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powering a light from 2 different sources

Discussion in 'LEDs and Optoelectronics' started by charlestt, Feb 16, 2013.

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  1. charlestt

    charlestt

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    Feb 16, 2013
    Hi guys i’m trying to wire up some drls on the car so that they come on with the ignition and also come on when you unlock the car.

    I have the power sources worked out but i cannot figure out how to wire it all up so that there is no feed back through the system.

    so to clarify what i want

    unlock car lights on
    start car both feeds will be live until the interior light dim off, lights then running with the ignition feed.

    thanks for any help
     
  2. Harald Kapp

    Harald Kapp Moderator Moderator

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    Nov 17, 2011
    A simple way is to use two relays.
    Relay 1: coil in parallel to interior light
    Relay 2: coil controlled by ignition feed (between ignition and chassis/GND/-)

    The contact sides of both relays are connected in parallel, one contact pin-pair to 12V, the other pin-pair to the load.

    So if either relay is turned on, the load will see +12V.
     
  3. charlestt

    charlestt

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    Feb 16, 2013
    Hi Harold thanks for the quick reply, i'm kind of new to relays but if i understand correctly what you are saying is to connect both outputs of the relays together and then connect that to my led drls..
     
    Last edited: Feb 16, 2013
  4. charlestt

    charlestt

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    Feb 16, 2013
    What sort of relay would i have to use ?
     
  5. Harald Kapp

    Harald Kapp Moderator Moderator

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    Nov 17, 2011
    That depends on the load (voltage, current). You can use any relay that haas:
    - coil voltage 12V
    - load voltage and current fitting the load
     
  6. charlestt

    charlestt

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    Feb 16, 2013
    If both are seeing current and therefore connected is there any chance of any feed back ?
     
  7. Harald Kapp

    Harald Kapp Moderator Moderator

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    Nov 17, 2011
    What feedback? From where to where?
    Think of the two relays as two switches in parallel. If eiterh one or both are on, the lights are on, too. If both are off, so are the lights.
     
  8. charlestt

    charlestt

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    Feb 16, 2013
    sorry your right, i was just being over cautious.

    I was just thinking if both were on would it cause any issues with the cars systems but i guess it wont make any difference.
     
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