Series or parallel

[bryanl]

charger has always killed the second by puekerting the acid dry

In my setup, I have two 12V batteries, approx 3 years old, with individual switches. When boondocking, I run just one battery until the monitor panel shows its voltage dropping.

It seemed like any mis-match between parallel batteries resulted in the charger trying to top off the low battery and frying the already hot one. At that time I was using a 3 stage charger and no battery disconnect switches.

Q 1: if you are loosing electrolyte, your battery is being overcharged. This has nothing to do with how current draw can influence battery capacity.

Q 2: switching batteries is like running 12v in series in time. For typical 12v wet cell lead acid batteries, that technique will get you about 15% less available energy than if you just ran them in parallel, the way Airstream provides them.

Q 3: a mismatch in parallel batteries will not cause topping off one battery to fry another. That could only occur if there was a shorted cell and in that case it is the battery with the bad cell that would overheat and be destroyed. The good battery might suffer a bit of discharge until you discovered and removed the bad one, but that is all. Shorted cells are fairly rare these days as a cause of battery failure.

There are reasons why Airstream provides 2 12v batteries in parallel in its trailers.

Most RV's charge their house batteries in parallel with their starting batteries even those batteries are of different type (deep cycle and SLI), and often of different age and capacity. Both get charged. Neither suffer as a result.

[HiHoAgRV]

Originally Posted by Leipper

Q 1: if you are loosing electrolyte, your battery is being overcharged. This has nothing to do with how current draw can influence battery capacity.

Q 3: a mismatch in parallel batteries will not cause topping off one battery to fry another. That could only occur if there was a shorted cell and in that case it is the battery with the bad cell that would overheat and be destroyed. The good battery might suffer a bit of discharge until you discovered and removed the bad one, but that is all. Shorted cells are fairly rare these days as a cause of battery failure.

There are reasons why Airstream provides 2 12v batteries in parallel in its trailers.

Most RV's charge their house batteries in parallel with their starting batteries even those batteries are of different type (deep cycle and SLI), and often of different age and capacity. Both get charged. Neither suffer as a result.

I'll inform my pile of dead batteries to quit faking and get back to work

[benwd]

Leipper-----Your Understanding Peukerts paper shows a 100 ah battery [like a typical 12 volt] at 5 amps [its 20 hour rate for which its nominal capacity was determined.]
So, whatever was involved in that determination results in 100 ah. Both of the two internal resistances and conversion loss were accounted for in the test and the nominal capacity comes out to 100 ah. That's clearly the case.

It also shows a 200 ah battery [like a typical 6 volt] at 10 amps [its 20 hour rate at which its nominal capacity was determined].
So, whatever was involved in that determination results in 200 ah. Both of the two internal resistances and conversion loss were accounted for in the test and the nominal capacity comes out to 200 ah. That's clearly the case.

The chart shows the same %diff in time for both battery examples for the same peukerts.

If I take two of the 100 ah batteries and connect them in parallel and discharge them at 10 amps total [5 amps each, their respective 20 hour rate] then they would provide the same time to discharge as each would test alone at 5 amps for the same peukerts.

If I take two of the 200 ah batteries and connect them in series and since current passes through one, then the other, then 10 amps can be used [10 amps is the 20 hour rate] then they would provide the same time to discharge as each would test alone at 10 amps for the same peukerts.

Now, here is where it gets confusing. If the 100 ah battery tested the same in time at 5 amps as the 200 ah battery tested in time at 10 amps for the same peukerts then the above examples for battery pairs must be true It is self evident. An axiom.

Something else that is clear, that 'all' characteristics of a battery are involved in the 20 hour capacity test so no additional characteristics will become evident when batteries are paired and tested at the same net currents.

It appears that the paper provides a clear definition of net capacity difference for series or parallel for the same total capacity and same peukerts, all else equal. ie wiring, temperature, moon phase, etc. And that difference is zero.

It also shows that, while current is shared in the parallel 100 ah batteries that each battery still sees only the 5 amps [its 20 hour rate test current] So any 'stress' the batteries see while in parallel is identical to any 'stress' they saw in their 20 hour test. The same goes for the 200 ah batteries.

Would you agree?

[bryanl]

oh here we go again ;-(

the comment about 3 or 4 messages up was to use a 12v battery until it got too low and then to switch over to another one.

The suggestion was to just hook them up as Airstream Inc supplies them - both batteries together in parallel. When you do that - use them in parallel and together - rather than one after the other independently, you will gain about 15% in available energy capacity not to mention significant convenience by not having to rewire in the middle of a campout. see Understanding the Peukert Effect or other sites with the same calculation.

It appears that the paper

sometimes perceptions can be a bit off so we have to be careful about what "it appears" to be to us.

Perhaps looking at the context would help? That context was the guy with a single 12v battery looking to get a bit more battery capacity, what should he do? Can we understand what Airstream Inc (and many other TT mfg's) did for him and why?

Most of the recent questions in this thread had very little to do with available energy but rather with failure modes and lifespan. Those are separate issues and, from the traffic, they seem to be much more important than available energy capacity. That provides a perspective that should not, IMHO, be ignored.

