# connecting batteries in parallel or series, myth and theory

|> |> |> | Batteries are the very heart of your system. That should tell you |> | something about the choice of battery/ cell used. You sound like a guy |> | looking for an excuse to use golf cart batteries. |> |> You sound like a guy wanting to tell everyone to do things exactly the |> same way you do things, without being willing to tell them why, whether |> you actually know why or not. | | I have told you why, parallel strings do not charge/discharge in a | uniform manner. That is the truth.
I'm not doubting the truth of this. I'm wanting to understand the means by which this happens, and the degree to which it happens. I want to understand this enough to know how well it may be mitigated. For example the non-uniform charging may be dealt with by smaller chargers isolated on each string (not one big charger trying charge the strings in parallel).
|> | Best choice is a single series string of the correct capacity. Failing |> | that being possible the second best option is no more than 2 parallel |> | strings to make up the capacity. |> |> Why? | | I have told you why, parallel strings do not charge/discharge in a | uniform manner. That is the truth.
I'm not doubting the truth of this. I'm wanting to understand the means by which this happens, and the degree to which it happens. I want to understand this enough to know how well it may be mitigated. For example the non-uniform charging may be dealt with by smaller chargers isolated on each string (not one big charger trying charge the strings in parallel).
|> Specifically I want to know why for the "no more than 2" part. But I |> also want to know how to balance the decision between first best and |> second best against other factors that may push for that second best. |> Merely ordering the option into 1st, 2nd, 3rd, etc., is not it. | | Two strings is manageable without to much pissing about. The decision | is to buy a single string of the correct Ah capacity. | If this is not possible then use two parallel strings. Money before | good design is false economy.
I would not say it is not possible. But there may be (when it comes time to do this) reasons to prefer the smaller batteries. Reasons can include the desire for one man handling (can depend on available space). Or it could be the desire to start small and migrate to larger.
I want to explore means to manage the load balancing before deciding. Maybe it will be the case that those methods are not worthwhile. I cannot say today. Today is the learning time. The decision is later. The conditions will be known then.
|> | Your choice, you spend the money, you wear the consequences. Let's say |> | you are willing to spend half a million to build your house, you're |> | going to quibble over 50k to power it. |> |> If you have nothing more to add, then what you have said so far will not |> play much, if any, role in my evaluation of the designs to use. This is |> because you aren't providing information I consider useful. Again, I am |> interested in the technical information to go into a design decision that |> balances multiple needs, not the "what I did" or "what I would do" (unless |> I get a sufficiently significant number of those responses from verified |> engineers). | | Not true. You want someone to give you a good reason to choose the | lowest price option over good design.
No. I want to know all the reasons for all the choices.
| No matter what you decide, be it a single string or six parallel | strings, if one cell dies and the batteries are older than a yera or | two then you will be replacing th whole bank. That the way it works.
What happens if you have ONE string of several very large cells/batteries and one dies? Are you saying you don't have to replace the whole bank in this case?
|> I expect to pay more than the cost of being on-grid. But this is NOT an |> infinite finance to work in. | | You have a grid connection, you will find that PV can not replicate | that level of energy for what you feel is a reasonable cost. What have | you done to reduce your energy needs.
That is a work in progress. Much of it will be done when I start going with some battery power. More will be done later. This is not a one big step all the way project.
|> I want to do it with one person. Maybe that means a fork lift machine and |> the space to move the fork lift around. Or maybe it means a block and |> tackle assembly that can slide on an overhead rail. Or maybe it means all |> the cells/batteries placed on individual roller carts with locking wheels. |> Or maybe it means having smaller batteries and doing the lifting more often. |> All these options are best balanced out knowing all information (not just |> the cost, but also the technical implications, the latter of which I was |> hoping I could get pointers to from someone here). | | You have been given a great deal of information in this thread.
Quite a lot of it is unsupported "what to do" advice.
|> They can do things like ensuring that one bank does not cross change another. |> They can allow separate chargers for each bank. | | A diode is not a rectifier.
