In short
- Each JK inverter board needs its own address, set with its DIP switches; two boards with the same address confuse everything.
- One board acts as master and speaks for the whole bank to the inverter, which only sees one big battery.
- Packs drift apart over the years: watch the charge, the cell delta and the temperature of each pack, not just the bank.
A single 16S pack of 280 Ah cells stores about 14 kWh. Many homes want more, so they add a second or third pack, each with its own JK inverter BMS, all on the same DC bus. The power side is simple: thick cables of equal length to a busbar. The communication side is where most questions start.
Addresses on the DIP switches
JK inverter boards have a small block of DIP switches. Each position gives the board an address, and every board in the bank needs a different one. Two boards with the same address answer at the same time and the values you see jump from one pack to the other. Write down the address of each pack, and label the packs on the outside.
The master board
The boards are linked by their parallel RS485 sockets, usually with short RJ45 cables from one pack to the next. One board acts as the master: it gathers the others and speaks for the whole bank to the inverter, over CAN or RS485. On most hardware versions the master is the board at address 0 and the others take 1, 2, 3 and so on, but the scheme has changed between versions, so check the manual of yours. Whatever the version, the inverter sees one battery: total charge, one charge voltage, one current limit.
What the inverter does not tell you
Because the inverter only sees the bank, it cannot tell you that pack 2 sits 8 % below pack 1, that its cells spread more at the top of charge, or that it runs 4 °C warmer because it sits closer to the inverter. Those differences are normal at first and grow over the years. They matter, because the weakest pack sets the limits of the whole bank.
Checks worth doing every month
- Charge gap between the fullest and emptiest pack: a few percent is normal, a growing gap is not.
- Current share while charging: packs should share the current roughly evenly. A pack that takes much less often has a higher-resistance cable or connection.
- Cell delta of each pack at the top of charge.
- Temperatures of each pack and of each board.
Seeing every pack on its own
JK BMS Monitor connects to one RS485 socket and reads the boards of the bank. Tell us how many packs you have and how they are linked when you order: we prepare and test the box for that layout. The dashboard then shows each pack side by side, with the gaps between them in charge, voltage, temperature and cycles, plus the cells and balancer of each board.
Common questions
How many JK BMS can I run in parallel?
The DIP switches give enough addresses for a large bank, but the practical limit is often the inverter and the cabling. Check the manual of your board and of your inverter for the supported count.
My values jump between two packs. Why?
Two boards share the same address. Give each board its own address on its DIP switches, power-cycle the bank, and the readings settle.