Aux battery question

[Trailhead 4x4]

Are there any down sides to charging an extra battery off the 12v side of the charging system? I will be hauling a slide in camper and want to run a cable to charge the camper batteries. Will it unbalance the system?

 

[skysix]

Yes it will unbalance the charging load.

OR you could run 3 cables (-12v (aka CUCV ground), "camper ground" (aka +12v), +12v (aka +24v)) to the camper and install 2 batteries, each in parallel with one of the main batteries. Then keep the pos and neg 12 v circuits completely separate and put about equal loads on each battery. Just be careful with the camper ground as the center of the CUCV batteries is +12 from chassis so if the camper ground is bonded to the truck, the other batteries + terminal will sit at +24 volts from it. Essentially if you want to run a typical wiring circuit with a universal ground in the camper, it must be electrically isolated from the vehicle as it will be at +12 from the box/frame of the truck.

Mine is an old school wooden 10' CO Alaskan Camper so was easy to mod the wiring and keep electrically isolated...

 

[Ken_86gt]

Research RV battery isolators, you could use one of them. There are a couple of videos on youtube that show the operation of them.

You could convert the vehicle to 12v then you could have a dedicated 12v circuit (alternator and battery depending on the method used) to your camper if you wanted.

 

[CARNAC]

Yes it will unbalance the charging load.

OR you could run 3 cables (-12v (aka CUCV ground), "camper ground" (aka +12v), +12v (aka +24v)) to the camper and install 2 batteries, each in parallel with one of the main batteries. Then keep the pos and neg 12 v circuits completely separate and put about equal loads on each battery. Just be careful with the camper ground as the center of the CUCV batteries is +12 from chassis so if the camper ground is bonded to the truck, the other batteries + terminal will sit at +24 volts from it. Essentially if you want to run a typical wiring circuit with a universal ground in the camper, it must be electrically isolated from the vehicle as it will be at +12 from the box/frame of the truck.

Mine is an old school wooden 10' CO Alaskan Camper so was easy to mod the wiring and keep electrically isolated...

WOW, repeat all after "Yes it will unbalance the charging load."

You made my head hurt. Now I'm gonna have to go get a drink.

 

[MarcusOReallyus]

Yes it will unbalance the charging load.

OR you could run 3 cables (-12v (aka CUCV ground), "camper ground" (aka +12v), +12v (aka +24v)) to the camper and install 2 batteries, each in parallel with one of the main batteries. Then keep the pos and neg 12 v circuits completely separate and put about equal loads on each battery. Just be careful with the camper ground as the center of the CUCV batteries is +12 from chassis so if the camper ground is bonded to the truck, the other batteries + terminal will sit at +24 volts from it. Essentially if you want to run a typical wiring circuit with a universal ground in the camper, it must be electrically isolated from the vehicle as it will be at +12 from the box/frame of the truck.

Mine is an old school wooden 10' CO Alaskan Camper so was easy to mod the wiring and keep electrically isolated...

Yes, and unless you have a wooden or fiberglass or other completely non-conductive camper, this is a recipe for disaster. Sooner or later some insulator is going to wear through, or somebody is not going to understand how the system works, and you'll have melted wires or a fire.

With a completely wooden camper? And an owner who understands how this works? Okay, fine. You're a big boy, you know what you are doing.


For anybody else?

Insanity.

 

[MarcusOReallyus]

Trailhead, I see 3 good options for you:

1. Convert to completely 12 volts, and use the second alternator to charge your aux batteries. This could include the stock second battery AND some camper batteries. OR you could run the stock second battery in parallel with your starting battery, and use the second alt to charge the aux batteries.
2. Keep the system 24 volt, and get a 24v to 12v converter, use it to charge your aux batteries.
3. Add a third alternator to charge the aux batteries.

Battery isolators won't help you - all they do is to keep your aux batteries from discharging your starting batteries. It won't do anything to help the battery imbalance, which is your big problem here.

 

[Ken_86gt]

Which imnalance are you concerned with = the 12/24 stock battery system or with a new battery? If you are concerned about imbalancing the stock system don't worry as it is already imnalanced. The only load on the high side battery is strictly starting related- the low side battery does the same starting related and also everything else in the vehicle that is 12v such as the lights.

If you are converned about the imbalance with the new battery then my comments above stand- use an isolator or convert and use the new dedicated second 12v system for the camper.

 

[MarcusOReallyus]

Ah, now I see what Ken is saying. Using an isolator, you will load the alternator more, but you won't be putting any drain on the front battery, thus you won't be making the imbalance any worse. As long as you are driving long enough to fully charge both batteries (front battery and aux), then that's true. However, if you do a bunch of short drives, the front battery won't get charged sufficiently, so you will make the imbalance worse in that case.

The cure for that is a larger alternator.

 

[Ken_86gt]

The isolator works by charging the main battery before the aux battery is charged. This way you will always be able to start it. This how rvs handle multiple batteries. Check out the video of how they work on youtube. They are inexpensive.

 

[Skinny]

Why not just run a pair of batteries in series in the trailer? Use the isolator to tie it to the CUCV so they charge when the truck is running and isolate when turned off. Then buy a 24v inverter and wire the trailer with 120v off the inverter. Any DC accessories like lighting would easily be sourced in 24v if you look in the right place. Most LED's will go even higher than that...they don't care. I think this would be the simplest arrangement without cutting up your CUCV's charging system.

