Help me with Batt. to Alt. wire upgrade!

So I have decided to upgrade the main charging wires underneath the hood to solve the voltage drop issues I keep getting. I need to do the alt. to battery, battery to chassis ground, and block to chassis ground. I've got 1/0 gauge to do it with, and a bar style 175 amp fuse. I already read through the link in the Tech/ FAQ sticky, and I pretty much understand it, but I still need a couple of questions answered.

1. Which wire is the output wire on the alternator that I need to piggy back over? Theres three or four connections on the back of the alt. So which one do I need to piggy back over, A, B, or C?


2. Also, should I A.) go straight from the alternator to the battery with the bar fuse or B.) should I go from the alt. to the existing stud on the front of the PDC with the bar fuse, then from there go to the battery like the factory setup?

1) The screwpost with the large shield around it ("A" in your picture, I believe) is the output post. The other two are regulator inputs from the PCM.

2) It does not matter - electrically speaking - where the fuze output goes. Going to the battery post or the PDC post is electrically the same, as long as there's a cable directly between them as well. So, run the fuze lead to the PDC or the battery + terminal, and it will make no odds.

You should not need to "piggyback" the alternator output lead - it's simplest just to pull the damn thing out once you've got it replaced (so you don't have loose wires running around.) 1/0 cable is HUGE overkill - I selected 1 gage for wiring that I sell as a compromise between pure overkill and shipping weight. I use 1 gage welding cable, which offers greater flexibility and higher current-carrying capacity (both due to the finer strands used.)

Have you already got your crimper?

As far as the fuze goes, 175A may be too high - unless your running a 140-170A output alternator. If you're in the 100-140 range, you can use a 150A fuze, and if you're under 90A, then a 100 will be just fine. Remember that fuzes should be "upsized" just a touch - or you run the risk of popping them all the time - but not too much, or it won't be able to do its job. For something like this, I'd select the NEXT HIGHER fuze rating from max alternator output. If I'm right "on the line," then it's the next one up (for 100A output, go with a 110-125A fuze - whatever's next higher.)

Make sure your mains grounds will be clean - including the ground strap between the engine and the firewall. Clean a spot about the size of a postage stamp right down to bare metal, attach the ground, and use Ox-Gard to coat the thing. Check once a year, whenever you take your XJ swimming, or whenever you clean the engine bay - whichever comes first.

Just to confirm:
"A" is the alternator output
"B" is the regulator inputs from the PCM
"C" is the engine/alternator ground. Looks pretty shonky - I'd suggest cleaning that up and Ox-Garding as well...

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I am also in the process of doing an upgrade on the charging system on my 89, so I will need larger cables as well.

Check my website - I can save you a batch of hassles... I don't have a "kit" for the wafer fuzes yet, so that's optional. I'm working on a "kit" approach for RENIX, but I'll have to get test animals for later models...

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5-90 said:

1)
You should not need to "piggyback" the alternator output lead - it's simplest just to pull the damn thing out once you've got it replaced (so you don't have loose wires running around.) 1/0 cable is HUGE overkill - I selected 1 gage for wiring that I sell as a compromise between pure overkill and shipping weight. I use 1 gage welding cable, which offers greater flexibility and higher current-carrying capacity (both due to the finer strands used.)

Have you already got your crimper?

As far as the fuze goes, 175A may be too high - unless your running a 140-170A output alternator. If you're in the 100-140 range, you can use a 150A fuze, and if you're under 90A, then a 100 will be just fine. Remember that fuzes should be "upsized" just a touch - or you run the risk of popping them all the time - but not too much, or it won't be able to do its job. For something like this, I'd select the NEXT HIGHER fuze rating from max alternator output. If I'm right "on the line," then it's the next one up (for 100A output, go with a 110-125A fuze - whatever's next higher.)

Click to expand...

Mostly, I didnt want to go to the hassle of removing the other wires, if it turns out easy, I might just remove them. If i dont, its just one more wire to allow the electrons to flow through. And the 1/0 gauge is really not that big, its more the size of 2 gauge. I would rather go too big, than not big enough. Eventually I plan on running about 1300 watts of continuous power to a sub and some components, plus two pairs of rocklights, pair of lights on the rack, a pair on the bumper, and maybe a winch. I figure this should be the first step in not getting voltage drop problems, plus its not that expensive to do.

Already got a big crimper, also got a big bench vice that should work alright

As for the fuse, I was under the understanding that you are supposed to fuse based on the wire size. But if Im wrong on this, lemme know.

When I did mine I left the original running from the alternator to the PDC and ran the newer and heavier wire directly to the battery. Since i had an Optima in there I put the new wire on one of the lower screw terminals. Works great!

You select wire size based upon anticipate load, and you select fuzes according to the device you're protecting. There are "ampacity" ratings for wire & cable - which help to determine the maximum capacity (and I usually take the rating and drop 10% - as my own maximum. I'm less concerned about weight than I am electrical fires...)

I am quite familiar with large-size wire - from 8 gage on up (I've worked with most of it, also Buss strips and the like for REALLY high current!) I agree with the "too big, rather," idea, but sometimes you can go REALLY too big - and that usually ends up being a headache with cable routing and termination. Again, that's why I selected 1 gage - as I recall, it's got an ampacity (DC current) of about 300A or so for under 50 feet. I'd have to check my notes to be sure, but I chose it as a compromise between "pure overkill", material cost, and shipping weight. If it comes to it, I can terminate anything up to 4/0 - I've got the crimper for it.

As far as the "extra" loads you're running, I'd be inclined to get a distribution post (you should be able to get them from Gall's - they're used in police cars and ambulances, or an outfit like Del City or Waytek Wire) and feed everything off of that. That would minimise clutter at your battery, and make maintenance simpler. You could also branch out and feed nearly everything else with 4-8 gage, except the winch (which could take 1-2 gage, depending on current.)

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5-90 said:

As far as the "extra" loads you're running, I'd be inclined to get a distribution post (you should be able to get them from Gall's - they're used in police cars and ambulances, or an outfit like Del City or Waytek Wire) and feed everything off of that. That would minimise clutter at your battery, and make maintenance simpler. You could also branch out and feed nearly everything else with 4-8 gage, except the winch (which could take 1-2 gage, depending on current.)

Click to expand...

I've already got a relay box built at the back of the jeep with about 6 relays fed by one fused 4 gauge wire. As of right now, the only things runnin off the battery are 1 4gauge wire for amp, 1 4gauge wire for relay box, 2 12gauge wires for headlight harness, and all the factory wires that were on there.

Btw you definately sound like you know what youre talkin about, thanks for all the info!

I do what I can. It's funny - I'm going to school (in a couple more years) for mechanical engineering - but I've probably got more practical engineering behind me than most doctoral students of the subject. Go figure.

Anyhow, all this is borne of experience. That doesn't mean that I'm always right - just that it's a bit more spectacular when I'm wrong (and more expensive to fix...)

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