Question on connecting two batteries and stuff

[8ball_99]

I replaced my single battery on my cargo trailer with two matching 12v Deep cycle batteries. Now my plan was to connect the 8 gauge wire from the converter to one of the batteries and then run a short piece of 4awg from that battery to the other battery to connect them. Then the plan was to run connect the solar charger to the other battery. Then connect the inverter to which ever battery. Both the inverter and the solar charger is going to be mounted between the batteries right there in the box so your talking 15-24" of wire to run to one battery..

Now after reading up on chargers, multiple battery setups ect. It seems its recommended to have the exact same length of wire between the charger and the batteries. So for me to do this with my setup I would need to have some kind of terminal where everything connects to. As in have say 30" 4awg wire running from each battery to this terminal then also have the wires from both the power converter and the solar charger connect to the same spot. And I guess probably connect the inverter to this spot also. Now this doesn't seem ideal to me because I would have a little more wire between the batteries and chargers. It also would add more connections to the setup. I can't see one battery having an extra 30" of wire between it and the charger causing that much of an issue. Even more so if I go with a large wire like 4 gauge. But who knows it might. I'm just a little unsure whats the best way to go about it.

Here is a picture to show what I mean.. Don't laugh it was a quick mac paint scribble

[Martiangod]

I would connect to batteries to gether the way you are showing, but hook poositive draw/load to one battery and negative load/ charge to other battery, that way both batteries are charged and drawn from are equal, or install battery switch so one is drawn/charged, and when dead, switch to other one.

[Dale M.]

I would use the "bus bar" method (common connection point) .... Place two small bus bars in side of battery cabinet... Connect all battery and charging positive cables ( solar and (shore power) and loads cables (to fuse panel) to one bus bar and duplicate same procedure for negative connections.... Even your sketches look a little unmanageable, think how its going to be with wire.... Unless you are going have absolutely huge loads, #8 cable should be more than sufficient for any battery connections... The actual placement of chargers and whatever is not really critical.... Even wire lengths are not really critical in the practical world..... IN sub and micros electronics circuits wire lengths might be critical but this is just DC power to "everyday" appliances and lighting...

Dale

[droid_ca]

Hmmm this is an interesting topic
Cant wait to see what you decide to do
And how well it works out for you

[bobhenry]

MAYBE THESE PICTURES WILL HELP.....................

http://www.rvtechlibrary.com/battery/bat_convert.htm

[8ball_99]

I would use the "bus bar" method (common connection point) .... Place two small bus bars in side of battery cabinet... Connect all battery and charging positive cables ( solar and (shore power) and loads cables (to fuse panel) to one bus bar and duplicate same procedure for negative connections.... Even your sketches look a little unmanageable, think how its going to be with wire.... Unless you are going have absolutely huge loads, #8 cable should be more than sufficient for any battery connections... The actual placement of chargers and whatever is not really critical.... Even wire lengths are not really critical in the practical world..... IN sub and micros electronics circuits wire lengths might be critical but this is just DC power to "everyday" appliances and lighting...

Dale

The picture looks a little messy. But in real world the top method is much easier cleaner. It looks like a lot of connections to the batteries but really it would only be three connections on each terminal. Battery one would be converter, jumper wire and charge wire from towvehicle ( not in pic) battery two would be solar charger jumper wire and inverter. The second method would be the same as using a bus bar. Only one connection to the battery terminals. Then all the connections go to a terminal or bus bar. This adds an extra connection point in the box and more wire. Ike fine with that if it really does matter.

[Dale M.]

I would use the "bus bar" method (common connection point) .... Place two small bus bars in side of battery cabinet... Connect all battery and charging positive cables ( solar and (shore power) and loads cables (to fuse panel) to one bus bar and duplicate same procedure for negative connections.... Even your sketches look a little unmanageable, think how its going to be with wire.... Unless you are going have absolutely huge loads, #8 cable should be more than sufficient for any battery connections... The actual placement of chargers and whatever is not really critical.... Even wire lengths are not really critical in the practical world..... IN sub and micros electronics circuits wire lengths might be critical but this is just DC power to "everyday" appliances and lighting...

Dale

The picture looks a little messy. But in real world the top method is much easier cleaner. It looks like a lot of connections to the batteries but really it would only be three connections on each terminal. Battery one would be converter, jumper wire and charge wire from towvehicle ( not in pic) battery two would be solar charger jumper wire and inverter. The second method would be the same as using a bus bar. Only one connection to the battery terminals. Then all the connections go to a terminal or bus bar. This adds an extra connection point in the box and more wire. Ike fine with that if it really does matter.

Only three connections per terminal .... Messy and a maintenance nightmare because of corrosion at terminals and number of terminals to deal with..... With bus bar system you only have one connection at each battery and a lot cleaner setup to maintain....

If you put charger leads ( converter and solar units) and load leads on a bus bar it isolates them from corrosion problems.... Reducing the corrosion problem from about 12 possible corrosion points ( 3 per terminal x 4 terminals) to 4 corrosion points (1 per battery terminal) .... IF you move major amount of connections away from corrosion source ( battery acid (sulfuric) and oxygen) you maintenance issues drop considerable.... Also liberal application of dialectical grease (keeps oxygen off dissimilar metals) you will reduce maintenance issues....

Remember if you get this.... Its on all your connections...



You want to move as much electrical connections away from this sort of damage as possible ( hence remote bus bar) ..

And forget the washers, they are not really that effective....



Note washer, note corrosion...