Rectifiers are made of diodes (or other things).
|> |> I'm exploring all options. I'm not interested in specific advice on what |> |> I should do (at least not without well explained why) ... I'm interested in |> |> the information to make the best decision in the circumstances that will be |> |> present at the time the decision is to be made. |> | |> | You still sound like a guy looking for an excuse to use golf cart |> | batteries. |> |> I am someone looking for the technical information that would be a valid basis |> for deciding what circumstances that golf cart batteries can be used in, and |> what circumstances they cannot be used in, where "circumstances" involves a lot |> of things that I don't even know, yet. | | You can use golf cart batteries, they can be wired in series, parallel | and series/parallel in as many strings as you feel are required. Most | people only ever do this once. Their second battery bank is usually a | single string of cells with the correct Ah rating.
And maybe I will migrate to that. One possible path is that I would start with a small bank and migrate to a larger bank. I may parallel things in the interim. I will also be looking at possible circuits to manage the load balancing between parallel strings. Maybe that won't be practical. I'm sure you'll say it won't but I want to know why, if that's the case.
| Parallel strings do not charge/discharge evenly. Two strings and you | must monitor the state of charge and equalize the strings more often. | Basically twice the work of a single string. Three parallel strings | and you might expect to do four times the maintenance. In the end you | will have repetitive cell failure. Because of the cost you will | replace cells/batteries rather than replacing the whole bank, then you | will remove a string to use the cells/batteries to replace dead cells/ | batteries in the remaining strings.
If it is the case that cost is why I would replace one cell/battery at a time, then cost would clearly prohibit the monster cells.
| I know, you would never do that.
I believe I can make the right decision ... the one that is right for my situation, once I know all the issues, how they behave, their workarounds, methods of managing them, etc.
|> Days of autonomy will gradually shift to being whatever number of days God |> decides not to offer me the opportunity to charge up (e.g. no wind, no sun). | | No. you have to decide when designing your system. This is one of the | factors that sizes the battery bank. | God doesn't give a rats ass whether you sit in the dark or not,
|> I can't say some particular exact number of days I want to be sure the system |> will continue to operate in. If I say some number, I have to face the issue |> of what to do when it happens to turn out longer than that. I expect to start |> with a low number and build up to a higher number. | | "DAYS of AUTONOMY" is not a sliding scale. It is what your batteries | will provide at the load designed for. What are you going to do, add | and subtract batteries as required?
Apparently we have a different understand of this term. I don't know what yours is, then. So it's pointless to proceed on this.
|> |> |> And maybe some big rectifiers to isolate the strings from cross-charging might |> |> |> be called for. It would then seem to me the only way to keep the strings |> |> |> charged with the rectifiers in place is to separately charge each string. |> |> |> But that might be an economic benefit from smaller chargers. |> |> | |> |> | Been there, done that, didn't work and the tee shirt dissolved in the |> |> | wash. |> |> |> |> Do you know why it didn't work? Or are you just assuming that because it had |> |> rectifiers, that must be why? |> | |> | Sorry, no rectifiers. Did try diodes. Oh, it worked alright. It was |> | just not worth the effort. The strings always ended up at different |> | voltages and needing charging to bring them back into line. Then there |> | was the game of musical cells trying to get a balance in each string. |> |> Did each string have its own charger and charge controller? | | Hang on. You want the cheapest option. Now you want to build multiple | systems.
Your understanding of "cheapest option" is likely not the same as mine.
|> | But if you have the time on your hands, go for it. |> |> I don't know whether I will or won't. I'm looking for the specific technical |> info to learn that allows me to figure it out. I do not know if you know what |> it is I want to know, or not. But I do know you are not saying it, or pointing |> to it, for whatever reason that might be. | | Oh, I know what it is you want to know alright. But to understand you | need to listen. | You want some one to tell you what you want to hear.
