connecting batteries in parallel or series, myth and theory




You should be able to operate your battery bank and never see a "severely sulfated" battery. This is a case where "an ounce of prevention..." is likely to be all that's needed. Modern charge controllers and the simplest routine/scheduled maintenance should maintain a good balance and give you a longer lifespan for your batteries.
Of course, any drastic changes in the charging or discharging of your system, should be a reason to consider how the batteries may be effected, and appropriate action/ additional maintenance taken.
(Say a Hurricane knocks down your wind generator, and can't be or isn't replaced for months. Or there is a lot more use of the system than originally planed on, and there is insufficient charging to keep up, on a regular basis. You might need to use a gas generator to maintain the battery bank. )
If the situation becomes chronic then you need to redesign your setup. ( This might involve adding storage capacity and could well involve adding a matching parallel string to your existing setup, it would not mean any disaster is more likely. )
Some reasonable operating/maintenance schedule applied as a part of your weekly routine, will most likely prevent any problems developing. It's where people never bother with them, at all, until some problem develops, that allows the appearance of such conditions. It need not be any more lifestyle changing than adding a caged pet to your life, forget to water them or clean out the cage on a regular basis, and you will have problems.
Luck; Ken
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wrote:

I agree 100%, and should have mentioned that in my response. --ron
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| If the situation becomes chronic then you need to | redesign your setup. ( This might involve adding | storage capacity and could well involve adding a | matching parallel string to your existing setup, it | would not mean any disaster is more likely. )
What about, with 2 battery strings/banks, flipping the charge between them so neither spends too much time below 100%? Of course one problem with this is that it means a lot of cycles on both. That and since the process would not be 100% efficient, you'd be driving the discharge level further down, or need to supplement with some external power. What I am thinking, though, is if your external power level would take a long time to bring a bank up to 100%, maybe it would be of benefit for a bank that has been low for a while to drive it back to 100% using the other bank for now (hoping that maybe full external power will be back up higher once the 2nd bank needs to get recharged).
If linear accumulation of time discharged is the issue, as opposed to how long each discharge period is, then this would not work.
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wrote:

If you had it setup to provide some redundancy, that might make some sense, I don't know. Why don't you just get a good stable setup working, before trying to design something new?
For an initial design you would be sizing for a single string with the highest capacity cells you can afford. The addition of a parallel string for greater capacity, is just an affordable way to increase your capacity, when it turns out that your initial capacity wasn't enough. If you were rolling in dough, you could totally replace your existing battery bank and inverter, with a new larger capacity single string. There is no need to avoid the parallel string in that situation, as long as good normal maintenance practices are followed.
Luck; Ken
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| If you had it setup to provide some redundancy, that might | make some sense, I don't know. Why don't you just get a | good stable setup working, before trying to design something | new?
You mean, just do what someone else does, the way they do it, first, and see if that succeeds or fails?
| For an initial design you would be sizing for a single | string with the highest capacity cells you can afford. The | addition of a parallel string for greater capacity, is just an | affordable way to increase your capacity, when it turns out | that your initial capacity wasn't enough. If you were rolling | in dough, you could totally replace your existing battery bank | and inverter, with a new larger capacity single string. There | is no need to avoid the parallel string in that situation, as long | as good normal maintenance practices are followed.
The finances of the future are not predictable. I need to be flexible.
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wrote:> Why don't you just get a good stable setup working,

