pc fan control by temperature

Discussion in 'The Projects Forum' started by pete1986, Oct 29, 2013.

  1. pete1986

    Thread Starter New Member

    Oct 12, 2013
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    hi just looking for some advice from experienced people as im new and learning. im attempting to built a very cheap but reliable fan controller that alters the speed of the fan by temperature. am i right in thinking i can replace the resister in my diagram with a 10k Variable Resistor Pot. then this would give me precis control over configuring this device. so i can basically set the min voltage at a set temperature. say 25c = 5v ....40c = 12v so i can put the ntc in a cup of water that is 25c then i can alter the voltage using the pot to get 5v at that temperature ?

    replace R2 2K2 Resister with

    Type:103
    Power:0.1W
    Resistance:10k OHM
    10K OHM Trimpot Trimmer Pot Variable Resistor 6mm

    [​IMG]
     
  2. #12

    Expert

    Nov 30, 2010
    16,355
    6,852
    The load on the regulator must always be at least .005 amps or it will go high on its output. Assuming the motor always uses at least .005 amps, the maximum pot resistance will b 4042 ohms for a 12 V output. Put a resistor in parallel with the pot to reduce its value to 4042 ohms. That would be 6.8K.

    There are other ways to do this. Fan motors generally respond better to current supply pulses known as Pulse Width Modulation. However, my personal approach is to let you try it your way rather than spend half an hour designing a circuit and trying to make you use it.
     
  3. pete1986

    Thread Starter New Member

    Oct 12, 2013
    15
    0
    i did look at different designs but wanted something super cheap and fairly easy to make up. would you be able to look and tell me if i have done this right ? after looking online some people are showing to wire the LM317 up differently so im unsure if iv picked the right way or not.

    [​IMG]
     
  4. wayneh

    Expert

    Sep 9, 2010
    12,156
    3,063
    Did you do the math on the NTC470 to ensure you'll hit those two setpoints?
    I think a cap on the output is a good idea, too, as recommended in the data sheet.

    Have you checked your fan to see if it is compatible with your voltage control scheme? Many are, but not all.

    Where's the pot on your PCB?
     
    #12 likes this.
  5. #12

    Expert

    Nov 30, 2010
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    I'm having a senior moment and can't follow that drawing right now. Thanks for the help wayneh.
     
  6. pete1986

    Thread Starter New Member

    Oct 12, 2013
    15
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    i found the schematic online from the creator. he said you get them voltages at them temps.iv tested my fan at 7v and it was ok. it worked as low as 5v. i guess it would be better to put a 100nf 16v cap on the input and add another one on the output then ? the one on the output was not on the plans i found online. so im assuming it all works as he goes on to show it working. i haven't received my parts as of yet so i cant confirm myself. one thing i was worried about was the LM317 Im not 100% sure i have it connected correctly as i have seen other plans like this design but wired up differently and ill be honest im still very new to this. i havent replaced the 2k2 resister with the pot as yet. going t have to move some things around and make sure i have it wired up correctly too

    [​IMG]
    [​IMG]
     
    Last edited: Oct 29, 2013
  7. #12

    Expert

    Nov 30, 2010
    16,355
    6,852
    Always read the data sheet for your regulators. Most of them need capacitors and most of them are different from each other.
     
  8. pete1986

    Thread Starter New Member

    Oct 12, 2013
    15
    0
    just had a good luck at the data sheet and i think iv connected it all up correctly. to replace the resister with a pot do i simply connect the pots leg1 and leg to in place of were the resister was and leave leg wiper unconnected ? am i right in thinking there is no positive or negative on the pot ? simply treat it as a resister and leave the wiper leg unconnected ?
    [​IMG]
     
  9. #12

    Expert

    Nov 30, 2010
    16,355
    6,852
    The wiper gets connected to one of the other legs. If it works backwards, you chose the wrong leg.
     
  10. pete1986

    Thread Starter New Member

    Oct 12, 2013
    15
    0
    so i connect the adjust from the LM317 to the wiper pin on the pot ? also connect one of the wires from the ntc the the wiper pin aswell and the leg1 of the pot to ground ?

    [​IMG]
     
    Last edited: Oct 30, 2013
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