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Thread: Power Cable Wiring

  1. #1
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    Power Cable Wiring

    Hey guys,

    Just wondering, today I bought 8 gauge cable to wire in my Carnetix P1900. I bought a 5AG fuse holder to go inline with the 8 gauge cable. The only problem is that they lowest rated fuse I can get for the 5AG fuse holder is 20Amp. Would this 20Amp fuse be safe to use with a P1900? The wiring diagram says 15Amp.

    If not, are there any places where I can buy 5AG 15Amp fuses from in Australia, or worst case scenario, Internationally?

    Thanks,
    Matt

  2. #2
    Neither darque nor pervert DarquePervert's Avatar
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    You need to understand the purpose of the fuse. The fuse is will melt if there is a short that generates more current than the rating of the fuse. That will keep the wire and electrical components behind the fuse from receiving a level of current that would damage them. In the case of the wire, it will prevent the wire from heating up and potentially causing a fire.

    Knowing that...
    You want to have a fuse that is rated slightly above the normal current draw of the electronics behind it. If your vehicle PC draws 12a (as an example), you'll want a 15A fuse. If your vehicle PC draws 18A, you're young to want a 20A fuse.
    Chances are that the 20A fuse will be fine, but you really should measure the current draw form the PC to be certain.
    Have you looked in the FAQ yet?
    How about the Wiki?



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  3. #3
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    So a 20A should be fine but 15A would be ultimate?

    I have heard that fuses are only there to protect the car in the end?

    Also, the P1900 has was looks like a 15W fuse on its layout diagram near the power input side? does that fuse function for the power input side or the power output side?

  4. #4
    Neither darque nor pervert DarquePervert's Avatar
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    Quote Originally Posted by krobra View Post
    So a 20A should be fine but 15A would be ultimate?
    You didn't read what I said.
    You need to find a fuse that is slightly above the power draw for your equipment. I don't know what your equipment is, so I can't even begin to estimate the current draw. I suggest procuring a digital multimeter and measuring the current draw to determine the right fuse for you.

    I have heard that fuses are only there to protect the car in the end?
    Sort of.
    A fuse is in place to prevent excessive current from flowing into the wire and electronic components that are behind it in the event of a short circuit.
    The electronics need to be protected because the excessive current can damage or destroy the components.
    The wire needs to be protexted because excessive current can heat the wire, causing the insulation to melt and possibly start a fire.

    While the purpose of the fuse isn't to protect the car, per se, the car is protected indirectly as a result.

    Also, the P1900 has was looks like a 15W fuse on its layout diagram near the power input side? does that fuse function for the power input side or the power output side?
    That protects the power supply from input voltage that is more than the rating of the fuse. In other words, if you send more than 15A to the PSU, the fuse will pop, cutting the circuit and preventing damage to your PSU.
    In regards to your first question...
    If the Carnetix has a 15A fuse onboard, then a 15A fuse inline (within 18 inches of the battery) would be appropriate.
    Have you looked in the FAQ yet?
    How about the Wiki?



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  5. #5
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    Ok, thanks. When I get it all in I will get a multi-meter and measure the current.

    In my last post I meant 15A fuse, not a 15W fuse sorry. But let me get something else straight. The PSU is the only thing that is being connected to this cable coming from the battery. Therefore, is it safe to say that the 15A fuse on the P1900 will adaquately protect itself and components under it?

  6. #6
    Neither darque nor pervert DarquePervert's Avatar
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    Yes, but it will not protect the wire in case of a short circuit.
    If there's a short, the wire could overheat and cause a fire. Because of this, you want to fuse the wire near the battery, as well.
    Have you looked in the FAQ yet?
    How about the Wiki?



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  7. #7
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    By short, you mean the power cable being somehow shorted so the power goes straight back into the battery, thus the wire heating up alot, and creating a possibly fire risk? If this was the case, then it really would not matter if it was a 15A or 20A fuse in line to prevent this from happening? Or is my logic totally incorrect lol?

    Thanks for the advice so far.

  8. #8
    Neither darque nor pervert DarquePervert's Avatar
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    Quote Originally Posted by krobra View Post
    By short, you mean the power cable being somehow shorted so the power goes straight back into the battery, thus the wire heating up alot, and creating a possibly fire risk? If this was the case, then it really would not matter if it was a 15A or 20A fuse in line to prevent this from happening? Or is my logic totally incorrect lol?
    You are correct about the definition of "short".
    Realistically, a 20A fuse on the power line would be sufficient, I'd think. If the current is over 20A, then one or both fuses may pop. If the current is between 15A & 20A, then only the one on the PSU will pop. The 8AWG wire should be able to hadle a 20A load with no problem, so any more than that, you'll want the wire protected.
    Have you looked in the FAQ yet?
    How about the Wiki?



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