No, I mean that it's best to build a known practical design, before attempting to create a modification to that design. The point being that, done properly, it will work/succeed. It is only your modification where there is a need to "see if that succeeds or fails". (See below)
I'm beginning to get the impression that you actually have no intention of building a viable system, and that this is a purely "intellectual" endeavor, for your personal entertainment.
If that's the case: then the ideas you presented in your last post display a great lack of understanding, of the basic physics involved, and can't work.
Luck; Ken
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You will find that there is nothing "intellectual" about his attempt to find someone to tell him it is okay to do stupid things. Also a fair bet that "he" is in fact a sock puppet of either wayne or ron.
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In alt.engineering.electrical snipped-for-privacy@gmail.com wrote:
|> |> wrote: |> > | Why don't you just get a good stable setup working, |> > | before trying to design something new? |> |> > You mean, just do what someone else does, the way they do it, first, and |> > see if that succeeds or fails? |> |> No, I mean that it's best to build a known practical |> design, before attempting to create a modification |> to that design. The point being that, done properly, |> it will work/succeed. It is only your modification |> where there is a need to "see if that succeeds or |> fails". (See below) |> |> I'm beginning to get the impression that you actually |> have no intention of building a viable system, and that |> this is a purely "intellectual" endeavor, for your personal |> entertainment. |> |> If that's the case: then the ideas you presented in your |> last post display a great lack of understanding, of the |> basic physics involved, and can't work. |> |> Luck; |> Ken | | You will find that there is nothing "intellectual" about his attempt | to find someone to tell him it is okay to do stupid things. Also a | fair bet that "he" is in fact a sock puppet of either wayne or ron.
You sure are big on assumptions about things you know nothing about.
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| No, I mean that it's best to build a known practical | design, before attempting to create a modification | to that design. The point being that, done properly, | it will work/succeed. It is only your modification | where there is a need to "see if that succeeds or | fails". (See below) | | I'm beginning to get the impression that you actually | have no intention of building a viable system, and that | this is a purely "intellectual" endeavor, for your personal | entertainment.
The impression is off. I intend to be a viable system. But I do intent to jump directly to a different design (which has already changed as a result of info others have posted in this thread).
| If that's the case: then the ideas you presented in your | last post display a great lack of understanding, of the | basic physics involved, and can't work.
If something I suggest can't work, I'd like to know which that is, and to the extent possible, why. The "why" part might lead to a variation of design that perhaps could work. There are things I still don't know about batteries. But based on the experience reports here, it seems clear that if I install some battery system, and replace it a few times, and end up with a massive single cell string system, I still won't know anything about any of this. So just building and having and running a conventional system is not a very good way to learn. My approach is to learn as much of the science as I can, then plan my approach to experiments, and actually try things.
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wrote:

Well, good luck with that, and since you have no more to provide to a discussion of the subject, farewell. If you ever have any actual practical information to impart someday, let us know. If you should ever be willing to disclose this "different design", there might be something to discuss.

For those of us in alt.energy.homepower we don't construct systems that employ battery banks strictly for the learning experience. (In fact I suspect most of us would rather avoid as many "learning experiences" as possible, as they are often painful.) It seems that you want to design "something different" based on our experience, but aren't interested in acquiring any of your own. You expect us to provide answers to suit your needs, but we just like to examine subjects of interest to us.
By "learn as much of the science as I can", you mean seeing what NewsGroup posters have to say about a subject? To be fare, I should inform you that we seldom cover as much "of the science" as you expect. Some things get left out of the discussions. But if you actually build something that works, you would have to have learned a few more things, related to the issue, than what might appear in a dozen threads.
Then there is the fact that actual projects get a lot of support from interested posters ("z" and his pelton wheel micro-hydro project for example.) If or when, you actually are trying to design or construct something real, try posting again. (Hopefully not too many will remember this run around.)
Luck; Ken
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|
| wrote: |> |> | No, I mean that it's best to build a known practical |> | design, before attempting to create a modification |> | to that design. The point being that, done properly, |> | it will work/succeed. It is only your modification |> | where there is a need to "see if that succeeds or |> | fails". (See below) |> | |> | I'm beginning to get the impression that you actually |> | have no intention of building a viable system, and that |> | this is a purely "intellectual" endeavor, for your personal |> | entertainment. |> |> The impression is off. I intend to be a viable system. But I do intent |> to |> jump directly to a different design (which has already changed as a result |> of info others have posted in this thread). |> | | Well, good luck with that, and since you have no more | to provide to a discussion of the subject, farewell.
I'm here trying to get information. Some people have provided some. Maybe they will provide more.
| If you ever have any actual practical information to | impart someday, let us know. If you should ever be | willing to disclose this "different design", there might be | something to discuss.
Sure thing. If I come up with something better, I will. In the mean time I will continue my research and study, which does include talking about it.
| For those of us in alt.energy.homepower we don't construct | systems that employ battery banks strictly for the learning | experience. (In fact I suspect most of us would rather avoid
Neither do I. That's why I'm doing the learning ahead of the design and construction.
| as many "learning experiences" as possible, as they are often | painful.) It seems that you want to design "something different" | based on our experience, but aren't interested in acquiring any | of your own. You expect us to provide answers to suit your | needs, but we just like to examine subjects of interest to us.
So are you saying I should skip the learning and construct every possible design I come up with?
| By "learn as much of the science as I can", you mean seeing | what NewsGroup posters have to say about a subject? To be
Sure. Maybe they know about actual science, or know where they have seen it before.
| fare, I should inform you that we seldom cover as much "of | the science" as you expect. Some things get left out of the | discussions. But if you actually build something that works, | you would have to have learned a few more things, related to | the issue, than what might appear in a dozen threads.
I'll learn as much as I can before I build anything.
| Then there is the fact that actual projects get a lot of support | from interested posters ("z" and his pelton wheel micro-hydro | project for example.) If or when, you actually are trying to design | or construct something real, try posting again. (Hopefully not too | many will remember this run around.)
I'll continue to post when _either_ I have some useful information to offer, or have a question soliciting useful information. For the latter, I have learned that most posts in response fall into these categories:
1. people providing actual useful information 2. people intending well, but provide useless information 3. people providing useless information but really don't care 4. detractors that just like to post drivel 5. responses to any of the above
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In alt.engineering.electrical snipped-for-privacy@gmail.com wrote:
|> No, actually I'm not setting out to simply mimic what someone else does. |> I had something in mind that no one has apparent ever done before, but |> with some good information I've found here (not what you've given, as |> your info just chalks up one more vote against paralleling anything), |> I've modified by ideas. I haven't given out what these ideas are, yet. |> I might. Or I might not. It will be a new thread if I do. | | Chances are it has been done before and discarded as pointless.
Maybe so. But apparently not by you. I'd think you'd remember it if you did. You'd be able to say what you actually tried, and what degree of effect it had (even if none at all).
I'm not yet going to describe my ideas because they are too numerous in combinations of doing things. I believe they will work. But they may not be ultimately practical. For example, elements of the design may be subject to excess failure (of a circuit, for example), or excess maintenance.
And FYI, most of the ideas actually do _not_ involve parallel batteries.
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On 20 Aug 2008 18:18:03 GMT, snipped-for-privacy@ipal.net wrote:

