BATTERIES Two 6's in series or two 12's in paralell

This is more of an RV question but can apply to tractors or my RV when I go to a Tractor Show, I also posted it on RV Net so here goes:

Okay, I'm a retired Electrical Engineer so understand most of this topic, HOWEVER Im always puzzled when I hear someone say "its better two operate two six volt batteries in series then one twelve volt" (or two 12's in paralell if you run two batteries).

FIRST THE GIVENS: Now if maximizing your total "stored energy" is your main concern (thats mine when I dry camp), let me offer this.

1) Stored Energy is measured in Volts x Amps (instantaneous power) x Time, thats what the utility charges you (Watt Hours) for and thats one battery energy storage rating i.e. its Amp Hours of STORED ENERGY.

2) If you run two 6's in series, the voltage is additive, but the CCA nor the AmpHrs of stored energy is additive i.e. if you have two 115 AH 6 volt Trojan Golf Cart batteries wired in series, the total AH the two can store remains only 115 AH (its just that its now at 12 volts. The thing is the two in series cant pump out any more amps then either one can (CCA doesnt double), the amps dont add like if they were in paralell. Similar, if one can provide x amps at 6 volts for x minutes (stored energy), then two in series still can still only deliver that same x amps for the same x minutes. CCA NOR AH ADDS IF WIRED IN SERIES. In a series circuit the amperage is the sameeeee.

3) HOWEVER if you place two 12's in paralell BOTH the AH and CCA is additive i.e. if you have two 115 AH 12's in paralell, the total stored energy is now 230 AH AND MORE STORED ENERGY IS WHAT I WANT DRY CAMPING. Similar, if one can pump X amps of CCA, the two in paralell can pump out 2X of CCA.

4) Now, deep cycle Marine or RV or Golf Cart batteries are ALL designed more for a slower deeper discharge and then they get replenished versus an auto starting battery. You hear people bragging about using two Trojan 6 volt golf cart batteries in series, but they, like marine or RV deep cycles, are still designed for deep cycle use, so unless theres some hugeeeeeee difference in quality and design I just dont see why the two 6 volters in series is so much better????????

5) CAVEAT its true if two are in paralell and one is bad it can cannibalize the other. Thats why I ALWAYS run the same type size brand and age of batteries if wired in paralell. However, this isnt quite as bad with two in series (cannibals) although the two are no better then the weakest.

QUESTION So if I want to maximize my STORED ENERGY I say (and I do) use two twelve volt batteries in paralell instead of two six volt batteries in series. Now tell me why thats wrong if you can show it is????? I'm lookin for science and engineering here not just me n dad prefer two 6 volt Trojans and used em for years. If AH and CCA adds if wired in paralell but not if wired in series and more AH of stored energy is my goal (more dry camping) THEN WHY WOULDNT I USE TWO 12 VOLTERS IN PARALELL?????

As Jimmy Buffett sings in "He went to Paris lookin for answers" Im lookin for answers to questions that bother me so lol

Old John T and all

Series doubles voltage parallel doubles current.
Series connect - to +

This has been discussed at length and if there's been a DEFINITIVE answer given, I don't recall it. I'll be interested in seeing some facts........as opposed to opinions. Mr. Deere thought that two sixes were better on many of his tractors (I've got some), but I'm not sure of his reasoning...............

You are an Electrical Engineer, but you don't understand this ....... right.

If you're an electrical engineer and don't understand it, I won't even try.

All I know is I've had far fewer battery issues on my D19 since I put two 12's in parallel in place of the original configuration of two 6's in series.

Goose, that's the same experience, that I had with my D-19. I know it aint the answer John's lookin for, but I never were too technical, as long as the answer is right! Back in college they were big on the metric system, said we had to learn it. One professor asked me to convert 12 ounces to milliliters. I rattled off 355, without batting an eye, or lifting a finger. He said to prove it mathematically, so I lifted up the Bud can I was drinking from, and said, label says so right here. He stopped askin me questions, after that.

last time the 4630 needed new batteries, it was a no-brainer for me. i replaced 2 6V with 2 12V, each 12V battery cost less than each 6V, and each 12V was same CCA as each 6V. so for less $$ i got twice the CCA. at the same time i also made up new cables, #00 and soldered my own ends on. after that it spun over faster than i EVER remember before. i just chose a 12V battery that fit in the same box as the 6V that came out.

The part I DO NOT UNDERTAND is why some folks insist two sixes in series is somehow better??? Its their reasoning Im lookin for, cuz maybe Im missing something and a body is never too old to learn I figure

John T

Deere did it way back when because the batteries werent available that are available today

John T

Goose may given the best answer,but I have found there is two answers.Depends on your load,for short heavy draws=2-12s,but for long steady draws your 2-6s will still be going a lot longer because the 12s never fully recover. I have had to go to 3 or 4 12s(27M or 31HM) to last as long as 2 6 volt golf cart,(in a trailer)that I can't find in my book now,they are apx.14x24-26x12 and weight about 110 to 120# apiece,almost like a fork lift.The 12s are more practial because they can be used for something else.May not be your answer,but for parking 1-2 weeks was mine.

I'm not going to debate any of the answers given, i just know that when i replaced my r-v batt, the tech suggested putting in two 6-v golf batt, they worked really well for me, good power to drain down, recharges better and quicker, the only mistake i make when i traded r-v in for another, i didn't keep 6-V's to put in new one...oh well maybe next time.

the 6 volt bat has more staying power. it will crank longer more torque. but not as fast.

