2-6v series / 2-12v parallel , 50% draw = Ah ?

[regis101]

Hello. I'm kinda missing something here. I did a search and read a few threads/pages but...

Using two six volt , ~200 Ah batteries, in series gives 12v and ~200 Ah.
Using two twelve volt, ~100 Ah batteries, in parallel gives 12v and ~200 Ah.
If any of this is incorrect , please advise.

My question then,
Would the 6v set up be a ~200 Ah draw down to 50% and the 12v set up be a 100 Ah draw down to 50% ?

Thanks,

 

[tx2sturgis]

Your math is good.

And the 50% depth-of-discharge on either combination is 100ah. (half of the 200ah total on either combination)

 

[regis101]

Cool. Thanks. It's good to read stuff and be able to bounce it off someone.
I surmise the conclusion is the two 6v setup will last longer, comparatively speaking.
Thanks again.

 

[highdesertranger]

however the 6v are true deep cycle the 12v are not. of course this a generalization but is true 90% of the time. highdesertranger

 

[tx2sturgis]

The theoretical draw to 50% is 100ah in both examples assuming both pairs are true deep cycle.

But HDR is correct also: the design of the batteries may mean longer service life from the two 6v batteries, especially if the two 12v batteries are not true deep-cycle.

 

[Ticklebellly]

My question then,
Would the 6v set up be a ~200 Ah draw down to 50% and the 12v set up be a 100 Ah draw down to 50% ?

No.   In both examples, you create a 12 Volt pack of 200 Ah.

 

[DannyB1954]

The 6 volt batteries tend to have thicker lead plates in them so they are better at low drains over longer periods. The 12 volt batteries have thinner plates so they can put out more amperage quicker but for less time. One advantage to 12 volt is if one battery dies you can still make due with the single battery for a time. Batteries in series need both batteries to function. I also have had better luck replacing one 12 volt than replacing one 6 volt battery. In series you will only get what the weaker battery has to offer as the currant has to flow through both batteries.

It also depends on what type of loads that you have. I am running an air conditioner off of my solar, so I need batteries that can not only put out surge currant for starting the compressor motor , but also recharge quickly. When clouds go over the solar panels, the batteries have to bear the load. When the sun is back out the solar needs to run the A/C and recharge the batteries. I went with two 12 volt. As long as they can run a fan and my refrigerator over night, My solar will recharge them quickly once the sun comes up, ( I have 960 watts on the roof).
I am happy with my 12 volt Walmart maxx 29DC batteries, But most likely someone will jump in and tell you what an idiot I am because I don't jump on the deep cycle band wagon. For me, deep cycle would not work. Paying $400 per battery also will not work. If my $100 Walmart batteries die in two years, I can go to any Walmart and get a new one for free. If they die after that, oh well I got more than my money's worth out of them.

Figure out what your loads will be and how much time it will take to replace that energy. If you are running a low load for a couple of days before a recharge, (maybe because of weather), a deep cycle may be for you. If you recharge by driving or with a generator and battery charger every day, you may want something that takes a charge quicker so that you can turn off your charger after a couple of hours. The maximum rate that you can charge two six volt batteries in series is what a single battery can take. The maximum rate of charging two batteries in parallel will be double what a single battery can take, (each battery will take half of the currant). If you have a kick ass charger, do you want to spend half the day recharging at the lower rate?
The same size shoe does not fit everybody. What fits one may not fit most. Don't let experts insist what you should use.

 

[regis101]

* In both examples, you create a 12 Volt pack of 200 Ah. * I was hoping to be able to lean on the 6v setup a bit more, from a mechanical viewpoint of each being a 200 Ah capacity, but watts is watts.

* The maximum rate that you can charge two six volt batteries in series is what a single battery can take. The maximum rate of charging two batteries in parallel will be double what a single battery can take, (each battery will take half of the currant). * This is good to know if/when designing a system.

 

[Ticklebellly]

I was hoping to be able to lean on the 6v setup a bit more, from a mechanical viewpoint of each being a 200 Ah capacity, .........

Not sure what you mean by "lean on".   It might help if you consider why 6 Volt packages are offered for sale.   Generally, 6 Volt batteries are intended to be used as traction batteries.   In a warehouse or golf cart situation, traction batteries typically come off overnight charging and get used without much attention to how far they are drained in daily use.   These batteries then go on charge at the end of the day.   A 6 Volt package is also about half the weight of a similar capacity 12 Volt package.   A 6 Volt package is much easier to handle and install because the weight can be handled by one person.   One small caveat to think about, a traction battery is generally known to get a hard life in use so plate design is often designed to be a bit more robust.


The major difference between a 6 Volt battery and a 12 Volt battery of similar technology and design is the number of individual cells in the package.   A deep cycle design spec is essentially the same and only the number of cells in the package varies.