Cussing is not un-civil, dude.
Walking around a free forum acting like some sin free judge most certainly is, however.
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|
| wrote: |>> |>>|>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? |> |> Same difference. Whether it's 1 day or 10, ignore the need to get |> batteries fully charged regularly and it won't matter whether they're |> 5 or 20 year batteries, whether they're wired in series or parallel, |> charged fast or slow, etc. | | Explain to me this... How do you go from sub 50% State Of Charge to 100% SOC | in one solar day?
With a very fast charge?
| Explain how that is suppose to work in a real life system.
If I'm aiming to charge at a C/20 rate, I wouldn't expect to get a full charge back within, say, 6 hours of good sunlight in the winter. So it would seem to be a good idea to rate the system so that if it takes 4 days to recharge from an XX level of discharge, you need to rate the system capacity and manage your usage so you would discharge it to no more than XX level of discharge during both the unlit times of those 4 days PLUS the number of days between those days of light (e.g. the cloudy/snowy days). So we need a new ratio: rate of usual discharge divided by rate of usual charge. And since we want to charge slowly while also avoiding a deep discharge, the rate of discharge needs to be quite small, such as C/100. That means a BIG system, possibly larger than practical to do with a single string of single monster cells.
I wonder where those replaced submarine batteries end up :-)
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In alt.engineering.electrical snipped-for-privacy@citlink.net wrote:
|>Sounds like a design problem. | | It can be, but it's more often just life. For example, a setup can be | well designed for say, 2 hours use of TV per day. But if the user buys | a larger model and/or watches it longer then he's likely to have a | problem. The key IMO is a proper battery monitor. That provides the | user with a routine method of knowing his battery's true SOC, which | gives him a chance to adjust habits or hardware if needed. DJ, a solar | dealer who used to post here, once wrote that he wouldn't sell a setup | anymore unless it included a battery monitor. Either the customer | would pay for it or he'd include it free if necessary. I'll add that | I'd question the business sense of any dealer who installs a | whole-house setup without a proper battery monitor. Besides doing the | customer a disservice, he's inviting call-backs that will eat up his | profit margin. In my own experience with strongly encouraging friends | and acquaintances to buy and use battery monitors for their home power | installations, I've yet to have anyone regret their purchase. Most | rave that they should have had one from the beginning, and some blame | their dealer for not including it. The necessary $50 shunts are | installed in the popular Outback power panels, so many owners need add | little more than the meter itself, which only costs about $150.
Based on the description of there being just one monitor wired in at the inverter, it would seem this monitor only checks the health of the whole string, not each individual battery/cell.
Exactly what parameter(s) does this monitor check?
|>| 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. | | Batteries are rated to supply a specific number of amp-hrs. The amount | will vary with the number and depth of discharge cycles, and can | certainly be less than spec if subjected to poor maintenance or bad | habits. But it can't be more unless you've discovered something that's | escaped everyone else.
If the manufacturer rates the battery for its most ideal circumstance, then sure, you can't get the battery to do better than the rating. And most of the manufacturers are interested in diverting all sales to their products, so of course they will rate as high as they can. If there is some independent source of battery rating information that rates batteries based on how well they do in real life scenarios, then I'd be more inclined to use those kinds of ratings, which are likely to be less where the real life scenarios are not what is ideal for the battery.
| Of course, that's the prevailing wisdom, and this being Usenet, there | are certainly alternative theeries. For example: "A lead acid battery | stores a chemical reaction. Therefor every time you charge/ discharge | the battery you use up some of the chemicals involved. Also the | greater the depth of discharge the more chemical used = fewer cycles.
A theoretically perfect battery will perfectly reverse the discharged chemical reactions during the charging cycle. Even if real life gets very close to that one big issue is that the reaction doesn't reverse in the same way (for example the lead that redeposits on the plates does not form the plates in the same way as they were formed in manufacturing). And of course, as soon as any gassing occurs and the gas bubbles move someone else, that's rather hard to reverse without some means to move the gas back. The best we can do for loss of water is to add some pure water back.
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On 15 Aug 2008 02:30:50 GMT, snipped-for-privacy@ipal.net wrote:

