Common Fault F7900 in Siemens S120 Drives and Troubleshooting Methods

As a high-performance servo drive, the Siemens S120 is highly regarded and favored by users for its robust functionality and superior control performance. While powerful commissioning software makes the setup process convenient, engineers new to the product may occasionally encounter straightforward issues that prove difficult to troubleshoot due to a lack of experience. In this guide, we will examine the common S120 fault "F7900" and how to troubleshoot it.
1. First, what is the F7900 fault, and what criteria trigger it?
The S120 drive issues an F7900 "motor blocked" (stall) alarm when the motor operates at its torque limit for a duration exceeding the time defined in parameter p2177, while the motor speed remains below the threshold set in parameter p2175.
2. You may follow the procedure below to troubleshoot the fault.

3. Relevant Notes
(1) The effective torque limit is the minimum value among the current limit, torque limit, and power limit (all converted into torque terms). The logic diagram is shown below. Therefore, if R1538 or R1539 are observed to be zero or very small, you should determine which limit is currently active and adjust it accordingly.

(2) 如果空电机不带负载运行正常，带载运行报故障F7900，此时应该核算驱动器和电机是否过载，如过载，需要更换大的电机及驱动器或减小负载；如未过载，可以通过减小P2175或增大P2177解决。

(3) 对S120驱动第三方伺服电机的情况，有可能出现P1300=20能正常运行，且此时R60与R61大小相同符号一致，但P1300=21运行报故障F7900的情况，此时应该进行绝对值编码器调校P1990=1（对绝对值编码器和带有C/D信号的增量编码器）或磁极位置识别P1982=1（对增量编码器）。

如按以上流程检查，可解决大部分F7900故障。如有更多需求欢迎与我们沟通。