80amp fuse popped
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This is a discussion on 80amp fuse popped within the Interior Mods forums, part of the Tech & Modifying & General Repairs category; can someone please remind me what the math equasion (*sp) is for how to determine what size fuse i actually ...

  1. #1
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    80amp fuse popped

    can someone please remind me what the math equasion (*sp) is for how to determine what size fuse i actually need. i have a 1000w amp and a 4 gauge wire suppling it.

    someone please help i need a fuse so i can have my system going.
    06' STI - blue on silver
    *stage 2 via cobb TBE & AP / perrin turbo inlet
    *perrin LW crank pully / SPT intake
    *kartboy pitch stop
    **kenwood dvd #DDX6019
    **JL 1000/1v2 amp / JL W7 12"

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  3. #2
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    well, here is what i have... all JL amps also, (2) 250w x 1 mono blocks and (1) 400w x 4 amp and i have a 100amp stinger circuit breaker.

    IMO the circuit breaker is the way to go. a lil bit more money, but worth it.

    hope that helps

  4. #3
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    Quote Originally Posted by legend99 View Post
    can someone please remind me what the math equasion (*sp) is for how to determine what size fuse i actually need. i have a 1000w amp and a 4 gauge wire suppling it.

    someone please help i need a fuse so i can have my system going.
    The way to calculate the fuse rating is as follows:

    You need to calculate how much current the amp will draw. Look at the RMS rating. (Not peak current. RMS)

    This needs to be divided by the efficiency of the amp. (This takes into account how much of the amp's draw is being converted into heat). For example, an class-D amp that's 80% efficient, will require 1000W of input current to produce 800W of output. The rest becomes heat. If you divide 800 / 0.80 (RMS / Efficiency) you obtain the input wattage (1000W)

    Say for example, in your case, your amp has an RMS rating of 400W into 4Ohms at 14.4V. 75% is usually a good estimate for the efficiency of a class D amp.

    So for your amp, input wattage would be: 400W / 0.75 = 533W (Input)

    Next, you calculate current for a certain voltage (By Ohms law current = power/voltage)

    so 533W / 14.4V = 37 A
    So your fuse would need to protect you against a 37 A draw (40 A is the closest commercial fuse size). The number might change a bit depending on what the actual efficiency is. I just ballparked 75%, assuming it's a class D (Monoblock). For a class AB amp, figure 60% efficiency.

    Source: Current and power article series.

    Hope that helps!

  5. #4
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    You should go for a circuit breaker 130-140 amps. and your good to go.

  6. #5
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    aight sounds good i think i gonna go with a 140 breaker, shouldnt have to worry then.

    but now i got that figured out, im think of doing a CAP just so i have steady voltage at the amp at all times and it wont surge from a power loss.how can i determine what size CAP to get?
    06' STI - blue on silver
    *stage 2 via cobb TBE & AP / perrin turbo inlet
    *perrin LW crank pully / SPT intake
    *kartboy pitch stop
    **kenwood dvd #DDX6019
    **JL 1000/1v2 amp / JL W7 12"

  7. #6
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    [QUOTE=legend99;2225045]aight sounds good i think i gonna go with a 140 breaker, shouldnt have to worry then.
    /QUOTE]

    You are making a big mistake, that could end up being VERY costly for you.

    What wire gauge are you running to the trunk?

    AWG 4

    Did you know that AWG 4 is only rated to 135 Amps???

    If the circuit shorts, the wire will get VERY hot. The insulation can melt before the breaker stops the flow of current, causing a fire in your car.

    Your 80 Amp fuse popped, because your amp can draw close to 100 Amps at maximum power. (Did you follow the formula that I posted???).

    Do yourself a favor and get an ANL 100 Amp fuse. If you have an accident, you will burn down the car.
    Last edited by Gamma; 03-07-2008 at 04:30 PM.

  8. #7
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    hum i just learned something i didnt know that a 4ga wire was only rated at 135-140.now that i know that i will back things down a bit.i cant seem to find a 100A fuse locally, so thats why i was going to go with the 140CB just b/c i can find those easy.

    how would a 100A circuit breaker do? i have found some on line but still none locally.i hate to keep buying fuses they get expensive, i got another 80 just b/c that all i can find a the time and to get me back going until i find exactly what i need.
    06' STI - blue on silver
    *stage 2 via cobb TBE & AP / perrin turbo inlet
    *perrin LW crank pully / SPT intake
    *kartboy pitch stop
    **kenwood dvd #DDX6019
    **JL 1000/1v2 amp / JL W7 12"

  9. #8
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    Yeah, 100A protection will be ok.
    You just have to do a bit of research before messing with a system. Not saying you can't do it, just saying that you have to do your homework first. (Especially when it comes to the electrical system...)

    If you get a 100Amp fuse or breaker, it shouldn't keep burning out, as the amp will not exceed it's rating. You can use the 80A in the meantime, just don't turn your amp all the way up, and you'll be ok.

    Quote Originally Posted by legend99 View Post
    hum i just learned something i didnt know that a 4ga wire was only rated at 135-140.now that i know that i will back things down a bit.i cant seem to find a 100A fuse locally, so thats why i was going to go with the 140CB just b/c i can find those easy.

    how would a 100A circuit breaker do? i have found some on line but still none locally.i hate to keep buying fuses they get expensive, i got another 80 just b/c that all i can find a the time and to get me back going until i find exactly what i need.

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