SAX SAX Power Home (Plus) (battery)
The SAX Power Home (Plus) is a residential AC-coupled battery storage system with an integrated inverter function, eliminating the need for a separate hybrid inverter. It uses LiFePO4 cells and connects to the grid as a single-phase AC unit. This Modbus TCP template reads battery state of charge and instantaneous storage power from the SAX Power Home (Plus), and writes the discharge power limit via the batterymode register. Connecting via the ModbusCloud Gateway gives installers and building owners live battery data and remote mode control in one place.
- Protocol
- Modbus TCP
- Connection
- Ethernet, Modbus TCP
- Registers
- 3, read and write
- Brand
- SAX
- Last updated
Registers (3)
2 read, 1 write
| Name | Unit | Access | Address (Hidden until you enter your email) | Function (hidden) | Type (hidden) |
|---|---|---|---|---|---|
| power | W | Read | |||
| soc | % | Read | |||
| batterymode | W | Write |
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Use cases
- Monitor battery state of charge continuously to verify the system charges fully during midday solar production.
- Track storage power in real time to confirm the battery is discharging as expected during evening peak consumption.
- Alert on sustained low state of charge readings that may indicate a degraded cell string requiring service.
- Report daily charge and discharge cycles over months to assess long-term capacity retention of the LiFePO4 cells.
- Write a zero discharge limit via the batterymode register to hold the battery during EV charging sessions.
Installation
Enable Modbus TCP on the SAX Power Home (Plus) unit by confirming it is connected to your LAN via the RJ45 port; Modbus TCP is active on port 502 by default.
Connect the ModbusCloud Gateway to the same local network as the SAX battery so it can reach the device IP on port 502.
In the ModbusCloud portal, add a new device, import the SAX Power Home (Plus) template, and set the Modbus unit ID to 64 (0x40) as documented in the SAX register specification.
Verify the integration by checking that the soc register at address 46 returns a plausible percentage and the power register at address 47 shows a value near 16384 when the battery is idle.
Things to watch for
Why does the power register return values around 16384 when the battery is idle?
The SAX Power Home applies a fixed offset of 16384 to the raw value at register 47. Subtract 16384 from the raw reading to obtain the actual storage power in watts. Positive results indicate discharge; negative results indicate charging.
No values appear even though the gateway connects. What should I check?
Confirm the Modbus unit ID is set to 64 (decimal), not the default of 1. The SAX battery uses unit ID 0x40 (64 decimal). A wrong unit ID produces silent timeouts. Also verify the device is reachable on port 502 from the same network segment.
Values are erratic or all registers return errors after a firmware update.
SAX has two Modbus modes in later firmware: Mode 1 (native register table, used by this template) and Mode 2 (SunSpec-aligned). If the device was reconfigured to Mode 2, the register addresses for SOC and power will shift. Confirm Mode 1 is active in the device communication settings.
Is it safe to write to the batterymode register during normal operation?
Use caution. Register 43 controls the discharge power limit. Writing 0 blocks discharge immediately, which can affect household self-consumption and may interact with the battery's own protection logic. Always restore the original value after an automation sequence, and do not write values exceeding the unit's rated power. Incorrect setpoints can void warranty support.
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