Electric fan... automotive

Discussion in 'The Projects Forum' started by CA180, Dec 30, 2006.

  1. CA180

    Thread Starter New Member

    Dec 30, 2006
    3
    0
    Hello all... new here. Stumbled into the site while searching on google.

    Here's my issue. I have an old chevy pickup, and i decided to get rid of the mechanical fan and install an electric. I have a relay wired up to provide power to the fan, and a temperature sensor in the intake manifold. The temp sensor was supposed to gound the coil side of the relay and tuen it on. Well, the temp sensor doent complete the circuit untill way past the temperature that the engine should be.

    It is a negative temperature coefficient sensor. As the engine warms up, the resistance drops.

    I tried supplying 12volts to one side of the sensor and measuring the voltage out of the other side. At 185 degrees (when i want the fan to come on) i was getting 6 volts.
    Is there a way that i could set up the relay to come on at 6 volts and go off below that? This needs to be fairly accurate, to pretect the motor.

    If you guys could help, i would greatly appreciate it. And if you know of a better way to do what i'm trying to do, let me know.

    Thanks in advance.
     
  2. Distort10n

    Active Member

    Dec 25, 2006
    429
    1
    What is the part # of the relay and the temperature sensor?
     
  3. CA180

    Thread Starter New Member

    Dec 30, 2006
    3
    0
    eh..... dont know either.

    The relay is just one i had laying around here at the shop. The temp sensor is out of a dodge. It fits in the instake manifold just like most automotive temp sensors.

    Sorry, thats no help
     
  4. beenthere

    Retired Moderator

    Apr 20, 2004
    15,815
    282
    Hi,

    The temp sensor in the intake manifold is signifcant for controlling the air/fuel ratio. It's the coolant temp in the engine water jacket that you need to monitor.
     
  5. mrmeval

    Distinguished Member

    Jun 30, 2006
    833
    2
    You really want to install a sensor in the water jacket. There are kits available to do this. This has some explainations.

    http://www.diynetwork.com/diy/ab_auto_cooling_system/article/0,2021,DIY_13676_2271300,00.html

    Vendor link added http://www.flex-a-lite.com/auto/html/electric-fans.html

    The circuit you're looking for is a mechanically controlled temperature switch that is threaded into the proper area of the engine water jacket. When under the rated temperature the switch is open, when over the rated temperature the switch is closed turning on the fan. The fan and switch are in a series circuit. +12 goes to the switch, the switch goes to the proper terminal on the fan and the other terminal on the fan goes to ground. You may have to drill and tap a place for this sensor to go.

    The kit may have a means of running both the switch and the dash board temp sensor from the same opening.
     
  6. CA180

    Thread Starter New Member

    Dec 30, 2006
    3
    0
    ok.... i dont think we are on the same page.

    This truck is an 81, it is carbuerated... The sensor has nothing to do with anything on the vehicle. I installed it to control the fan. It is installed in intake manifold beside the thermostat housing. It is in the cooling system reading the temperature of the water.

    It is a two wire negative temperateure coefficient sensor. I'm asking how to trip the relay on at the set voltage.
     
  7. Distort10n

    Active Member

    Dec 25, 2006
    429
    1
    Sounds like the sensor is not allowing enough current through the coil to create a strong enough magnetic field to allow the arm to make contact.
    What you have works fine but you need a relay that is more 'sensitive' to less current or a different sensor. I am not familiar enough with relays to know what their specifications are.
    I would use a digital temp sensor and a microcontroller, but that sounds like overkill for what you want to do.
     
  8. beenthere

    Retired Moderator

    Apr 20, 2004
    15,815
    282
    Hi,

    The sensor you describe sounds like one for a temperature gauge. What is more likely to do the trick is more like a Clixon control that closes current-carrying contacts when an operating temperature has been reached. A radiator fan is going to pull a fair amount of current, probably on the order of 10 -15 amps. Even a T90 relay is going to need more ciol current that a tdr can carry.
     
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