Background
In a project, the inverter communicates with the SmartLogger 2000 over RS485, and the inverter near the SmartLogger COM port is disconnected.
Problem Description
The customer in South China reported that the SUN2000-36KTL inverter connected to the SmartLogger 2000 in serial mode over RS485. The SUN2000-1 inverter closest to the COM port of the SmartLogger was disconnected, but the other inverters connected to the SUN2000-36KTL were properly communicating with the SmartLogger. The voltage of the RS485 port on the disconnected inverter is normal. Use a serial port tool to access the disconnected inverter. The response is normal.
Fault Locating
The onsite sampling RS485 communication is interrupted. The main factors are onsite construction or product quality problems. Therefore, the onsite engineers need to check the problem.
Problem Analysis
The communication link was interrupted due to the product quality. The customer used a multimeter to measure the voltage of the RS485 IN/OUT port. The voltage was 0.5 V. The RS485 cables of other inverters were disconnected and the serial port tool was used to send packets to the faulty inverter. Therefore, the communication failure was suspected to be caused by the RS485 daisy link.
It is suspected that the RS485 link is abnormal. Therefore, instruct the field engineer to use the serial port tool to access the communication disconnection inverter packet over the COM port of the SmartLogger. The packet returned abnormal garbled characters. Therefore, the inverter is not faulty and the onsite construction needs to be checked.
The RS485 communications cables are armored shielded cables. The cable sequence is correct and the RS485 port is not pressed. Inquired about the RS485 shielding layer grounding onsite. The customer reported that the shielding layer of each inverter was twisted together and then a ground point was found for grounding, as shown in the following figure.
The RS485 shielding layer of each inverter needs to be grounded. Therefore, the onsite construction does not meet the construction requirements. Instruct the site to ground the shielding layer at a single point and restore the communication.
Note
The SUN2000 RS485 shielding layer single-point grounding has been described in the user manual and quick installation guide. The shielding layer of each SUN2000 needs to be grounded only. The SmartLogger or other communications devices do not need to be grounded.
Problem Summary
If the RS485 communication is abnormal, check whether the cable wire sequence is crimped properly, whether the cable is loosely connected, whether the shielding layer is grounded on one side, and whether strong-current signal interference exists.
If the problem is caused by the product, measure the voltage of the RS485 port on the inverter or use a serial port tool to test the inverter packets to check whether the response is normal.
