Dual battery in series. Where to attach load?

[dmwhiteman]

I've been doing a lot of research on wiring up house batteries and I think I have found the correct setup but cannot find a definite confirmation. I am going from 1 12v 92ah battery to 2 6v 200ah batteries. I chose this option as it doubles my time while keeping the amount of cells to a minimum. The setup is in the bed of my truck.

I run them in series to obtain 12v, correct?
Connect the positive from battery 1 to the battery isolator (which attaches to the + of my starting battery).
Connect the negative from battery 2 to the chassis.

Here lies my question. I found a lot of information on charging them so power is distributed equally, but adding the load is what is questionable. Does it matter where the + and - go as long as it bridges both batteries?

Here are my mockups. Is there a difference?



All help is greatly appreciated. Thank you.

 

[DaveNay]

I'm pretty sure method #2 will result in zero voltage at your fuse box.

Method #1 is the correct wiring.

 

[AndrewP]

LOL. The first diagram is correct.

The second diagram is zero, not even +6Volts.

 

[dmwhiteman]

I'm pretty sure method #2 will result in zero voltage at your fuse box.

Method #1 is the correct wiring.

Your first example is correct for powering 12v systems.
Second example would provide 6v between positive & chassis.

But !
If you happen on a 6v appliance, dont get any bright ideas of utilising this as a 6v source.
It will work, but its a big detriment to battery longevity.

LOL. The first diagram is correct.

The second diagram is zero, not even +6Volts.

I am so glad I have this forum! I have a general understanding of wiring, but I have never done anything with more than 1 battery. Thanks so much. Can't wait to get my rig the proper power. I tried running an Igloo Kool Mate yesterday and after about 6 hours depleted nearly half of my 92ah battery. Next step, convince the wife to let me buy an Edgestar fridge!

 

[rayra]

I think your entire base premise is mistaken -

" I chose this option as it doubles my time "

400ah @ 6v vs 184ah @ 12v. A 6v amp-hour is not the same as a 12v amp-hour. Consider the Watt / power formula, you aren't gaining double the duration, the total power at 12v is nearly the same.

The only thing you are gaining - or should be going after - in a 'house' configuration utilizing 6v DEEP CYCLE batteries is the ability to draw them down to a greater degree without doing them any great harm. Where a similar draw down on an automotive starting battery design would damage the battery.

 

[Hopeless Diamond]

His single 12v was 92amp-hour. The 2 x 6V 200ah connected in series will provide 12v 200ah, so double the capacity of what he had

 

[rayra]

If you are incurring the double battery footprint and weight, it's nearly the same. Then the only significant issue is the draw-down I referred to. He's not getting double the runtime because of using 6v, he's getting doubling because he's using TWO batteries. He could have nearly the same runtime using TWO 12v batteries instead. My point was a poor attempt to make that clear.

And I'd further add that in a mobile vehicle rig, I'd rather use two standard 12v automotive batteries so that my aux can be used to replace a failed primary. Then use a passive solar to keep the house loop boosted, or idle the vehicle for some period when needed. If it was a fixed location, then 6V deep cycle all the way. BIG 6v as in golf cart batteries. For a mobile rig, it would be ebetter to use a 12v deep cycle battery a la an Optima Yellow top or similar product as both primary and aux, for interchangeability. IMAO.

 

[4x4junkie]

200Ah @12V is actually more than double 92Ah @12V. The battery configuration he used to attain figure that isn't relevant.

I would agree the idea of keeping with 12V batteries for interchangeability does have some merit though. I went back & forth a few times debating whether to convert my two 12V deep-cycles to two 6V deep-cycles a bit over a year ago, but wound up sticking with two 12V ones just for the redundancy it provides.

 

[dmwhiteman]

I think your entire base premise is mistaken -

" I chose this option as it doubles my time "

400ah @ 6v vs 184ah @ 12v. A 6v amp-hour is not the same as a 12v amp-hour. Consider the Watt / power formula, you aren't gaining double the duration, the total power at 12v is nearly the same.

The only thing you are gaining - or should be going after - in a 'house' configuration utilizing 6v DEEP CYCLE batteries is the ability to draw them down to a greater degree without doing them any great harm. Where a similar draw down on an automotive starting battery design would damage the battery.

I chose 2 6v over 2 12v to keep my "moving parts" to a minimum. Less prone to failure. As well as the ability to run them near dry.

200Ah @12V is actually more than double 92Ah @12V. The battery configuration he used to attain figure that isn't relevant.

I would agree the idea of keeping with 12V batteries for interchangeability does have some merit though. I went back & forth a few times debating whether to convert my two 12V deep-cycles to two 6V deep-cycles a bit over a year ago, but wound up sticking with two 12V ones just for the redundancy it provides.

It was a tough decision. Do I use an extra 12v in case my starting battery dies, or do I take the risk and have more run time? I always wheel with several people and figure if I wake up in the morning to a dead starting battery, there is always someone to give me a jump. And living on the east coast, there is never a place that is so far from civilization I couldn't easily pick up a new battery.

 

[dwh]

Diagram 1 for sure.

Addressing the reliability/redundancy point..

If you use 2x6 and one fails, you have no aux battery bank at all. Using 2x12 and one fails, you can cut out the dead battery and still have a functional 12v aux - but with half the capacity..

 

[calicamper]

I recall the primary reason we used 6v batteries in the boats I sailed on was due to constrained space and limited locations where we wanted the weight and where we wanted the batteries mounted. There was no advantage running 6v batteries over 12volt batteries other than you typically had more potential locations you could stow smaller batteries. With a vehicle like a truck or RV that doesn't make a whole lot of sense as pointed out that the more batteries your using the more parts you have prone to failure and if one 6volt battery fails the other 6volt battery is pretty much useless for any sort of power use. So from a vehicle stand point it makes more sense to fit a 12volt battery which can be used for the vehicle if needed.

 

[dlh62c]

The first diagram is correct.

You'll want to add a fuse or circuit breaker between the positive post and the fuse block. Adding buss bars coming off the load side of the battery bank will facilitate any connections you need to add for solar, the fuse block and monitoring the state of charge of the battery bank.

 

[dmwhiteman]

The first diagram is correct.

You'll want to add a fuse or circuit breaker between the positive post and the fuse block. Adding buss bars coming off the load side of the battery bank will facilitate any connections you need to add for solar, the fuse block and monitoring the state of charge of the battery bank.

Do you mean fuse the fuse box? I have a fuse between the secondary batteries and solenoid, and the solenoid and the main battery

 

[dmwhiteman]

Here is the box installed. 2x215Ah GC2 batteries. There are several holes drilled around the sides and back to help with venting. Hopefully that won't be an issue. 150A fuses between the solenoid and batteries. There is plenty of room inside the box for additional pieces as the setup grows.

 

[workerdrone]

I understood that the argument for 6v batteries vs 12v batteries was that the plates in a 6v battery would be made thicker and more durable, since there were ½ as many of them in the enclosure. So yes, you don't get the redundancy and ability to fail back to only one battery - but, the resulting bank is likely to last longer (more abuse handled, more discharge cycles)

So - more durable? or redundancy? Pick your preference