SDM120 CT meter ID fix

The Eastron SDM120 is the single-phase CT meter commonly paired with Deye hybrids. The classic gotcha: the inverter expects the meter at a specific Modbus address, but the meter ID won’t change.

What’s going on

• Deye firmware polls the external meter at a fixed Modbus ID and 9600 baud.
• Some SDM120 variants ship with the address effectively locked, so the usual menu route to change it doesn’t stick — the meter answers on the wrong ID and the inverter sees “no meter”.

The workaround

1. Confirm the meter is wired and powered (the display is lit) and RS485 A/B are correct — see smart meter wiring.
2. Enter the meter’s setup menu — hold the single front button for 3 seconds; a short click scrolls the display. Then set:
   • Baud rate: 9600. It leaves the factory on 2400, so this one always has to be changed.
   • Address / ID: the value the inverter expects (commonly 1). Factory default is 001.
3. If the address won’t save, the unit is the locked variant.

While you are in there: set CT 1 to 120 for the ESCT-TA16. Eastron’s own note is that on a MID SDM120CTM the CT ratio can be set once only — check the CT before you commit it. Defaults and menu order are on p.1 of the SDM120 series manual.

The proper fix

Use the newer meter variant with a user-changeable ID — the SDM120CT-MID style unit — which lets you set the Modbus address from the meter keypad. Set it to the inverter’s expected ID, 9600 baud, and it’s recognised immediately.

Keep one known-good meter in the van. Swapping a locked SDM120 for the user-settable variant is usually faster on site than fighting the menu.

Still no meter comms after this? See SDM120 / external meter not communicating.