[lewster]

Originally Posted by Leipper

Q 1: if you are loosing electrolyte, your battery is being overcharged. This has nothing to do with how current draw can influence battery capacity.

Q 2: switching batteries is like running 12v in series in time. For typical 12v wet cell lead acid batteries, that technique will get you about 15% less available energy than if you just ran them in parallel, the way Airstream provides them.

Q 3: a mismatch in parallel batteries will not cause topping off one battery to fry another. That could only occur if there was a shorted cell and in that case it is the battery with the bad cell that would overheat and be destroyed. The good battery might suffer a bit of discharge until you discovered and removed the bad one, but that is all. Shorted cells are fairly rare these days as a cause of battery failure.

There are reasons why Airstream provides 2 12v batteries in parallel in its trailers.

Most RV's charge their house batteries in parallel with their starting batteries even those batteries are of different type (deep cycle and SLI), and often of different age and capacity. Both get charged. Neither suffer as a result.

Bryan,

I have been following this thread with some interest and I have to say that I find a HUGE difference between theory and practice in the RV world, and I thought that it was time that I added something to this thread.

I must respectfully request that you fully substantiate the following statement from the above quote "Most RV's charge their house batteries in parallel with their starting batteries even those batteries are of different type (deep cycle and SLI), and often of different age and capacity. Both get charged. Neither suffer as a result."

Where do you get 'most RV's' from? How many have you worked on? Which ones are you specifically referring to? In my experience, most of the RV's that I actually work on with both house and starting batteres would be motor homes. I have found that most motor homes I have had the opportunity to repair DO NOT HAVE A CHARGING SYSTEM FOR THE STARTING BATTERIES FOR THE ENGINE. They rely on the engine's alternator for the charging circuit and the engine must be running to affect this. The inverter/charger system is connected solely to the house batteries. In fact, I have been called numerous times to add a totally separate charging system for the engine batteries.

This is not done for simple reason.......THESE BATTERIES DO NOT CHARGE AT THE SAME RATES DUE TO DIFFERENT INTERNAL RESISTANCE AND CONSTRUCTION, and when you do not fully charge a battery, it leads to premature failure. If you look at most battery companies sites, they say to only charge similar type and size betteries that have the same manufacture date. Simple statement. They make the batteries, they tell you how they want them charged.

The only motor coaches I see on a regular basis with 2 charging systems for the batteries are the ultra high-line ones....Prevosts and Newells. Most others do not use this type of system.

What I have seen and currently sell and install is a solar charging system that WILL acommodate charging BOTH house and starting batteries, but note that the charge controller for these systems DO NOT CHARGE THESE TWO DIFFERENT SYSTEMS IN PARALLEL, rather, there are separate, independent sections of the charge controller that provide the current for the house and starting batteries.

Thanks for your time! Now back to your regularly scheduled academic discourse.

[benwd]

leipper----There are two perceived subjects in this thread. You can work both. I have no interest in one of them. Do you agree with the conclusion in my last post?

[bryanl]

Lew, I respectly request you get off your high horse and start thinking a bit. please. there is no need for challenges when there is some confusion. This win/lose crap (good example right above) is a good way for everyone to loose. It is much better if we express a more collegial attitude and try to learn from each other.

Where do you get 'most RV's' from?

Every Airstream trailer that I have run across uses 12v systems and RV/Marine or deep cycle batteries. (although I did have a 24v system in one for a while). I have yet to find a TT with onboard power that does not use a 12v system although I have no doubt that 24v will creep in sometime. - and yes, I know, there are a few exceptions like those 50's park models and such. Those are exceptions.

Every tow vehicle I know of in common use uses an SLI (starting, lights, ignition) battery that is also a 12v system. I know that 48v systems are starting to show up but that seems to be ways off yet.

Most trailerists I have run across have a charge line so that their vehicle charges their RV battery when their tow vehicle is running. This is sometimes done by just hooking the TT charge line to the vehicle battery (a couple of rallies ago we had one participant with a dead car battery because of this). Better practice is to isolate the systems with a relay or diode so the RV battery does not drain the tow vehicle battery.

In all of these cases for the 'on the road' condition, the RV and SLI batteries are in parallel and being charged by the engine alternator.

The basics of charging a battery include the fact that the charge current is determined by a voltage difference, and that all lead acid wet cell batteries have cell potentials that are very very similar. You can tell the SOC by the voltage - think about what that means in charging. Think of the definition of the absorption phase of 3 stage charging. Do I need to spell out that which you should already know about what this means in charging batteries en masse?

Consider that one of the concerns about diode isolation of the RV battery was how the voltage across the diode influenced the ability to completely charge it. Think about what that is saying - you do remember these devices and the discussions?

When you do not fully charge a battery, it leads to premature failure

Very much so. This is why you need to fully charge your batteries and also one of the reasons why making sure a bank is fully and completely charged is good maintenance. A good full charge makes sure that all batteries in the bank are each fully charged and that helps equalize them promoting more even usage and consistency in overall performance and life.

