diff --git a/rdtech-controller-c3.yaml b/rdtech-controller-c3.yaml
index f2b258e..31d8dbf 100644
--- a/rdtech-controller-c3.yaml
+++ b/rdtech-controller-c3.yaml
@@ -6,6 +6,14 @@ substitutions:
   device_friendly_name: "RD 6006"
   device_description: "Power Supply"
   time_timezone: "Europe/Amsterdam"
+  # Modbus slave address. Must match the "Address" value in the PSU's
+  # System menu. The PSU exposes the address knob (1–247 per Modbus
+  # spec), but the stock dongle is a one-PSU device, so most users will
+  # never touch this. Custom multi-drop setups (one ESP driving several
+  # PSUs over an external TTL→RS-485 transceiver pair) need a unique
+  # value per PSU; in that case build a separate firmware per device
+  # with the matching slave_address rather than sharing a binary.
+  slave_address: "0x01"
   
   # Model specific settings (Don't change these!)
   RD6006_voltage_maximum: "60"
@@ -105,7 +113,7 @@ modbus:
 modbus_controller:
   - id: powersupply
     ## This address should be set to the "Address" value in the config menu
-    address: 0x01
+    address: ${slave_address}
     modbus_id: modbus1
     setup_priority: -10
     update_interval: 5s
diff --git a/rdtech-controller.yaml b/rdtech-controller.yaml
index d87db69..67e1a5e 100644
--- a/rdtech-controller.yaml
+++ b/rdtech-controller.yaml
@@ -6,6 +6,14 @@ substitutions:
   device_friendly_name: "RD 6006"
   device_description: "Power Supply"
   time_timezone: "Europe/Amsterdam"
+  # Modbus slave address. Must match the "Address" value in the PSU's
+  # System menu. The PSU exposes the address knob (1–247 per Modbus
+  # spec), but the stock dongle is a one-PSU device, so most users will
+  # never touch this. Custom multi-drop setups (one ESP driving several
+  # PSUs over an external TTL→RS-485 transceiver pair) need a unique
+  # value per PSU; in that case build a separate firmware per device
+  # with the matching slave_address rather than sharing a binary.
+  slave_address: "0x01"
   
   # Model specific settings (Don't change these!)
   RD6006_voltage_maximum: "60"
@@ -103,7 +111,7 @@ modbus:
 modbus_controller:
   - id: powersupply
     ## This address should be set to the "Address" value in the config menu
-    address: 0x01
+    address: ${slave_address}
     modbus_id: modbus1
     setup_priority: -10
     update_interval: 5s