Look at the front panel of a BSLBATT rack or wall battery and you will find several RJ45 sockets, labelled CAN and RS485, sometimes with DIP switches nearby. They look identical, they are not interchangeable, and plugging into the wrong one is the most common reason a monitoring device or an inverter "does not see" the battery.
CAN: the conversation with the inverter
Most hybrid inverters talk to lithium batteries over CAN. Through that link the battery tells the inverter its state of charge, the voltage and current it accepts, and whether charging or discharging must stop. The inverter adapts its behaviour accordingly. This is the closed-loop communication installers set up during commissioning, and it should stay exactly as it is.
RS485: the detailed view
RS485 is often used for the same purpose with some inverters, and for detailed reading of the BMS: every cell, every temperature, the alarms and the state of each pack in a bank. This is the port monitoring tools use. On many batteries, the inverter takes one protocol and a monitoring device the other, so both can coexist without interfering.
| Port | Typical use | Change it? |
|---|---|---|
| CAN | Closed-loop link to the inverter | No: leave the installer's setup in place |
| RS485 | Detailed BMS reading, some inverters | Free on many installations, ideal for a monitor |
| Link ports between batteries | Chaining packs in a bank | No: part of the bank wiring |
DIP switches and addresses
In a bank of several batteries, each pack needs a unique address, set with DIP switches or a rotary selector depending on the model. The first battery, the one connected to the inverter, is usually the master. If two packs share an address, they answer at the same time and the communication becomes unreliable, which shows up as missing packs or intermittent faults. Always check the addressing table in your battery manual before changing anything.
Connecting a monitor without touching the inverter link
- Identify the port your inverter uses today and leave it plugged.
- Use a free RS485 port on the master battery, or the one your manual recommends for monitoring.
- Tell the monitor how many packs the bank has, so it reads each of them.
BSLBATT Monitor comes with the RJ45 cable and plugs into that RS485 port. It reads every pack and every cell, shows them on its own screen and on your Wi-Fi, publishes them to Home Assistant over MQTT and, with the free Cloud, makes them available from anywhere with three years of history. It is read-only: it never sends a command that could change the battery's behaviour, so the inverter link keeps working exactly as before.
Not sure which port is free on your model? Send us a photo of the front panel when you order and we will tell you.