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Aux batt system - Where to tap into the jeep?

Mash5

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Where I’m at now-
I have a small AGM aux battery mounted in the bed. All it does is power the Dometic fridge. It is charged by a Renogy DC-DC charger/isolator (DCC1212-20). I have it set up on one of the high current Aux switch outputs, which acts as an isolator, so I just have the D+IGN running to the input lead of the DC-DC. If there is voltage on the Aux line, the charger runs. It’s a simple system, and it works fine-ish. I did it one night before a trip… you know how it is… and it works.

Where I’m going-
I’m upgrading the battery here shortly to a cheap 50Ah LiFePO4. If I find a good deal, I may go a bit bigger, but I think 50 should work fine, and weight is a concern. I want to switch the DC-DC over to direct wiring (no aux switches) and run the D+IGN correctly so that the isolator function works as intended. The main reason will be that the switch has been turned off on a couple of occasions and nobody noticed. This resulted in the battery not getting a full charge, and it takes a few days for it to recover with how marginal the AGM already is. It also uses up a switch and doesn't really need to. The charger needs to be able to pull up to 30 Amps.

My question-
With the Aux wiring, I know the vehicle was designed to provide current through those lines. Other than the Aux switches, where is the correct place to “tap into the jeep” to get power? With past jeeps, I have always just run NATO-style battery terminals and pulled whatever I need from there but I understand that with this highly controlled, smart alternator, duel battery, situations we have now, pulling current from the wrong place could be the source of unintended problems, like causing the batteries to be unbalanced. Does anyone know of a designated spot? Where do the Aux switches connect to the Jeep, for instance?

Thanks for any help.
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The battery voltage/current sensor is on the negative terminal. So you should use either a chassis ground or other source before the BMS. But for power depending on your charger a DC-DC charger can pull some serious amps and should go directly to the battery positive. The aux switch can be used as a signal wire instead of using a standard key on 12v source. But using the aux switched power directly to the charger is asking for problems.

i would run a positive and negative to the house battery. Positive of course for the dc/dc input and negative to the geound post next to the battery. That way it will make a full circuit and include the BMS in the system
 

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Where I’m at now-
I have a small AGM aux battery mounted in the bed. All it does is power the Dometic fridge. It is charged by a Renogy DC-DC charger/isolator (DCC1212-20). I have it set up on one of the high current Aux switch outputs, which acts as an isolator, so I just have the D+IGN running to the input lead of the DC-DC. If there is voltage on the Aux line, the charger runs. It’s a simple system, and it works fine-ish. I did it one night before a trip… you know how it is… and it works.

Where I’m going-
I’m upgrading the battery here shortly to a cheap 50Ah LiFePO4. If I find a good deal, I may go a bit bigger, but I think 50 should work fine, and weight is a concern. I want to switch the DC-DC over to direct wiring (no aux switches) and run the D+IGN correctly so that the isolator function works as intended. The main reason will be that the switch has been turned off on a couple of occasions and nobody noticed. This resulted in the battery not getting a full charge, and it takes a few days for it to recover with how marginal the AGM already is. It also uses up a switch and doesn't really need to. The charger needs to be able to pull up to 30 Amps.

My question-
With the Aux wiring, I know the vehicle was designed to provide current through those lines. Other than the Aux switches, where is the correct place to “tap into the jeep” to get power? With past jeeps, I have always just run NATO-style battery terminals and pulled whatever I need from there but I understand that with this highly controlled, smart alternator, duel battery, situations we have now, pulling current from the wrong place could be the source of unintended problems, like causing the batteries to be unbalanced. Does anyone know of a designated spot? Where do the Aux switches connect to the Jeep, for instance?

Thanks for any help.
It's not really a smart alternator as some say. It's pretty standard, controlled by the PCM. The intelligence such as it is, comes through the use of the IBS and PCM controlling things.

Whatever you do, for a ground, do not go directly to the negative terminal - connect either to body ground or the top side of the IBS (Intelligent Battery Sensor)

If I need full, unfused power, I take off the main or crank battery pos and the top of the IBS or body ground for negative.
 
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Mash5

Mash5

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Update

After working fine all summer and for the last 8-10 months, the inline fuse holder I used at the battery has melted. This is the diesel, so the turbo and exhaust stuff is near the battery in that corner of the engine compartment. My best guess is that extra heat explains the melting. I figure over-current alone should not have melted the fuse holder, it should have blown the 30A fuse… or maybe the fuse holder was just a cheap piece of crap. I don’t know.

