HI there, I’m building a 48V LiFePo4 battery bank like Deep and I’M wondering witch setup I should go with between 16S2P with two BMS (one for each 16S string) or 2P16S with one BMS. What are the pros and cons ? Do cells in parallel will be well taken care by the BMS in the 2P16S config ? Any advise for me ?
48V LiFePo4 battery 16S2P or 2P16S
- Thread starter PopCycle
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BentleyJ
Solar Wizard
16S2P does provide redundancy in the case where one cell or BMS fails, that battery pack can be shut down and disconnected while the other is still active. It adds cost and complexity and depends on how critical the loads are. If there is only 1 inverter then that would represent a single point of failure making battery redundancy less of a factor.
2P16S with 1 BMS is simpler and the charge/discharge current is not limited by the BMS if an external contactor is used instead of the FET based products.
2P16S with 1 BMS is simpler and the charge/discharge current is not limited by the BMS if an external contactor is used instead of the FET based products.
PreppenWolf
Solar Wizard
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I opted for parallel strings each with a BMS to be able to see each cell. My issue with pairing cells is you will not see if a cell fails immediately and you lose the BMS's ability to react to the failure and shut the bank off.
Downside to using multiple BMSs is you'll need a shunt for monitoring the whole system and more breakers/fuses to isolate each pack.
Downside to using multiple BMSs is you'll need a shunt for monitoring the whole system and more breakers/fuses to isolate each pack.
Monitoring each cell independently was one of my concern and the other was the ability of the BMS to take care of multiple cell in parallel ? What’s is more prone to imbalance multiple cell in parallel in a 2p16s or batterie in a 16s2p ? Here’s my complete setup 32 cells Eve 304Ah in a 2p16s or 16s2p configuration for 48V with 1 or 2 JK 200A BMS, inverter is a Magnum MS4448 (4400W) but I’ll maybe add one in the futur. I’m completely off grid so I thought that 2 string in a 16s2p was better for me in case of a problem with one branch the other would be able to take the entire load. For monitoring the entire bank I understand that I’ll need a shunt installed on the wire that see the total current draw from the two batterie bank. I’ll have to check if the JK BMS can handle this but I’ve doubt about it. Do you have a BMS to suggest ? I think I need a BMS that can supervise two parallel bank with a common brain instead of two separate BMS that don’t talk to each other…Maybe a BMS with a single brain able to supervise two string will be able to share load equally!? Am I dreaming ? Sorry for this long post, lot of questions…
BentleyJ
Solar Wizard
Batrium BMS may be worth looking at. I'm not an expert on their product line up but seem to remember they have a products that can help with what wish to do.
MisterSandals
Participation Medalist
I'll be the dissenting voice. I like 2P pairing and have had great luck with my 2P4S battery.
With a 2P16S setup, you have the opportunity (aka a bunch of work) to create equal pairs of cells based on capacities.
So if you have 32 cells of varying capacities, you can make equivalent pairs by pairing the highest capacity with the lowest capacity, second highest capacity with second lowest...
With 2x 16S batteries, you'd be better off putting your highest 16 cells in one battery and your lowest 16 cells in the other battery.
Do you have any idea what your 32 cells' capacities are?
To answer your question (finally! sorry!), BMSs have a limited amount of balance current. If you double up cells in a 2P configuration, theoretically it would take double the current to balance the cells.
Conversely, if you created equal pairs of cells, you would have less need to balance.
HI Bentley,
I only have one inverter, a magnum MS4448 and never had any problem with it or any of my other components. I’m currently running on 24 cell Pb-Ca from Oldham they are model VTC6 466AHC8. They are almost 20years old and the last capacity test end up with a result of 85%. I’m really concern about the reliability of LiFePo4…I understand they are monitored cause it’s important they stay in their operating range in terms of voltage and temp but sound a bit scary for me, it let me think I’ll often have problem with individual cell compare to my big Pb-Ca!? Cost for one BMS more is not really a problem cause the JK is not to pricey but maybe you’ll tell me I should not go with it ? The Complexity of installing two BMS is not a point for me. I’m trying to build a robust setup that I won’t need to worry about every hour for imbalance, or other concern I don’t know yet with LiFePo4. I’m completely off grid, only solar and generator when no sun. Any advice for the BMS to use and the cell connection I should go with is welcome. Thx in advance ?
MisterSandals
Participation Medalist
Hey, thats what we're all striving for too! Sometimes our worry and efforts are dictated by the quality and similarities of our cells.
I hate to say this and I am sure you're not happy hearing this but you may be forced to choose 2P16S or 16S2P based on the cells that you receive. Having a couple extras to choose from will create more flexibility.
BentleyJ
Solar Wizard
All things considered the JK BMS is a good choice. It has built in active balancing, good feature set and is a good value/price proposition. I'm using an alternative type of BMS that uses external contactors not internal power FET's to turn current on and off.