You want some one to do what you tell them to.
I can see I'm not going to get anything useful from you.
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| snipped-for-privacy@gmail.com wrote: | |> You sound like a guy |> looking for an excuse to use golf cart batteries. | | I take that as a personal insult. There is nothing wrong with golf cart | batteries if his storage needs are modest. If the discharge is kept at | some respectable level, they will last decades. Most batteries don't | die, they're murdered. | | Not everyone needing a car needs a limousine.
I think he's upset that I haven't ruled out golf cart batteries long before the time to make the decision(s). Who knows, maybe I will rule them out at that time. Or maybe I will find an effective way to manage a dozen strings of them.
| Now you can take that as an insult if you like. But, Golf cart | batteries only last for decades if they are used as door stops. Most | people who are capable of learning only ever buy one set of GC | batteries for their house system. Those that have bought two sets have | a learning disability.
The real question is, who knows the science behind why this is so? Maybe you do or maybe you don't. I'm not expecting you to write papers for me. But if your knowledge is limited to hearing people say things like "I had GC batteries and I will never do that again", that isn't ruling out to me that someone just didn't build it right. If you know of the science behind this, please point it out (e.g. PDFs of papers with graphs and charts and basis in physics, etc). Otherwise, its doubtful I'd ever get anything useful from you.
| |>> FWIW, when commercial applications such as large UPS and even larger |>> (submarine batteries are about the largest in the world), the |>> engineers have always opted for special 2V cells that have the right |>> A-H rating and as many such cells in series as needed to get the |>> desired voltage. I've never seen a commercial UPS system (or |>> submarine battery) that was connected in parallel. (maybe they know |>> more about this than alt.energy.homepower posters :-) |>> |>> Depending on the voltage needed, I've seen UPS systems with 36 12V |>> batteries connected in series (about 430V). Submarines used about |>> 128 2V cells (about 270V). |>> |>> daestrom |>> |> |> Don't you think there may be a few less budget constraints, |> for those building "a commercial UPS system (or submarine |> battery)" system? (Boy!- the "homepower" system I could |> build if I had an unlimited budget, it would not look anything |> like what I can realistically expect to build on my own. It would |> be neat to design a system that included dedicated "operators" |> and maintenance men. That could really change a few things.) | | Do you think that commercial UPS systems build them in series because it | costs more than a bunch of 12V batteries in parallel? Wouldn't the | manufacturer that wanted to corner the market do a 'forehead slap' and say | "Doh! We can use the cheap stuff like homepower systems and beat everyone | else in the market on price!" Ever wonder why none of them have opted for | the lower price "homepower" system methodology?? | | Properly sized cells in series cost *less* in the long run.
Commercial UPSes are put in place usually to prevent _any_ downtime where even a 5 minute outage every 5 years means a major loss of money (directly) and/or reputation (which translates to money).
Homepower systems being down can be inconvenient ... as inconvenient as the utility going out is to the typical grid powered home. You fix up the system (for example, take a bad string offline and reset the breakers for the others, and cut the loads down a bit).
I'm sure people vary in how much they consider it inconvenient to have to go make an adjustment to their battery system. If I have to swap out a GC battery which I can pick up, vs. have to wait until I can swap out a 250 lb monster cell and have zero power in the interim, well ... different people have different needs.
|> Are there a lot of "Homepower" battery systems running at |> 430vDC or 270vDC? Neon John is having trouble finding |> simple, cheap 48vDC inverters. | | I should think since there are a lot of grid-tie inverters with voltage | inputs in that range, there should be inverters available.
Grid-tie inverters I have seen need the grid present and online to run. When the grid goes down, they go down. These are not homepower inverters.
| The topic is the best way to connect cells together for large capacity. | Just about every commercial battery bank is strickly a single string in | series. Even those manufacturers that are trying to make money selling | their product (where cost is obviously very important).
