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Old 10-05-2007, 08:30 PM   #15
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leipper quote---"If someone thinks the situation was analyzed incorrectly, they should say how."

The equation in the owners guide is for calculating the capacity for adding a parallel battery across an existing battery, not for calculating any capacity advantage for parallel over series.

Parallel and series provide the same power as stated by Inland RV Center above given all else equal.

The owners guide Parallel or Serial for your Battery Bank? states "A parallel arrangement means that current is shared between batteries and this means that each battery is exercised less vigorously which may increase usable capacity."

Actually, the batteries would be exercized the same, ie, same current density because the 12 volt batteries would be half the capacity [AH] each of the 6 volts in series for the overall same power total. That is, 6C+6C=12C/2+12C/2 same lead, same current density, same performance.
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Old 10-05-2007, 09:10 PM   #16
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I drank too much wine once and had a peukert effect.
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Old 10-06-2007, 12:03 AM   #17
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The equation in the owners guide is for calculating the capacity for adding a parallel battery across an existing battery, not for calculating any capacity advantage for parallel over series.
You really really need to look at the quick answer and summary provided on that page!

adding a second battery in parallel to the existing battery is what a lot of people (and Airstream Inc) do.

and no, the batteries are not exercised the same. By definition, the voltage is shared in series while the current is shared in parallel. The current is what exercises a battery, not voltage.

and no, you can't just add some AH spec together, either, because you have to choose _which_ AH spec to use (and, as Andy noted, convert to watt hours if comparing batteries at different voltages). The reality is that just adding the common 20 hour spec together is usally close enough for most folks, but it doesn't seem to be for those who get into threads like this one.

The key is on any spec sheet. A good spec chart will have AH ratings for the 6 hour, 20 hour, and 100 hour rate as well as the reserve minutes capacity. You can easily see just how much a difference reducing current draw can make in the available energy in a battery.

consider a scenario:

If your single 12v RV battery will run a 10 amp furnace for 10 hours, you'd have a 100 AH (1200 watt hours) of usable battery energy. You figure you want to run for 2 cold nights instead of just one. So you go get another battery just like the first. You think: the first lasted 10 hours so the spare battery will give me another 10 hours for 2 nights or 20 hours total furnace time. That would indeed be the case if you ran just one battery and then the other.

But, if you hooked them up together in parallel, you'd find you could run that furnace for maybe 22-25 hours instead of just 20. Why? Because, in parallel, each battery would be supplying 5 amps to the furnace instead of 10. A 5 amp draw doesn't exercise the battery as much as 10 amps does and that means that there are lower internal resistance losses (which is basically what Peukert's relationship is all about). Since there is less loss in the battery, there is more energy available to run the furnace.

You can't do this experiment with a 6v battery because you can't realistically run a 12v furnace off a single 6v battery to get a base for comparison. All you can do is to go theoretical on load profiles, wiring, and battery specs and that is really a matter of comparing batteries, not bank configuration.

Then there are the other factors, such as temperature that can make a similar very large difference. The biggest one is how you use and maintain your batteries. As batteries get old, they loose capacity and you can do a lot of things to help them age less rapidly.

Now the question that puzzles me is why this is such a big deal for some folks?
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Old 10-06-2007, 12:30 AM   #18
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hi bryan

how ya been!

the 6v vs 12v debate is important for this reason...

mostly we a/s owners, have one or 2 12v batteries...

the '6v' proponents rave about the change over,

often without providing the relevant details/comparisons.

this leads some current 12v users to consider ditching what they have...

for something better...

which really isn't better.

i just hate 2c folks toss what they have (12v parallel) without considering all aspects of the issue.

4me it's easy. the 12 v agms in parallel work great!

it would be simple to add one or 2 more for extra capacity.

IF starting from a blank slate, with LOTS of space and no worry about weight, like the biggie mohos...

and IF expecting to power heavy loads via an inverter...

