Ohm's law perp?

[ajay]

Electrical options are very confusing to me. Thinking about our 21, we want solar panels and don't really understand 2x6 volt batteries v 12 volt system. I think 2x6v system provides more storage, is more durable, more expensive, and has longer battery life. Also much larger and heavier.

What about using 2 x 12 volt batteries? Might not last as long, but smaller, lighter, and cheaper. Would this double 12 volt hookup provide a lot of electrical storage?

My goal is to be able to camp w/o hookups without running out of juice.

I read about standard controller(?) doesn't fully charge battery(ies) from solar panels. What substitutions/modifications are necessary for any of the battery combos above?

Thanks for your help.

[cpaharley2008]

Here is a good start The 12volt Side of Life (Part 1)
parts 1 and 2

[escape artist]

Hi: ajay... Just replacing our 2007 Interstate Magnatron Grp. 27 Deep Cycle 12V. My discounted $$$'s for a Trojan SCS200 is $193.99. Should last another 6-8 yrs with proper care.
Granted we haven't done a lot of dry camping our style seems to be changing that way. What I'm saying is double dollars for 2 batteries will be expensive. Alf
escape artist N.S. of Lake Erie

[Vermilye]

More than anything else, what determines how long you can boondock (electrically) is amp/hrs. Whether you use 12V or 6V batteries is really irrelevant. Another rough method of comparing the capacity of batteries is by weight. That said, there are differences between battery types.

Most 6V batteries are deep cycle and will stand up to repeated deep discharges & recharges better than the standard automobile starter battery. There are deep cycle 12V batteries that cycle just as well as 6V batteries, however they are expensive & more difficult to find. For example, a 12V true deep cycle battery (Interstate US 185HC XC) provides 220 amp/hrs and costs around $370.00.

There are also 12v batteries with a combination of deep discharge as well as low internal resistance that are a good source for powering inverters (better for that purpose than a single pair of 6V batteries). They don't hold up to deep cycling as well as a 6V battery, but are generally less expensive.

For a general comparison, the Flooded Cell 6V batteries supplied by Escape for my 17B are Interstate U2200s rated at 232 amp/hrs. Since you must series the batteries to obtain 12V, the total amp/hrs available are 232. Each battery weighs 62 lbs. Typical pricing runs around $130.00 each.

A pair of Flooded Cell 12V Group 27 deep cycle trolling batteries are rated at around 105 amp/hrs each. Since they are wired in parallel, the amp hrs add so you end up with around 210 amp/hrs for the pair. Each battery weighs around 70 lbs. Typical pricing is around $150.00 each. If you want a sealed battery, they run closer to $200.00 each for AGM technology with around the same amp/hr capacity.

The typical Everstart Marine starting battery you will find at Walmart rarely lists amp/hrs so it is difficult to compare them to deep cycle batteries. At 50 lbs each, there is far less lead, and far fewer amp/hrs. Price around $78.00 each. You need to shop carefully for their deep cycle trolling batteries - they sometimes list amp/hrs, but not at the standard 20 hour rate, making it difficult to compare them with true deep cycle batteries.

[Brian B-P]

Although people often claim differences between 6V and 12V batteries, they're usually comparing apples and oranges. You can buy batteries in 2V, 4V, 6V, 8V and 12V which are constructed exactly the same way, with the same performance. If you can find the right sizes, you can build up a 12V bank from three 4V in series, two 6V in series, or one 12V... and double the capacity of any of them by adding another set in parallel. The construction matters, but how many plastic boxes you split the lead plates up into doesn't. As Jon mentioned, desirable batteries in 12V are available, just not as common as 6V and thus expensive.

There is a legitimate difference between series and parallel. If you resort to putting two 12V batteries in parallel because one is not big enough, the two batteries don't share the load perfectly, which doesn't help reliability.

Usually, people are comparing relatively inexpensive consumer-grade 12V deep cycle batteries (two of them in parallel) to commercial-grade 6V deep cycle batteries (two of them in series), to conclude that the 6V are more durable.

Battery trivia: for RVs, the popular setup is two 6V batteries in series, in a size referred to as the "golf cart" size. I looked for data about golf carts (which are actually called golf cars in the industry), and all three of the manufacturers I checked actually use six 8V batteries to form the 48 volt bank that they need, not eight 6V batteries... those golf carts don't use the "golf cart batteries"