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relay help

Discussion in 'General Electronics Discussion' started by charlestt, Feb 25, 2013.

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  1. charlestt

    charlestt

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    Feb 16, 2013
    i've wired my cars fog lights so that they come on when i unlock the car. It all works fine apart from one problem, it operates fine normally unlock/ lock the car and they come on and go off fine but when i start the car they stay on.

    I'm using a 4 pin 40amp relay i have a feed coming from the interior lights that feed the coil and activate the fogs so when the lights switch off the power is off and so the coil should de-activate as well.


    i'm confused.

    Charles
     
  2. (*steve*)

    (*steve*) ¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd Moderator

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    Jan 21, 2010
    Try locking the doors when you're driving.

    From what you say, the lights are on when the doors are unlocked. Or is it more complex than that?
     
  3. charlestt

    charlestt

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    Feb 16, 2013
    When i start the car the interior lights fade out but the fogs are staying on
     
  4. (*steve*)

    (*steve*) ¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd Moderator

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    That doesn't help.

    You need to tell us what the modifications were, how they are supposed to work, and exactly what you're expecting to happen (and why).
     
  5. charlestt

    charlestt

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    Feb 16, 2013
    Ok basically what i want to happen is for the front fog lights to come on when i unlock the car and then go off when the car is locked or when the engine is running.

    What i have done so far is to connect a relay to the input of the fog lights this is triggered by a feed from the interior light which comes on when you unlock the car and then goes off when you lock the car. It also switches off when the ignition is on.

    So the theory was when the interior light is off then there is no power to the coil of relay so the fog lights should switch off.
     
  6. charlestt

    charlestt

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    Feb 16, 2013
    check the link it may explain better

     
  7. (*steve*)

    (*steve*) ¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd Moderator

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    Jan 21, 2010
    Can you verify that the lead you have connected to the interior light does what you expect?

    i.e. does it do what the interior light is doing, or does it do what the fog lamps are doing?

    The question being -- have you hooked up to the right place...?
     
  8. charlestt

    charlestt

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    Feb 16, 2013
    I've got some other lights inside of the car hooked up to the feed from the interior light and they are behaving perfectly.

    My next job was to check outputs with a multi meter
     
  9. charlestt

    charlestt

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    Feb 16, 2013
    this is how i have the relay wired.

    87 to foglight
    86 to earth
    30 to power
    85 to feed from interior light

    All seems to work when using the remote on the key fob to unlock and lock the car, but once inside the car even if i switch off the interior lights the fogs stay on.

    i have checked the voltage from the interior light feed and when the lights are off there is still a small voltage around 0.5v, would this be enough to activate the relay ?
     
  10. charlestt

    charlestt

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    Feb 16, 2013
    Well after a lot of head scratching i've found the problem, the interior lights are negatively switched, the positive is live all of the time and the only time that feed is off is when you lock the car from the remote.

    So i guess i can't do what i want to do.
     
  11. (*steve*)

    (*steve*) ¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd Moderator

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    I wouldn't think that 0.5V would be anywhere near enough to turn on the relay.

    The problem doesn't happen when the interior light goes off slowly does it?

    Try giving the relay a light tap with the handle of a screwdriver. It's not beyond the realms of possibility that the relay is sticking. Alternatively, try removing the connextion to pin 85 and see if you hear the relay open (and the lamps go off).
     
  12. charlestt

    charlestt

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    Feb 16, 2013
    I've discovered the problem, it's the feed coming from the interior light. the interior light is negatively switched so power is going to the light all of the time it is only off when the car is locked from the remote central locking.
     
  13. charlestt

    charlestt

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    Feb 16, 2013
    what if i switch 85 and 86 ?
    so give 86 constant power and then activate and deactivate it with the negative feed coming from the interior light.
     
  14. (*steve*)

    (*steve*) ¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd Moderator

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    Jan 21, 2010
    The problem you may have then is that the lights will go off when the ignition is turned on, but may stay on otherwise.

    But I'm not 100% certain of the wiring, so give it a try if you think it may work.
     
  15. charlestt

    charlestt

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    0
    Feb 16, 2013
    that didn't work either.

    I have given up for now it's too cold lol 2c
    I've connected the feed to my led day time running lights i fitted that way it doesn't matter that they are on all of the time.

    I can't think of a way to operate the relay only having a negative feed to switch it..
     
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