In my simple days of wanting to re-charge my single deep cycle 85AH Interstate battery in as short of time as possible I tried a 6, 10, and 20AMP smart-mode portable battery charger settings... the 6AMP charger took around 10 hours to charge back to 12.5VDC setting after setting disconnected for 5 minutes or so. The 10AMP setting of the charger would do the same in about 6 hours time and the 20AMP setting would be around 4 hours. Running two 85AH batteries in parallel on the 20AMP setting for two batteries in parallel took around 6-8 hours to re-charge.
In my three 85AH Interstate deep cycle battery bank I had to use at least a 40AMP smart mode battery charger to re-charge the three batteries back to to their settled 12.5VDC reading.
Nothing scientific here just playing around with smart-mode battery chargers.
I ended up getting a PD-9260C 60AMP Smart-Mode battery charger and when my three batteries would be run down to around 11.9 to 12.0VDC I would start my smart mode charging using the PD-9260C 60AMP converter/charger. It would produce 14.4VDC for about two hours and I would always start out reading around 53 AMPS for maybe the first 10-15minutes (sometimes lower). Then after the 10-15mins of running high current it would start coming down in amps until it was around 6-AMPS of charge at 14.4VDC. After two hours of this then the smart-mode converter would drop back to 13.6VDC and continue charging. My amps at this mode would be around 4-5 AMPS for another hour or so. Then when I let the battery settle for about 3-5minutes I would take a DC voltage reading with nothing connected to the battery terminals and I would read around 12.5-12.6VDC which I guess is around 90% charge state.
My three batteries would then run my 300 WATTS or so 12V current drain pretty steady then for 8-10 hours before dropping back to 11.9 to 12.0VDC.
then I would do the cycle all over again to get ready for the next day/night battery run of my OFF-ROAD POPUP.
"Progressive Dynamics ran this test on the amount of time it took a PD9155 (55-amp) converter/charger set to three different output voltages to recharge a 125 AH (Amp Hour) battery after it was fully discharged to 10.5-volts.
14.4-VOLTS (Boost Mode) – Returned the battery to 90% of full charge in approximately 3-hours. The battery reached full charge in approximately 11 hours.
13.6-VOLTS (Normal Mode) – Required 40-hours to return the battery to 90% of full charge and 78-hours to reach full charge.
13.2-VOLTS (Storage Mode) – Required 60-hours to return the battery to 90% of full charge and 100-hours to reach full charge."
This sort of fits Progressive Dynamics brochure report on how long it took them to recharge a deep cycle battery. I was trying to figure out what AMPS setting I would use to duplicate this report the best I could. For my situation I'm thinking my best results would be minimum 10AMP per battery and a maximum for each battery and not charge more than 10 hours. The 2-3 hours battery charge time was perfect for me when camping off the power grid for my usual three day weekends.
I hope my memory is ok on these numbers - been awhile since I have reported them from memory. I was so scientific I never recorded anything...
I just know when my battery banks gets down to the 11.9VDC to 12.0VDC charge state I have to re-charge and then I am good to go for the next day/night battery run... The three 85AH Interstate batteries would be arund 250AHs connected in parallel.
I have been using this method camping off the power grid for around three years now with no ill effects. Got home from every trip without assistance... My 85AH Interstate batteries are around five years old and I am down to two good ones starting this camping season - time for me to start looking for replacements now...
* This post was
edited 08/05/12 07:58pm by RoyB *
My Posts are IMHO based on my experiences - PM me Roy and Carolyn
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Would you care to offer a better way to connect batteries together?
The author in the link you provided doesn't provide any math to conclude he is either right or wrong. He just provides conclusions based on what I believe is a faulty set of assumptions. He expects the reader to close his eyes, open his mouth and swallow hook line and sinker. I have been in the engineering business long enough to doubt anyone who does not provide either real and complete engineering calculations or the results of a rigorously conducted life cycle test of a statistically valid quantity of samples.
If you will carefully read my post again, you will see that I didn't disagree with his connection methodology. I believe it offers some benefit. I just think his predictions of what will happen if you don't use it are wildly exaggerated. I offered reasons for my opinion based on the energy budget of the individual batteries. Would you care to point out the flaws in my logic? I'm not being facetious. If my thoughts are flawed, I would like to know it.
* This post was
edited 08/05/12 10:08pm by Cedarhill *
Salvo independently did the math and said it was correct.
Salvo has made a lot of posts! I tried for several minutes to find that discussion but couldn't come up with some clever search parameters to go right to it. Please provide a link if you can find one.