HI Sir, I have not receive my cell yet probably in the end of February. As you can see with my other reply I’m concern about having a robust setup, peace of mind relatively to balance cell or batterie and load/charge sharing. As upon reception I’ll test every cell I’ll be able to match pair or string like you suggest and thx for the advice. But you dissenting voice just get me uncertain ? of the setup to with…grrr lol ?
MisterSandals
Participation Medalist
Don't get me wrong, having 2x 16S batteries is a great setup. Using the JK/JBD/Overkill BMSs is a very solid solution (i have a Overkill on my 2P4S battery that i made from selecting and matching 8 cells out of 13).
My main incentive to go 2P4S was to use a single BMS for simplicity in my RV. I did not need the 2x amp draw that having 2x BMSs allows.
I've offered a second choice; "dissenting view" was not intended to mean that "i believe otherwise". Both options work, and having 2 choices is better than 1.
HI Bentley, why choose a BMS that drive an external contactor instead of FET ? Sorry I’m new in Lithium batterie. A quick look In the JK manual and Ilearn that it can turn on and off the charge or discharge independently. Do your BMS can do that or charge and discharge are stop by a contactor that completely disconnect the battery from the inverter and charge controler?
a lot depends on what value judgments you place the different aspects of each setup.
I don’t think you need two bms’s that talk to each other. Separate would be fine.
What is the max load in amps that the battery pack needs to deliver- can one BMS deliver that?
For me, I would value 16s2p for the redundant aspects. However, the battery I built for my MotorHome was a 2p4s 544ah 12v battery. Space and high amp draws being the deciding factors (I used a Batrium bms to get the high amp draw).
Good Luck
I don’t think you need two bms’s that talk to each other. Separate would be fine.
What is the max load in amps that the battery pack needs to deliver- can one BMS deliver that?
For me, I would value 16s2p for the redundant aspects. However, the battery I built for my MotorHome was a 2p4s 544ah 12v battery. Space and high amp draws being the deciding factors (I used a Batrium bms to get the high amp draw).
Good Luck
? nice! I’ll probably go with 16s2P with 2 BMS. Other concern I have is that some BMS and is the case of the Jk are equipped with communication link. This link and correct me if I’m wrong can be used to link it to the charge controller/inverter to tell them for exemple to stop charging or lower the charge amp. If my charge controller can‘t be Link to the BMS is it a big issue ? However, my charge controller can receive the voltage of a shunt and I can program a fonction called endamp to change the state of charge of the controller. My charge controller is a Midnite Solar Classic 200.
BentleyJ
Solar Wizard
I prefer a mechanical contactor to handle large currents. The ZEVA BMS does have outputs to drive 2 contactors, 1 for charge and 1 discharge. I've chosen to jumper the outputs together so only 1 contactor is needed and yes that means if it does ever trip then manual intervention is needed. So far that hasn't happened in 4 years.
The down side to mechanical contactors is the 24/7 parasitic current required to keep them closed, even the ones with economizers. FET's also waste energy because they do have some forward current resistance, although small.
My solution was to use a magnetic latching contactor.
Rocketman, I’m actually running a 4400w inverter but plan to Stack another in the futur. Actually, only one BMS is able to feed all the load.
MisterSandals
Participation Medalist
I just happened across this 2P16S installation pic in a different thread. Looks to be using a JBD solenoid BMS too.
Maybe @42OhmsPA can offer some insight on his install with 2P16S. I do not see a "show and tell" thread.
diysolarforum.com
Maybe @42OhmsPA can offer some insight on his install with 2P16S. I do not see a "show and tell" thread.
JBD AP21S002
I am connecting balance leads and missing clear guidance on the connection for the last cells in a 16S. Anybody know how this goes? The first connector seems clear enough and takes care of cells 1-13. But I have no 16S guidance on this 2nd nine wire for the last three cells. I think it's easy...
diysolarforum.com
42OhmsPA
What's in a title?
You caught me not doing a show and tell for the build ?. I'll work on getting something together, my bigger focus is getting at least 9 more panels up and a 3rd pack together.I just happened across this 2P16S installation pic in a different thread. Looks to be using a JBD solenoid BMS too.
Maybe @42OhmsPA can offer some insight on his install with 2P16S. I do not see a "show and tell" thread.
JBD AP21S002
I am connecting balance leads and missing clear guidance on the connection for the last cells in a 16S. Anybody know how this goes? The first connector seems clear enough and takes care of cells 1-13. But I have no 16S guidance on this 2nd nine wire for the last three cells. I think it's easy...
The BMS confused the heck out of me, until it didn't. I found the attached diagrams here, I think. They were helpful
Attachments
MisterSandals
Participation Medalist
The OP of this thread was asking about 2P16S vs 16S2P. I also am wondering what your thoughts are on your battery setup. How did you match your cell pairs? Any balancing issues?
