connecting batteries in parallel or series, myth and theory

wrote:


Geez, Ron, give it a rest, willya? Everyone knows that *eorge is a dick and most of us have him killfiled. He's talking to himself and you. Killfile him and get on with life.
John -- John De Armond See my website for my current email address http://www.neon-john.com http://www.johndearmond.com <-- best little blog on the net! Tellico Plains, Occupied TN Nuke the Whales!
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Good advice. Thanks. I just have to figure out how to do it -- shouldn't be hard. --ron
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wrote:

In Agent, simply be on an article authored by the target, hit ^k and make your selections. Agent and that stuff from microsloth both call the process "filtering". Check your help file for details.
This (I'm posting from AEH) is a great group once a few card-carrying *ssholes are filtered out.
John -- John De Armond See my website for my current email address http://www.neon-john.com http://www.johndearmond.com <-- best little blog on the net! Tellico Plains, Occupied TN In theory, there is no difference between theory and practice. In practice, there is.
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Thanks, John.
Done. --ron
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Ron, how hard is it?
Kill file is for wimps. But is dead easy. Funny you should find it hard, I assume that it is easier than telling us how you designed your system.
Still glad to be rid of another talker, non walker.
Like wayne you never designed your system.
Bye (I hope)
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addresshttp://www.neon-john.comhttp://www.johndearmond.com <-- best little blog on the net!

Yeah, run away from the hard questions.
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A rather conspicuous lack of system design information. No energy audit. No sizing calculations.
I do believe that the closest you ever got to actually designing your system was when you said okay to the salesman.
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On Thu, 07 Aug 2008 21:38:17 -0400, Ron Rosenfeld

Presumably he's talking about the course he took titled "Introduction to Renewable Energy Technologies". Which he quoted: "Lead Acid) are suitable for use in solar power systems, but AGM batteries are generally not". http://groups.google.com/group/alt.solar.photovoltaic/msg/77d8d63366a6ff9e But then later contradicted by writing "AGM and Gell batteries can be very effective. such batteries can offer good life expectancies." http://groups.google.com/group/alt.solar.photovoltaic/msg/4cbc1e896cfd71a6 So he doesn't take the course's gospel very seriously himself, yet for some reason expects that others are interested in his hearsay remembrances.

It's an Australian organization designed to prevent an unknowing public from being BSed by nitwit PV installers. So of course he's not a member.

He's complained several times that the organization isn't up to his high standards. <snorf> The two things I know about them are that the ghinius doesn't like them, and they put him out to pasture. Which means that they're obviously on the right track.
Wayne
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In alt.engineering.electrical snipped-for-privacy@gmail.com wrote: | On Aug 8, 4:43 am, snipped-for-privacy@ipal.net wrote: | |> |> Who here thinks connecting batteries (one cell or multi-cell) in parallel is |> bad ... and why (if you don't know why, I'll assume it's myth). | | Series parallel batteries. | | First, whether you use 2V cells or batteries you end up with "A | Battery"
Right. But there is distinction of paralleling single cells individually versus paralleling a single battery of N cells, or a string of N cells. The latter do not have any cross connects at each cell connection. One consideration is whether there is any advantage to that. When I put some thought into it, I could not see any issue with lead-acid batteries.
| The problem with parallel strings is that they do not all charge or | discharge together.
If one discharges more, its voltage would drop, and others would take up the slack. At least that's the way I see it. A posted paper URL in this thread earlier suggested it's OK to parallel different strings or batteries with different capacities and they would discharge in proportion to their capacity. I'm guessing that is because of the voltage balance effect (the stronger string with the slightly higher voltage carriers more of the load).
| When I was getting my accreditation for solar design and installation | we were shown the results of a series parallel bank, if memory serves, | of 36 x 2V cells. That is six parallel strings of six cells. | | The up shot was that under charge or discharge the strings did not | operate as a single battery. i.e. Under charge the strings would | charge one at a time.
So from a deep discharge position (20-50%) a recharge would not bring each string back to 100% at the same rate, and if a discarge was needed before all of them are fully recharged, it would present an imbalance not in capacity, but in charge level.
Does that apply to both slow and fast recharge?
| The same for discharge. There were also very high transient voltages | across the array.
What would be causing a transient?
| Parallel string should be avoided wherever possible.
Why?
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snipped-for-privacy@ipal.net wrote:

