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  • need help asap

    need to know what i need to keep power to cigarette lighter a few seconds longer i have a car that the power to lighter shuts off when car is off i need it keep it on a few seconds longer then the the radio i have a external hdd hooked up to the radio it needs an extra power to run it so i hooked it up to the cig lighter but it shuts off as soon as i turn the car off the radio stays on about 5 seconds after i turn the car off so when the hdd shuts off before the radio the radio thinks it was unplugged and when i turn the car back on it restarts to detect hdd and will not replay where i left off if i turn the radio off first then shut car off then back on it will leave off on the song i was playing

    need to know what kind of relay or something i need to put on cig lighter wire to stay on longer then the radio

  • #2
    you could add a capacitor inline to the cig lighter or you could jumper off the radio power line and route it to your lighter socket, or bust off the plastic housing from your cig adapter and wire pos/neg from radio to that directly just a couple of ideas for you SNO


    • #3
      It depends on the car - modern vehicles especially may not like it.

      And caps could be powering other stuff - like the radio that will stay on.

      Adding a inline diode before the cap will isolate it from the other stuff, but it will cause ~0.6V drop and has to be rated for the current involved.
      Or add a relay before the cap which opens when ACC turned off - hopefully before discharging the cap

      Or the cig socket (or ACC line) controls a battery-powered off-delayed relay. (That will require a much smaller capacitor if a cap is used for the time extension.)


      • #4
        Would it be too off-the-wall to suggest to buy a large capacity USB memory stick (however large your collection is)? I have seen sticks up to 256GB in size (although kind of spendy). I mean, you would only need a 32GB stick if you only had under 32GB of music, and that would be cheaper.

        The other option, is you could always wire in a cig lighter under the seat which has power all the time (or you can build a timer delay circuit into it for delayed shutdown).

        The last suggestion would be to buy a drive bay off eBay like this style:

        ...which comes with a special USB cable that has 2 USB ends on it that plug into the computer, and it uses only one of those for data transfer, but uses both plugs to combine power (500mA + 500mA = 1000mA) so then it can run off of your laptop. I have a few of these drive bays and really like them a lot ( ). They have a snap design (screw-less disassembly) so you can swap the drives out inside rather easily. And they do not require any external power source, due to the dual USB plug design.


        • #5
          another idea-- you could get a 12v dc-dc power supply, and configure it to hard-off a couple of seconds after the ign turns off..
          My OLD 2001 Mitsubishi Eclipse GT:
          "The Project That Never Ended, until it did"

          next project? subaru brz
          carpc undecided


          • #6
            I just thought of one last idea. If you bought a relay with a 5v trigger coil on it, and then you could take an old USB cable and cut it up so you could use the power leads from it (google around for 'USB pinout', there are 2 wires for data and the other 2 wires are for 5v + and 5v - so it would be easy to do). So you'd use the USB power from the laptop to trigger the relay's 5v coil (USB standard is 5v @ 500mA), which you'd wire in a completely separate cig lighter circuit (contant-on power source) under the seat but wired with that relay in the middle so the USB off will open the relay and thus the cig lighter circuit. Then the HDD wont die until at least the computer dies, and the caps built into the power supply of the HDD, might make it stay on for 1 more second after the laptop dies anyway.

            ...hope this helps
            EDIT: It would be wise to put a diode on the relay trigger circuit (the USB 5v trigger wire) either across the 2 leads, or in-line on one of the leads (in the appropriate direction) to dissipate recoil collapse. That is when you turn off the relay and the relay coil's field collapses, it will protect the laptop's USB power supply driver circuit from the possibility of damage (kinda like static discharge). I could provide some details if necessary. Only requires one small diode and there are 2 ways you can wire it in and they are both effective at dissipating recoil current.