2003 f150 5.4 v8

going to replace my alternator, what amp size should I buy? I dont have anytbing other than an aftermarket radio, but not subs or anything other than stock speakers. I see options ranging from 95 amps all the way to 200amps. I do live in a cold climate. Thanks

 

My 2001 5.4 has a 130 amp and that's what it came with stock.

 

Probably have to take those numbers with a grain of salt, but the stock 130 amp alternator will do anything you needed to do. Generally. ....Unless your battery is dead at same time .... Or you have the true 1500 watt RMS stereo cranked and headlights on.....or you're powering something very heavy duty...3000w inverter, etc

 

Check this guys other thread, we tried to tell him...a few of us new this was going to happen.

https://www.f150forum.com/f6/alternator-swap-580722/

 

What is wrong with a stock size alternator?
Your wiring loom is designed for a particular sized alternator
I had a 69 Camaro with a 37 amp alternator when I was 17
Right, put subs in it and a 75 amp alternator
Used to watch the amp gauge I put in there while listening to Tone Loc thump
Cooked the alternator harness going down the freeway one day
So, if you do up the amps, add a bigger charge wire from the alternator to the battery

 

You need to have something to draw amps too. Unless powering something unusual it makes no difference

My rich kid buddy in high school had $6000 of alpine stereo in his bronco in 1984, 15" sub, 2000 real watts. His battery went dead in short time driving down road with lights on. . Had to put in second battery, bigger alt. Thieves ripped it off one night under his carport ....right outside his parents bedroom window, yes had alarm...page alert back then.... The alarm paged you with a pager. We used to screw with him when we saw his truck parked somewhere ..we would bump it and set off the alarm, knowing he would get paged and come check on his truck .

 

This!

amperage is pulled not pushed. You can get a 10k amp alternator (not really) but if your electrical usage only requires 30 amps, you will only be puling 30 amps. The issue with adding too much power comes in when you have a dead short and an improperly fused line. That will cause a fire because it will pull 100% of the amperage avaiable until the circut is broken. As long as the proper wire is used and proper fusing is done, you can run as large of alternator as you like, if you want to spend more money than necessary. For some reason automakers don't fuse alternator positive wires the way all other fusing is done (with the fuse within a few inches of the power source).

on any vehicle, you will have a fuse on the line coming from the battery to the fuse box. Whatever the rating on that fuse is is the max amperage that can be pulled into that box. There will be some resistance so if we assume 90% efficiency in your line that will give you the highest alternator you will need for running anything that goes through the fuse box. So if the fuse is 100 amps, divide that by .9 and you get 111 amps. You won't need more than 111 amps coming from your alternator. Your fuse box can't pull more than that. Now if you add additional electronics that bypass the fuse box like an amplifier, that is when you need to start adding addtitional amperage.




Spent a lot of my early 20s heavily invested in car electronics. Here is a build thread for the two 15 set up in that picture.
https://www.hondaaccordforum.com/for...r-39855/page4/