Commercial battery banks tend to be there to ensure zero outage, or that famous "five nines" up-time. There's a serious cost to any downtime, even briefly.
Some homepower users want batteries to do similar things. Others want them as the primary source (to smooth out solar/wind availability) and some occaisional downtime is not a big problem.
The only problem with GC batteries in a solar power system is normally the design of the solar power system, not the batteries. GC batteries are designed to be used in a certain way. But people design solar power systems with GC batteries without taking that into account.
A solar power system that discharges/charges it's battery bank by 60 to 70 percent capacity on a daily basis will quickly kill the GC batteries. Heck, it will kill almost any normal battery. If there is a cloudy day the system will stop working. Or, basically 0 days of autonomy. Yet, in most sunny places, that is the design spec.
Most normal deep cycle batteries are designed for a C/20 charge rate. (ie) capacity /20 = charge rate. A 200Ah battery is designed to be charge at 10A. About one day to go from dead to full charge. You can not charge a battery bank by 60 to 70% of it's capacity in 4 hours of sun with a C/20 charge rate. Usually, the charge rate is in the order of C/5 or higher. That is hard on most batteries. The high price "solar" batteries that companies cell are designed to take that, but that doesn't mean that they wouldn't do better if they were charged at a more modest C/10 to C/20. Just because they can take it, doesn't mean they like it.
A system 12V system that has to have a 1200W (100 charging amps) of solar panels should have about 2000Ah of battery capacity. That would support about a 200W average load. It would support about 5 days of autonomy.
So, a basic rule for GC batteries is, if you put them in any system that doesn't have at least 5 days of autonomy, then you are going to kill them. That is because the charging , and discharging rates are going to kill them. As for as GC batteries go, it's mainly the charging rates that get them.
If you keep the charge/discharge rate in line with design specs then they will last for decades.
I have seen them in the field, they have two parallel battery strings. They don't say it on the website, but that is the way they are wired. That is why I posted the link to the picture. If you look at where the battery + leads connect to the fuse block and the negative leads to the - negative terminal block, then you will see two wires going from each. One to each string.
On Thu, 14 Aug 2008 03:26:18 -0500, "N9WOS" percent capacity on a daily basis will quickly kill the GC batteries. Heck,
Bullsh*t.
And yet, somehow, we EVers manage to get thousands of miles out of golf cart batteries, discharging them daily to 50-80% at amp draws up to about 500 amps.
I had about two years on my last pack when I sold the car. That's 2 years worth of daily driving. You can count the cycles. I had my controller's battery amps programmed to 400 amps max, a limit that I hit fairly often. No significant loss of capacity or range.
John -- John De Armond See my website for my current email address
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This is off the thread subject, and I am not up on current submarine technology, but there would be little incentive for nuclear submarines to use anything but lead acid batteries.
First, lead acid batteries are low-risk proven technology. The US Navy is very risk-adverse when it comes to nuclear technology, and nuclear reactors (not to mention the submarine itself) need a reliable source of emergency power or really bad things can happen.
Second, the weight of lead acid batteries is usually a disadvantage in mobile applications, but in submarines it is not a problem. On my nuclear submarine, the batteries were located deep down under the deckplates where their weight contributed to the stability of the hull. Under and around the batteries was tons of lead ballast. If you substitute a lighter battery technology, you just need more lead ballast.
I am probably making a big mistake jumping into the line of fire, between you two, but it appears to me that both of you have valid points. And both of you are providing information to support the idea that Golf Cart batteries can be useful, when the charging and discharging characteristics (as provided by their makers, for their intended purpose) are taken in consideration and adapted to how they would apply to the new purpose.
EV use, (and a Golf Cart is an EV) would certainly involve heavy discharge rates into a motor, the GC battery would have been designed with that in mind. It is my understanding that batteries are more open to degradation during the charging process than the discharging process.
