Top balancing with BMS and invertor - any issues to expect?

[uapower]

Hi there,
May I ask which Equipment did you use to sample the cell voltages and the current?
Regards Hans

I use RPI4 with USB - RS232 (DB9) adapter to pull the data from inverter, and just RPI built-in BLE to connect to BMS.
I also use https://github.com/jblance/mpp-solar to pull the data and send to influxdb via mqtt.
The biggest issue so far is the connection reliability (mpp-solar is able to connect once per evey 5-10 requests), so instead of getting data every 5 seconds, I have it every 1 minute or so. The once-connect and then periodically pull would be better model, than to connect-pull every time, but this is not implemented yet in mpp-solar to my knowledge.

I consider switching to RS485 cable connection for better connection reliability, but even with BLE I see lots of value in the data.

 

[kanelr]

SOOO is there a good balancer for 5s2p? I have resorted to manual balancing and do not like the amount of time it takes.

 

[MisterSandals]

So what exactly do you have 5S2P?
Cells or batteries? Neither makes any sense.

5S LiFePO4 cells would be 16V, 2 of those in parallel for the 2P part.
Would require 2 BMSs and 2 balancers.

5S 12V batteries is 60V…

Happen to have a pic and a little info on what your mystery battery bank is experiencing?

 

[kanelr]

So what exactly do you have 5S2P?
Cells or batteries? Neither makes any sense.

5S LiFePO4 cells would be 16V, 2 of those in parallel for the 2P part.
Would require 2 BMSs and 2 balancers.

5S 12V batteries is 60V…

Happen to have a pic and a little info on what your mystery battery bank is experiencing?

Sure on the pic, but no mystery, Maybe I got the lingo wrong. In words I do know they are ten 12v 100AH LiFePo4's in two 5 battery banks. Each set of 5 are wired in paralel, (12v 500AH), and then placed in series for 24 volts. And, for us, there were good reasons to not just go with 24v cells here. THESE pix were before we soldered everything. The wiring drawings were based on the factory suggestion for a 400 AH version. made before we added another set of two batteries. the dissimilar resistance issues are pretty small with the 4o and 2o cabling and the torqued-to-Venus-then-soldered split bolts. The small jumpers were already on hand and #2, hence doubling them. I basically made a bus with what I had available after tearing out our old floodeds (see pic ). They work pretty well. (Home backup and bill reduction no grid tie )

 

[MisterSandals]

in two 5 battery banks. Each set of 5 are wired in paralel, (12v 500AH), and then placed in series for 24 volts.

Ok good, 5P2S.

I know you have them soldered and you have not mentioned what you are seeing or trying to fix.

Here is an interesting thread. Looks like post 50 is your setup (5P).
Read posts 1-4 to get a good understanding of the methodology.

Calculation of parallel string battery currents

Can your mathematical model confirm that wiring each battery to a common bus bar, using equal length cables to each battery, provides a balanced charge/discharge?

diysolarforum.com

 

[kanelr]

Ok good, 5P2S.

I know you have them soldered and you have not mentioned what you are seeing or trying to fix.

Here is an interesting thread. Looks like post 50 is your setup (5P).
Read posts 1-4 to get a good understanding of the methodology.

Calculation of parallel string battery currents

Can your mathematical model confirm that wiring each battery to a common bus bar, using equal length cables to each battery, provides a balanced charge/discharge?

diysolarforum.com

will read now. thanks

 

[kanelr]

Ok good, 5P2S.

I know you have them soldered and you have not mentioned what you are seeing or trying to fix.

Here is an interesting thread. Looks like post 50 is your setup (5P).
Read posts 1-4 to get a good understanding of the methodology.

Calculation of parallel string battery currents

Can your mathematical model confirm that wiring each battery to a common bus bar, using equal length cables to each battery, provides a balanced charge/discharge?

diysolarforum.com

I looked at the drawing and can likely benefit from a 5 or 7" move. only our crimps are soldered but not the split bolts, so i can move the points of connection. Question- in his test the middle battery received the least charge, Does this make it the battery most needing to be rotated to an end? Does anyone rotate?

 

[MisterSandals]

Does this make it the battery most needing to be rotated to an end? Does anyone rotate?

Probably not.
Have you tested or otherwise determined the state of each of your batteries? This i think is an important step in solving your issues (that we have not identified, right?).

 

[kanelr]

Probably not.
Have you tested or otherwise determined the state of each of your batteries? This i think is an important step in solving your issues (that we have not identified, right?).

hi I don't think I have an issue so much as developing new protocalls (sp?) for this system. I added 2 more batteries five months into the build and I want to now make sure they are all playing nice. to date none have cycled very deep we just use for LED lighting and a sump pump. One time we used down to 50%, then panels brought back to 100% the next day usually sits around 70-90% Too often at 100% and am still working out the best diversion load.(I have a neat refrigerator and relay for diversion setup for another thread). I am floating low a tad (27.6), and trying to let these simmer and wait for the day when its needed for more circuits during outages sorry I don't think in terms of 3+v cells was not raised that way