10kWh LifePO4 DIY Battery Addition..... Here is my write up.

Can you even have two seperate 16S BMS connected to the one inverter, wouldnt you need some sort of shunt or DC:DC converter? The voltages wouldnt match.

I have 4 dyness batteries that are 15S config and I plan to sell them when I get the calb cells because I can't join them together.

I have two packs in parallel, one 50kWh, the other 5kWh. Not always are they both connected to the inverter, but exactly like @graememk says, if you connect one and some time later the other one, they then very quickly equalise the voltages. Has to be the same chemistry and the same number of cells in series though. Mine are all 16S. Both my packs have their own BMS but I have only coms between the large pack BMS and the inverter. The small pack does its own thing

Guys I just want to share with you my build, together with some tips and tricks for beginners(like me).

I started to look into buying a Pylontech 5000US battery, and ended up in building my own 15KW DIY battery which I am very proud of...

Supplies:

Batteries ordered from NKON in February, I got 280A CALB aluminum ones, which were all tested by them(and me) to over 300A each.

Seplos BMS 150A with LCD and Bluetooth ordered from AE Minerals store

Battery box built from 18mm plywood bought and cut in B&Q, painted in gloss black paint

6 X 8mm threaded rods with ~ 100KgF springs(when compressed to ~ 45%)

NEEY active balancer

3D printed case for Seplos BMS and support for NEEY active balancer

25mm cables with 6mm and 8mm connectors (6mm for battery terminal, circuit breaker, inverter and BMS, 8MM for other connections like terminal blocks)

4mm connectors for balancer and bms wires.

Flexible chopboards as insulator between batteries, bought from Homestoreandmore

transparent hose for threaded rods

100A circuit breaker (changed with 150A one).

A lot of valuable information from this thread, thank you guys!

The build:

I started with the box, I cut and built the box , it's very sturdy, and the plate where the springs are is floating, it doesn't touch any other side of the box, to allow for movement if needed. However, after charging the batteries to 100% the movement measured was 0 , so no, or very little expansion.

After the box was finished, I started to fit the batteries with insulation and the threaded rods (which are protected with transparent hose to avoid battery damage) and then the springs. The seller of the springs(40mm length) is claiming 128kgf if compressed over 50%, I only compressed them 18mm, so I expect somewhere around 100KGF for each).

The next step was to prepare the connection between batteries, as I didn't want to add the BMS and balancer wires to the battery terminals, therefore I made M3 thread on each busbar for these connections.

Nest step was to prepare wires, all wires (BMS, balancer, battery, BMS, Inverter) are crimped then soldered(where possible). After all connections were done and checked I pressed the reset button on BMS and started... not from the first time as I had few issues, but I'll explain that next.

Final result:

Issues I've run through(note that this is my first contact with a BMS, battery cells etc...):

• When I powered up the BMS a message on the screen with the text "Abnormal Communication" was showing up, and Bluetooth didn't work. I went back to the seller and they advised that this functions have to be enabled with the Battery Monitor app, so everything worked after I did this, but I spent few hours looking for a solution.
• After previous issue was resolved I started to charge the battery, but inverter wend into error short time after, so I had to reduce the charging current to 90A (100 by default). After this inverter was fine, but the 100A breaker was tripping. I reduced to 80A, but still tripping, then reduced further more to 75, then 70A where tripping stopped). Ordered now a 150A circuit breaker.
• on the first charge after I reached maximum voltage on a cell and the the SOC was reset to 100%, then I started to discharge the battery in my car to do the first calibration of SOC, but SOC was staying at 100% all the time. I went back to Seplos and they gave me their engineer contact. After I sent him the history log he quickly replied telling me that the B- and P- have to be reversed. I knew about that, but I always had the impression that for negative is only one connection point, and it doesn't matter where the wires are connected on this connection point... Apparently it does, as I swapped the cables and everything was fine after another full charge...

Now battery is fully functional, so I just enjoy the free energy also during the night now :). Next project is to connect BMS, balancer and inverter to Home Assistant ( another great thing I recently discovered, and already made a lot of great things with it as I have a lot of smart devices around, and now I can control and check all in the same place).

Pictures here: https://postimg.cc/gallery/wDDgsPL

I hope you like it :)

Very neat job, recently got a 6kW solar system and already would like more battery capacity. How much do you reckon the entire set up cost you?

Love this. That looks very neat and tidy and have to say is enticing me to follow the same.

Be careful about swapping that 100a breaker out for a 150A. Depends a little on the inverter, but you may be opening yourself to trouble there if the inverter can't handle it. That said a 100A breaker shouldn't be tripping at 80A, so maybe you have a faulty breaker? I'd probably replace the 100a with another 100a unless your sure your good across the board with wire guages, etc.

Respect.

Is in the Attic, but the box has small vents all-round , just under the top cover. If getting too hot I can lift the cover a bit, and even add a small cooler to move the hot air.

I already have a 120A breaker in my Amazon basket(same shape), found it from another seller, and inverter is limited to 90A charge/discharge so I should be OK.

That smoke detector is there just because I had it lying around, as I have wired smoke detectors everywhere in the house. I may buy another smoke detector and add it above battery/inverter, but I don't rely on this one. The inverter is mounted on a fireproof board, and I will use something similar everywhere around that area. I also have a camera so I can see the Battery and inverter, see the view from camera:

So if we go with discharge to 10% it's about 14ish kwh usable, not bad.

The price is not as decent as from China from NL, but to be honest if I can be guaranteed A-grade and 300ah it might be worth the extra cost, and for the usual CALBs you need 32 cells for 20kwh anyway, so you save on space too as you can get 30kwh for 32 cells.

The only thing holding me back is the s**t show that is the seplos.

We need a proper BMS and active balancer that just works 100% of the time all the time, without these silly hacks.

Maybe it just doesn't work right with the Solis? I have seen people getting errors all the time when getting close to 100% and have to wait for a bit to start discharging etc.

I'd love to see a 100% seplos/neey combo working on a sunsynk 😀