6volt batteries in series

[mcgovski]

I am about to upgrade my 12volt Battery system in my camper (no its not a fancy custom camper, just a normal cab over), I have got my choices narrowed down to using:
2 x Interstate 2200 6 volt
or
2 x Deka AGM 6 volt

By going in series I will increase my amp hours from 84(current) to 225, that is my motive. I want to plug in less. I also have 2 x 100 watt solar panels.

Other questions:
My current battery box is in between the aluminum studs of the camper and the box is not big enoug for 2 batteries. But I do have room behind the box, that I could access from the galley. So, would it be possible to store the 2nd 6volt in this space in a separate, secure box and "plumb" the boxes together for the wiring and venting?

Also, I have heard that AGM batteries dont off gas and dont need venting...true/false...it sounds too good to be true.

Thoughts, pros/cons to the battery types and the storage/plumbing idea?

Thanks
(please dont tell me to go to RV.net, its rare that questions I have posted there actually get addressed. Replied to, but not addressed... thats my rant, sorry.)

 

[peekay]

I don't see why not. Keep in mind though, the farther apart they are, the thicker wire you'll need to connect them. This wire will likely function as your limiting factor, so the heavier gauge the better. If it's within 6' of each other, I would go to the auto parts store and buy some replacement battery cables in 0 or 2 gauge. Or you could always add two wires to each terminal if you find out that 0 or 2 gauge is not enough.

AGM's aren't supposed to vent toxic fumes when being charged. That would probably make it ideal since your second battery will be indoors and probably enclosed. They also sell vented battery boxes, you may consider those. Check out arrow trailer supplies.

 

[ntsqd]

When I was on the school's HEV team we got a bank of Optima yellow tops for the car. The Optima rep told us that if we hear the batteries venting during charging that we are hurting them, that under normal usage they should not vent.
I would imagine that this would hold true for any AGM battery.

 

[\\'anderer]

Separating the batteries should not be a problem. The camper is not drawing large amounts of amperage. These batteries are for the camper and not the vehicle itself?

Use a large gauge wire, no need to go overboard ,2 gauge is probably more than enough, and keep it as short as possible. I also like to make my own cables rather than buy the pre crimped. Any of the better auto parts stores can get cables and ends. Crimp them and solder them and heat shrink the ends.

Two AGM style batteries would be the way to go especially around aluminum. Battery acid likes aluminum:eatchicke

 

[mcgovski]

Thanks for the feedback. I think I know what I am going to do. I know there are not a lot of cab over campers here, but I will take pictures and post up the battery job if anyone is interested. We are hitting the road on wednesday, so I am hoping to get it done over the weekend.

Thanks again for your suggestions.

 

[egn]

I wouldn't separate into two 6 V batteries because in the long run both batteries will more and more get different voltages. This cause one of them overcharged and the other one overdischarged. The life time of both batteries will be reduced drastically. The reason for this is that the lead poles within a battery have a much lower tolerance than two separate batteries.

Problem like this can be only reduced by balancing both batteries. There are several methods to do this:

1. overcharging of wet lead acid batteries with voltage clamper
2. electronic balancing device
3. separate chargers for each battery block

For my 24 V system I use the battery equalizer from Power Designers. But this is not available as 6 V device. So I would recommend to use two separate 6 V chargers for occasional charging to prevent long-term unbalance.

 

[mcgovski]

I am running the batteries in series, so the draw will be 12 volt balanced. This is not in parallel but in series so I dont think the drain will be imbalanced (if that is what you are saying). Also, I am getting a battery conditioner, for the batteries. That is recommended to keep the batteries memory as close to new.

If I am missing something please advise.

I am getting my info out of:
"Photovoltaics, Design and Installation Manual"
by Solar Energy International

Thanks

 

[egn]

I am running the batteries in series, so the draw will be 12 volt balanced. This is not in parallel but in series so I dont think the drain will be imbalanced (if that is what you are saying).

The problem is that is with the connection in series. As both batteries will be not totally equal they will have slightly different voltage.

Example:
The voltage of the battery string will be 12.6 V. But this voltage can be the result of one battery having 6.2 V and the other 6.4 V.

Now lets charge this battery string with 14.4 V. Each single battery should have 7.2 V. But the reality will be that one may have 7.5 and the other 6.9 V. The result is that the first battery is overcharged and the second is undercharged. When the charger terminates charging one may have 100 % state of charge and the other only 80 % state of charge.

Now when you discharge the string to 20 % state-of-charge. The first one may have still 40 % SOC and the second 0 % SOC. The second one will have a deep discharge and fail within a few cycles.

After first installation the difference between both batteries may be only a few millivolt. But after a few cycles the difference may become larger and larger.

For more information please read http://www.powerdesigners.com/pdf/PowerCheq Paper - Motive Power.pdf . There are also some more detailed (scientific) papers available in the internet. An more easy description you can find at http://www.batteryuniversity.com/partone-24.htm

Also, I am getting a battery conditioner, for the batteries. That is recommended to keep the batteries memory as close to new.

A battery conditioner doesn't help here if it works at the complete string. If you have 6 V battery conditioners and use them regularily then you get the same effect as 6 V chargers.

If you really want to connect batteries in series than you have to balance them first by putting them in parallel and charging them with a 6 V charger at least for 24 h. And you should repeat that if the voltage of both batteries differs more than a few milli volt under load or during charging.

 

[mcgovski]

I think I am following you, but I am not quite sure.
Thanks for the links and the info