Neon John's post speaks to the hardiness of the GC battery during discharge, and should be taken to indicate no problem with the occasional discharge below a 60% design level. Fortunately a home running on wind or PV power, has many smaller loads/demands instead of a single large motor to feed.
N9WOS's post points to the need for sufficient capacity so that the slower charging rate from alternative sources, are practical. The less aggressive charging should indeed extend the operating life of the battery bank, ( with proper maintenance including a schedule of "maintenance overcharging").
Golf Cart batteries may be less efficient or practical than a number of newer alternatives but they have a long history of availability and low cost for less demanding homepower use.
If you are thinking of powering John Edward's house, you should probably give the Golf Cart batteries a pass.
Luck; Ken
I have never sold GC batteries, but I sure have replaced lots of them with single series strings of 2V cells of the correct Ah rating for people who thought that they were saving money buying GC batteries. I have also swapped out parallel strings of batteries, not just GC batteries, for single series cells.
I can only repeat what I learned getting my accreditation. That was many years ago and I am sorry that I no longer have the notes to show you.
The science says that parallel strings do not charge and discharge equally. Parallel strings should be avoided where ever possible and GC batteries belong in a golf cart.
If you want to use them, fine. But in the long run you will say, "That bastard was right".
The tests were done at Royal Melbourne Institute of Technology in Melbourne. The test was done on a rig of six parallel strings of six two volt cells. They tried all the tricks like isolating the strings with diodes and fancy interconnecting of cells. The results were always much the same. Unbalanced charging across the array.
Feel free to use GC batteries. They will work. For a while. You might get five years maybe six in a home power system. I have seen single series string 2V cells last 26 years.
Good luck
Not at all. Many people use GC batteries. Most only once.
It happens because every cell has a different internal resistance. You may see nothing wrong with spending the rest of your life trying to get several strings of batteries to a balanced state of charge but most peopls have lives beyong the battery room
Starting small and adding to a system is another false economy.
Start with your energy audit. Size a system to suit and play what if on paper for a while.
Until you know what goes into system design you will fail to understand the relationship of the parts.
That is absolutely right, one dead cell in a bank of batteries more than a year old, you replace the lot.
Parallel strings are more prone to cell failure due to unequal charging.
You will find that is incorrect. You size a system to your need and build it.
Yep. that's often the case. You might try Swinbourne University and see if they will sell you the notes and work book for the "Introduction to Renewable Energy" course.
Yes that's right. They are used to change AC to DC.
The reason why is that all cells have different internal resistance, so they all charge/discharge at different rates. As a battery a single series string has the aggregate of all the cells resistances and is basically balanced. Parallel strings must be constantly monitored to keep them in a balanced state of charge.
And when it comes to using a hydrometer, a single string is a lot nicer to do than a number parallel strings.
A single series string of the correct Ah rating will, with proper care, out last parallel strings. Good quality batteries will have a longer warranty that cheaper batteries.
Time will tell.
Days of autonomy is how long your batteries will supply your daily load with no input.
Could be.
No, I have given you information. What you decide is your choice.
You got an awful lot if you listened. You are fishing for an answer that fulfills your idea of solar power. Reality may be different.
Learn to size a system, play what if with the numbers, cost your sizings. Parallel strings are second best choice for home power systems and should be avoided wherever possible.
No need to feel offended by anything the ghinius writes, particularly if it's about batteries. Consider that he's on his fifth set with his own very small power setup. Do you know of anyone else who's gone through so many? I sure don't, it's a record. In his own words:
"I have just installed my fourth set of batteries in 14 years"
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"1st System 4 sets of batteries. 3 sets of which were second hand. 2nd system 1 set of correctly sized batteries"
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Anybody with even a little common sense could have used GC batteries and needed only half as many replacements.
Nevertheless, you could reasonably think that someone who's learned the hard way might know *something* worth relating. Unfortunately that's not true either because those quotes demonstrate that he can't keep his stories straight. We don't know if it's 4 sets or 5 or maybe more. As if that point needed any reinforcing, consider another quote from him:
"Then I went shopping. I bought what was required (all top quality) and assembled it correctly and turned it on, fifteen years ago."
