12v Deep Cycle Battery Set-up for Camper on 24v '68 M35A2

I have a '68 Kaiser-Jeep M35A2 with a custom built camper on it. The truck is 24v system and I have two 12v batteries connected in series for it. I have 2 more deep cycle batteries that I wish to be connected in parrell so I can get 12v to the camper and have them be charged while the truck is running.

My first attempt was to connect 1 of the deep cycle batteries in parallel to the starting battery which has the cable going to ground on it, so that it would get just 12v charge going to it. I put my solinod and automatic circut breaker in between on the + cable with the activation wire that I ran off the wire going to the in tank fuel pump, so that it would charge my deep cycles whenever the accessory switch was on. However, that wire had 24v going though it and it seems to have fried my solinod(repairable?). So I just tried connecting it without the solinod, but now what seems to have happened is the deep cycle and the starting battery that it was connected to are at 11.5v and the other starting battery is at 13.25v. So it seems one is under-charged and the other is over-charged and they won't equalize. Any ideas of how to make this set-up work?

Thank you very much.

RE: 12v Deep Cycle Battery Set-up for Camper on 24v

Add a 12 volt alternator and keep the batteries separate.

RE: 12v Deep Cycle Battery Set-up for Camper on 24v

Batteries change resistance as they charge. So you've got a problem with two different sized batteries connected in Parallel to each other. The Deep Cycles will charge at a different rate and their resistance will drop off as they charge.

What I would do is get a 24-12 volt voltage converter from someone like NewMar Power. They have a range of units that are sealed, designed for marine environments and will work as a charger for a system that has a battery on the 12 volt side. Two of the same sized 12 volt batteries in series will work well too. The DC-DC converter needs to be setup for the correct mode as either JUST a power supply or as a power supply that also charges batteries.

http://www.newmarpower.com/dc-dcconvertersstandard/dcdcconvertersstandard.html

I would also install a low voltage disconnect for the 12 volt batteries to prevent the 12 volt deep cycle string from being discharged too much.
http://www.newmarpower.com/lowvoltdiscnct/ldv.html

An Ammeter would be good too. A low voltage disconnect to prevent drawing power from the 24 volt side such that you can't start the truck. I think newmar might make something like that, but I couldn't find that.

Dittto on both...

I did the 12 -24V converter on a Penz about 8 months ago using a control relay and a diode which is a pretty simple set up but I was not very happy with the limitations of the transformer and charging. If you go this route spend the bucks on a GOOD self regulating unit.

This time around I am using an 12V alternator which I have much more confidence in and know I can use and do whatever I wish with the 12V side of the system.... Very simple bracket to make, need one pulley adapter for the water pump pulley and using a self igniting alternator you only need one wire to the battery.

Good job on the bracket! Could you detail the "water pulley adapter", please.
Bet you could sell a few if you had them made up (bracket plus adapter).

Soon as my damn R&D department gets done with it... The SOB is slow as all get out and seems to be insulating the bottom of the cab rather than doing to pulley he should be working on... This would of course be myself!!! lol Gimme 3-4 days and you will have pics and sizes... Will also take a pic of the bracket with out the alternator.

Thanks for the reply.

On a side note: I'm installing a deep water fording kit on my deuce and starting thinking won't my Walmart batteries short out if I drive them under water. Are special water proof military batteries need for deep water fording? Or can I just seal the connection with water proof tape or something else?

I use Napa 9934/78 gel cells... They are much smaller, lighter, sealed, have a much higher CCA and are 84 month battries. If your going to use a 12 /24 system the 3rd battery fits into the box with 3!

The military batteries have "valves" that seal the batteries when under water. Commercial batteries caps/covers need to be coated with grease for the under water trip...
All exposed terminals are also supposed to be coated, but for fresh water, it may not be crucial. You can also move the batteries up into the cab for the trip, which should be good for at least 4 ft of water.

I know I am going to show my ignorance of electrical system functioning so please explain to me why this won't work: connect a second battery in parallel to each of the individual 12 volt serial connected batteries; then connect the two parallel batteries to one another in parallel. It seems that if all batteries were of equal condition and quality this would produce a usable system. Again, please educate me on this.

Because when you activate the trucks electrical system your 12 /12 becomes 24V... The scenario your describing would simply double your battery capacity and you could pull 12V (as you can now) oof of any one battery... Until you activate the ignition switch.

Essentially all I would be doing is adding amps to the 24 volt system?

Yep... adding amps

Thought of something I should have said before in regards to mounting an alternator... The other side of the motor would be easier (I have a AC compressor in the way)... I have a bracket template for the compressor which could easily be made into a alternator bracket... You would not have to do any mods to the pulleys to run it, just get longer belts and a double sleeve alternator... A much easier way to go...

In a 2 batteries in series situation, each battery has a certain resistance. As they drain, that resistance goes up, which means they need more voltage to charge and take more amps to charge. If one of the two batteries in series is drained more than the other (if you tap one of the 12 volt batteries off of the 2) then it's resistance goes up more and the other battery doesn't drain as much in use. As they charge again, the resistance of the batteries is now out of sync and the more discharged battery draws more current than the one that is in more charged and you end up cooking the battery that's charged more and undercharging the other lower battery. By putting additional batters in parallel to these, you alter that resistance even more and make it worse.

Best draw 12 amps with a converter that can charge batteries OR get a second alternator.

Here's the $100 question, what are you running that requires 12V? Yanno, there are 24 to 110 inverters out there that work wonderfully.

THEE single most important accessory a vehicle can have... My cigarette lighter!!! LOL

Hey Mike, you gonna put an overhead console in that truck? Someplace to stash your smokes yanno!

Dont know yet... I've thought a lot about it and I am kinda waiting to see how my windshiled wiper set up is going to play out. I might HAVE TO do one just to hide the rods and arms. The center console is a done deal too!

For me coming up with a 12 v source is just a way of adding some of those little accessories that civilian life has given me a taste for. A radio/mp3 player, my coleman electric cooler and a little 12 volt fan that I have. I just can't see myself cruising down the road with a boom box and a box fan in the cab, though it is a comical image and my wife would think that was just typical for me. Hey by the way, can you believe that she said the deuce makes the house look bad! I should have told her its not the deuce its the wife (not really, she's great just hates the other woman).

If you don't go with a 12v alternator, you could also get a solar charge controller and feed it the 24v from the original alternator. The charge controller has to be the pulse width modulated type (rapid on-off), and not the shunt type (designed to short out the solar panel to control voltage). I am converting my van box to a camper and have it wired this way using a Xantrex C-60 charge controller. I also plan to add solar panels, so this allows me to feed the solar panel into the same charge controller. When the truck is parked, you can feed the controller through some sort of power supply to keep the batteries up. These controllers are 3 stage charging, which is good for the batteries.

You should probably run the alternator through a battery isolator to keep the 24v batteries from dumping heavy current to the controller when your 12v batteries are discharged, though the controller has current and overtemp protection.