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Electronics A-Level Project - Fan Monitoring System

Discussion in 'Modding' started by Chey, 10 Dec 2001.

  1. Chey

    Chey What's a Dremel?

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    Right, as many ppl might already know, I'm doing an A-Level D&T Course and for my final project, I decided to make an External Monitoring system. I decided to do that mainly because I am an overclocking "fr33k" and also cos my system temps can get pretty hot at times... (not often but hey... this project is just a piss about)

    Anyways, what my initial idea was to basically have 4 knobs which control 4 fans. As the knob got turned more, an led corresponding to that will get brighter and if the knob was turned down, the led would get dimmer (basically like the PCMODS Rheobus Kit). All the fans rpm, case temps, cpu temps etc will be displayed on an LCD.

    Right.. simple eh? Thats what I thought!. The problem comes in when the max Rheostats i can buy (or have found to buy) is only a mere 3.5W!!!! The fans I want to control are rated at 7W-11W.

    Now obviously, i can't use the 3.5W rheostat with the 11W fan cos then the rheostat will just fry... as i found out :eek:(

    So, i am needing a way to control my fan rated at 11W using a 3.5W rheostat.. I have not a clue how i am going to do this btw...

    Anyways, after some research, i found out that a certain chip know as the "LM317 Voltage Regulator" is possible to adjust my fan speed with a 3.5W rheostat even though the fan is rated at 11W right? (correct if wrong)

    I was wondering how the hell that works? I heard it gives off a lot of heat and going by the name of the thing, it regulates current i presume so its putting more stress on the LM317 chip than on the fan???? (correct if wrong)

    I was wondering if anyone could help me by just simply telling me what that mofo chip can do and if anyone has got any circuit diagrams on how i can do this project...

    The components i have are the following...

    - 4x 3.5W, 100ohm Rheostats
    - All sorts of capacitors, resistors etc (i in college so i got access to loads of components)

    So far thats it. If these LM317 is the chip i need, i will be getting 4 this week.

    I also need to know what the chip is that gets used in the PCMODS rheobus kit which determines if a fan is plugged into a particular channel... thats the chip that brightens/dimmers the led as you turn the knob....

    If anyone can help, it will be much appreciated. The fan controlling section is going to be 1 circuit, the LCD part and displays is gonna be another...

    I have a few plans on how to get everything working (i got an A at Electronics GCSE's but its been 2 yrs and i forgot most of stuff).
    I have got several plans drawn but i just need to know how to wire up the LM317 and if they are the right chip for what i am going to do..

    if you forgot, i want to use a 3.5W, 100ohm Rheostat (from maplin) to control a 11W fan. Anyone know if its possible or have any other suggestions, please reply back.

    Sorry for such a long post...

    Chey
    chey@phearfactory.co.uk

    Phear Factory
    http://www.phearfactory.co.uk
    Computer Hardware, Modding & Reviews
     
    Last edited: 10 Dec 2001
  2. WilHarris

    WilHarris Just another nobody Moderator

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  3. Chey

    Chey What's a Dremel?

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    Erm....

    Does this thing allow me to do what i want? As in, control a 11W FAN with a 3.5W Rheostat (and LM317 Voltage Regulator chip) ?

    I'm looking of really how to wire up a LM317 to work with just a rheostat. If that is possible to do that will be great. I've seen the circuit put up here on the bit-tech site before it was put down and a new design was put up.

    Any ideas Koolvin where that article is and if you still have it?

    I was wondering what the guy did to his that allowed his to work. I could use that as a template to work on mine. I've got several ideas on how to get it to work.

    Please write back.

    ANYONE else that may know how to wire up a LM317 Voltage Regulator chip with a rheostat, could they PLEASE post a reply on here.

    That will be much appreciated.

