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Thread: Need a 2 second delay on 12v wire

  1. #1
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    Post Need a 2 second delay on 12v wire

    Is there a way to put about a 2 second delay in the power wire from my battery to my inverter? I was told a capacitor. If this is true, could someone tell me what value and type? Thanks

  2. #2
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    Olympia, WA USA
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    Lightbulb

    Here's something you can try...
    Police cars sometimes use electric locks to secure their shotguns in the car. These locks are actuated with a solenoid that is on a delay circuit, I think 10-15 seconds, so the lock would stay open for a bit after the engine was shut down. You can get the delay circuits separately, or at least you could. Try law enforcement supply websites. If you're not having any luck, drop me an email and we can negotiate for the one I have.
    >T

    ------------------
    Keep thinking! =)
    Keep thinking! =)

  3. #3
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    Post

    You could use a capacitor/resistor network to provide a delay, but I think you would be better off using something else.

    A capacitor charging through a resistor does so at a predictable rate.

    +12V ---------/\/\/\/\--------o Vo
    R |
    _|_ --- C
    |
    |
    GND

    When +12V is applied, the capacitor will begin to charge, and Vo will rise from 0 volts to 12, in an exponential curve. The time it takes to charge to 12V can be calculated by selecting R and C appropriately.

    If you need EXACTLY 2 seconds, this is not a good way to do it, because the time delay will change with temperature. If you don't need an exact delay, you could do this, but there is another problem: Because the voltage at Vo rises exponentially, Vo will start at 0 volts, then go through 1 volt, 2 volts, etc. until it gets to 12 volts. I don't know how your inverter will like this, or at what point it will turn on, but I suppose you could try it and experiment.

    The other problem is that you are adding a resistance to your +12V line, which means that your inverter will never get 12 volts, and the more power it needs, the less voltage it will get. The resistor will also need to be pretty beefy to handle the current.

    You could use this circuit to trigger a relay which supplied power to your inverter, instead.

    IMHO, you would be better off making a simple circuit with a PIC and a 12 volt relay, which you could program for just about any delay you wanted. But that's just me...

    -Good luck!

  4. #4
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    Post

    Here's another try to post a legible circuit:

    <pre>
    +12 V _______/\/\/\/\___________o Vo
    R |
    __|__+
    ----- C
    |
    |
    GND
    </pre>

  5. #5
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    There are a couple ways to do this without running into the problems of using a simple capacitor circuit.

    It basically depends on whether you want to buy something or DIY.

    If you want to DIY, go to Radio Shack and pick up one of those little schematic books- the one on the 555 timer. You'll find simple circuits to make that will work just great. The 555 chip is the same chip that all those shutdown circuits that I've seen use.

    If you want to buy something, a time delay relay would be just the thing. Here's an example: http://www.natcon.com/timer1-9.htm It is a little big for what it is though- it's 2 inches square, by a little over 3/4 thick and bright orange. But it'll work just fine.

  6. #6
    Constant Bitrate
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    Post

    For what purpose? I can't figure it out from your question as to why and where you need th 2 second delay. At power up or power down?

  7. #7
    Retired Admin Aaron Cake's Avatar
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    Cool

    A capacitor and resistor will not work for this purpose. Check out http://www.aaroncake.net/circuits/relaytim.htm for what you need.

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  8. #8
    Low Bitrate
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    Post

    Probedude_2000: He needs it at power up. I have the same problem. When I start my car, all of the electronic crap in my car takes too much of the power and my inverter won't get enough to make it happy. But once everything has started the inverter is fine.

    He's just wanting the delay so he doesn't have to sit there and wait to turn it on.

    OEP

  9. #9
    Constant Bitrate
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    Post

    How about a 5 second power up delay. And if needed a momentary relay closure to start up your ATX motherboard. Also has a 30 second shutdown delay. http://www.dschmidt.com/autooff.html

  10. #10
    Constant Bitrate
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    Post

    what ever the circuit up there. if you put put an D-flipflop with it, it will work

    try this

    ****..i can not draw the damn flip flop up here.
    anyone here has a website so i can upload the picture and share it with everyone ?

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