4-6 6v batteries might make sense.

otoh i'm happy with the 12v batteries, a touch of solar and a small genset.

juice from all angles bro!

cheers
2air'
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Old 10-06-2007, 02:10 AM   #19
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Quote:
Originally Posted by benwd
In the airstream owners guide...
now that i've read the entire thread over on the escapees site...

it appears this thread/post may be a lame attempt to start the same arguement/conflict here on this site...

while singling out the sierra nevada website content and author for attack.

just a suspicion, but my crap/troll detector is firing 4 bars!

so benwd, you then follow this with the question 'have any of us chosen 12v parallel based on the peukert's effect?'

look, most a/s start with a single or paired parallel 12 battery arrangement.

that's how the factory builds them!

so the answer to the question is NO NO NO...

none of us has opted for this arrangement based on mr peukert's calculation....

it's how a/s are born!

the fable is that golf cart batteries are 'better' and some have opted for 2x6v...

the comparison (6v/12v, s/p) isn't simple, with or without peukert.

i see no error in bryan's assertion that higher current draws result in less available amps/hours and conversly that...

lower current draws result in a small gain in available amps/hours...

lets NOT have that lame/childish escapee thread repeated here...

cheers
2air'

btw benwd ...
what a/s model are you considering?
what is your tv?
what hitch ya gonna use?
and so on...
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Old 10-06-2007, 07:50 AM   #20
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hey, if 2 6v are better than one 12v, maybe i'll just get 10 1.2v batteries!

i like the 12v batteries, there are less terminals to keep clean than going the 6v route.

did any of the early streams have 6v systems like cars did?
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Old 10-06-2007, 10:33 AM   #21
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I've been experimenting with a dedicated third battery this summer. This one is only hooked up to the fridge, because the beer cooler is #1 priority. This batt is rather small a 31 AH (20 hr) 12 volt gel cell. It is mounted in the rear ot the fridge access area.I've got a switch on the solar panel to flip flop between this batt and the main array of 2 - 12V parallels. Then the Honda 1000 for the hair drier and compressor.We use mood candles at nite for a romantic setting while pounding down the cold Duffs.
Why all this need for power?
Where's all the romance gone to anyway?
I'll soon by tryiny to power the fridge with a 4 amp lipo 14.8V, just for kicks.
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Old 10-06-2007, 10:14 PM   #22
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With regard to bringing it over from the escapees forum. That is what it is and the OP gave the link to the other forum. No secrets about where the information comes from.

The subject was series or parallel, and the author of the airstream owners guide came it with claims, you read it and saw the post, and the subject went from series or parallel to the claims in the airstream owners guide. The thread needs to be here so airstreamers can discuss what is in the guide.

The quick answer in the guide says to consider several factors when selecting battery configuration and that makes sense, but, if everything is a wash and the claim that there is a capacity advantage to parallel, all else equal, then some may choose to go that way when series might have been a better choice.

The term in the guide (C/I^n)-(C/(2I)^n) is the term to determine discharge time of a battery or battery set for a given current drain and twice that current drain. It has been mis-applied to the series vs the parallel configuration to argue that the parallel configuration has more capacity because each parallel battery sees half the current. Read the discussions in the other thread.

The parallel batteries have twice the number of plates that the series batteries have for the same total capacity therefore the plates are half the mass of the series configuration and see half the current for the same current density in the plates. The current density is what is overlooked in the equation. If it were taken in to consideration there would be no capacity advantage shown for parallel.

It is happenstance that the author of the owners guide is an a/s forum person but that isn't the issue. The only real issue is that the guide mis-applies the equation.

The guide is confusing in the area of batteries and several things can be read from it, but the claim of parallel capacity advantage is clear.

