Power on/time delay

Discussion in 'General Electronics Chat' started by kevlo911, Jul 4, 2008.

  1. kevlo911

    Thread Starter New Member

    Jul 4, 2008
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    0
    I tried searching on the forum but could not find exactly what I am looking for, so I figured I would go ahead post.

    I have my fog light hids on a relay and the relay is triggered by my corner lights. Well when I installed them yesterday I forgot that my alarm flashes the corner lights when I lock and unlock the car. This causes the hids to flash as well. I do not want to wire the fogs to the lo/hi beams since I want them on with the corner lights. Is there some kind of timer I can put on the relay trigger? So that way the fogs turn on after like 2-5 seconds of continuous power? I tried looking at 555 circuits but got confused and figured you guys could help with a simple solution.

    http://www.circuitdb.com/show.php?cid=25
    I found this but radioshack doesn't sell a 2n3053, any substitutes?
    Or any easier circuits just using a cap?

    Any help? Basically I want my relay to turn on after 2-7 seconds AFTER it gets power
     
  2. Wendy

    Moderator

    Mar 24, 2008
    20,765
    2,535
    [​IMG]

    The transistor isn't critical (almost any power transistor), the relay has to be rated for the voltage used (12V in this case). If you want a variable time delay replace R with a variable resistor.
     
  3. SgtWookie

    Expert

    Jul 17, 2007
    22,182
    1,728
    Another possibility would be to require that the Accessory circuit be energized before the fog lights come on. That way, no delay, and they wouldn't come on unless the ignition switch was on.

    You could accomplish that by adding a transistor and a resistor, connecting the base of the transistor (Darlington power transistor preferred) to a circuit that only has power when the ignition switch is on, the collector to the ground path of the relay, and the emitter to chassis ground.

    See the attached schematic.
     
  4. kevlo911

    Thread Starter New Member

    Jul 4, 2008
    2
    0

    Sounds like a plan. http://www.radioshack.com/product/index.jsp?productId=2062617&cp=
    So I will use that and 1k resistor, thanks guys.
     
  5. pntrbl

    Active Member

    Apr 21, 2008
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    kevlo, depending on how much current your relay draws that 200mA 3904 you linked from Radio Shack might just blow up. If your relay has less than 60 ohms of resistance in it's pick up coil the 3904 won't be alive for long.

    Radio Shack also has the TIP120 SgtWookie referenced that will handle 5A. Hard to hurt one of those .... unless you're me! LOL!

    SP
     
  6. SgtWookie

    Expert

    Jul 17, 2007
    22,182
    1,728
    Yikes! :eek:
    Good catch, SP!
    Yes indeedy, the magic smoke would roar right out of that poor little 2N3904 if you tried to use it to sink the current from your relay. That's the big reason I specified the TIP120; it's a power Darlington transistor that you can pick up at any Radio Shack (and virtually any other electronics store) that will handle over 50x the current of that 2N3904 - plus due to the fact that it's a Darlington, has far more gain.

    Clicky here: http://www.radioshack.com/product/index.jsp?productId=2062617&cp=

    It's more expensive than the 2N3904, but won't vanish in a puff of smoke the first time you turn on your fog lamps.
     
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