Megafuse amperage with battery wire upgrade

Replacing all the battery wiring with 4awg wire, what amp megafuse do i need??

124 amp alt, audio system w/ approx. 900 watts...........thats pretty much the only high draw thing i'll have

i ordered the 100amp fuse......i was wondering if i should get the 125amp??

I usually suggest taking the "peak output" alternator rating, and going to the next higher. With a 124A alternator, a 125A will be just ducky (assuming you're replacing the OEM MAXI fuses or fusible link in the alternator output circuit.)

If you're doing accessory fusing, you'll want to take the listed current consumption of the device, and run that rating of fuse (if it's "on a notch,") or the very next higher one (if it's in between.) For instance, if you have a device listed for a 10A draw, then get a 10A fuse. If you have a device listed for a 6A draw, then use a 7.5A fuse (there are no 6A fuses in the ATO line, as I recall.)

Simple rules that have served me in good stead for more years than I'd care to admit to...

5-90

Oh - with what you're running, you're right about at the edge of 4AWG, as far as I'm concerned. Just so you know, in case you plan to upgrade again later. I do mains wiring in 1AWG, just to give me some room (1AWG is good for something like 350-400A, in short runs. 4AWG is, I think, good for something like 125-150A.)

5-90

I used a 180 amp mega fuse when I did my cable upgrade only because thats the only size the parts store had in stock and I have a 160 amp alt.I would feel more comfortable with a fuse rated at 160 amps,but so far so good.

If your alt truely puts out 124 amps I would go with a bigger mega fuse that is atleast 124 amps.So the answere is yes you should go with the 125amp fuse.

hth.

Looks like 5-90 beat me to it......

thanks for the replies

will i run into problems running the 100amp fuse??i kinda already ordered it, lol

Yea...if your alt tries to push 124 amps through a 100 amp fuse=burned fuse.Try it.the worst thing that could happen is a burned out fuse.

Fred85 said:

thanks for the replies

will i run into problems running the 100amp fuse??i kinda already ordered it, lol

Click to expand...

Maybe. The alterantor will only put out what the system "wants" at the time, so if you're not running everything, you should be fine. Since typical output will probably be less than 100A (you won't have everything electrical running at once, will you?) you should be fine.

However, if you have a winch, you'll probably be running full output during and for a little while after a pull, which WILL pop your fuse. I'd get a 125A before you go off-road, or maybe at 150A (since most alternator ratings are "nominal," and you can vary by 10% or so. I've got a "nominal" 150A Delco that has been tested at full output of 185A...)

5-90

What he said. The bottom line is that with a 100 amp fuse you will not ever be able to push more than 100 amps through the system. If you try the fuse will fry. So why did you waste time and money on a 124 amp alternator? You can't use its full ability. Might just as well have stuck with a 100 amp alternator (or a little less, actually).

See, that's why you really should get a 125 amp fuse.

well, i guess i messed up.......glad these things aren't terribly expensive

new question then since i have to order a new one, 125 or 150 amp?? seems like ya'll agree on the 125 amp, i doubt i'll ever add any other high current drawing accessory such as lights and i'll definately never have a winch either

figured i'd ask though.....

4 ga. wires for the short runs that you have ought to handle 150 amps just fine so I'd get the 150 amp fuse. On the other hand, with a 124 amp alternator you should--theoretically at least--never try to push more than 125 amps through the system so the 125 amp fuse would probably work fine, also.

The thing is this, most people look at wiring an fusing backwards. The "proper" way to go about it is to determine the amperage that you expect the circuit to carry. Then you choose wire sizes that will carry that amperage without overheating and with a minimal (or at least acceptable) level of voltage drop. Then you choose a fuse that will protect the wire. Yes, the fuse is really intended to protect the wire, because if you push too much amperage through an undersized wire it gets hot, overheats, and eventually catches on fire--not a good thing.