Enlighten me plz

[Flex68 10+ year member]

Aksing for a "mathematical" explanation before fusing is kinda like telling your homeowner's insurance agent you ain't buying any effing insurance until he/she shares all his/her vast insiders insurance knowledge with you first, gives you all the stats on how many houses burn down or get hit with wind damage in your area, etc.

Good remarks in the last 3 or 4 posts for you....dunno why you'd want to have more than what has already been offered, but I'll toss this in:

1) Fusing is just like insurance;

2) Forget what you're saying about 270 amps, 500 amps, etc....if you end up with that unforeseen dead-short-to-ground, the batt's are sure as hail gunna send way more current than this, which likely results in a lot more worries than a couple cheap fuses.

Fuq the math, do the work

 

[MECHMAN 10+ year member]

Because 270 amps is still enough to do alot of damage... I dont get why you think only 500 amps needs to be fused? tiny little 1 amp things get fused all the time

It's not the 270a of the alternator, think about the amperage discharge from 3 batteries if one of those 1/0 cables grounds. Bad stuff happens. The cable can weld to the metal, then it's total meltdown and possibly vehicle fire.

It has nothing to do with how much current you will be pulling through the wire! If you have two batteries connected together and the wire gets a cut or something and touches metal, its going to cause a fireHaving a fuse in line will help prevent this because the fuse will blow if that happens. You're complicating something that is so simple...lol

Think about safety in a crash, metal deforms, things short out, fire happens. If you can't get out of the vehicle because of a crash you don't want to be stuck in it with those batteries discharging through a shorted cable.

Lol if the wire gets cut, where I have ran then the wire, the that will be the least of my worries. Everything's grommeted and above the for I've the vehicle. Not to mention the transfer case, frame, ect... So the wires being cut are the least of my worries

There is no mathematical reason. There is no "technical" reason. It IS NOT NECESSARY!!!!. We do it for piece of mind IN CASE something happens. Say one of our batteries fails its possible it causes a short in which case it can pull ALL available current form the front cell which can be well over the amperage the wire is rated for. If this happens (not saying it will) the wire will get hot, melt and catch on fire. It is possible your vehicle will go with it. If you fuse you will prevent the wire from melting etc...
Your alternator is not putting that much power through it, your correct but its not for that reason. The ONE and ONLY reason to fuse is to protect yourself or car in case of a dead short. It will also serve as a second layer of protection to your equipment because a surge of power like that will most certainly smoke your stuff if its own fuses dont blow or there isnt any internal.

SOOOO is it necessary? Nope, but it is most certainly recommended.

Hope this helps ya //content.invisioncic.com/y282845/emoticons/wink.gif.608e3ea05f1a9f98611af0861652f8fb.gif

This is sound advice.

Heres the truth. If you get in a wreck, or if a wire gets pinched on a hot day when that grommet is nice and soft, the power wire will short to the body. It happens. You may think it can't, but you also don't know what a dead short is so you need to admit that you don't know everything right there and just say "it can happen". When power and ground touch, your batterys terminals are shorted together. This means it has 0 or nearly 0 resistance between the two terminals. It will dump infinite current out at this point until it dies. You cannot shut a batter off like you can an alternator. For this reason we fuse, because while that battery is dumping everything it can into the wire, the wire has to drop all of the voltage. This causes it to become red hot. It will ignite carpet or anything it touches, or heat other metal it is touching so that IT ignites something flammable it is touching. If you were to get in a wreck, you'd want fuses so the car didn't ignite while you were trying to get out. Just because you went with small batts doesn't mean they can't dump a ton of current under a short. You want math? Look up the current ratings for your batts under a short. You'll see how high it is and understand your power wire can't handle it.

This is also good.

It is not your alt. If the wire shorts it will pull all you juice from the battery - turning it into heat and burning up your ride! (or at least ruining all your batteries.)

Correct.

Many competition vehicles don't run fuses, but I do not recommend this on any vehicle to protect the occupants and the vehicle itself.

It also eases disconnecting safely if you need to work on the electrical system.

 

[Mitch86 5,000+ posts]

Maybe he will actually listen to MECHMAN... lol

He wants a mathematical formula.. the only one I could come up with was dumbass + no fuses + short = possible fiery death.

 

[SourDeez 10+ year member]

It's not the 270a of the alternator, think about the amperage discharge from 3 batteries if one of those 1/0 cables grounds. Bad stuff happens. The cable can weld to the metal, then it's total meltdown and possibly vehicle fire.

I was just trying to say.. doesnt matter where your main source of power is.. any current should be fused in a vehicle..

 

[Falcons 5,000+ posts]

your amps are pulling 200 more amps than two runs of cca is rated for, you may want to fuse everything. lol

 

[Exist_ential 10+ year member]

you also need to take into consideration mechanical\manufacturing defects in your equipment. "technically" your vehicle "could" just be sitting there doing nothing and burst into flames. are you positive there are no defects in the wires you have run from one place to another, i seriously doubt it especially with the amount of wire i assume you have run everywhere.

i don't NEED circuit breakers in my house but you bet your a$s i have them. in fact i have 3 different breaker boxes in different locations in my house.

 

[sexy 10+ year member]

All right officer but can you tell me the mathematical reason why I cant go 70mph in a school zone. //content.invisioncic.com/y282845/emoticons/rolleyes.gif.c1fef805e9d1464d377451cd5bc18bfb.gif

 

[hispls 5,000+ posts]

Yea I know on the safe side it's good but I'm not seeing where the back could pull >500+ amps of power from if my alt is 270 and my batt is 75 ah but I have a basic understanding of electronics

Tl/dr Point is if the insulation fails in the cable and you have a catastrophic short fuse pops and you don't burn your car down.

IMO fuses are for pvssies but fusing within 18" of batteries going each way is generally accepted safety precaution.

 

[Tom760t]

Hi

it doesn't matter how many amps your alternator is producing it is hooked i parallel with your start battery? correct? if so the cca of your start battery combined with the output of your alt is going to be far greater than 500a. therefore if your setup requires more than 500a for any reason whether it be amplifier current draw or a short circuit this will protect your system.

IF there is a short circuit in the system it will Max out the alternator and draw 'short circuit' current from your front battery which WILL be probably in the area of 800A-1000A

hope this helps.

Tom

 

[Flex68 10+ year member]

Hiit doesn't matter how many amps your alternator is producing it is hooked i parallel with your start battery? correct? if so the cca of your start battery combined with the output of your alt is going to be far greater than 500a. therefore if your setup requires more than 500a for any reason whether it be amplifier current draw or a short circuit this will protect your system.

IF there is a short circuit in the system it will Max out the alternator and draw 'short circuit' current from your front battery which WILL be probably in the area of 800A-1000A

hope this helps.

Tom

I don't even understand half of what he wrote, but now you've also got the opinion from Australia, OP.

lmfao

 

[Morals 10+ year member]

Here is your math

1+1= your a freaking idiot.