Battery monitor shunts are wired in series at the negative battery cable so that they count all battery current. For example, in my case that's routine PV and wind charging, occasional DC backup charging, rare AC backup charging, routine AC loads from 3 inverters and a tiny DC load.

Yes. One still needs to use a hydrometer occasionally to check for the need to equalize, and to verify that the monitor is synched.

Monitor features vary, but for a Link 10: Volts, amps, watts. Applies charge efficiency factor and Peukert to establish Ahrs below full, also displayed as SOC percentage, along with a 4 segment bar graph that can be set to display useable storage (usually the top 50%). With some juggling of breakers etc, the device can be used occasionally to compute individual sources and loads. The Link10 manual is a useful read. http://www.xantrex.com/web/id/72/docserve.aspx

Most batteries are rated at multiple discharge levels, one can make reasonable extrapolations as needed.

You're over-thinking the issue IMO, and you're unlikely to find independant testing results. But if you don't trust the maker then you might ask for clarification about exactly what some specs and warranty terms mean.

Dang, there goes my idea to market orgone to Usenetters. :-)
Wayne
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In alt.engineering.electrical snipped-for-privacy@citlink.net wrote:
| Battery monitor shunts are wired in series at the negative battery | cable so that they count all battery current. For example, in my case | that's routine PV and wind charging, occasional DC backup charging, | rare AC backup charging, routine AC loads from 3 inverters and a tiny | DC load.
Current alone (which, BTW, is a single value for the whole string) is going to tell you what about the condition of each cell in the string?
You don't measure the voltage anywhere?
|>it would seem this monitor only checks the health of the whole |>string, not each individual battery/cell. | | Yes. One still needs to use a hydrometer occasionally to check for the | need to equalize, and to verify that the monitor is synched.
I'd like to figure out a means to have the check automated. That might mean a built-in factory-calibrated hydrometer interfacing to an optical sensor that can be attached over the window that accesses the hydrometer.
Then if the science tells me that for certain conditions, a different level of charge or discharge should be applied to that cell, then either that would be done if the design has the means, or the operator would be warned if it can't.
|>Exactly what parameter(s) does this monitor check? | | Monitor features vary, but for a Link 10: Volts, amps, watts. Applies | charge efficiency factor and Peukert to establish Ahrs below full, | also displayed as SOC percentage, along with a 4 segment bar graph | that can be set to display useable storage (usually the top 50%). With | some juggling of breakers etc, the device can be used occasionally to | compute individual sources and loads. The Link10 manual is a useful | read. http://www.xantrex.com/web/id/72/docserve.aspx
Volts of each cell?
|>|>| 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. |>| |>| Batteries are rated to supply a specific number of amp-hrs. The amount |>| will vary with the number and depth of discharge cycles, and can |>| certainly be less than spec if subjected to poor maintenance or bad |>| habits. But it can't be more unless you've discovered something that's |>| escaped everyone else. |> |>If the manufacturer rates the battery for its most ideal circumstance, then |>sure, you can't get the battery to do better than the rating. | | Most batteries are rated at multiple discharge levels, one can make | reasonable extrapolations as needed.
The biggie 2V Surrette cell (shown in the PDF file) had a lot of them listed.
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Open mouth, insert foot. You undercut your own argument with your own statements. Example.
http://www.cdstandbypower.com/product/battery/vrla/dcs75bt.html
Here is the specs for the C&D 75AH battery. They recommend a MAXIMUM of C/5 Any faster than that, then the amount of damage far outweighs any benefit of reduced charging time.
And if you do charge at the C/5 level to the 14.7V.
http://www.mil.ufl.edu/projects/koolio/Koolio/offline_webpages/battery_charger_info.htm
You will have a battery that is only 85% full at the end of the day (considering that you have a panel just big enough to supply the total load demand.
If you take 60% out of the battery then you have a 25% SOC battery at the start of the next charge level. Then recharge it to 85% then to 25% Repeat infanitem
It never gets close to 100% charge. So it sulfates and dies.
If you up the panel size so you get C/3 charging, you end up with 75 when you go into float. And with the added float time you get with the change in charging level, you won't get much over 87% charge level. So you won't gain anything by just increasing the size of your solar array.
For EV people, the general consensus is that C/10 is about the fastest you will want to try to charge your battery system. But slower than C/10 is preferable because it increases charge efficiency.
On the solar front here is what other people have to say. http://www.solarquest.com/Schoolhouse/Task.asp?id 23
"The best overall charging rate for deep cycle lead-acid batteries is the C/20 rate."
And if you take a C/20 rate, it will give you about 95% full batteries when you go into float. With if far better than 85%.
So you can step up your final charge level from 85% to 95% by just increasing the size of your battery bank by 4X, That reduces sulfating from chronic undercharging, and you reduce the charging stress on each battery at the same time, so the lifetime improvement is in orders of magnitude. A win win situation.
And when you are not at the house using a bunch of stuff, then it will give the system time to push it up to close to 100% SOC with a few hours of float charge every day..
It just makes logical sense to me.
The key to high peak charge level is by reducing total charge current. Which reduces battery charging damage and increases total final charge level. As I said, a win win situation.
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You've been making a habit of it, such as the other day for example when you wrote that narrow-minded baloney about off-grid AC lighting being "stupid".