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In fact, from the first two quoted posts we know that his current installation is only about 7 years old.
So, George Ghio not only holds the record for most dead batteries in a home power setup, he also lies so much that one would need a second opinion before accepting his word on the time of day. His battery lectures are about as credible as someone giving healthy-living advice based on their claimed personal good health, while alternating between drags on a cigarette and an oxygen cannula.
Many more examples of his astonishing BS here
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Wayne
On Thu, 14 Aug 2008 03:26:18 -0500, "N9WOS" If you keep the charge/discharge rate in line with design specs then they
No. Batteries have a finite life-rating usually stated as a number of cycles at a particular discharge level.
Wayne
That's debatable in the context of home power setups. I tell people to buy the best batteries they can afford, but only if they've crested the typical learning curve or can be reasonably expected to do so quickly. The classic mistake of home power newbies is to over-tax their installation, resulting in chronic undercharging. The situation is worst for those who refuse to learn the basics about watt-hrs and therefore can't relate to the difference between a coffee maker and a coffee grinder for example. Combine that with a low budget that saves the cost of a proper battery monitor and there's a high likelihood of seeing few days or none when the batteries get fully charged. Knowing all that, some dealers refer to T105s as "training batteries". It's the smartest and lowest cost (short *and* long term) strategy for many. How do you tell who needs the training wheels? That's a tough one. I visited a couple recently who'd let some mid-priced batteries run very dry. An otherwise intelligent pair who'd probably have been better off to start with the cheapest batteries since apparently they intend to learn the hard way. Besides, the cheapest batteries might cost 4 times less and last 5 times less than the best. Add in the cost of money and there's not much difference in cost.
Wayne
Yes, but how fast do you charge them? Amperes over what time period? I would say that it isn't close to the rate at which you charge them. The key isn't how fast or how much you discharge them, it's how fast you charge them.
Typo's I would say that it isn't close to the rate at which you DIScharge them.
|> |> |> | |> |> |> |> | Batteries are the very heart of your system. That should tell you |> |> | something about the choice of battery/ cell used. You sound like a guy |> |> | looking for an excuse to use golf cart batteries. |> |> |> |> You sound like a guy wanting to tell everyone to do things exactly the |> |> same way you do things, without being willing to tell them why, whether |> |> you actually know why or not. |> | |> | I have told you why, parallel strings do not charge/discharge in a |> | uniform manner. That is the truth. |> |> I'm not doubting the truth of this. I'm wanting to understand the means |> by which this happens, and the degree to which it happens. I want to |> understand this enough to know how well it may be mitigated. For example |> the non-uniform charging may be dealt with by smaller chargers isolated |> on each string (not one big charger trying charge the strings in parallel). | | It happens because every cell has a different internal resistance. You | may see nothing wrong with spending the rest of your life trying to | get several strings of batteries to a balanced state of charge but | most peopls have lives beyong the battery room
This argument can also be applied to limit the number of cells in series, too. Are you limiting your thinking about charging to one which only involves one single charger system and charging all batteries together?
| Starting small and adding to a system is another false economy.
And you suggestion is to start out as big as you will ever need all at once at the start, even though you don't need anywhere near that capacity now, and may not for years?
|> I want to explore means to manage the load balancing before deciding. |> Maybe it will be the case that those methods are not worthwhile. I |> cannot say today. Today is the learning time. The decision is later. |> The conditions will be known then. | | Start with your energy audit. Size a system to suit and play what if | on paper for a while.
This does little good until _after_ one has all the scientific information about batteries.
|> No. I want to know all the reasons for all the choices. | | Until you know what goes into system design you will fail to | understand the relationship of the parts.