I have never seen single cells paralleled. They are always connected in series to get the desired voltage. Then, another group of identical series cells may be paralleled with it.
mike
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| snipped-for-privacy@ipal.net wrote: | |> Right. But there is distinction of paralleling single cells individually |> versus paralleling a single battery of N cells, or a string of N cells. | | | I have never seen single cells paralleled. They are always connected in | series to get the desired voltage. Then, another group of identical | series cells may be paralleled with it.
So the "reason" is "everyone else does it".
Aren't all the plates within one cell already parallel? By extension of that, paralleling individual cells would make sense because it retains the very same concept.
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snipped-for-privacy@ipal.net wrote:

Not at all. If you want 48 volts and have two volt cells to play with, that is 48 jumpers for the paralleling the 48 cells. Add another 24 for the series portion. That is a total of 72 jumpers. It's easier to make two batteries first, then parallel them with two jumpers.

No. They are each in series with the one next to it. The power comes in on one terminal, through the electrolyte and out the other plate. There is no chance of any circulating currents within one cell. They all share the same electrolyte bath. If there were only two large plates in a battery, we wouldn't call them paralleled. Take those two plates and roll them up in a cylinder shape. It may look a lot different, but they're still not paralleled.
Now, there *are* multiple plates on each polarity because of space constraints. There's no room for two huge plates with the same surface are. Changing the shape of each polarity plate won't make it parallel.
mike --
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Not at all. If you want 48 volts and have two volt cells to play with, that is 48 jumpers for the paralleling the 48 cells. Add another 24 for the series portion. That is a total of 72 jumpers. It's easier to make two batteries first, then parallel them with two jumpers.

Yes your correct plates within a single cell are paralleled and always 1 more neg plate per cell. The power available from a given cell is given by the area of active material in contact with the electrolyte as it's a chemical reaction that provides the power the more power required the more plates are paralleled inside the cell, which is why you end up with a 2 volt nom cell and AHrs dependent on number of plates inside a cell.But it is hard to keep the parameters of each cell identical, in series this is not much of a problem in discharge there will be slight diferences but will be corrected but cells or batteries in parrallel have general recharge problem as the charging device only see's the best voltage of the strings and inevitably sulphation will occurr in some cells this will degrade the available capacity of the cell and will lead to early failure unless a manual charging system is employed to ensure all cells are fully recharged at regular intervals.
No. They are each in series with the one next to it. The power comes in on one terminal, through the electrolyte and out the other plate. There is no chance of any circulating currents within one cell. They all share the same electrolyte bath. If there were only two large plates in a battery, we wouldn't call them paralleled. Take those two plates and roll them up in a cylinder shape. It may look a lot different, but they're still not paralleled.
Now, there *are* multiple plates on each polarity because of space constraints. There's no room for two huge plates with the same surface are. Changing the shape of each polarity plate won't make it parallel.
mike
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Uh no. the best two volt cells have "L" shaped posts that bolt together and are then soldered.

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snipped-for-privacy@gmail.com wrote:

You know what I was getting at. Let's not put too fine of point on it. It is electrically more sound to make the proper voltage battery first, THEN parallel them, if absolutely necessary, to increase capacity.
mike
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That depends on how you look at it. What is electrically sound??? The point could be made, very convincingly, that a series/parallel connection should be exactly that. A GRID connection, placing 2 sets of cells in parallel, AND 2 strings in series, with each pair of cells connected together, and each string of cells connected together. Strings + to - and pairs + to + and - to -.

