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Old 10-04-2007, 09:34 PM   #1
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Series or parallel

In the airstream owners guide Parallel or Serial for your Battery Bank? it states that a parallel arrangement of two 12 volt batteries in parallel gives more capacity because of peukerts effect. A discussion on the another forum has proven otherwise Peukert Says 6v Batteries Same As 12v - Topic Powered by eve community some may have given up the advantages of six volt in series for 12's in parallel in order to take advantage of the unsupported claim of parallel capacity advantage.
It appears that that the effect of adding a second battery in parallel to an existing 12 volt battery, more than doubling the capacity because of the peukert effect, ie, less current draw per battery has been confused to mean that parallel is superior to series with regard to capacity, all else being equal.
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Old 10-04-2007, 10:02 PM   #2
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Either way will work. Each has its benifits and problems. The upshot. Two six volts in series lots of capcaity but if one goes bad both might as well be dead. Two 12Vs not quite as much capcity but if one goes dead you can diconnect it and run on one.
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Old 10-04-2007, 10:20 PM   #3
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12V batteries are cheap, easy to get, and generally reliable. 6V batteries are only available from specialty battery companies, and often carry less warranty.
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Old 10-04-2007, 10:48 PM   #4
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Yep

Quote:
Originally Posted by uwe
12V batteries are cheap, easy to get, and generally reliable. 6V batteries are only available from specialty battery companies, and often carry less warranty.
Agreed. Any extra storage capacity thought to be derived from 2 -6V batteries connected in series is defeated by the extra cost and decreased reliability. Deep cycle 12V batteries connected parallel are much more practical.
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Old 10-04-2007, 10:54 PM   #5
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I support the second source cited above, that says series connection is no worse than parallel. I think the Sierra Website is great and they are an outstanding source of information. However, in this case I think they analyzed the problem incorrectly.

Also, in a practical sense, most 6V batteries have MUCH lower Peukert factors (better) than 12V batteries. So I am willing to believe that series is better when used to power heavy loads, like lift trucks and golf carts.

I don't think it's what I would use to decide on a RV battery system. I would choose 12V on price and redundancy.

If I was installing a big bow thruster on a 40ft boat it would be a different matter.
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Old 10-04-2007, 11:57 PM   #6
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Quote:
Originally Posted by CA Streamer
Agreed. Any extra storage capacity thought to be derived from 2 -6V batteries connected in series is defeated by the extra cost and decreased reliability. Deep cycle 12V batteries connected parallel are much more practical.
CAS,

I must beg to differ! Your statement might be true for just any run-of-the-mill batteries, but if you have read any of my numerous posts on this topic, I am a strong believer in Lifeline AGM batteries with their 5 year warranty and normal 6-8 year effective life when kept properly charged. I've seen a few Prevosts with 8/9 year old Lifeline 8-D batteries and they are still going strong!

Extra cost....yes. Decreased reliability....sorry, but I must disagree and I have a very large contingent of high-end motor home manufacturers who are on the same page with me. These batteries are built better than anything else out there with larger, heavier plates and stronger cases. You will also find them on all of our military's aircraft.

On just about every new MoHo I service with a cost over $200K, you will find 6 volt golf cart batteries, usually 4 of them, connected in a series/parallel fashion. They yield much more useable amperage, deeper draw downs and longer battery life. I change out at least a dozen coaches a year that have 12 VDC batteries to the 6VDC golf cart array every year. I'm talking actual useage here, not some numbers printed on the side of a battery or a manufacturer's claim.

And if you are talking Lifeline AGMs, You can also add just about every major solar power supplier to this list, as AGMs provide much faster charging from the solar arrays, much deeper discharge capacities than any other battery, and much longer life.

My information and opinions come from my real-life experiences in the field and not some manufacturers theories. Also, as a new dealer for AM Solar, these are the only battery that we will install in a new solar system.