Until you are offering this level of information, what good is your advise?
|> What happens if you have ONE string of several very large cells/batteries |> and one dies? Are you saying you don't have to replace the whole bank in |> this case? | | That is absolutely right, one dead cell in a bank of batteries more | than a year old, you replace the lot. | | Parallel strings are more prone to cell failure due to unequal | charging.
But _you_ don't really know why that happens, and as a result of that, _you_ are not able to envision ways around it. But the important thing is, _you_ can't offer real scientific information because you simply don't have it. All you have is specific "do what I (would) do" advice, and nothing more.
|> That is a work in progress. Much of it will be done when I start going |> with some battery power. More will be done later. This is not a one big |> step all the way project. | | You will find that is incorrect. You size a system to your need and | build it.
Such an idealist. Maybe you should work in the _commercial_ UPS market or something.
|> Quite a lot of it is unsupported "what to do" advice. | | Yep. that's often the case. You might try Swinbourne University and | see if they will sell you the notes and work book for the | "Introduction to Renewable Energy" course.
Is that a course on the science of how batteries work, or just a technician class on how to install batteries using common "still thinking in the box" approaches?
|> Rectifiers are made of diodes (or other things). | | Yes that's right. They are used to change AC to DC.
That's not the only thing they can do. Do not assume that because there is more need for one thing (converting AC to DC) that no other need (isolating DC directions) is valid to consider.
|> |> |> I'm exploring all options. I'm not interested in specific advice on what |> |> |> I should do (at least not without well explained why) ... I'm interested in |> |> |> the information to make the best decision in the circumstances that will be |> |> |> present at the time the decision is to be made. |> |> | |> |> | You still sound like a guy looking for an excuse to use golf cart |> |> | batteries. |> |> |> |> I am someone looking for the technical information that would be a valid basis |> |> for deciding what circumstances that golf cart batteries can be used in, and |> |> what circumstances they cannot be used in, where "circumstances" involves a lot |> |> of things that I don't even know, yet. |> | |> | You can use golf cart batteries, they can be wired in series, parallel |> | and series/parallel in as many strings as you feel are required. Most |> | people only ever do this once. Their second battery bank is usually a |> | single string of cells with the correct Ah rating. |> |> And maybe I will migrate to that. One possible path is that I would start with |> a small bank and migrate to a larger bank. I may parallel things in the interim. |> I will also be looking at possible circuits to manage the load balancing between |> parallel strings. Maybe that won't be practical. I'm sure you'll say it won't |> but I want to know why, if that's the case. | | The reason why is that all cells have different internal resistance, | so they all charge/discharge at different rates. As a battery a single | series string has the aggregate of all the cells resistances and is | basically balanced. Parallel strings must be constantly monitored to | keep them in a balanced state of charge.
If the resistances in _series_ are different, that can result in an imbalance as well. It's just more easily hidden becuase the single string still has a behaviour like a single string. It charges up at whatever rate it can and it discharges at whatever rate is demanded up to what it can. All this while one cell is forced to go along until it dies. But you won't see it coming unless you are monitoring each cell separately by some other means. And then you are into the same amount of work to manage the system, anyway.
| And when it comes to using a hydrometer, a single string is a lot | nicer to do than a number parallel strings.
For a moment there, I thought you might say that BIG MONSTER CELLS are easier to measure than dozens of little batteries because the latter means taking a measurement dozens of more times.
|> If it is the case that cost is why I would replace one cell/battery at a |> time, then cost would clearly prohibit the monster cells. | | A single series string of the correct Ah rating will, with proper | care, out last parallel strings. Good quality batteries will have a | longer warranty that cheaper batteries.
But your advice is to not have any strings of batteries at all until such time as one can have the biggest baadest string bought all at once. No economic planning involved.
|> Apparently we have a different understand of this term. I don't know |> what yours is, then. So it's pointless to proceed on this. | | Days of autonomy is how long your batteries will supply your daily | load with no input.
