Will this work in a series/parallel battery configuration

[loreoff]

I found this on a charger company website series-parrallel.pdf

[daz]

It is generally not recommended to charge/discharge batteries in parallel, as this will shorten the life of the battery (due to charging/discharge imbalances). It is better to rather go with larger batteries, or a higher voltage with the batteries in series (or both).

For example, if you needed 200AH of batteries at 12V, instead of getting 2 x 10oAH 12V batteries and placing them in parallel, rather just get 1 x 200AH 12V battery. Or if you have the 2 x 100AH 12V batteries, rather place them in series to make 100AH @ 24V.

However the above being said, there are ways of placing batteries in series/parallel configurations to try ensure that all the batteries are balanced. There is actually numerous threads about this topic, so I would recommend having a look in the battery section in the off-grid part of the forum, as it will answer most of your questions.

[mapmaker]

The pdf file you linked shows a configuration that is the wrong way to charge those batteries from a 24 volt charger. Two 12 volt batteries should be placed in series, to make 24 volts. Then the two 24 volt strings should be paralleled.

The configuration you linked is the way to doit if you want to charge the batteries from two 12 volt chargers.

That all said, 'daz' is correct that you should avoid parallel batteries if you can.

--mapmaker

[loreoff]

Will this work in a series/parallel battery configuration

Look closer at the pdf, u will see a wire from + to - between the parallel sets

[mapmaker]

Look closer at the pdf, u will see a wire from + to - between the parallel sets

I see (and saw) that. It's still wrong. This is correct:
diagbat.jpg
--mapmaker

[Sunking]

Here is the deal. There are two rules.

1. Never parallel batteries unless you have to.
2. Unless you need more than 4000 AH there is never a reason to parallel batteries.

Problem is folks get stuck in a 12 volt box. Largest 12 volt battery you can find in 12 volts is around 350 AH weighing in around 250 pounds. However there are 2, 4, 6, and 8 volt batteries. In 2 volt cells go as high as 4000 AH.

Telecom and Data do use parallel batteries for redundancy although never 12 volt batteries. They use special designed over head buses to equalize connection resistances and very heavy duty switches to take one string off-line for maintenance. However since Data and Telecom never really discharge the batteries remain in float service so charge and discharge currents are not an issue. When the time comes for them to discharge from a power failure is only a few minutes until the generator kicks on. They are designed to run the equipmen tfor 4, 6, 8, and up to 48 hours but that would be very rare and the onsite genny would have to fai which is highly unlikely.

[mapmaker]

Here is the deal. There are two rules.

1. Never parallel batteries unless you have to.
2. Unless you need more than 4000 AH there is never a reason to parallel batteries.

I'm in total agreement with you, at least for RE systems.
At least a few folks have used this paper as a justification for parallel battery banks:
http://www.battcon.com/PapersFinal20...lPaper2002.pdf

The arguments presented in the paper do NOT apply to RE systems with (hopefully) high cycle life and PSOC charging, and in my opinion the authors do not make that clear enough (as you have explained with your example of telecom systems).

--mapmaker

[loreoff]

Will this work in a series/parallel battery configuration

thank you for the information

[daz]

thank you for the information

Have a look at the picture in Mapmaker's post (post #5), and see if you can see the difference?

Paralleling batteries requires a bit of work, as you have to make sure all resistances are the same, which means using interconnects that are all identical. This is why parallel batteries are not recommended...they have different charge/discharge characteristics, which shortens the life of batteries. However, you can still parallel batteries, just bear in mind that it shortens the life of batteries.

[mapmaker]

This is why parallel batteries are not recommended...they have different charge/discharge characteristics, which shortens the life of batteries. However, you can still parallel batteries, just bear in mind that it shortens the life of batteries.

Even if you had perfect (zero resistance) wiring and impossibly identical battery cells, parallel batteries are thermally unstable, and at best they are in an unstable equilibrium.

If one string is slightly warmer than another (inevitable) it will draw more of the charging current which will make it warmer which will make it draw more of the charging current which will make it warmer which will....

In reality your battery cells are not identical, therefore they do not even start out in a stable or unstable equilibrium.

Another reason to avoid parallel battery banks is stochastic. Your entire bank is only as good as its weakest cell. The more cells you have, the greater the chance that you have an outlier weak cell that will bring down the whole bank to its level.

This stochastic argument applies to both series and parallel batteries. The fewer the cells the better. Stochastically, the ideal system would be just a single 2 volt cell, but of course that is not practical. Best practice is to use a single string of cells at the lowest voltage that is practical for your application.

--mapmaker

[daz]

Even if you had perfect (zero resistance) wiring and impossibly identical battery cells, parallel batteries are thermally unstable, and at best they are in an unstable equilibrium.

If one string is slightly warmer than another (inevitable) it will draw more of the charging current which will make it warmer which will make it draw more of the charging current which will make it warmer which will....

In reality your battery cells are not identical, therefore they do not even start out in a stable or unstable equilibrium.

Another reason to avoid parallel battery banks is stochastic. Your entire bank is only as good as its weakest cell. The more cells you have, the greater the chance that you have an outlier weak cell that will bring down the whole bank to its level.

This stochastic argument applies to both series and parallel batteries. The fewer cells the better. Stochastically, he ideal system would be just a single 2 volt cell, but of course that is not practical. Best practice is to use a single string of cells at the lowest voltage that is practical for your application.

--mapmaker

Yep...that was what I meant...didn't feel like adding an edit just to clarify my last statement...bleh!

Unfortunately batteries being chemical in nature makes it almost impossible to control everything, however there are some things we can try do to ensure a longer life on them, such as avoiding the whole parallel thing. Most people here tend to want to parallel a whole lot of cheap batteries together, and they think it works, but it just costs money in the long run and creates headaches! Same goes for a lot of people wanting to run huge inverters and solar systems on 12V.....

[Sunking]

The arguments presented in the paper do NOT apply to RE systems with (hopefully) high cycle life and PSOC charging, and in my opinion the authors do not make that clear enough (as you have explained with your example of telecom systems).

Well I have read this article before and know the author. Telecom is a small world. With that said it is implied the reader knows it is directed at Telecom because Battcon and Intelec are Telecom organizations and the paper was written for the Telecom industry.

Yes Telecom as I stated earlier does parallel batteries. I have built plenty of them. When you have a 48 volt 10,000 amp battery plant with 4 hour reserve capacity, you have to parallel batteries because there is no such thing as 48,000 AH battery. That forces you to use 12 parallel strings of 4000 AH batteries. The cells are 2 volt 4000 AH and each cell weighs in around 600 pounds, and it 24 batteries per string x 12 strings is 288 batteries. The buss bar to interconnect such batteries are custom designed by a company called Alber Corporation. The bus bar has to be designed to fit the room layout made out of laminated copper bars and can weigh as much as 10,000 pounds suspended from the ceiling or below a raised steel deck flooring system. The battery racks are either made from composite materials or plastic coated steel as not to be conductive.