 

[Trailhead 4x4]

I have thought aboutconverting to all 12v, but i am mostly interested in if I could just tie into the 12v side of the original charging system and have it charge my camper battery without upsetting anything too badly. I have wired up isolator kits for dual battery systems in the past, it's not hard and works well, and it seems like I should be able to get away with it here. Not to over-simplify, but it almost seems as though the 12 and 24v systems on this truck could be considered separate and I should be able to add what I want to the 12v side and not affect the 24v side.

 

[Cleveland Iron]

It's all good until something shorts out... All kidding aside, I like the seperate 12V system. Either some form of alternator with 12V and 24V taps, a battery equalizer or the device they call a DC autotransformer. The main advantage to the last gives you the ability to charge the 24V batteries from a 12V source.

I'm a paranoid type. with either of the last two, I'd do an OPCOM and attach those gadgets to the system with a couple of nice relays. With any thing set up for camping, extra fusible links are also a good idea. I recall a thread where the owner of a deuce camper lost his dog from, I beleive, a battery fire. I'd hate to see anything like that happen to anyone else...

 

[MarcusOReallyus]

Not to over-simplify, but it almost seems as though the 12 and 24v systems on this truck could be considered separate and I should be able to add what I want to the 12v side and not affect the 24v side.

Nope. They are not two separate systems. The 24v system piggybacks on the 12v system. It's really two 12v systems, but they are not separate. One of them is parked "on top" of the other to make 24v.



Let's see if I can make this diagram in ACII art:

+ 24v
------------
------
------------
------

|
|
|
+ 12v
------------
------
------------
------
|
====
===
==
=

​

That's two 12v batteries in series. The negative terminal of the TOP battery connects to the positive terminal of the BOTTOM battery. That symbol at the bottom made of equal signs = represents the vehicle ground. There are +24 volts between the positive terminal of the TOP battery to vehicle ground. There are +12 volts between the positive terminal of the BOTTOM battery to vehicle ground. Oh, that's the same thing as saying there are +12 volts between the negative terminal of the TOP battery and vehicle ground. These two locations are electrically equal - the negative terminal of the top battery and the positive terminal of the bottom battery are connected.


You don't have two separate systems. You have ONE system, with two alternators, and we tap between the two batteries to get 12v for running most of the vehicle's systems (lights, radios, heater, etc.).

We take juice from the positive terminal of the TOP battery to get 24v for the starter (and the glow plugs, if it's still in stock configuration).

The BOTTOM battery is battery 1, the FRONT battery. His positive terminal is where we get our +12v stuff.

The TOP battery is battery 2, the REAR battery. His positive terminal is where we get our +24v stuff.


Clear as mud?


Hey, just be glad these things aren't positive ground. That gets REALLY fun when you are trying to add +12v accessories!

 

[skysix]

@ MarcusOReallyus, probably... especially the bit about some tech not understanding the wiring diagram. Although it is not that much different in concept than the 240v 2 phase power than enters the house to be split and used as two 120 volt single phase halves in the wiring (and the 240v to the heater/oven/dryer).

My camper does not have a ground like many modern ones do - which is as you mentioned the ESSENTIAL key. All the 12v wiring is 2 conductor. So really there is nothing (except the supply cables) to short out against the frame etc.

 

[MarcusOReallyus]

My camper does not have a ground like many modern ones do - which is as you mentioned the ESSENTIAL key. All the 12v wiring is 2 conductor. So really there is nothing (except the supply cables) to short out against the frame etc.

I would do the same with that setup. No problem for you or me.


But I wouldn't recommend it to someone who doesn't understand electricity.

 

[Trailhead 4x4]

Thanks for the advice. I'm really throwing around the idea of converting to all 12v, keeping both alternators and both batteries. Don't really want to though

 

[Recovry4x4]

If I recall correctly, the system, in it's very design, is factory imbalanced. That is exactly why the charging system is set up the way it is. There should be no problem tapping the 12V side for an isolator to charge a house battery. What will be the demands on the house battery? Knowing this will help a bunch. If it's going to be a high demand setup, further consideration should be made. If it's just for running lights and small fans etc, the isolator will be fine. Consider some solar as well.

 

[MarcusOReallyus]

Thanks for the advice. I'm really throwing around the idea of converting to all 12v, keeping both alternators and both batteries. Don't really want to though

Well, the civvy version works just fine with 12v, so it's not like you'd be losing reliability. AFAIK, the only reason the military did the 24v setup was for compatibility with other MVs for jump-starting.

So, if you convert, you can run one battery for the truck, and one for the camper. Completely separate systems. That would be the most reliable, I think.

But then, if you enjoy the collectible/historical aspect of the beast, you would be losing some of that. The other fly in that ointment is that you wouldn't be able to get as much help here on the board for starting issues, since it wouldn't be stock.

 

[Trailhead 4x4]

The camper battery will be only for some interior lighting, maybe some exterior LED flood lighting, my ARB fridge, and a 10 inch vent fan. I think the 12v side will be up tp the task of recharging a pair of deep cycles. The biggest reason I want to keep the 24v in place is because I already have a 24v warn 15k winch that I want to use on this truck.

 

[MarcusOReallyus]

Doesn't sound like me you have a problem, then. Do the isolator to keep your starting battery protected, and if you find the alternator isn't keeping up, you can look into upgrading just that part of it. Since it's the front battery alternator, you don't need to worry about an isolated ground, so bigger alts shouldn't be a bear to find.

Yeah, that winch is worth keeping.