Solar panel and battery combinations for a
DXM Modbus Slave
system
Solar Panel
Battery Capacity4
Days of Autonomy
DXM mA
DXM Controller
5 watt
10 Ahr
10 days
25 mA
DXM Slave Controller - ISM radio and I/O base board
20 watt
14 Ahr
10 days
30 mA
DXM Controller with ISM radio
20 watt
20 Ahr
10 days
35 mA
DXM Controller with ISM radio and Cellular Modem
5.3.4 Monitoring Solar Operation
The DXM solar controller provides Modbus registers that allow the user to monitor the state of the solar panel input voltage,
the battery voltage, the charging current, and the temperature in °C. The DXM Modbus Slave can be configured to monitor
the health of the charging system as well as send an alert message when the battery is too low.
The charts show a typical charging cycle, with each vertical grid representing about eight hours. The chart shows three
days of charging.
Figure 6. Solar Panel Voltage (mV) -- Cloudy First Day
Figure 7. Battery Voltage (mV) - Cloudy First Day
5.4 Connecting the Communication Pins
The base board communications connection for external Modbus device uses the primary RS-485.
RS-485. The primary RS-485 bus is a common bus shared with the ISM radio board (Modbus Slave ID 1).
RS-232. The RS-232 bus is not currently defined.
Pin
Parameter
Description
Pin 6
Primary RS-485 –
Running Modbus protocol at 19.2k baud, use this bus to connect to other Modbus Slave devices.
The DXM150-Sx Wireless Modbus Slave is a Modbus Master device on this RS-485 port.
Modbus Register 6101 = Baud Rate
0 = 19.2k
1 = 9600
2 = 38400
Modbus Register 6103 = Parity
0 = no parity
1 = odd?
2 = even?
Pin 7
Primary RS-485 +
4 Battery capacity (amp hour) is standard amp rating taken for 20 hours. Battery capacity should be monitored for reliable system power and may
need to be increased for cold weather locations.
DXM150-Sx Wireless Modbus Slave
28
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