So what? Home power batteries tend to be discharged a fraction of their capacity per day, and (ideally) recharged at a rate that will get them fully recharged most days. The charge rates tends to rise during the morning, and fall in the afternoon or anytime with concurrent loads. Batteries that are discharged over several days tend to take days to reach full charge again, and owners who suffer that scenario frequently, probably wish they had some overcharging to limit. In the case of grid-connected setups with batteries designed to be discharged in a shorter time, the charger is programmed to recharge at the ideal rate.

Nobody has said that exceeding recommended charge rates is good practice, and you're the only one who's claimed it's necessary. You're arguing with yourself.

So you've invented an unlikely scenario to support your case. I'm not impressed.

That's the first thing you've written that relates to a common problem with home power batteries.

So basically you're saying that if you start with a strawman-battery sized to prove that overcharging is a big issue in home power applications, and then enlarge that size to about what most people actually have, the problem goes away. IOW, it only exists in a tortuous Usenet post.

That's done automatically by modern multi-stage chargers. They supply full available current (which is highly unlikely to exceed the recommended rate in my experience) until bulk voltage is reached, tapered current as needed to maintain bulk voltage for a set time, then further reduced current to maintain a lower float voltage. PV is generally too expensive to size for overcharging, but generators are sometimes capable of it, so AC chargers are programmable and are normally set to the proper rate, then shut down after absorption. Finish charging is optionally delayed until PV is available again in order to prevent extended generator run times.

But this "damage" only exists in your strawman scenario. In normal home power applications, it's *low* charge rates that tend to be symptomatic of bad design or operation. The closest I've seen to an overcharging problem is where people who are chronically short on supply raise their bulk and float voltage settings to limit throttling. Which isn't too terrible unless there are days when the batteries are charged early, which wouldn't be often considering the shortage of supply that prompted the fiddling. My own setup suffers from that overcharging scenario but for a different reason - I have a single stage turbine charge controller in parallel with an MX60. The turbine charging voltage is set a little higher than the MXs bulk setting, which means that when the batteries are full but the wind is still blowing and loads are minimal, the batteries are being floated at above normal bulk voltage. That only happens occasionally and doesn't tend to last long, so it hasn't been a factor in my battery life which is 13 years and counting.

<sigh>
Wayne
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wrote:

OK - now can either of you say "Equalization" or as I put it earlier scheduled Maintenance Overcharging?
It is not only important for parallel multi-string operation but for multi-cell battery operation in general.
Luck; Ken
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