I did locate a discussion with Salvo and myself having to do with measuring the internal resistance of a battery. I said the same thing there that I said here. Battery internal resistance, as well as output voltage, is a moving target that changes with state of charge, among other things.
In order for your guy's calculations to remain valid over the whole discharge cycle, the internal battery resistance, as well as the output voltage of each battery, would have to remain constant or at least change at precisely the same ratio. If they don't, then the calculations really do get complex. My theory is that these parameters tend to equalize the discharge rate of individual batteries so that the effects of interconnection resistance are partially neutralized.
I think my most valid argument is still the one having to do with energy loss. It is a safe assumption that a bank of identical fully charged batteries will have approximately the same stored energy content. It is also easy to measure, after several hours, that same bank of batteries will have a lower energy content. That loss is directly proportional to voltage and the voltage of all batteries is within a hand full of milli-volts of being the same. Conclusion - each battery dissipated the same amount of energy and current over whole discharge cycle. Battery one started out supplying more of the current but the situation didn't remain that way over the whole discharge cycle.
So far as I understand it, the smart gauge calculation only deals with the resistance created at external connections. You would have to search the archives. The regular search only goes back one year.
So far as I understand it, the smart gauge calculation only deals with the resistance created at external connections. You would have to search the archives. The regular search only goes back one year.
That is exactly my point. You can't neglect the effects of falling voltages and rising resistances over time internal to the individual batteries when you do the calculations. As I said before, the guy talks about the complexity of his calculations but then assumes out of existence some essential parameters that go into a correct final prediction.
My guess is that the internal resistance would exacerbate rather than mitigate the results. Then there is the statement that he did not believe that the results would be from the predictions of the mathematics. Therefore he did real life testing and found that they were as predicted.
I have looked for other places that did testing and have found none.
So far only two persons have doubted the results at the page. Some think that the differences are too small to matter. I think the difference in cost is too small to matter (especially for twin twelve volt units) and that it the wiring diagrams are ideal.
First of all,as far as I can tell, the author of the article didn't do any sort of experiment with any relevance. He simply confirmed that his initial voltage predictions were correct. I don't doubt his original predictions or measurements. What I am saying is that they are irrelevant. The situation will change dramatically as the discharge cycle progresses and that apparently didn't occur to this "expert". Please look again at his first example and follow my logic.
He predicted and confirmed by measurement that the first battery in the row of four surrendered 35.9A whereas the last one in the row gave up just 17.8A initially. That is entirely expected but that situation cannot possibly remain that way for long. The first battery will discharge much more quickly that the forth one which will result in a drop in output voltage and increase in output resistance as compared to the fourth one. As a consequence, the output current of the first battery will trail off in comparison to that of the fourth battery. As the discharge cycle progresses, the voltage and resistance of all four batteries change so as to equalize the amount of output current from each one.
More to the point, at the beginning of the discharge cycle, all the batteries have nearly the same amount of stored energy because they are physically identical and at the same SOC. At the end of the discharge cycle, the batteries still have the same, though lesser, amount of stored energy because they are physically identical and are at the same voltage and SOC. Big interconnection wires force it to be that way. If the first battery in the series gave up substantially more energy than the last one, then where did all that extra stored energy in the fourth battery go?
The author of the article has one thing right. The calculations are very complex and a sophisticated circuit simulation with high accuracy battery models would be required to get believable results. He apparently didn't realize just how complex the computations truly are or how accurately the behavior of a discharging battery must be modeled.
* This post was
edited 08/06/12 10:19am by Cedarhill *
Well, get out your tools and do the experiment for us? Or do the higher math required?
Or should we just accept that method #3 is the best for odd numbers of batteries, that method #4 will work for even numbers of batteries, and that method #2 can not be improved upon for twin twelve volt batteries?
The whole idea presented in the article was that banks of batteries hooked up in an asymmetrical fashion exhibit a large variation in lifespan of individual batteries due to the nature of the interconnect configuration. The only valid way to prove or disprove this hypothesis through experiment is to acquire several sets of new batteries and proceed to repeatedly charge and discharge them in various configurations until they begin to fail. Obviously, that could take weeks and cost hundreds or thousands of dollars.
There is a law of diminishing returns here. I have thought through the situation carefully and convinced myself that the author's hypothesis is exaggerated, though not entirely false. I have solicited contrary opinions backed up by appropriate logic and nobody has responded so far. I am the only one I need to convince for my own purposes unless somebody comes up with some money to hire me to analytically prove what I'm saying. Fat chance of that!
I will use the configuration recommended by the author provided it is convenient and doesn't cost much more. Otherwise, I will just wire multiple batteries in daisy chain fashion like in method 1 and wait several years to see if one battery fails far more quickly than the other(s).
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