    Chey
    chey@phearfactory.co.uk

    Phear Factory
    http://www.phearfactory.co.uk
    Computere Hardware, Modding & Reviews
     
  4. SuperScrubber

    SuperScrubber Mad Chemist.....buwahahaa

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    Have a look here m8;

    http://casemods.pointofnoreturn.org/vregtut/

    .......actually used the same circuit myself last night, worked fine with a 6.8w sunon 120mm fan ....... they allow up to 1.5A output so you should be fine for your 11w one aswell (I = power/V hence is less than 1A), just be aware that the current draw increases as you turn the voltage down so dont go sticking loads on one circuit!! Also these generate SERIOUS heat - I was thinking maybe a small HS would do but not anymore, get the biggest ones you can !! Apart from that it really is a piece of pi55.......:)
     
  5. Alaric

    Alaric code assassin

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    hehe for my A-level DT coursework i'm designing a lightweight hybrid sportscar - only get to make a model of it tho :(
     
  6. cpemma

    cpemma Ecky thump

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    With a regulator circuit, the potentiometer controlling the output voltage is only carrying a few milliamps, not the fan current, so forget your 3.5W rheostat. A 1/4W or less is ample.

    LM317T will handle 1.5A, L200C 2A, both much more with a pass power transistor tacked on.

    Mind you, if you want a real meat-eating rheostat, check out the RS range of Vishay-Sferenice models. :D

    Not quite, the current gets less but the regulator wastes a higher fraction of the supply as heat. So with 12W (1A at 12v) of fans, at a 6v output setting the fan current is halved to 0.5A, so fan and regulator each handle 3W.

    So with a little 25deg/W heat sink, it will get rather hot. ;)
     
    Last edited: 14 Dec 2001
  7. Holst

    Holst What's a Dremel?

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    I had a similar problem a few monthe aggo.

    I have two 120mm fans in the top of my case and wanted to slow then both down together.

    I bought a 3.5watt 30ohm speaker volume controll rheostat but i quickly realised it would blow up if used for any length of time.

    So i used the rheostat to find the resistance at which the fans stopped. IT was 25ohms.

    I then found the point ot which i though the niose was unbearable, this was 10ohms or less.

    Then i stuck a 10ohm 5watt resistor and a 3.5watt 15ohm potentiomiter in seriese and the 10ohm resistor takes just enouh wattage from the rheostat to keep it running cool, even with 12watts or fans on it.

    I know its not pretty, but it works :)
     
  8. cpemma

    cpemma Ecky thump

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    Holst, the other reason for your success is that the 15R pot is made with thicker wire than the 30R. The 15R is designed to take 480-600mA, the 30R only 340-425mA.

    So you're still overclocking a tad, but if it works... :cool:

    Hang on, just dun sum sums...so you've got 12W of fans (=12R) in series with 10R and the noise is just bearable? The fans are only getting 6.5v with the rheostat on full blast.

    You need quieter fans or less sensitive ears. ;)
     
    Last edited: 14 Dec 2001
  9. djivesp

    djivesp What's a Dremel?

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    Chey man,

    Have you thought about using a small potential divider circuit? :idea:

    For example a quarter-bridge wheatstone circuit,

    Its usually used for amplifying resistances with a strain gauge, but if you replace that with a variable resistor or rheostat or whatever, you can control the PD (voltage) for your fan (s)

    The equation is

    Vout = Vin x (Resistor 1 / (resistor 1 + resistor 2))

    Im not sure if this would help, but instead of using a single or multiple rheostats in series, you would have in this case four resistors in total, if you were to draw it, you would have 2 columns of 2 resistors in series for each column, and your output would be connected from the middle of one column to the middle of the other (and 1 resistor would be the rheostat or could even be a very small value variable resistor)

    goto http://www.vishay.com/brands/measurements_group/guide/tt/tt612/612a.htm
    for an explanation of my splurge. im at the moment doing A level Systems&Control with Physics aswell and this is the first time its become useful so far :D :D. Thats a damn good idea for my final project ;) mite just borrow some intellectual property if you dont mind :)
     
    Last edited: 17 May 2004
  10. RTT

    RTT #parp

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    Sorry to piss on your chips djivesp but this thread is over two years old :D

    Welcome to bit-tech though :)

    (and moving this to the electronics forum)
     
  11. djivesp

    djivesp What's a Dremel?

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    :hehe: and i thought i was being clever :wallbash:
     
  12. cpemma

    cpemma Ecky thump

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    Holy thread move, RTT! :jawdrop:

    This thread is probly older than the Electronics forum. :eyebrow:
     
  13. Hazer

    Hazer In time,you too will be relixalated

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    And to think I was gonna suggest using a PIC would make this project easier.......
     
  14. Anator

    Anator What's a Dremel?

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    Murdoc did something quite similar to this for his AS Electronics project.

    Might be worth asking him exactly how he did his :p
     

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