Big 3 upgrade for 2021 Ford F150....Fuse or not to fuse?

[MikeyD812]

Hello all!

I going to be doing the Big 3 upgrade to my truck this coming weekend. I have 2/0 wire skyhigh wire OFC to run from alternator to the battery. Since this is being connected to the battery does it or should it have a fuse? I have a mechman 370 to install along with an XS power AGM to go under the hood.

What is your opinion?

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[HardofWhoring]

Yes. Your factory alt to batt wire, should be a 'fusable link' (or at least it is on my vehicle, but were different makes and many years apart). You may not see it fused, but a fusable link will burn through the wire if it exceeds its limits, but it doesn't burn through the sheath/casing so that it won't create a hot circuit.

Fuses are added to create a weak point in the circuit where it can be protected, and fixed easily. Fuses need to be capable of handling more than what the alt (/load) is, but less than the capability of the wire. You are adding it in because if your alt goes bad and overcharges it will burn through that wire.

If you fuse it and it burns through, then you just don't charge your battery. You have also protected where it will burn through so there is no risk of that wire flopping around and contacting something that can burn your truck down. With that size of amperage, it would fuse together quick, melt together so fast, you might be sitting in the cab, and not be able to save the vehicle. If you add a fuse, and your alt goes nuts, then your battery drains slowly until you replace the fuse and fix the alt.

 

[MikeyD812]

Since my alt is a 370 would a 400 amp fuse be suffecient you think?

 

[HardofWhoring]

That's what I would do, even 500 would still be plenty safe with a short 2/0. If its your first time, you can always test it out. Turn your AC on, your stereo on full, all lights and make sure you are draining your electrical as much as you can, and cruising at an RPM high enough where you are charging at full rpm needed. Give it a go for 30 minutes or so. Then check it out if you don't see the battery dropping. That or throw a couple 400 in the glove box, or even a 500 and you wouldn't even have to turn the stereo off to get you back going.

Anyone who sells a quality 370 alt should be able to tell you exact amperage to expect. I'll bet it's within 1%.

 

[MikeyD812]

So for sure going to fuse this. I have my main fuse block going to the back with one slot open. Could i use this or will this need a seperate fuse block? I have attached a crude drawing lol. IS this a good idea or?

 

[spokey9]

Decide on your fuse size based on your wire's carry capacity...that way the fuse will pop before the wire fails...that said I didn't fuse between my alt and battery...

 

[HardofWhoring]

I wouldn't run from the alt to the fuse block, I would run it to the battery. There are going to be times where your stereo is off. Not sure where you plan on mounting it, but to the battery should be a much shorter and easier run.

Whether or not you want to also run it to the distribution block, I wouldn't. I can't give you a very knowledgeable answer as to why, other than what I THINK is unless that is a fuse block rated for all that you might cause problems, and you are causing resistance going through the block and then another wire before it gets to the battery. You might be creating a voltage issue. AGAIN JUST A GUESS, hopefully someone else knows.

I would look into that fuse block or contact the manufacturer if you need to, but that seems like a lot of amperage for one fuse block. Is that the knuconceptz block? Unless you have a solid metal piece of machined aluminum or copper, you aren't going to need two runs of 2/0 OFC from battery to fuse block. One run should far exceed the capabilities of the block.

 

[Firewalker]

Decide on your fuse size based on your wire's carry capacity...that way the fuse will pop before the wire fails...that said I didn't fuse between my alt and battery...

Same here been doing systems for 30+ years now and not once have I fused the wire from the alternator to the battery when doing the big 3 and never had one fail. Then again the quality of the wire matters also. I wish my buddy wasn't retired and still working at the factory he did in Kankakee, IL. All they made there was pure copper wiring from the stuff we all use to the stuff the electric company uses to the government. I used to get 100 foot rolls of it so cheap. Most I paid was something like 15 bucks for a roll and it should have been 75-100. All because they had over run of it so they had to clear it out to people they knew. If he was still there still I would have stocked up again when I go back down to Illinois in August. I still remember one time I bought was icr if it was a 500ft or 600ft roll of it and sold a bunch of it, made a like 700-800 dollars on that purchase and still covered my costs and left me an extra 50 feet on top of the 50 feet I used in the car and boat.

 

[audiobaun 5,000+ posts]

Same here been doing systems for 30+ years now and not once have I fused the wire from the alternator to the battery when doing the big 3 and never had one fail. Then again the quality of the wire matters also. I wish my buddy wasn't retired and still working at the factory he did in Kankakee, IL. All they made there was pure copper wiring from the stuff we all use to the stuff the electric company uses to the government. I used to get 100 foot rolls of it so cheap. Most I paid was something like 15 bucks for a roll and it should have been 75-100. All because they had over run of it so they had to clear it out to people they knew. If he was still there still I would have stocked up again when I go back down to Illinois in August. I still remember one time I bought was icr if it was a 500ft or 600ft roll of it and sold a bunch of it, made a like 700-800 dollars on that purchase and still covered my costs and left me an extra 50 feet on top of the 50 feet I used in the car and boat.

Same here. Ive never Fused between the Alt and battery for over 15 years on multiple vehicles. I have never had an issue once. Most stock Alternator wiring Ive seen over the years ranged from 8 ga to 4 ga, and adding to the alternator and not removing the existing with 0-1/0ga to the battery, Ive never had any problems. Fuse from Battery to amp supply /additions is necessary for my use, and Fused to sources of additions.

 

[MikeyD812]

I am running a 3 way SMD fuse block in 2 locations. I have one next to the battery and one in the back on my amp board. Eventually i plan on adding some TITAN 8 batteries to the back.
Here is a link to the ones i have.
https://wccaraudio.com/smd-triple-anl-fuse-block/

I do not see a maximum amperage listed on these fuse blocks.

On my truck (2021 Ford f150) the battery is on the passenger side and the alternator is on the driver side down low. This will end up being about a 10 foot run. That is what scares me about not having it fused. That long of a run attached straight to the battery or batteries in my case eventually.

 

[MikeyD812]

Decide on your fuse size based on your wire's carry capacity...that way the fuse will pop before the wire fails...that said I didn't fuse between my alt and battery...

I have sky high 2/0 wire. From what i have read it is around 370 amps? Hard to find a more accurate number or hard for me to find anyway.

 

[spokey9]

The carry capacity changes based on the length...but honestly you should be fine without a fuse on your alt to battery...

I have sky high 2/0 wire. From what i have read it is around 370 amps? Hard to find a more accurate number or hard for me to find anyway.

 

[metalheadjoe 10+ year member]

The carry capacity changes based on the length...but honestly you should be fine without a fuse on your alt to battery...

Resistance and voltage drop change based on length.

 

[Deiimos]

While I do always promote using fuses, and still do for the main run(s), I also skip the short length alt to battery fuse on my own vehicles. I do use loom and make sure it isn’t rubbing on anything, and doesn't hurt to inspect it periodically.

Technically, the 2/0 from alt to battery, should be fused right by the battery with a 400A fuse and is a good idea to do so.