This gets interesting on solar systems and winter use. I've encountered one case of advanced sulfation due to a weak solar system and adverse conditions resulting in weak charging that often takes a long long time to get the battery to full.

For those with a parallel problem, they should really get off my case and go find out why Airstream provides 2 batteries in parallel in their trailers, why the common diesel pickup uses parallel batteries. There are good reasons but no way some folks here are going to accept they exist - or so it seems from the creativity invoked in trying to deal with it.

I have to say that I find a HUGE difference between theory and practice in the RV world

generalizations like this don't help much. All a difference between theory and practice does is to tell you the accuracy and precision of the measurements (or, perhaps, the quality of the theory).

As far as the 'Peukert' theory - I can see this at every rally. The heavy TV and movie watchers have to run their gensets more often than those who just read. Those who like to keep the rig warm also need more frequent charging. Those who do both ... ;-)

[benwd]

I was remiss in saying that your paper Understanding the Peukert Effect 'appears' to say---, so let's change that statement to say---

'The paper unequivocally provides a clear definition of net capacity difference for series or parallel for the same total [initial specified] capacity and same peukerts, all else equal. ie wiring, temperature, moon phase, etc. And that difference is zero.'

Given that change you would agree with the obvious, unequivocal conclusions of the paper that I addressed in my earlier post.

Whether an rv, airstream or anything else, comes with parallel batteries or series. is a choice by the manufacturers. Both provide service and some people change to a different arrangement for whatever reasons they choose. Since either provides the same capacity for the same peukerts and amount of total lead then their reasons for changing isn't about capacity.
Diesel engines need the cranking amps of parallel in cold weather. Has nothing to do with capacity.

[bryanl]

you would agree with the obvious

where my opinion differs is that I do not insist that others adhere to my opinion such as appears to have been your purpose in this whole thread.

To the contrary, I will respect others by not foisting my opinion on them, not insisting that they polarize issues to my liking, not trying to finesse reading web pages or messages to create straw men I can combat, or otherwise trying to do more than just help others see things from different perspectives and learn more about those things they use and observe.

I think there is nuance that you are missing but, it seems to me, there is no way anything I can say to try to explain it can cut through the fog. Change has to start with a disposition open to new horizons.

[ve3czn]

I am not a high capacity expert But I do know electricity. The problem with series is just that each battery has an individual internal resistance, and no two batteries are alike,
They charge differently and if one has more resistance than the other then they both suffer from that resistance., both in charge and discharge.
In a parallel connection one battery will not limit the current capablility of the system.
Current handling capability is dependant upon the battery and not the means of connection.
two Batteries of 100 amps in parallel hopefully delivers about 200A.
and two in series of 100A will deliver again hopefully 100A. depending upon the internal resistance of the cells. Series is not better than parallel.

Rae Baker
ESL labratories.

[benwd]

There is no opinion in my post regarding the conclusions I quoted in my post. Your paper factors the capacity to time which is fine and the outcome of your findings are clear. When the results are extrapolated to series and parallel combinations the results become clear regarding equal capacity for series and parallel. I can see your paper is a good effort and serves the rving community well.

I know that you do not insist that others adhere to your opinion as all the threads on this subject attest to, however, we're discussing the results of your work which isn't opinion, but rather, fact. I would suggest you add a couple more columns to your data showing the 100 ah batteries in parallel and the 200 ah batteries in series as well as another % diff column for each. I have no desire to get anyone to adhere to my opinion. Your paper solicits corrections or comments. I have no corrections as I see no errors, however, adding more information regarding battery configurations would be helpful for the technically challenged.

[CanoeStream]

Please, please, please! I would recommend that the strongest opinionators take this somewhere else for 24 hours. I highly appreciate the practical in-the-trenches opinion of Rae Baker's post. Let's welcome input from our broader membership. It remains that we cannot fill the county with mega candlepower glow and 100db of the Doobie Brothers without depleting all battery setups. This would be a simpler issue if we discussed how to get 3, 5 or more days of boondocking endurance out of our batteries. The individual usage pattern becomes much more important than the nth detail of the setup.

Make no mistake -- there is no doubt that this discussion has had moderator attention for a couple days now. We'll gladly take the stage if the tone does not change. For one, I'd rather hear more about practical experience with either setup and let it be. I'm waiting fondly with ampicipation...

[wheel interested]

Bob would that be the SOC here? I hear you about most of us wanting more charge and life out of our batteries. Or is that me wanting to be charged to get more out of life?

Brad's first honey do of retirement is installing the AGMs and the WFCO upgrade kit to the Paralax converter and a Xantrex battery monitor. This is in parallel to the thread I think. Brad installed the 3 stage converter today and will put in the shunt for the monitor tomorrow. Once we get the wiring kit and the temperature sensor he'll put in the new batteries and I hope we will be able to boondock longer. I have high hopes of that monitor "teaching" us better conservation and the batteries coming right back up if we do manage to discharge them too much.

Actually if anyone has a diagram of the Airstream wiring from the batteries Brad wants to triple check on it. The diagram he has is not of this Airstream wiring. He will be putting a call into AS. But if you know where we can locate the particulars online, we would greatly appreciate it. Thanks.