0.5 seconds relay

Discussion in 'General Electronics Chat' started by orwikcons, Aug 2, 2008.

  1. orwikcons

    Thread Starter Member

    May 2, 2008
    22
    0
    Greetings!

    A few months ago I posted where I asked how to make a circuit which will, after plugged on, hold on for a few moments, and then turn off, although it is still turned on.

    You gave me this scheme:

    [​IMG]

    And it worked in my car, but only when the engine were not running. When the engine was on, when circuit turned off, it did it but with reclamation (probably the electricity which comes from alternator is not so stabilized, as from the battery). How can I surpass this problem?
     
  2. SgtWookie

    Expert

    Jul 17, 2007
    22,182
    1,728
    OK, what do you mean by "reclamation"?

    The section I bolded is worded rather oddly, and I can't make heads nor tails of what you're trying to say.
     
  3. orwikcons

    Thread Starter Member

    May 2, 2008
    22
    0
    Ok, I am sorry for bad English...

    So, when the conductor is charged, the relay turns off, and it works when the engine is not running. When the engine is on, relay turns off, but it immediate turns on (it changes on/off a few times per second), but on/off time period reduces, so that after about 2 seconds relay is finnaly turned off. It is probably the effect produced by alternator. The same thing happens when I plug the circuit on the battery charger (12V) at home. How can this effect be neutralized?
     
  4. nanovate

    Distinguished Member

    May 7, 2007
    665
    1
    put a diode anti-parallel across the relay coil
     
  5. SgtWookie

    Expert

    Jul 17, 2007
    22,182
    1,728
    OK.

    I would expect that kind of performance when you ran it from a battery charger, as the charger's output is simply a rectified sine wave with no filtering.

    However, the output from a car's alternator should be a relatively smooth output, as it's rectified 3-phase and constantly regulated.

    I suggest that you may have a problem with your alternator. I suspect a blown rectifier bridge or perhaps a bad diode trio (GM alternators) - these parts go bad quite frequently, as they are subjected to quite a bit of current, and lots of heating/cooling cycles. One indication of these kinds of failures is the ALT light on the dash glowing very dimly; it can be difficult to see during daylight.

    Many shops will test your battery and alternator for no charge. Fixing them is another matter. If you pay a shop to replace an alternator, it could cost you several hundred dollars. But if you're handy with tools, you can re-build an alternator in a couple of hours (if you take your time with lots of coffee breaks) for under $30.

    If you DO have alternator problems, it's best to find out now. Otherwise, you will be buying a new battery along with buying a new alternator.
     
  6. orwikcons

    Thread Starter Member

    May 2, 2008
    22
    0
    Thank you very much, I'll see what I can do!
     
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