Automotive 12v-14v fan controller

Discussion in 'The Projects Forum' started by siris, Nov 3, 2013.

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  1. siris

    Thread Starter New Member

    Nov 2, 2013
    I'm interested in building a fan controller from a gm Coolant temperature sensor (thermosistor) and a npn transistor for my car, I know there are fan controllers out there, however I would like to make this a learning experience, and see if I can produce one cheaper than buying one.
    My research so far has led me to this:Java Applet Circuit simulator

    The potentiometer is to fine tune the fan on temp.
    The dtsp switch at the bottom is to represent the the sensor. It should reach around 350ohm at 190 degrees, and it should be around 175 degrees at 500ohm.
    The Lamp on the far right is to represent the fan motor it will be a fused 25 amp circuit.

    Now that circuit has 2 major problems that I can see.

    One being that the temp sensor loses impedance as it warms. That means with that circuit I have cobbled together I would have to run a spdt relay and wire the fan to the N.O. terminal, which I would like to avoid for the sake of keeping the coil on the relay from over heating.

    The second problem is this circuit has no hysteresis, and I cannot make the fan cut run until it reaches a certain temperature. This is not as big a deal to me, I don't particularly need it to have a certain run time. Just so long as it does not run over the temp I have designated. I would guess a capacitor could maintain a minimum run time?

    I have a very limited knowledge of circuits and components and any help would be appreciated. I plan to build it with breadboard and a plastic enclosure once I get it sorted out.
  2. MikeML

    AAC Fanatic!

    Oct 2, 2009
    Can't see your circuit....
    siris likes this.
  3. lightingman

    Senior Member

    Apr 19, 2007
    This thread may be closed soon, as they do not permit automotive projects to be discussed here.
    siris likes this.
  4. siris

    Thread Starter New Member

    Nov 2, 2013
    Well that sucks about the automotive part.
    Also it will not load the circuit when you click the link?
    Here is a screencap:
    Drop Box Screen Cap
    Also I apologize for posting an automotive project. But in its essence it is no different from designing an in-expensive geo-thermal heating setup.
    Last edited: Nov 3, 2013
  5. Dodgydave

    Distinguished Member

    Jun 22, 2012
    Use an op amp to set the desired temp..with hysteresis
  6. Wendy


    Mar 24, 2008
    The owners of All About Circuits has elected not to host discussions of automotive electrical system modifications/enhancements due to safety concerns, the potential of legal ramifications and the possible circumvention of vehicle regulations at the state and federal level.

    This thread is against the AAC forum rules, Chapter 6, as seen here:

    This can be found in our Terms of Service (ToS)

    Automotive modifications of any kind are strictly forbidden. Therefore, this thread will be closed.

    Please try to understand the reasons behind this action, and feel free to browse and use the forums.

    You might find answers to your questions in one of these forums:

    Another good forum that shares many of the same membership is . Good luck.
  7. Georacer


    Nov 25, 2009
    Last edited by a moderator: Nov 4, 2013
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