhole trim, and bl00 zalman chipset sink)
    Quasar Electronics (for the dc sockets that Maplin wont be gettin in for another 5 weeks!!!!)
    UltraLeds (for the best customer service i have EVER had, and dirt cheap LEDs to boot - i even got a lil LED torch cause they impressed me so much)
    Crucial (my own little luxury - a damn fine stick of ram, at a damn fine price)

    so, bsides the ram and chipset sink, im sitting here with all these bits and cant do a damn thing till Maplin re-delivers :wallbash:

    ill update again soon.
     
  16. Pygo

    Pygo Rick Relixed

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    hmmm... update soon eh??? lol
    just buggin ya ;)

    Anyways, I have built this circuit on some breadboard, and the output will top out at 10V at about 1/3 turn... Or well, in turns of ohms, it is at 330ohms, outputing 10V. 1k is still 10v. then turing down to 0k, it is 5v. It varies between 10v and 5v for 330ohm down to 0ohms.

    Could anyone pls explain why? I was really hoping to have an elscheapo fan controller that I could use until I have completed my lcd w/pic controlled fan controller...
     
  17. Hazer

    Hazer In time,you too will be relixalated

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    The 7805 is just a 5V regulator. The LM317 is an adjustable voltage regulator. In order to stay within specs, most common voltage regulators need some supply voltage 'over-head' in order to guarantee a nice output voltage that is desired. 5V regulators would like to see a minimum of 6.5-7V supply voltage.

    The exact reason is a bit vague to me ATM. It mostly has to do with transistor junction requirements.

    For a higher adjustable voltage, I preffer the Emitter-follower circuit. This still has a 0.7-0.5V drop (11.3-11.5 top voltage from 12V), but its still a simple circuit with cheap parts.

    Of course, there is always the low-dropout version of the LM317.
     
  18. Pygo

    Pygo Rick Relixed

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    Well. I found a resolution to my problem... on cpemma's site here:http://www.cpemma.co.uk/diodes.html

    I looked at the formula and punched in a few different values for R1, and wasn't too amused... but decided to play around with some values physically. I found that a 470k resistor was perfect for it. I get about 9.95V out of the circuit at max, and about 5.04VV minimun. And to acheive 12V, I just use a swicth...
    Now I happy... :clap:

    So I suppose the 680ohm resistor was the problem.
     

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