What kind of an a/s am I looking at? Maybe some help here. Our best friends have one and I've helped with some of the restoration and rewiring. I would dearly love to have one as I'm a nostalgic type. Our rv is for sale but there isn't much market. If someone with an airstream wants a coach we might talk.
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Old 10-06-2007, 10:34 PM   #23
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Quote:
Originally Posted by richinny
did any of the early streams have 6v systems like cars did?
Ricky,

Early Airstreams, as in 63 and earlier, had very little in the 12V category. No converter, no charger, just a battery that would charge from the tow vehicle's charging system while driving. Most of the interior features were dual voltage, 110V, and 12V. Light fixtures were dual voltage, so were ceiling fans etc.
I am not aware of there ever being a 6V system for Airstreams.
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Old 10-06-2007, 10:40 PM   #24
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Here is a case for discussion. This member could have gone out with one 12V battery just fine......
http://www.airforums.com/forums/f449...oke-36635.html
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Old 10-06-2007, 11:29 PM   #25
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"the author of the airstream owners guide came it with claims"

This is an error of jumping to conclusions. It is an example of the kind of irrational logic being used in much of this discussion.

"The term in the guide (C/I^n)-(C/(2I)^n) is the term to determine discharge time of a battery or battery set for a given current drain and twice that current drain. It has been mis-applied to the series vs the parallel configuration"

This is a specious claim. The terms are simply the statement of Peukert's relationship applied to the current of a single battery compared to the current from a bank made of two batteries just like the single battery, which is what the website says it is.

"Read the discussions in the other thread."

Like many, it is an ad hominem attack that is trying to deny such things like 'sky is blue' and 'grass is green' - even the title of that thread is contradicting what you can find on any website that credibly discusses the behavior of lead acid batteries.

"The parallel batteries have twice the number of plates that the series batteries have"

Another interesting example of the confusion that exists in trying to refute what is well established. Depending upon the batteries used, the number of plates may be equal or less or greater. But that begs the question about what the point of this assertion may be. The number of plates may influence total capacity (easiest determining by battery weight) and the insternal resistance. This could be an interesting discussion because it gets into the difference between RV and starting batteries.

"but the claim of parallel capacity advantage is clear. "

That perception is interesting because it is so far off the mark and so definite. It is so definite that anyone who might possibly have a different perception is maligned and impugned. That is not an indication that profitable discussion is being sought.

"The thread needs to be here so airstreamers can discuss what is in the guide. "

Hubris, maybe?

Why should anyone here have a 'need to discuss' what is on some RV oriented web page? Is there something else going on, here, to make it a need?

If a discussion was desired, it would be asking for clarification of what was meant and how things fit together. The fact is that the effort started with, and continues to be, an absurd fault finding expedition aimed at a particular individual. Bashing and trashing is no way to promote a productive conversation, especially when it so off base in methods of inference, matters of basic fact, and civility.
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Old 10-06-2007, 11:37 PM   #26
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Quote:
Originally Posted by benwd
With regard to bringing it over from the escapees forum. That is what it is....
as suspected.

the sierra nevada unit website is chock full of great info...

and like all written communication shouldn't be taken as gospel.

it's unlikely that very many (if any) here choose to spend 100s of bucks ...

on the 6v conversion based on the p equation, properly applied or not.

so the post has been made,
the public service announcement has been served
it is archived here for all eternity...

and so on.

i almost joined the escapee forums JUST to support the one member beat on unnecessarily in that thread.

i will defend those who have worn the rasta beret!

and bryan has

ok mon?

now let's get back to making sparks in d'moonlight!

candles, romance and cold beer...

doorgunner has spoken,

and clearly has a soft side.

cheers
2air'
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Old 10-06-2007, 11:55 PM   #27
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Battery's

You guy's have way too much time on your hands. The question has more than one right answer, depending on need and space available. I was a master mechanic for 20 years and I can tell you that both 6v and 12v batts. have there place depending on what result you are looking for. Just to ad a note, the battery technology has come so far in recent years that anyone who thinks 6v batts. are a thing of the past, is living in the past! All that said I'm sure after reading this someone will disagree.
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Old 10-07-2007, 12:10 AM   #28
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That was a very fair post. The very last person I would listen to is one that doesn't listen to his audience.
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