DC Power Delay - 5 seconds ON and 190 seconds OFF | HELP

Discussion in 'General Electronics Chat' started by we87, Sep 15, 2006.

  1. we87

    Thread Starter New Member

    Sep 15, 2006
    2
    0
    Hello to all... I am a member of many different forums on the internet, but I am new to this one. And I know how frustrating it can be for these types of posts: But I am a newbie when it comes to these kinds of electronics. I am no stranger to soldering, but I dont know that much about capacitors, resistors, etc.... But, I have a pretty straight foward question to ask so hopefully, I wont be too much of a PITA ;)

    What I have done is put a computer in my car, or a Carputer if you will. For anyone interested in the hobby, you can go to www.mp3car.com to learn all about it. But, what I am trying to do is get my computer to Startup and Shutdown with my cars ignition. So it would be turn key on>start computer>drive. Then turn off ignition>remove key>shutdown.

    I have built a series of relays to do this, but the problem is my particular DC-AC Power Inverter does not survive crank. So when I turn my car on, the inverter dies.

    Now what I have tried to do is build a power on delay circuit that I found online at this site: http://ourworld.compuserve.com/homepages/Bill_Bowden/page2.htm#delay.gif It works just fine and I have gotten a 5 second delay out of it.

    Also, I have built this circuit: http://www.mp3car.com/vbulletin/showpost.php?p=465359&postcount=29 which uses the power from the capacitors after the 12volt line is cut to keep the relay alive for around 2 minutes and 30 seconds. Which gives the PC enough time to properly shut itself down. Again, this works just fine.

    HOWEVER, I cant figure out how to wire them in sequence because they both use a trigger output of negitive ground. So if I use the power on delay circuit to supply ground to the power off delay circuit, when the car is shut off everything dies with no power off delay.

    So, what I am trying to ask is: Can anybody tell me how to wire those two circuits up to give me a 5 second power on delay, and a 190 second power off delay. OR, is there a better way to do what I am trying to do, and another circuit I should use....

    Thank you very much in advance for any help you can give me. I apreciate all comments, and ideas. And again, I'm sorry for the lack of electronics knowledge to properly word my question :)
     
  2. Søren

    Senior Member

    Sep 2, 2006
    472
    28
    Hi,


    Try this:
    [​IMG]
    R5, C2, Q2, Q3. D4 and the relay are from Bills circuit and the rest is a timeout arranged to first kick in when:
    1 The output has gone active.
    2 The ignition is removed.
    Then the timeout begins, goverrned by the discharge of C1 through R2 and the b-e junction of Q1 (you might wanna play around with the value of C1 (and perhaps R2) to get the exact time you want).

    Any further questions, then drop me a line, either here or by email.


    An overlay (very messy, but hey I'm ill and my body temperature is going through the roof, so cut me some slack, I can rearrange later if you need it :))
    [​IMG]
    Your relay will most certain be of another kind, but since I don't know which type you'll use, or if you'll use a PCB at all, I just threw in a random type.
     
  3. n9352527

    AAC Fanatic!

    Oct 14, 2005
    1,198
    4
    There is an engine on signal that you can use to turn on the inverter instead of the 5s delay. Maybe putting a few seconds delay after the signal is asserted is also a good idea just to make sure things properly stabilise first. I think it is just a better solution rather than continously setting and resetting the timer, especially if it takes more than one crank to turn the engine on.

    Having said that, you should actually put a good power filter and conditioning at the inverter input just to make sure it doesn't continuously quit on you. If it doesn't survice a crank, then it'd be likely to quit at other times too. Car electric is a hostile environment, you should protect the equipment accordingly.

    To turn off the inverter, you could use the signal from the motherboard that indicate the PC is shut down, then turn off the inverter.

    With these approaches, the system doesn't depend on any timer for correct operation, and no need to adjust the timers to cover worst-case conditions or putting extra margins for safety.
     
  4. Søren

    Senior Member

    Sep 2, 2006
    472
    28
    Hi,

    Not all cars have them unfortunately, but if they are on the one in question, this is the best solution of course.

    A NiCd or small lead/acid battery to drive it through cranking would be my solution, although I'd never use a 12-240V inverter, as it is a waste of energy to do double conversion.
    A switchmode inverter will usually have enough filtering though.


    Absolutely!


    Which signal are you thinking off ?


    I do agree, if the other means exists, but even with those in place, more is needed to ensure it never gets a brown out in an inconvenient moment (like when you use it for GPS-navigating through unknown places) - A mini UPS with a separate small lead/acid battery would be a possible solution.
     
  5. n9352527

    AAC Fanatic!

    Oct 14, 2005
    1,198
    4
    There are many signals that can be used, the core voltage for an example, or maybe its control signal, or simply the power LED, or maybe the hard drive power, or tap it from one of the PCI slot, except for the standby power pin. There are so many of them to choose, the sky is not quite the limit I'm afraid, but creativity is....

    True, not all cars have the engine on signal. But I think that cars that were built for the last 10 or maybe 12 years and did not belong to the very basic models, probably do have them. So far, almost all cars that I've hotwired :p have the engine on signals, as long as there is an ECU under the bonnet, or where ever Ford decides to hide the ECUs next, then the signal is there.

    Here's a scenario to think of, what would happen when I turned the engine off and then crank it on again before the computer had finished shutting down? This would kill the inverter right? Maybe something along the line disabling the inverter while cranking is necessary...
     
  6. Søren

    Senior Member

    Sep 2, 2006
    472
    28
    Hi,

    Oh, I thought you had found a special "power is off" indicator since you wrote "use the signal from the motherboard that indicate the PC is shut down". Thought I could learn something new :)

    I stopped getting greasy hands on cars a while back and since the last of my cars I cared to get down and dirty with was a '72 Dodge Dart (with a carburettor of course), I am not very much into ECU's and their signals - so there's an engine running signal that's only on when the engine IS running ? (Nice, gotta think of ways to use that :))


    Nah, just use a UPS. Any other way might cause bad happenings - that's probably the number one reason I'd never stuff a regular PC in a car, they were never built for it, so better use or build something that can handle the environment, like getting an MP3-handling car CD player (they're down to a price the equivalent of about one or two hours of work, so why fiddle with an inferior solution anyway) ?
     
  7. kubeek

    AAC Fanatic!

    Sep 20, 2005
    4,670
    804
    what about a diode and small lead-acid battery befoe the converter, to provide power while cranking? It would re-charge itself as the motor runs...
     
  8. n9352527

    AAC Fanatic!

    Oct 14, 2005
    1,198
    4
    Or maybe just forget the inverter and use a DC/DC converter like picoPSU or the M2-ATX, which is specifically designed for car application and specified to survive engine crank? As long as you don't exceed the power rating then you should have none of the above problems. It would also be more efficient due to only one conversion.
     
  9. Søren

    Senior Member

    Sep 2, 2006
    472
    28
    Hi,

    That should do (except for cranking on a really cold morning :))
    It may seem a little expensive, but if the spec sheet don't lie, it's a genuine find at that price.

    However, it still needs a timer to allow for shutdown.
     
  10. we87

    Thread Starter New Member

    Sep 15, 2006
    2
    0
    Thanks everyone, I apreciate all of the informitive post's!

    Now, everything is working like a charm :D

    Sorry for the late reply, but I havent had any down time.
     
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