# big3, adding a fuse to the alt-batt 4ga wire, question



## SleekB (Jun 10, 2010)

jbl gto7001
alpine type r 15'

bought a 1000watt amp kit which included 4 gauge wires and a 100A fuse for $100
then bought 4 gauge wires for the big3 upgrade $20

and just bought 150A fuse with a 'CMWFH Mini Wafer Fuse Holder' that look like this:








for $30 both

i already spent $150 on wires and fuses. fml.
i hope that the 150A fuse is good for the alt-batt connection (with a 4ga wire)

ps. the dealer at the store said that i dont even need a fuse for my alt-batt connection, i told him that you guys recommended getting a fuse and he said thats fine.. but he said that my system will be going through a tiny metal fuse instead of flowing free in a 4ga wire.
i told him ill get it just in case and since i trust you guys more.

is there a factory fuse currently in my 2010 civic lx? the alt-batt wire is tiny and im not sure if there is a fuse anywhere

i got my dad explaining to me some things and here is what he told me,
W = U*I
700watt = 12I
I = 58.3A (+20% just in case) = 70A
since stores dont sell 60A, 61A, 62A... they sell 60A, 80A, 100A (approximately) so from what i understand i got a bit more than needed but unless i crank the volume all the way up and leave it there for an hour, shouldnt be a problem.
as for the alternator to battery, my dad said that he saw that the factory fuse is 100A (but he's not too sure), and if i put a 4ga wire with 150A fuse in parallel to that factor wire (with the factory fuse), ill pretty much cancel out the factory wire and the current will go through the new wire. as he said, if the can is designed for 100A fuse, and i put 150A fuse, and suddenly there is a jump in voltage lets say 110A goes through, then the alternator will get f-ed. and from what i understood is that 100A would melt down and stop the current flow if those 110A suddenly come by..
hope that makes sense :S

so pretty much what he is saying is that he doesnt see a reason for doing this upgrade and thinks that it even puts the car in risk if i put 150A fuse..
he is an electrical engineer so i obviously trust him, but on the other hand, so many people do it and you guys tell me to do so what should i do.. could someone explain to me the deal with this whole thing?


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## rekd0514 (Sep 24, 2006)

Well, I have heard you don't need the fuse as well. I did it anyways because if you have both the stock alt positive wiring and the new 4 AWG in place, the electricity should follow the path of least resistance. That would be the 4 AWG wire unless the stock wire is the same size and in that case you probably don't need to upgrade it. I think it's just safer in case the wire were to get pinched or the amperage exceeds what the 4 AWG is capable of handling.


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## kyheng (Jan 31, 2007)

Make it this way : If there's anyone dare to say you no need a fuse from battery till the amp, you make a claim letter that when your car got burnt down because of this power cable and he will pay all the cost incured, ask him to sign for it..... If he dare to sign then you no need add a fuse.

On he calculations side, your dad is not 100% right as he missed out the amp gain and your loudest listening volume. When put this in to the calculations, you won't need 70A, it will be lesser than that. But for the main fuse, just stick with 100 or 150A. There's nothing wrong with it as when there's any short, it will blow anyway.

Lastly, your original cables no need to remove, just add your new cables on top of it.


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## jstutzman (Aug 11, 2009)

Are you talking about a fuse from the Alt to the battery? Maybe i read that wrong in the original post. I have never seen one done that way and personally dont see a need for it. All systems should have a fuse pretty close to the battery on the wire that feeds the amp. If you dont have one, you could end up with a fire hazzard. Remember that any calculation that you use, you have to account for amplifier efficency.


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