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What size fuse should I connect to the battery? If needed at all..

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  • What size fuse should I connect to the battery? If needed at all..

    Hello, just looking for some some advice really.

    I've recently bought a 1800W Sub with built in amp, all enclosed with it's own fuse. I'm connecting 2x 375W speakers to it. Do I still need to fuse at the battery to protect anything major? Such as the speakers? Or will the built-in fuse be sufficient?

    If so, what size fuse do I need? (375 + 375 + 1800) / 12 = 212.5 amps?

    Cheers.
    Last edited by Shallice; 03-13-2011, 08:35 AM.

  • #2
    The built in fuse is to protect the equipment and the fuse by the battery is to protect your wiring, if you don't protect your wiring you could damage your cord and even worse start a car fire.

    I would look to see what size of fuse is already on your equipment and put the same size fuse at the battery.

    Also you might find this CALCULATOR helpful!!
    Last edited by knownchild; 03-04-2011, 09:30 AM.
    Never accept STOCK equipment.

    Comment


    • #3
      what he said.

      the whole reason is a extra layer of protection-- if you car gets split in half in a horrifying wreck, the last thing you want is a cut power wire shorting out, and catches the gas tank on fire... the fuse at the battery would prevent that(the fuse would blow as soon as the power wire got sheared)..

      the IASCA rule is less then 18" from the battery, but i always say to keep it less then 12"...
      My OLD 2001 Mitsubishi Eclipse GT:
      "The Project That Never Ended, until it did"


      next project? subaru brz
      carpc undecided

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      • #4
        Thanks for your help, I got everything fitted but I just can't get the main cable from the battery to the boot. I don't really want to drill through the dashboard..
        Last edited by Shallice; 03-06-2011, 05:24 PM.

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        • #5
          Got it done and the battery died.

          Comment


          • #6
            Good job on the wiring. You generally don't have to drill through the dash, as there should be some wires coming through the firewall from the engine compartment already. So next time, just share that opening.

            As said before, the fuse at the battery is to protect the wiring and stop a fire, not protect the equipment. The size of the fuse is dependent on the gauge (size) of the power wire, not the draw of the electronics being powered. Higher power electronics draw more current, so require a larger wire to supply, and therefore a larger fuse. Use the calculator above to ensure you used correct size power wire. You can always use larger wire to run the power (say 2-4 gauge), with a little signal loss and greater expense. Overfused smaller wires may draw too much current to handle, overheat, melt the insulation, and either short to a ground and blow the fuse, or in the worse case, cause a fire.

            The battery dying is indicative of the amp not shutting off with the ignition, an inadequate charging system, bad battery, or a leak (short) to ground.

            Good luck...

            Comment


            • #7
              Originally posted by Thefdog View Post
              As said before, the fuse at the battery is to protect the wiring and stop a fire, not protect the equipment. The size of the fuse is dependent on the gauge (size) of the power wire, not the draw of the electronics being powered. Higher power electronics draw more current, so require a larger wire to supply, and therefore a larger fuse. Use the calculator above to ensure you used correct size power wire. You can always use larger wire to run the power (say 2-4 gauge), with a little signal loss and greater expense. Overfused smaller wires may draw too much current to handle, overheat, melt the insulation, and either short to a ground and blow the fuse, or in the worse case, cause a fire.
              to a extent, your correct.. i get what you're saying, but had to re-read it a couple of times to understand it.

              recap:

              you always fuse for the end-load, this way any substantial draw will blow the fuse and protect the wire.

              as a example-- i tend to run wires that are way too large for their intended purpose. my carpc has a 8ga wire run to it-- according to my brief search, 8 ga wire is rated for about 45-50A maximum draw. my carpc power supply has a 20 amp fuse.. so i installed a 20A fuse on the wire. this way, if something went wrong with the carpc, i might blow 2 fuses instead of one, but i protect everything.
              My OLD 2001 Mitsubishi Eclipse GT:
              "The Project That Never Ended, until it did"


              next project? subaru brz
              carpc undecided

              Comment


              • #8
                Exactly, trust soundman he is 100% correct.

                By the way could somebody give me +rep cuz when i got negative it was when i was being a noob LOL
                Never accept STOCK equipment.

                Comment


                • #9
                  ya gotta earn it!!

                  but really, i don't pay attention to the e-rep stuff... i think it is always important to remember that some people know a lot on certain topics, others know a lot about other topics, and all of them are usually misinformed on the rest...
                  My OLD 2001 Mitsubishi Eclipse GT:
                  "The Project That Never Ended, until it did"


                  next project? subaru brz
                  carpc undecided

                  Comment


                  • #10
                    If it's a really fat wire, it could run under the vehicle - but must be well protected, some use conduit or garden hose etc - but NEVER without a fuse!!!

                    1800W (+700W) suggests a 250A fuse (divide by 10 rule), but that assumes an RMS rating.
                    If it is 1800W RMS, its own fuses will exceed 150A.



                    Originally posted by soundman98 View Post
                    you always fuse for the end-load.... (this way any substantial draw will blow the fuse and protect the wire).
                    [I added the (parentheses).]

                    I too want to support Soundman's advice. Too many follow the "fuse for the wire" doctrine.

                    Sure, the fuse size cannot exceed the capability of the downstream cable. (Otherwise the cable will fuse instead of the fuse, hence a likely fire etc.)
                    But that does NOT mean it cannot be smaller.


                    I too often do as soundman98 and use much heavier wire/cable than is required. (Why? Less voltage drop. Future expansion.)
                    But then I will fuse for the load - especially if using 400A cable for a 10A load (compare the fuse or circuit breaker prices and see. (And not that reducing cable for a fuse seems normal or easy, but it is a valid practice.)

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                    • #11
                      Thanks for all the help guys, after getting a new battery it all works fine. It turns out that the Sub I bought came with all the necessary cables anyway, including an inline fuse.

                      Got an even bigger problem now though lol. How to connect a separate speaker amplifier to the sub+amp using only 1 set of RCA cables and 1 12v power supply cable.

                      Comment


                      • #12
                        the rca connections are easy-- as long as you have a stereo signal going into the amp. if one of the amps has "passthrough" audio connections, you can use those to feed both amps

                        ie: if your fullrange amp has this, but the sub amp doesn't, connect the signal from the pc to the input on the fullrange amp, and run the other rca's from the "passthrough" connection on the fullrange amp to the inputs on the sub amp.

                        the power wire is a little trickier.

                        what gauge wire do you have run? i assume you just used whatever came with the sub/amp kit? if so, it will probably be too small of a gauge, so you will need to re-run the wire with a larger, correctly sized wire(now do you see why i try to run larger wire then i first need?!? ). just add up the fuses on the amps, and check some wiring gauge charts for the correct wire run/size. the best way to do it is to run a larger, thick cable near to both amps, and then use a distribution block, and a smaller gauge wire off that to feed the amps. the ground just needs to be at least as large as the power wire going into each amp.

                        like these charts:

                        My OLD 2001 Mitsubishi Eclipse GT:
                        "The Project That Never Ended, until it did"


                        next project? subaru brz
                        carpc undecided

                        Comment

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