temperature controll fan using lm35

Discussion in 'General Electronics Chat' started by pawanlamsal, Jul 12, 2017.

  1. pawanlamsal

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    Jul 10, 2017
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    Can u provide ma a circuit diagrm and explanation.
     
  2. MrChips

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    Is this homework?
     
  3. crutschow

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    Can u (you) explain what this is for?
     
  4. strantor

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  5. GopherT

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    [​IMG]
     
    Reloadron and pawanlamsal like this.
  6. pawanlamsal

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    Jul 10, 2017
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    Ok thank u
     
  7. pawanlamsal

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    Jul 10, 2017
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    Is there any idea to control speed of fan on this circuit
     
  8. GopherT

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    No.
     
  9. pawanlamsal

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    Jul 10, 2017
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    Any other circuit..
     
  10. GopherT

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    What size is your motor? Voltage/amp rating. Simple motor or gear motor?
    What power supply (batteries? What size and how many)
    Do you have an ammeter? What is the max amperage it can measure?
     
  11. GopherT

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    I'll be back in an hour or so.
     
  12. pawanlamsal

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    Jul 10, 2017
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    Motor 12v 1A simple dc motor 1000rpm
     
  13. GopherT

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    After answering above questions about your motor,
    - What temp do you want it to turn on (barely),
    - what temp do you want it to be half speed,
    - what temp do you want it full speed?
     
  14. pawanlamsal

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    Jul 10, 2017
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    Is u telling about microcontrollor?
     
  15. pawanlamsal

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    Jul 10, 2017
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    25° C turn on
    25°- 30°C half
    35°C above full speed
     
  16. Dodgydave

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    Use an Lm35 with a Window comparator, set it to 250mV low 300mV high, that will give you two outputs...
     
  17. pawanlamsal

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    Jul 10, 2017
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    window compearator ??
     
  18. GopherT

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    Hi, you need two Pots, one for the offset to raise the output voltage of the LM35 to a voltage high enough to turn on the Transistor (about 1.2 V). The quiescent current of LM35 (existing ground pin) is a fairly constant 60 microAmps. To add about 1V to the room temp output of LM35 (0.25V), you'll need to use ohms law to see why I selected the pot size that I recommended with the 60 microvolts.

    The high-gain of a darlington transistor is needed because you are trying to go from zero current to full power with only a 10 degree (100 mV) change.

    My recommendation of a 5k assumes a full stall torque (1A) range. I don't have enough information to get free running current to see your real max current for your application (fan pitch etc). In reality, you may need a 100k pot there to really get a slow-fast transistoon over the 10-degree temp change. A 5k ohm may give more of an on/off effect.

    IMG_0029.PNG
     
  19. pawanlamsal

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    Jul 10, 2017
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    Ok I will try it thanks
     
  20. GopherT

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    It will be a lot easier with an op amp between the LM35 and the transistor. Or even using Pulse Width Modulation (PWM) to control the transistor - especially if you add a micro controller.

    PWM allows much lower speed to be maintained than straight analog like my latest circuit.
     
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