Dale

[eamarquardt]

At the risk of being called a "know it all" I've read, but I can't back up my recollection with a reference right now, that it isn't "good form" to connect two 12 volt batteries in parallel on a permanent basis. I think it's OK while they are actively being charged and discharged (as in being used). As I understand it, if you leave them connected while in storage, and don't apply a "maintenance" charge, they will kind of "see-saw" between themselves and discharge each other.

Just food for thought.

Cheers,

Gus

[8ball_99]

Dale, I understand what your saying about corrosion and really I hadn't thought about it. I do use dialectical grease on all my battery connections. My current battery that has been on the front of the trailer since last year was still spotless. Three connections didn't seem like much to me because I already have two per terminal with my current setup. I would Never let my terminals get anywhere near that funky before cleaning them. These are standard wet deep cycle batteries so a couple times a year I will have to remove the holding straps check the water level and check the cells with a hydrometer. Giving the connections a little TLC at the same time is really not a problem. I was more concerned with how to connect everything from the point of view of keeping the cells charged evenly as I can and having the setup optimized best I can as far as price, amount of wire, ect, ect. Now if these batteries were AGM batteries and they were tucked away in cubby in boxes having pull them out to clean the connections would be a Pita. The cargo hatch is very easy to access though. And I even made the hold downs so removing one wing nut allows you to check the water or remove the battery.


eamarquardt, Seems like I have also read that somewhere, But in my case I don't think it will be a problem. The trailer is parked at my house and stays plugged in 99.9% of the time. I do have a 3 stage WFCO power converter now that keeps the battery charged. Now once the solar is on there I plan on letting it maintain the batteries while parked at the house. If I park the trailer inside my shop then I will plug it in. This was some of the reason why I wanted to add the solar. I figured if it was going to be sitting outside in the sun might as well use that to maintain the batteries. I have a feeling the 160 watts of solar will not be enough to keep up with all our usage while dry camping. It should be plenty to maintain the batteries while not in use. Besides once I add two more 80 watt panels or 100 watt panels I know I'll have plenty.

All my stuff is here now so I plan on tomorrow after work setting everything in place and taking a look at what lay out works best in the space I have. Looking forward to getting it all connected and testing it out. Should make our up coming camping trip a little nicer! I did some testing the other afternoon and my TV pulls 27 watts AC and the bluray pulls 8 watts. I was pretty happy with that since one of the main reasons I wanted the inverter was to be able to run those two things at night when our 4 year old is winding down for bed. We tend to be outside at the campfire while he is laying in the bed watching a movie before bed. Besides that we only have a couple of very small things I plan on using it for. Walkie talkie charging base, digital camera charger, ect. Stuff I really don't want to go out and buy 12v chargers for each thing. It would have been nice to have an inverter large enough to run the microwave for a couple mins here and there with out needing the generator. But since its running wattage is 950 watts AC It just wasn't practical to try and run it off an inverter. It would zap a lot of juice and the size inverter I would have to step up to just for that one item simply wasn't worth it.

[IndyTom]

From everything I have ever read, it is not a good idea to charge batteries in parallel Because no two batteries will charge EXACTLY the same, one battery could be overcharging while the other is still in the bulk charge state. On the other hand, charging in series is just fine. It is possible to wire a battery bank so that it is charged in series and discharged in parallel. Dont have a decent graphic program here at work or I would draw a schematic of it. Anyway, just what I have read.

Tom

[eamarquardt]

From everything I have ever read, it is not a good idea to charge batteries in parallel Because no two batteries will charge EXACTLY the same, one battery could be overcharging while the other is still in the bulk charge state. On the other hand, charging in series is just fine. It is possible to wire a battery bank so that it is charged in series and discharged in parallel. Dont have a decent graphic program here at work or I would draw a schematic of it. Anyway, just what I have read.

Tom

Batteries should only be charged in series if they are identical in manufacture, age, and state (meaning charge/discharge). Otherwise, one may be overcharged and the other may be undercharged.

Cheers,

Gus

[H.A.]

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[eamarquardt]

.............. over-analise.................

I'm not "entirely convinced" that it was a typo.

Gus

[8ball_99]

Thanks for all the replies. I figured I'd post an update. Got most of my new add ons in now. The hatch is all done, Both batteries are in and wired. I went with the first figure except for each item I pulled off each battery. Meaning like the inverter is connected to the postive of one battery but the negitive of the other. I did that with all the connections. So this should cause the drain or charge to be spread even over both batteries.
I got my 600 watt True sine wave inverter in as well as a remote power switch for it. Its hardwired into one circuit with a transfer switch. So its very simple to use.. No moving plugs around or flipping breakers on and off.. Just push the button and the inverter comes on and powers what ever is plugged into that circuit. Again main reason for getting it was to power the TV and to power some of the various chargers we have that are only 110v AC. I almost wish I would have went ahead and gotten the 1000 Watt one so we could run the microwave for a min here and there with out needing to run the generator. But that inverter was almost twice the price and from what I've read pulling that much power off of just two batteries even for a short time isn't a great idea. I have the solar charger wired and installed. I also have wires ran from a junction box on the roof down to the charger. The only thing I like is getting the panels mounted on the roof. I'm waiting because I ordered 2 more 80 watt panels. They should be here in the next few days. Plan on installing all 4 at the same time. I was going to just mount the two I have and see how it goes. But the more I think about the numbers I don't think two would do what I wanted. Besides with the way I plan on mounting them it will be easier to mount all of them at the same time vs trying to add the other two later.
Inverter mounted under the cabinet

Inverter power switch

Solar charger with the cover off,

Hatch with the two batteries all wired up. And some camping chairs, fold out grill table and my leveling blocks. With all that there is still room for more in the box!

Hatch closed