It's your money and you of course can spend it any way you please, but if you want the best batteries out there, Lifeline AGMs win hands down!
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Old 10-05-2007, 12:15 AM   #7
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Old 10-05-2007, 07:26 AM   #8
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Two six volts in series will only deliver the cap. ie. reserve of one, four or more in a series parallel arangement will greatly increase capacity, that is the reason for high end MHO's using six volt 31's. Have you got room for six or eight batts in your AS?
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Old 10-05-2007, 08:30 AM   #9
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Quote:
Originally Posted by jkcru
Two six volts in series will only deliver the cap. ie. reserve of one, four or more in a series parallel arangement will greatly increase capacity, that is the reason for high end MHO's using six volt 31's. Have you got room for six or eight batts in your AS?
Beg to differ, but most of the units I work on (Monaco, Newmar, Tiffin, American Coach, Prevost, Newell) use 4CTs and now the newer high capacity 6CTs. The 4 batteries that I see in most (with the exception of the all-electric coaches) yield 440 amp/hours and the new ones provide 600 amp/hours.

The 2 GPL-4CTs that I have in my 19CCD added insignificant weight, yet yield more useable amp/hour draw down time than the garbage Interstate GP-24s that it came with.
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Old 10-05-2007, 08:48 AM   #10
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What are you differing with Lew? Series or parallel, capacity or what? My Monaco Exectuive has Six 6 volts in a serries parallel arangement, it' heavy and takes up more space than I have in my 23 ft. AS, Which has space for only 1 batt from the factory. I have gotten Two in it but, my only option was dry cell 12 volt in parallel at about 180 amp hr ea.
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Old 10-05-2007, 12:56 PM   #11
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so lew, can we say you might be a series guy in a parallel universe? ;-)
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Old 10-05-2007, 07:26 PM   #12
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The owners guide says that parallel will give more capacity than series because the current drain is less per battery in parallel. But, in parallel the capacity of the 12 volt is half that for the 6 volt for the same overall energy per battery. The reduced current per battery of the 12 volt parallel is the same as the reduced capacity for the same overall current density in the plates for series or parallel.
Has anyone out there chosen parallel in the belief they will get more effective capacity due to peukerts?
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Old 10-05-2007, 08:01 PM   #13
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Quote:
In the airstream owners guide Parallel or Serial for your Battery Bank? it states that a parallel arrangement of two 12 volt batteries in parallel gives more capacity because of peukerts effect.
This is another one of those nifty, constructed, 'debates' based on misrepresentation and innuendo, I think.

The owners guide uses a simple calculation of Peukert's relationship between current draw and available energy capacity in the typical RV battery as an example and illustration that there is no simple answer to the serial or parallel question.

If someone thinks the situation was analyzed incorrectly, they should say how. You can see exactly the same results as the owners guide obtains in any spec sheet for batteries that lists two or more AH ratings at different current rates.

One problem is that you can't really compare 6v and 12v batteries in single vs bank configurations because the Airstream RV load is 12v and you can't run that from one 6v battery. That is why "The reduced current per battery of the 12 volt parallel is the same as the reduced capacity for the same overall current density in the plates for series or parallel" is nonsensensical.

So much nonsense on this topic - just look at the quick answer given on the page in question and then wonder why some folks take off on an example used to illustrate it? Are they looking for - what? It's certainly not lookin for learning about batteries and their behavior in RV service.
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Old 10-05-2007, 08:04 PM   #14
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batterys

Parallel batteries offer something series batteries can never do.

When batteries are in series and one gets weak, it's over and done, just like the series Christmas lights.

Batteries in parallel can have one get weak as well. Simply disconnect it, and you still in business.

Watts are watts, series or parallel, doesn't matter. Two six volt batteries in series that each have 200 amps totals 2400 watts.

Two 12 volt batteries in parallel at 100 amps each, gives 2400 watts.

A 1200 watt battery, for all purposes, is the same size, regardless if it's 6 volts or 12 volts.

Ohms law, is never wrong. W=EI

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