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Best configuration for 16 cell 12V system

Tomadoggy

New Member
Joined
Apr 13, 2021
Messages
34
Location
Loveland Colorado
I have (finally) pulled the trigger and have 16 320AH cells headed my way. I am building a 12V system for an overland rig that I am designing and building from the ground up. I have a Victron Multiplus 3000 12V Inverter and will be using an Electrodacus SBMS0 for battery management and Electrodacus DSSR20's for connecting the panels (size TBD).

My head starts to spin when considering all of the various methods to connect the cells so am seeking best practice here. My main concern is to ensure proper power flow through all the cells for longevity and maintaining proper cell balance. So far I "think" 4s4p is best...but again I get lost in all of the opinions. Thanks in advance!!
 
I have (finally) pulled the trigger and have 16 320AH cells headed my way. I am building a 12V system for an overland rig that I am designing and building from the ground up. I have a Victron Multiplus 3000 12V Inverter and will be using an Electrodacus SBMS0 for battery management and Electrodacus DSSR20's for connecting the panels (size TBD).

My head starts to spin when considering all of the various methods to connect the cells so am seeking best practice here. My main concern is to ensure proper power flow through all the cells for longevity and maintaining proper cell balance. So far I "think" 4s4p is best...but again I get lost in all of the opinions. Thanks in advance!!

4S x 4.

4x 4S batteries each with their own BMS.

Is there a reason you went with Electrodacus? It is EXTREMELY limited and primitive. You must ONLY use "12V" panels in parallel on SBMS0, and your panels will NEVER output more than about 70% of their rated power.
 
I don't think your comment about the 12V panel is correct, but please feel free to educate me if I am thinking about this incorrectly. Here is the specification on the DSSR20. Also I generally like tinkering and at least for now can integrate the data from the SBMS0 into the Home Assistant dashboard that I am building for the rig.1737307629328.png
 
I don't think your comment about the 12V panel is correct, but please feel free to educate me if I am thinking about this incorrectly. Here is the specification on the DSSR20. Also I generally like tinkering and at least for now can integrate the data from the SBMS0 into the Home Assistant dashboard that I am building for the rig.View attachment 271293

It's right there in the specs:

1737310709064.png

32 or 36 cell panels are "12V" panels. They typically have a 20-24Voc rating and a 16-20Vmp rating.

The DSSR20 works by shorting the panels to the battery directly. This forces your ~18Vmp panels to operate at battery voltage, thus your power is limited to 13.6V / 18V = 76% of max rated. You've built in a 24% permanent penalty to the system.

If my choice of monitoring and control forced me to select a 1960 Chevy Corvair for compliance, I would look for a different solution. I suspect there are far more capable BMS that integrate into home assistant... like a JK BMS (first Google result for "home assistant BMS"):

 
Thank you for your insights, I am still learning and with what you have shared will reconsider my BMS choice. Here is the intended layout for verification.

1737312343615.png
 
Thank you for your insights, I am still learning and with what you have shared will reconsider my BMS choice. Here is the intended layout for verification.

View attachment 271323

That's a 4P4S configuration, and it's problematic.

By having multiple interconnects between the 4P cells, you create multiple paths and almost guarantee uneven current flow through cells. If you were to connect your main +/- at the top of the battery, the top row of 4S cells would bear the brunt of all charges and loads and likely wear out first.

I have modified your diagram indicating only a single bus bar between 4P groups:

1737312730891.png

This will encourage all cells to share the load, though the center two rows will bear less of the load than the top/bottom.
 
Once again, thank you. Would the best scenario be to eliminate the buss bars between the groups? Would that more evenly distribute the load? I still struggle to understand the current flow.
 
If you eliminate the vertical connections between cells and then have one per row, this changes the configuration to 4S4P,i.e., my original recommendation: 4x 4S batteries in parallel, and each would need its own BMS.

1737314038830.png
 
OK so with further research the JK BMS's can be integrated into Home Assistant, thank you for that video and lead! If I may ask another question...there seems to be competing opinions on BMS pros/cons of using multiple. If I go with a single BMS for the 16 cells I cannot figure out if each cell can be individually balanced with the 4S4P but if I use 4 discrete BMS's then I could get individual cell balance? Sorry but I cannot find a straight answer within these forums. The configuration shown below from another post I "think" would use a separate BMS for each battery, but If the single BMS can maintain cell balance I would prefer to go with that to avoid complexity/cost.
1737316861583.png
 
The diagram you have included is a 4S3P arrangement - 3 separate 4S batteries in parallel.

4P4S is just a 4S battery. Each 4P unit is a "cell". They are always at the same voltage. The concern is that if a single cell fails, you have no idea which one is bad, and you have to take the whole battery down and determine which of the 4 is bad while you're completely down.

4S4P would require a BMS per 4S string, so it's 4x 4S batteries in parallel, 4x BMS.

A compromise in your case would be 2x 2P4S batteries, each with a BMS. That way if one cell fails, you can just take the ONE 2P4S battery offline but still have half your battery capacity available while you troubleshoot.
 

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