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Thread: power on delay

  1. #1
    Constant Bitrate
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    edit: power on/off delay

    hey gusy i was looking at aaron's page and came across this http://www.aaroncake.net/circuits/relaytim2.htm

    my car (2003 protege 5) cuts the power to the acc line when the starter is engaged so when the car is started the radio (computer. . whatever) would turn off until the starter is done cranking. . .so with this circuit i could add lets say a 5 sec delay (time it takes for me to insert key and then engage starter) until the inverter would turn on and then when the acc goes hot again (starter disengaged) the computer would then turn on eh?

    also for this circiut it calls for a 6V relay. . .would using a 12v relay instead giving a 12v input change any of the timing calculations and still make the circuit function?

    thanks guys

  2. #2
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    wouldn't it just be simpler to use a resistor, cap, general transistor and a normal relay?

    The idea is that while the cap is charging it is taking all of the power, so the relay will not close. Once the cap has finished charging, the relay will close and remain closed until the power is cut off, at which point the relay will remain closed until the cap discharges.

    You can change the amount of time before the relay closes, and the amount of time the relay will remain closed after power is turned off by changing the values of the resistor and cap.

    The type of relay in either circuit is not important.
    IN DEVELOPMENT -- '96 Mustang, lilliput with PII/450 laptop, custom DC-DC power supply, 60GB; Garmin GPS; 802.11g; compact keyboard, small graphical LCDs, OBDII.

  3. #3
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    ok. . .i understand about the Resistor and Cap relationshiop and how that can cahnge the time delay but i don't totally understand how a transistor would work in this circiut.

    essentially what i want to do is use jeff's shutdown circuit for powering down my comp and that will take care of the delay off and i would like to use this circuit in conjunction with that in order to delay the powering up of my computer..

    a better schematic would be helpful for what impose. if someone could help me out with that that would be greatly appreciated

    thanks

  4. #4
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    In that case you don't even need a second relay

    I'm no expert, so this may not work, but try this:



    The time can be adjusted by changing the cap and resistor values.

    The transistor can handle loads of up to 200mA. The shutdown controller uses only 80mA on the switched line, so all should be good.

    Basically the transistor acts as a switch. When a positive voltage is applied to the collector (center pin, on left side), current will flow between the base (top right) and the emitter (bottom right), allowing the shutdown controller to stay on.

    So when the car turns on the cap will charge, essentially grounding the connection, so no power will go to the transistor. Once the cap has charged, the flow stops though it, and the power can now to flow to the transistor to "turn it on".

    Once the car shuts off, the capacitor will slowly discharge through the resistor to the transistor, once the available voltage falls below 0.7V, the transistor will "turn off", and the shutdown controller will see the remote line turn off, shutdown will begin.

    The diode is there to prevent other accessories on the switched line from draining the cap.

    The resistor on the other side of the emitter is used to create a ground connection, because the transistor will only turn on once there is a 0.7V potential difference between the collector and the emitter (not a worry as less than 1mA will flow through it).
    IN DEVELOPMENT -- '96 Mustang, lilliput with PII/450 laptop, custom DC-DC power supply, 60GB; Garmin GPS; 802.11g; compact keyboard, small graphical LCDs, OBDII.

  5. #5
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    hound i dont understand what exactly you wanna do... correct me ...

    a) your car cuts acc line when you crank your car and when your car is running the acc is hot again .... Y/N..?

    b) You wnat to delay the acc line so when you when you put the key and turn the car to acc nothing happens and waits till you crank the car ...Y/N..?

    c) Does your system (deck, comp..etc ) go on when you put the key and turn to acc only ... and then what happens when you crank .... ? system goes off and starts again when engine running ..Y/N..?

    let me know , will suggest something ..

    Mastero

  6. #6
    Constant Bitrate
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    a: yes

    b: yes. . .but i figure ill never just leave it in acc and i always start the car withing about 10 seconds unless there is a better way

    c: when i turn the key to acc the stereo turns on but when i crank there is a relay attached to it that shuts the acc line until the starter solenoid has stopped. .then the acc goes hot again

  7. #7
    FLAC Mastero's Avatar
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    ok got it ..

    Dont go for delay on Use delay OFF

    So when you put the key in and turn. The dealy Off cuircut gets the acc pluse and supplys power to the inverter then when you turn more and start the car the car cuts off the acc line but the delay power off does not cut the power to the inverter and waits (time as desired) and keeps the line HOT as soon as the car is running the acc comes back on and the delay off does nothing similary when you remove the key the delay off is triggered and with in say 5~10 sec as set shall cut the power to the inverter making it think the acc is off ..

    PHEW .. i am tired .

    Well i think the design is there on aaroncake site ..

    Good luck

    Mastero

  8. #8
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    No, Maestro, that will not work.

    The delayed off circuit requires to charge a capacitor for a little amount of time before trying to discharge it.

    You have about 1/2 a second between putting the key in the ignition and turning it through the sequence to start the car, which is not enough time to charge the cap, so the "delayed off" would not last long enough to keep the ACC line high for the shutdown controller.

    Unless you use an actual timer chip, but this is much simpler and cheaper, and what's better it does what he wants. Additionally this also acts as a delayed off, so once the cap charges for X seconds (or however long it takes to charge), once the power is cut off it will stay on for a certain amount of time too.



    Actually hold on a second, what is the actual problem here? From having the car in ACC to starting, or just from sticking the key in the ignition and the starting?

    If the latter, what's the problem? The ACC line will only remain high for about 1/2 a second before you start the car, so nothing will get the chance to power up, no?
    IN DEVELOPMENT -- '96 Mustang, lilliput with PII/450 laptop, custom DC-DC power supply, 60GB; Garmin GPS; 802.11g; compact keyboard, small graphical LCDs, OBDII.

  9. #9
    Constant Bitrate
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    "If the latter, what's the problem? The ACC line will only remain high for about 1/2 a second before you start the car, so nothing will get the chance to power up, no?"

    actually in my car the stuff will power up as when the inverter is plugged in i hear the low voltage warning as the led on the unit shuts off as the starter cranks so what i want is that delay so that the inverter won't even power up at all until the engine has started so i won't ever have to deal with voltage fluctuations taht i hear about with the pc just powering up but not booting since there wansn't enough voltage b/c of the starter surge

  10. #10
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    But the inverter only turns on once the car is in ACC or ON mode, right?

    Isn't there like normally a 1/2 delay betwen ACC and START? My inverter beeps when I turn on the car too, but it doesn't actually start anything up yet.

    However the circuit that I showed you is very simple and cheap and should work.
    IN DEVELOPMENT -- '96 Mustang, lilliput with PII/450 laptop, custom DC-DC power supply, 60GB; Garmin GPS; 802.11g; compact keyboard, small graphical LCDs, OBDII.

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