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  • Fuse blows with crank

    I have a carnetix power supply and I have it connected to the battery directly with a 10A fuse inline. The shutdown controller and power supply work great if I just move my key from off to acc and back , however, as soon as I crank the engine the fuse blows every time yet it never blows unless I crank the engine. The fuse blows before you hear the cranking sound though. Any ideas? Hopefully this is my last problem, thanks.

    Jason
    My obligatory progress meter.
    [|||||||||||||||||||-] = 95%
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    Need: GPS, OBD

  • #2
    There is something shorting between your ignition system and your computer power.

    I would check all of the power cables going from your battery to your computer.

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    • #3
      I just tried a 15A and 20A fuse and it completely fried them both. I but a 10 amp fuse back in and measured the voltage at the battery with a volatage meter and during crank the voltage does not drop below 10 volts. I don't think it is because the system is pulling to may amps. What is different when you crank that would cause the fuse to blow?

      To Achi: Why would it only blow when you crank if there was a short. Like I said as long as you don't crank it works great.
      My obligatory progress meter.
      [|||||||||||||||||||-] = 95%
      Basic Install done and all bugs fixed.
      Need: GPS, OBD

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      • #4
        My guess would be that the voltage dips down as the starter motor draws a huge chunk o' current for spinup, the computer power supply tries to compensate for the dropped voltage by drawing more current, and this blows the fuse.
        Once the switch hits Start, even if the starter motor isn't spinning yet, it's still drawing current to get it spinning.

        If your battery is too old, it may need to be replaced to keep the voltage up during cranking. Hmm. Or you're using too small a gauge wire to the Carnetix supply...smaller gauge wire increases the amount of voltage drop per unit length. With the vehicle off, check the voltage at the battery, and then again at the Carnetix. There shouldn't be a lot of difference. If there is, you need a bigger power cable. Also, leave a voltmeter wired to the battery and crank it, see how low it dips.


        You can also ask on the Carnetix forums at http://www.carnetix.com/forum
        System status: in progress

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        • #5
          Like I said I measured the voltage at the battery during crank and it did not drop below 10 amps. I am using 10 gauge wire from the battery. I also tried a 20 A fuse and it blew so that would mean the voltage would have to drop to 3volts to fry a 20 amp fuse since my system has a 60W power supply. I am totally confused, any ideas? Thanks Jason
          My obligatory progress meter.
          [|||||||||||||||||||-] = 95%
          Basic Install done and all bugs fixed.
          Need: GPS, OBD

          Comment


          • #6
            Voltage is pushed through a circuit, Amperage is pulled through a circuit.

            The only way you are going to blow a 10amp fuse is if something on the circuit the fuse is protecting is pulling more than 10 amps.

            If you have a short in the system, where there is no resistance between positive and negative, then your car battery or starter motor will pull the maximum amperage they can.

            Your PSU is not what is blowing your fuse.

            Unless I'm on crack.

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            • #7
              Something's not wired correctly. Post pics if you can or explain your set up as far as how you have the wires running(power that is). Also do you have amps?
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              • #8
                dont keep upgrading your fuses. thats the last thing youy want to do.

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                • #9
                  wire is grounding out
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                  • #10
                    Originally posted by swingpoha
                    I just tried a 15A and 20A fuse and it completely fried them both. I but a 10 amp fuse back in and measured the voltage at the battery with a volatage meter and during crank the voltage does not drop below 10 volts. I don't think it is because the system is pulling to may amps. What is different when you crank that would cause the fuse to blow?

                    To Achi: Why would it only blow when you crank if there was a short. Like I said as long as you don't crank it works great.
                    If your blowing fuses, why did you measure the voltage durring cranking? You should have measured current. Try this, throw a N4001 or a N4004 before the fuse.

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                    • #11
                      I agree that the PSU is not blowing the fuse, obviously I am shorting or it is grounding out like some above have said. The question remains what is different when I crank the starter vs. just switching to the acc setting with the key. If the system has a short, it should always blow a fuse and as far as I know there is no contact between the computer system and the ignition wire to the starter. I was asking if anyone knew what is changing to cause the short when I crank the starter.
                      My obligatory progress meter.
                      [|||||||||||||||||||-] = 95%
                      Basic Install done and all bugs fixed.
                      Need: GPS, OBD

                      Comment


                      • #12
                        My setup is simply a wire directly from the battery running directly to the carnetix(with fuseholder in-line), I have looked at every inch of the wire between those two points, there is no obvious place where it could be shorting out, perhaps it is shorting somewhere in my computer but again, why would it only happen specifically when I crank the engine.
                        My obligatory progress meter.
                        [|||||||||||||||||||-] = 95%
                        Basic Install done and all bugs fixed.
                        Need: GPS, OBD

                        Comment


                        • #13
                          Originally posted by swingpoha
                          My setup is simply a wire directly from the battery running directly to the carnetix(with fuseholder in-line), I have looked at every inch of the wire between those two points, there is no obvious place where it could be shorting out, perhaps it is shorting somewhere in my computer but again, why would it only happen specifically when I crank the engine.
                          No ground wire? How about remote/acc?
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                          • #14
                            Originally posted by ppgt94
                            No ground wire? How about remote/acc?
                            Yeah, please tell us where you ground wire and acc wires are connected to and from.

                            I don't know much about the carnetix PSU, but if it has a remote/acc wire, then try disconnecting that, and just hook it up to the +9v on a 9v battery, and hook the 9v battery ground to the PSU ground. That way you should be able to tell if it is the acc wire from your ignition or head unit that is causing the short.

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