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Dome light

Discussion in 'The Garage' started by broc944, Jul 24, 2006.

  1. broc944

    broc944 1/2 ton status

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    My work truck which is a F##d, has a feature I like, open the door the dome light stays on for a couple of minutes and then shuts off. I want to do the same thing for my Sub. I have not found any kit to do this.

    My first idea was using a capacitor, but I do not think it would have enough storage to keep the light on for the two or three minutes I want it to. A adjustable time delay timer would work, but I can not find one.

    Anybody have any ideas on how to accomplish this? I just want the dome light to stay on for a couple minutes with the door open and then shut off, even with the door open. I want the manual dome light switch to work as normal.
     
  2. K5er4Life

    K5er4Life 1/2 ton status

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    So you want it to go off only when the door is open for a few minutes, or do you want it so when you close the door the light stays on for a few minutes? I know LMC or maybe it was chevy duty that has a little kit that allows the light to stay on for about a minute after the door is shut, I can look in my catalogs and tell you for sure which one it is.
     
  3. broc944

    broc944 1/2 ton status

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    I want it to go out if the door is left open.
     
  4. readymix

    readymix 3/4 ton status

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    The two circuits below illustrate opening a relay contact a short time after the ignition or ligh switch is turned off. The capacitor is charged and the relay is closed when the voltage at the diode anode rises to +12 volts. The circuit on the left is a common collector or emitter follower and has the advantage of one less part since a resistor is not needed in series with the transistor base. However the voltage across the relay coil will be two diode drops less than the supply voltage, or about 11 volts for a 12.5 volt input. The common emitter configuration on the right offers the advantage of the full supply voltage across the load for most of the delay time, which makes the relay pull-in and drop-out voltages less of a concern but requires an extra resistor in series with transistor base. The common emitter (circuit on the right) is the better circuit since the series base resistor can be selected to obtain the desired delay time whereas the capacitor must be selected for the common collector (or an additional resistor used in parallel with the capacitor). The time delay for the common emitter will be approximately 3 time constants or 3*R*C. The capacitor/resistor values can be worked out from the relay coil current and transistor gain. For example a 120 ohm relay coil will draw 100 mA at 12 volts and assumming a transistor gain of 30, the base current will be 100/30 = 3 mA. The voltage across the resistor will be the supply voltage minus two diode drops or 12-1.4 = 10.6. The resistor value will be the voltage/current = 10.6/0.003 = 3533 or about 3.6K. The capacitor value for a 15 second delay will be 15/3R = 1327 uF. We can use a standard 1000 uF capacitor and increase the resistor proportionally to get 15 seconds.

    [​IMG]
     
  5. K5er4Life

    K5er4Life 1/2 ton status

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    Yup, exactly what he said....heh. :confused:
     

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