megafuse size for 4g explorer

[7576]

Hey guys, how large does this mega fuse need to be for the explorer serp 4g alternator. The big fuse that is between the battery and alternator. Thanks

 

[brianstrange]

I try to run at least 60 amps, and up to 80% of the alternator output (depends on alternator) Do you have a lot of electronics in the rig? Cooling fan, winch? It's important to know how much you draw. IIRC, the 4G is a 130 amp, so 100 amp would be a good general rule of thumb. That said, I would use a 4AWG wire off the alternator.

 

[7576]

i do have a winch and a fan. Shouldnt the amp of the fuse be larger than the output of the alternator? If smaller, would it not blow all the time?

 

[phred]

I run a 175amp mega fuse with a 160 amp alternator. At full load, winching lights on and cooling fans running the alt is putting out near full power. Any fuse less than full load will not last. At least that's my understanding of electricity.

 

[fungus]

I run a 175A with my stock 130A 4G alt.

 

[badmuttstang]

From everything I have read and been told by my teachers you want to go about 10-15% larger than the given amperage or load.

 

[surfer-b]

Yes you need to go larger, if you don't you will be replacing fuses often, a 150~175 amp fuse should be good if you are using a winch and other acc's

 

[Broncobowsher]

You need a larger fuse then the possible output of the alternator. If it is smaller, it will blow at full load. When an alternator is at full output and the fuse pops, the power goes somewhere and often blows the diode pack. Now you have a bad fuse and a bad alternator. This is often when people get confused and think the alternator failed and the fuse saved a short. In reality the blowing fuse is what took out the alternator.

You can run an undersized fuse for years. So long as the battery does not get a low enough charge for the alternator to go to full output. But do a winch pull or two with the engine off. Maybe have a little engine issue and run the battery a little low with the starter. Now the alternaotr can go full load, blow the fuse, and you are dead again.

 

[Bronco_69]

does ford even put a fuse in line with them?

you would really need 2 fuses. one at the alternator and one at the battery to do any real good.

i have never fused one but i do take care and run the wiring away from heat and in a protective cover.

 

[brianstrange]

I have never blown an alternator fuse, and would never use a larger fuse than the alt is rated for. That's it's purpose, to blow when it exceeds the limits of the circuit, or a major circuit fault. Remember, people are welding with these alternators now. They are very powerful, and need to be treated just like a battery while the engine is running. Also, it can take up to twice the amp rating in draw for the fuse to blow. Especially larger fuse types. In the alternator's case, you need to factor two things, wire size, and circuit draw in amps. The output of the alternator should never be exceeded, but does not need to be matched. It's best to size the fuse and feed wire based on your power requirements, and the fuse should never exceed the rating of the feed wire or alternator (whichever is less) between your battery and alt. This fuse is also protecting the battery if a major circuit grounding alt malfunction occurs.

Alternators do not Push amperage, they can deliver it upon request, but just like a 600 CCA battery, it needs to be drawn. Have you ever seen a 600 amp battery be the cause for your 5 amp fuse to your dash lights fail?

 

[brianstrange]

does ford even put a fuse in line with them?

you would really need 2 fuses. one at the alternator and one at the battery to do any real good.

i have never fused one but i do take care and run the wiring away from heat and in a protective cover.

Most alternators have fuse links in the harness to the battery (or fuses between the two), on the alternator side. It protects the alt, and the battery should the alt fail and cause it to go to ground. The fuse links to the chassis wiring, protect the chassis wiring in the event of a short in that area. They serve two different functions.

Also, yes you can blow a diode pack if the alt fuse blows. Rating it at 80% of your alt output is a safe rule of thumb. On a 100 amp alt, an 80 amp fuse will blow in about 1 second with between a 100 to 160 amp draw (depends on the fuse type). If this blows, and your max draw is 80 amps, there was another issue. The battery is the electrical fuel tank of the system, and will help buffer loads when using a winch etc... And a dead battery alone will not draw 160 amps from an alternator. Example: Ever jump start a completely dead car with a 500+ CCA battery and an 80 amp alt? Jump starting isn't the best thing to do to your car, but it's always done without an issue.