I can't tell you what the future might hold in terms of the longest period that might be when dealing with solar and wind sources. But I guess you are the one with the crystal ball.
|> | Oh, I know what it is you want to know alright. But to understand you |> | need to listen. |> | You want some one to tell you what you want to hear. |> |> You want some one to do what you tell them to. | | No, I have given you information. What you decide is your choice.
You have not giving me the information I seek. All you have given is advice of what you think I should do, and simplistic reasoning (like "parallel will charge unevenly" without considering mitigating methods).
|> I can see I'm not going to get anything useful from you. | | You got an awful lot if you listened. You are fishing for an answer | that fulfills your idea of solar power. Reality may be different.
I don't have the idea, yet. I'm seeking scientific information (NOT The end results like "batteries will charge unevenly") that explains what is going on and what methods might exist to deal with it and manage it.
| Learn to size a system, play what if with the numbers, cost your | sizings. Parallel strings are second best choice for home power | systems and should be avoided wherever possible.
Learn the reality that size needs change, finances are not all at once, etc. Lots of that might work in commercial UPS systems for companies that need a short ride through an outage to maintain "five nines" uptime. My goal does not include any "five nines" uptime for my home.
|>So, a basic rule for GC batteries is, if you put them in any system that |>doesn't have at least 5 days of autonomy, then you are going to kill them. | | Baloney. Batteries can be well-maintained and last the maximum with | zero days autonomy. It's done all the time with grid-connected setups | that only have storage enough to last through short outages.
What about off-grid setups?
|>That is because the charging , and discharging rates are going to kill them. |>As for as GC batteries go, it's mainly the charging rates that get them. | | Nonsense. The #1 cause of premature failure of home-power batteries is | chronic undercharging.
Sounds like a design problem.
|>If you keep the charge/discharge rate in line with design specs then they |>will last for decades. | | No. Batteries have a finite life-rating usually stated as a number of | cycles at a particular discharge level.
Which is only a simplistic view of the usage patterns of batteries.
|> |> |> | Now you can take that as an insult if you like. But, Golf cart |> | batteries only last for decades if they are used as door stops. Most |> | people who are capable of learning only ever buy one set of GC |> | batteries for their house system. Those that have bought two sets have |> | a learning disability. |> |> The real question is, who knows the science behind why this is so? Maybe you |> do or maybe you don't. I'm not expecting you to write papers for me. But if |> your knowledge is limited to hearing people say things like "I had GC batteries |> and I will never do that again", that isn't ruling out to me that someone just |> didn't build it right. If you know of the science behind this, please point |> it out (e.g. PDFs of papers with graphs and charts and basis in physics, etc). |> Otherwise, its doubtful I'd ever get anything useful from you. | | I have never sold GC batteries, but I sure have replaced lots of them | with single series strings of 2V cells of the correct Ah rating for | people who thought that they were saving money buying GC batteries. I | have also swapped out parallel strings of batteries, not just GC | batteries, for single series cells.
So you are a dealer of very large cells/batteries.
| I can only repeat what I learned getting my accreditation. That was | many years ago and I am sorry that I no longer have the notes to show | you. | | The science says that parallel strings do not charge and discharge | equally. Parallel strings should be avoided where ever possible and GC | batteries belong in a golf cart.
That's not science. Science would tell you why and how that happens. Further, science would tell you how they behave under various methods of connecting charging and discharging circuits.
You're taking the training you've been giving regarding certain finite methods to install battery systems, and calling it "science". Real science comes from research laboratories and investigative processes that explore all options and find out why things really happen and how control methods may or may not work.
| If you want to use them, fine. But in the long run you will say, "That | bastard was right". | | The tests were done at Royal Melbourne Institute of Technology in | Melbourne. The test was done on a rig of six parallel strings of six | two volt cells. They tried all the tricks like isolating the strings | with diodes and fancy interconnecting of cells. The results were | always much the same. Unbalanced charging across the array.
What kinds of chargers did they use? Did they have separate chargers for each string?

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