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| snipped-for-privacy@gmail.com wrote: | |> Uh no. the best two volt cells have "L" shaped posts that bolt |> together and are then soldered. | | You know what I was getting at. Let's not put too fine of point on it. | It is electrically more sound to make the proper voltage battery first, | THEN parallel them, if absolutely necessary, to increase capacity.
If you are building a system from scratch, and selecting the cells/batteries, would it be your intent to find invidual cells/batteries of the intended AH capacity so you can have a single string (nothing paralleled)? If so, then what percentage of economic savings would half capacity cells/batteries need to be priced at to make you choose to split it into 2 parallel strings? Or the same for quarter capacity for 4 parallel strings? Would a 15% savings (in dollars per AH) be enough to make it worth splitting?
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But there is more to battery selection than just capacity vs. money, sometimes design issues get in the way.
As I stated earlier, my battery bank consists of two strings of two 6-volt batteries, but the two strings are not even in the same building! Electrically, they are all the same battery bank, but I keep one string near my generator to assure plenty of starting current, and the other string inside my house to potentially run inverter loads following a power failure. (I have never done it) Heavy paralled conductors connect the two strings, which make them effectively one battery bank, except for that tiny bit of time when there is a heavy load on one side or the other. (Ohm's law, if there is hardly any current, there is hardly any voltage drop) Also, that configuration gives me the option of splitting the strings to assure that I always have sufficient capacity to start my generator.
So you see, one string of big cells would not do.
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OK.
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| snipped-for-privacy@ipal.net wrote: | |> | I have never seen single cells paralleled. They are always connected in |> | series to get the desired voltage. Then, another group of identical |> | series cells may be paralleled with it. |> |> So the "reason" is "everyone else does it". | | Not at all. If you want 48 volts and have two volt cells to play with, | that is 48 jumpers for the paralleling the 48 cells. Add another 24 for | the series portion. That is a total of 72 jumpers. It's easier to make | two batteries first, then parallel them with two jumpers.
I was planning on looking at this, and other, costs later on. I wanted to know the technical, not economic, issues. Then I would balance between them. If method X costs more, but works better, I might still consider it over method Y that costs less, but doesn't work as well.
I'm focusing on the technical issues right now.
|> Aren't all the plates within one cell already parallel? By extension of that, |> paralleling individual cells would make sense because it retains the very same |> concept. | | No. They are each in series with the one next to it. The power comes in | on one terminal, through the electrolyte and out the other plate. There | is no chance of any circulating currents within one cell. They all share | the same electrolyte bath. If there were only two large plates in a | battery, we wouldn't call them paralleled. Take those two plates and | roll them up in a cylinder shape. It may look a lot different, but | they're still not paralleled.
How is it that the common electrolyte bath prevent circulating currents? Does it have circulating currents in the bath itself when plate surfaces are uneven?
Yes, I would still call a 2 plate (one "+", one "-") as parallel ... it is paralleling multiple spots of each plate with other spots.
More plate surface means more current and/or capacity. The distinction is whether the plates are in the same common bath, or separate. The problems that can happen because the bath is separate, I want to know about. But it needs to make sense in terms of the bath, so I'm looking also for theory, not experience alone (even if the theory is just theoretical).
| Now, there *are* multiple plates on each polarity because of space | constraints. There's no room for two huge plates with the same surface | are. Changing the shape of each polarity plate won't make it parallel.
Well, you could have a long battery :-)
I understand how they are physically constructed. There are lots of plates in an interleaved configuration so that instead of it being a big long thin cell, it's a convenient semi-cubic shape (and you can have most plates do double duty front and back facing).
If any part of a plate is in a weaker charge state, the other parts of the plate that are in a stonger charge state effective charge it, and it all gets balanced out. If two cells are paralleled, that should happen between the cells, as well. Now I could imagine that if the electrolyte condition is what causes the cells to be slightly different, that can impact how well the cells balance out their charge. Presumably within a single cell the electrolyte can circulate around (not considering AGM or gel-cell here) so each point on the plates gets an equivalent electrolyte.
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