A six volt battery is simply three battery cells hooked in series and stuck in a plastic box. A twelve volt battery is six battery cells hooked in series and stuck in a plastic box. So when all is equal, all IS equal.

The difference years back was that many 6 volt batteries had thicker plates and held up better in severe use; especially around vibration (like in tractors).

Now? There are plenty of HD 12 volt batteries around.

By the way, the Trojan T-105s are not really considered true HD deep-cycle batteries. Trojan L-16s are more HD. Rolls-Surrette even heavier.

I use a pair of Trojan T-105s in all my RVs simply because they are cost-efficient. Most I've had have lasted over 8 years and I've got a pair I'm using now that are approaching 10 years. Same with the equivalent from Deka that you can buy through NAPA.

Trojan T-105s were a great buy a few years back at $50 each. Now they're over $100.

As to your setup of two twelves in parallel being just as good as two sixes in series? Maybe. You'd have to define "good." To me, the cost over time is what makes that determination. You can buy 12 volt car batteries and get a long pro-rated warranty. You will NOT get much a warranty with HD, commercial, or deep cycle batteries. So, it's a toss up.

I've got a bank of 12 Deka deep-cycle six-volt batteries in my cabin that are now 8 years old. I've been contemplating what to replace them with when they go. When the time comes, it will depend on price and anticpated life - not whether they are 6 volt or 12 volt.

By the way, some of the longer lasting batteries on the market are sold as single 2 volt cells. They can last 20 years and are pricey.

One battery I'll never waste money on is an aborbed glass matt (AGM). I've yet to see where they are even close to being cost-efficient. But, you can run them upside down which might give some people a thrill.

Joining the dialog.
None of it matters very much.
All calculations depend, in fact, on two ingredients. The amount of surface area (including sponge architecture to enhance the active ion exchange surface) of active electrode in the batteries. and the chemical performance of that surface.
A small factor in parallel configuration is the doubling of cables where tey are attached in parallel.
Jim

Hello John T
When you series 2 batteries you double or add the voltage. When you parallel 2 battery you double or add the amperage. V X A equal watts or power. The more batteries in parallel the more storage of power you will have, 2 or 3 or 4 and all should be the same capacity. If you need 12 volts then use 12 volt batteries, as many as you need.
Guido.

Simply put, the old 12s were not well matched. Manufacturing processes did not produce units similar enough to prevent problems. The real issue is internal impedance, ie the drain while sitting doing nothing. One battery was typically a small load for the other at all times when sitting. If used/charged very very often then no harm, but in days gone by batteries that sat didn't tolerate that very well. Acid batteries just do not like being below their quiescent threshold. Chemically it kills them fairly quickly.

I just use a single 12, as it produces more than the original pair of sixes and I don't have to deal with cold all that often. A pair of jumpers can fix the occasional shortcoming.

John T I use two 12 volt deep cycle RV batterys in my Camper. 85 Yellowstone "Century" 23' pull behind. I am satisfied with performance. But have a 4 KW Kohler Gen Set on back bumper for recharging and AG when I need it. Run it about 2 to 3 hours a day to recharge Batterys. I can go about 4 Days on the charge without recharging.

I will take a shot:

Perhaps the difference is that the twelve volt array will have double the internal connections (in the batteries) and a longer current path to accomplish the same task.

It would seem that the six volt array would have less impedance. Whether it is measurable is probably debatable, however there would seem to be less connections to fail.

Brad. (definately not a 'lectical engineer)

Interesting question. I had to read it more than once. You want to know why they think two 6 volts are better. Thats like asking if Coke is better than Pesi. My guss it would be how some one heard or learned about battery's. No rhyme or reasen. Some people hear something and thats it.

When I need to make a choice of battery's I try to use the kiss method. (keep it simple stuped). Same when you try to dia. some thing. Look at the loads and intened use. Then make your choice.
David

i dunno....beats me. my old bucket truck had two 6v's in series to get 12v to run the boom. (now i just stick a couple 12v's in there, hook the generator up to the big battery charger in the back and head to the woods. i have a crown lift truck at the shop that uses 4- 6v batteries wired up so it gets 12v. beats me.

John,the JD 30-40-50 series tractors ran two 6V batteries in series, starting with the 55 series, they wired two 12V in parallel.
a real common conversion on the 30-40-50 series is to replace the two series wired 6V with a large single 12V in the left battery box and short heavy cables directly to the starter. They usually they pick up 50-100 extra cranking rpm. Removing that 3 ft jumper cable and two cable / post connections, seems to make all the difference.
One 1000CCA battery seems to do well in a "summer" tractor, while a pair of them using 4 cables directly to the starter do best for a "winter" tractor that sees long haed cranking during a cold start.
Never saw any of them that did not gain by eliminating the series wired double 6V setup.

I have three paralelled 125 AH deep cycle 12 volt batteries in my RV, thats 375 AH of stored energy plus a solar rooftop panel and an Onan 4 KW genset. If needed every 3 or so days I start the RV and let the engines 80 amp alternator top off the batteries, Im good to go

John T

YES you have it correct

Fun Chat, John T

My battery experiance tells me if I pick the wrong ground the alternator in my dads TD6 starts smoking (but only once).....