So as you guys recommended, I connected to the starting battery positive post and a ground lug that is right there next to the battery. The manual for the charger does not list a max amp draw. It says 250w is the “Max Rated Power” whatever that means... so even if I had a bunch of voltage drop in my run and only 10 volts was making it to the charger, it should only have pulled 25Amps at the charger. I honestly don’t know how to calculate the required wire size with a system that will pull more power if the voltage drops and thus cause more voltage drop. It seems like a runaway situation, but the manual does say you can feed it with 10AWG out to 10ft and 11~20ft needs 8-6AWG. As I had 10 AWG and connectors for 10 AWG and it seemed like less than 10, that is what I used for the run from the battery, down the firewall, along the frame, and into the corner/side of the bed where the charger is installed. I didn’t measure… maybe it is 12 or even 14ft. The only way to know would be to pull the wire out which I will do now that it has failed.

So, I am redoing it with 8 AWG like I probably should have in the first place and hoping I don’t need 6 AWG. I’m running it through some split loom to protect it from abrasion. Does anyone think I should ground it back closer to the bed rather than under the hood or both? Any other thoughts?

Jeep Gladiator Aux batt system - Where to tap into the jeep? AUXDC Power System
 

chorky

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You should be plenty fine with 8ga. But i would be curious to know the wire type used as well as what fuse type you used. Seems weird that it would melt like that. A poor connection somewhere can increase resistance thus increasing power draw so that is something to check too. Using the following calculations your pulling probably close to 25/30 amps

Jeep Gladiator Aux batt system - Where to tap into the jeep? 4DD72CD5-4F3F-4647-860A-150A305EA60C


In theory you would be fine locating a factory ground near the bed and connecting to that. Personally for myself I just ran another ground wire from the bed distribution panel to the body ground that the factory battery negative ties into next to the battery. I did this just to be sure of a good ground and avoid messing with various grounds across the vehicle. I also did this because the wire I purchased came with red and black wire. So 2 for 1. as for wire length, i dont know where your wore goes or how your bed setup is. My setup ran wire feom the battery through the aux 110V port would be if i had it. That took about 23‘ of wire.
 

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Mash5

Mash5

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I would be curious to know the wire type used as well as what fuse type you used. Seems weird that it would melt like that.
I pulled the old wire out last night and it is about 14ft long. According to the manual that is too long to be 10AWG and I should have used at least 8AWG, but it still does not really explain the fuse holder melting. The wire is Bonded "zip cord" from powerwerx. They charge enough that I assume it is quality stuff though the strands are not "tinned" like some nicer wire. The fuse on the other hand came out of my drawer of stuff, and I'm not sure where it is from. It could be an amazon delight. It looked like this: https://powerwerx.com/atc-ato-inline-fuse-holder-10-gauge-red but again I'm not sure if it was. My current theory is that it was Chinese junk and that is why it failed. With the upgrade to 8AWG and all quality parts, I'm crossing my fingers that this is the last time I have to do this job. ...Third time's a charm.
 

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8 ga should be fine for your use. For reference, i am using 4ga but have a capacity need fused at 100 amps, and maybe 60-70 continuous for 20 minutes or so With a potential peak to 85 amps for a few minutes.

That style of fuse holder is generic junk IMO. I would suggest an ANL style. Something like this https://a.co/d/jj0tiVc

Not having tinned copper isnt bad IMO as long as it is protected. My 4 ga wore is not tinned and is fine strand windynation wire. But, my ends are crimped good and heat shrunk with the adhesive glue style to really seal it off. All my 12 ga and smaller is tinned also by powerwrex and is decent.
 

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The only place where tinned copper wire is any better is for wet or humid environments. It slows corrosion where there are salts and a lot of moisture, or humid environments.
Otherwise, electrically there's no advantage. It conducts the same, acts the same.
All things being equal, tinned will withstand harsh wet environments better.
And if the insulation is good, doesn't get punctured or cut, and if you seal the ends properly, there isn't an advantage. Use good connection methodology, and if you expect it to get and stay wet, use marine type heat shrink and don't worry about it.

I've got 50 year old automotive wiring harnesses laying around that still have good copper wires and little corrosion.
 
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Mash5

Mash5

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chorky

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If I have any problems with this https://powerwerx.com/maxi-inline-fuse-holder-8-gauge-red I'll have to go with one that does not have soft plastic. I guess I'm going to give it one more chance. It's installed now.
Personally I would not use that fuse holder. It will melt from heat before the fuse will blow just like the last one. Get one with a bolt and lug at the fuse. the blue sea fuse holder he linked is a solid unit. Its good for 35-300 amps so you can get different fuses if needed or upgrading in future.
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