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Thread: Fuse size by battery

  1. #1
    Variable Bitrate TeamRSX's Avatar
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    Question Fuse size by battery

    I currently have my carputer up and running, but i am debatiing my power cable size and fuse sizes for my main power next to the battery.

    I have done some reading and testing and just want to make sure everything is correct.

    Here is the wattage for my system which is just a ballpark:

    ATX Motherboard - 25W
    Keyboard + Mouse - includedW
    CPU Fan - includedW
    AMD Athlon 64 3400+ - 68W
    sata Hard Drive - 25W
    1.5GB DDR RAM (3 Sticks) - 30W
    External DVD Rom (slim usb)- 5W
    Lilliput Monitor - <10W
    GPS Receiver - 5W
    7-Port Powered Hub - 17.5w
    AMP = 300w

    watts = 485.5w
    amps=watts/volts= 485.5/13.6=35.6 AMPS

    So, right now i have my main power wire from the battery as 8awg and using a 60a fuse. The power wire then runs into my fused pwr distro block which i have 20a fuse for my dsatx and 50a fuse for my amp(on my amp is has 2 25a fuses, so just added them up and put 50a in the distro block, same thing with my dsatx, its has a 20a on the hardware) then both those power wires run to the device again using 8awg wire.

    Since the max currect for 8awg wire is 50a, the power wire running for my dsatx and amp should be fine. since they are under the max current.

    My question is my main power by my battery. I am currently running a 60a fuse on 8awg wire. Now the fuse is not blowing becasue i am not exceeding the amperage on that power line since from my calculation above the computer is only drawing 35.6amp roughly.

    I was originally going to goto 4awg wire and put a 80a fuse by my battery becasue i though the fuse by the battery had to be the same current as all my devices. Since i have a 20a and 50a fuse in my distro block i though i had to add them up and us at least that. So i was going to put in a 80a fuse by my battery and use 4awg wire.

    I dont think i need to do that as the fuse is rated according to the size wire.

    Since i calculated the amperage for my system at roughly 37amps i was thinking just to keep my 8awg main power wire and put in a 50a fuse by my battery since i will never hit 60amps i think

    As i think it would be more safe this way then jsut putting a large fuse that will never blow.

    Am i on the right track? Just want to make sure i have my power wires and fuses correct.

  2. #2
    Neither darque nor pervert DarquePervert's Avatar
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    Yeah, you're on the right track.

    Understand that the fuses are to protect the wire from too much current. If too much current flows down the wire, the insulation could melt and cause a short and possibly a fire and all sorts of nastiness.

    You've already figured out that the fuse at the battery should be between the max rating of the cable and the total power draw of all devices on the cable.

    I'd think your 60A fuse should be fine, even with the thicker wire at the battery. If the fuse blows, replace it with an 80A fuse. I doubt it will be an issue, though.
    I use a 4AWG with a 100A fuse at the battery for the PC, a small inverter and two amps.
    Works like a charm and I don't fear a fire from a short-circuit.
    Have you looked in the FAQ yet?
    How about the Wiki?



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  3. #3
    Variable Bitrate TeamRSX's Avatar
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    Quote Originally Posted by DarquePervert View Post
    Yeah, you're on the right track.

    Understand that the fuses are to protect the wire from too much current. If too much current flows down the wire, the insulation could melt and cause a short and possibly a fire and all sorts of nastiness.

    You've already figured out that the fuse at the battery should be between the max rating of the cable and the total power draw of all devices on the cable.

    I'd think your 60A fuse should be fine, even with the thicker wire at the battery. If the fuse blows, replace it with an 80A fuse. I doubt it will be an issue, though.
    I use a 4AWG with a 100A fuse at the battery for the PC, a small inverter and two amps.
    Works like a charm and I don't fear a fire from a short-circuit.
    Ya, i think i will be ok with a 60a fuse. I would probably be ok with a 50a fuse, but i am eventually going to be putting in a mono amplifier for my subwoofer. Once i go that direction i will be using around 46a instead of 36a and my mono amplifier doesn't have as much watts as the amp in the car right now.

    So, i think i would be ok with using 8awg wire and a 50a fuse, but just to be on the safe side i will upgrade to 4awg and stick with my 60a fuse as you mentioned if i for some reason blow that than i can upgrade the fuse.

    I just dont like the idea right now that i have a fuse that is overrated for the wire (8awg 50a max and i'm running 60a). Even though the amount of amps will never exceed 50a according to my calculations its better to be safe. But in case i get more amps for some reason i want to be protected

  4. #4
    drk
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    Quote Originally Posted by TeamRSX View Post
    Ya, i think i will be ok with a 60a fuse. I would probably be ok with a 50a fuse, but i am eventually going to be putting in a mono amplifier for my subwoofer. Once i go that direction i will be using around 46a instead of 36a and my mono amplifier doesn't have as much watts as the amp in the car right now.

    So, i think i would be ok with using 8awg wire and a 50a fuse, but just to be on the safe side i will upgrade to 4awg and stick with my 60a fuse as you mentioned if i for some reason blow that than i can upgrade the fuse.

    I just dont like the idea right now that i have a fuse that is overrated for the wire (8awg 50a max and i'm running 60a). Even though the amount of amps will never exceed 50a according to my calculations its better to be safe. But in case i get more amps for some reason i want to be protected
    I would recommend upgrading that 8awg to at least 4awg when you add on that mono amplifier, just to make sure your equipment is getting the power it needs.

    Personally, I'd upgrade now, but that's just me. I absolutely refuse to run anything less than 4awg and prefer 1/0. Right now I'm running 2 4 gauge lines to just 2 amps. For my next install, I'll probably be doing 1/0 with a distribution block at the amp/PC rack. Overkill never hurts, especially when you tend to change/upgrade equipment as often as I do

    EDIT: And you should NEVER fuse above the max rating of the wire! According to your calculations, your equipment will never exceed 50A, but the fuse is not for the equipment draw, it's for if your equipment shorts out and you start drawing alot of current through the wire, melting the insulation, and starting your car on fire. Change that fuse to the max rating of the wire. You're probably safe now, but what if you get a small problem and starting drawing 58A?
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