Automatically switching between two 12v sources?

Discussion in 'The Projects Forum' started by MSCOSC, Aug 17, 2015.

  1. MSCOSC

    Thread Starter New Member

    Aug 17, 2015
    4
    0
    Hey guys, first part so forgive me if this has been covered,i found some results searching but not quite what i was looking for.

    I am trying to set up day time running lamps on my car utilizing one of the "courtesy lamp" bulbs. I basically want to trigger that bulb with a standard spdt automotive relay when the car is running which is easy enough taking accessory from the fusebox.

    Where I'm having trouble is also utilizing that bulbs oem input. It comes on when i unlock the car and even though minor i would miss that feature if i override that bulb to only come when the car is running.

    I'm basically trying to utilize 2 identical 12v sources for one bulb.

    Thanks for any input guys, if I can clarify on anything let me know.
     
  2. ericgibbs

    Senior Member

    Jan 29, 2010
    2,499
    380
    hi MS,
    If you mean that you want to turn the same lamp On, from two different switches.??

    Consider using diodes, one from each switch to the lamp.

    E
     
  3. MSCOSC

    Thread Starter New Member

    Aug 17, 2015
    4
    0
    Not really 2 different switches, 2 different sources. Typically only one would be on at a time but there would be times both sources could be on at once. So let's say I'm using diodes and both sources are on at once. Is that going to cause problems? I figured i wouldnt be able to have two 12v sources coming together like that.
     
  4. mcgyvr

    AAC Fanatic!

    Oct 15, 2009
    4,769
    969
    Google... Diode oring
    The source with the higher voltage will be the one providing the power.. When it drops out the other will take over..
     
  5. MSCOSC

    Thread Starter New Member

    Aug 17, 2015
    4
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    Does the switching go both ways or is one going to be the "primary"? I'm finding sons results on Google but not much i can find available to buy.
     
  6. ericgibbs

    Senior Member

    Jan 29, 2010
    2,499
    380
    Hi,
    Either one OR both diode sources could be On at the same time, no problems.
    E
     
  7. MSCOSC

    Thread Starter New Member

    Aug 17, 2015
    4
    0
    That's good to know. These diode lines would only be providing the "switch" voltage to a relay so it's not like much power will be flowing here, thank you for your replies.
     
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