> ## Documentation Index
> Fetch the complete documentation index at: https://learning.kent.co.in/llms.txt
> Use this file to discover all available pages before exploring further.

# BMS Comms Basics: CAN Link for Kent Lithium Battery

> Closed-loop vs open-loop operation, why lithium requires CAN, identical BMS RJ45 pinouts on both Kent inverters, and where each comm cable connects.

A Kent lithium installation without a live BMS communication link is running blind — the inverter is estimating charge state from voltage alone instead of reading it from the battery. This page explains what closed-loop means, how to confirm it on the display, and the pin facts you need to get the cable right.

## Closed loop is mandatory for lithium

There are two modes an inverter can use to manage a battery:

| Mode            | How it works                                                                      | When to use                                             |
| --------------- | --------------------------------------------------------------------------------- | ------------------------------------------------------- |
| **Closed loop** | Inverter reads live SOC, limits, and temperature from the BMS over the comm cable | **Required for all Kent Lithium Battery installations** |
| **Open loop**   | Inverter estimates everything from DC voltage alone                               | Lead-acid banks only — not for lithium                  |

On a closed-loop Kent lithium system, the inverter display **must show the battery model name and a live SOC percentage that updates**. If the SOC is missing, frozen, or reads 0 % while the voltage looks normal, the comm link is down — go to [Cable Checks](/battery/cable-checks) before touching a single setting.

## CAN vs RS485 — which link is in use

* **CAN is the lithium link on both Kent platforms.** The Kent Lithium Battery communicates over CAN to the inverter's BMS port.
* **RS485 is the alternative battery interface** on the same RJ45 port. It exists for battery types that use it — it is not the Kent Lithium Battery's protocol.
* **Lead-acid banks use no data link at all.** The inverter manages them by voltage, with a PT1000 temperature sensor on the Kent M1.

## The pin facts

Both Kent inverters define their BMS RJ45 port identically (EIA/TIA 568B):

| RJ45 pin | Kent G3 & M1 inverter BMS port | Signal                |
| -------- | ------------------------------ | --------------------- |
| Pin 4    | CAN-H                          | CAN high              |
| Pin 5    | CAN-L                          | CAN low               |
| Pin 6    | A                              | RS485 A (alternative) |
| Pin 3    | B                              | RS485 B (alternative) |

The **Kent battery's RJ45 is the mirror image** — CAN-L on pin 4, CAN-H on pin 5. That is exactly why the labelled Kent crossover comm cable exists. The full pin card, the continuity check, and the field fallback for re-terminating a cable on site are all on [Cable Checks](/battery/cable-checks).

<Note>
  Both Kent source manuals carry the same instruction when pin definitions differ between ends: check both ends before connecting, and if they differ, cut the RJ45 at one end and re-terminate to match. On a Kent lithium pairing that check always leads to the same conclusion — use the labelled Kent crossover cable.
</Note>

## Where the link plugs in

<CardGroup cols={2}>
  <Card title="Kent G3" icon="plug">
    The CAN cable enters through **COM1 or COM2** and connects to the **BMS RJ45** on the comm interface board. Routing and cable gland placement follow the Kent G3 Battery Wiring guide.
  </Card>

  <Card title="Kent M1" icon="plug">
    The BMS RJ45 sits on the **comm interface** panel. Routing follows the Kent M1 Comms & Datalogger guide.
  </Card>
</CardGroup>

**Multi-pack banks:** packs parallel among themselves. Only **one master pack's CAN port** connects to the inverter — one cable for the whole bank, no matter how many packs it contains.

## Common mistakes

* Chasing menu settings for a comm fault that is actually the cable. Check the cable first, always.
* Reading "battery voltage visible on screen" as "comms are fine" — voltage is analog; comms is the live SOC reading.
* Plugging the battery link into the wrong RJ45 on a multi-port comm strip. Label your cables and trace before you connect.
* Accepting a one-time SOC reading as confirmation of a handshake — the SOC must update continuously.

## Related pages

* [Cable Checks](/battery/cable-checks)
* [SOC Mismatch](/battery/soc-mismatch)
* [Kent M1 Battery Wiring](/m1/battery-wiring)
* [Kent G3 Battery Wiring](/g3/battery-wiring)