I have two LiFePo4 batteries wired in series (24v, 100Ah) and I am getting two more to wire in series and then parallel (24v, 200Ah). I came across a diagram that shows two sets of batteries wired in parallel and then in series. So I would describe the two setups as 2 in series and 1 in parallel vs. 2 in parallel and 1 in series. I don't know if that would be the right terminology, but it seems to be two different approaches to the same end. Am I mistaken on this? If not, is there an advantage on doing this one way vs. the other? I drew this out on a diagram and it seems that the basic difference would be that with 2 in parallel 1 in series that you would have 2 more posts with double lugs on them vs. 2 in series 1 in parallel. Also the parallel/series setup looks like it would use more wire than the series/parallel setup. Any thoughts on this or am I completely mistaken?
Wiring in series parallel or parallel series?
- Thread starter B.T.
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RCinFLA
Solar Wizard
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Assume your batteries are are presently two 12v 100 AH LFP with internal BMS's in series.
Not sure your descriptiion of connections but I believe you mean two separated serial strings versus strapping two 12v batteries together in parallel then putting the two parallel strapped batteries in series.
I generally do not like strapping cells directly in parallel. This needs matched cells which can only realistically be done by manufacturer. The fact that the additional batteries have not experienced the same usage and age is even more reason to maintain separate series combination of battery strings. BMS series resistance slight differences adds to the mismatching.
Be aware you will not likely get even current distribution between the two strings. You should get a clamp on DC amp meter to keep track of how the two strings are splitting the total charge or discharge current. Better then 20% current matching is considered good. Do not load them as if they are two times single battery for discharge or charging.
The fact you now have four independent BMS's create some complications. Any one of the four BMS's could open for whatever reason (overdischarge, too much current, overcharge on a cell, or temperature) so the safe way to run is to not discharge or charge any more current then could be handled by single string. You will still get near double the capacity having two strings in parallel.
Having at least a shunt and current monitor readout on each string would be a good idea so you can glance at current matching and know if a string went off line. I have ten strings in parallel, each with their own 100 amp shunt. This is in addition to a 500 amp shunt and full battery monitor on inverter main line. The more strings in parallel the better the odds most of the strings are in play so can raise the current charge and discharge to higher levels.
Another benefit of separate strings is you can pull one and still maintain inverter operation. I have my ten strings in five caster wheeled carts with Anderson SB350 connectors so I can easily pull a single cart out to work on.
Not sure your descriptiion of connections but I believe you mean two separated serial strings versus strapping two 12v batteries together in parallel then putting the two parallel strapped batteries in series.
I generally do not like strapping cells directly in parallel. This needs matched cells which can only realistically be done by manufacturer. The fact that the additional batteries have not experienced the same usage and age is even more reason to maintain separate series combination of battery strings. BMS series resistance slight differences adds to the mismatching.
Be aware you will not likely get even current distribution between the two strings. You should get a clamp on DC amp meter to keep track of how the two strings are splitting the total charge or discharge current. Better then 20% current matching is considered good. Do not load them as if they are two times single battery for discharge or charging.
The fact you now have four independent BMS's create some complications. Any one of the four BMS's could open for whatever reason (overdischarge, too much current, overcharge on a cell, or temperature) so the safe way to run is to not discharge or charge any more current then could be handled by single string. You will still get near double the capacity having two strings in parallel.
Having at least a shunt and current monitor readout on each string would be a good idea so you can glance at current matching and know if a string went off line. I have ten strings in parallel, each with their own 100 amp shunt. This is in addition to a 500 amp shunt and full battery monitor on inverter main line. The more strings in parallel the better the odds most of the strings are in play so can raise the current charge and discharge to higher levels.
Another benefit of separate strings is you can pull one and still maintain inverter operation. I have my ten strings in five caster wheeled carts with Anderson SB350 connectors so I can easily pull a single cart out to work on.
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Yes, I believe you have the idea of what I was trying to relate. My idea is to use my two batteries wired in series, take the two new batteries I'm getting and wire them in series also and then wiring the two sets in parallel for 24v and 200Ah (4 l00Ah LiFePo4 batteries). Then I came across a diagram that showed wiring two batteries in parallel with two others also wired in parallel and then running the pos from one parallel set to the neg of the other parallel set to create 24v and 200Ah.
So it seems that you would suggest the first method of wiring as opposed to the second method.
As far as the age of the batteries goes, I don't think I will have an issue because the set I have now are only about a week old and I expect the next set to show up in about two weeks. So it would not be like I was running two really old batteries with two brand new ones (and they are all the same brand/model).
I also have a shunt type battery monitor coming with the next set.
Thanks for your help.
Thanks, I have already downloaded this file. I will take some time to study it.
12VoltInstalls
life passes by too quickly to not live in freedom
While the info/logic relayed by posters above is right on, in some aspects you don’t need to think that far in practical use imho. Most often, the arrangement of devices, batteries, etc. are setup best with the least length of cabling. OP’s observation of less wire for his original plan reflects that loose “rule.”
