What is f7900 siemens fault?

If you’re working with Siemens SINAMICS S120 or G120 drives, seeing Fault F07900 on your BOP (Basic Operator Panel) can be a bit of a headache. In short, it means your motor has hit a Torque Limit for too long, and the drive has tripped to protect the hardware.

 

Think of it as the drive saying: "I'm pushing as hard as I'm allowed to, but the motor still isn't spinning at the speed you asked for."

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🔍 What Exactly is F07900?

The official Siemens designation is "Drive: Motor blocked / speed controller at its limit." This fault triggers when the following conditions are met simultaneously for a specific amount of time (defined in parameter p2177):

1. The speed is below the "threshold for motor blocked" (p2175).

2. The speed controller is at its upper or lower limit (it's "flooring it").

3. The motor is producing (or trying to produce) maximum torque.

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🛠️ Common Causes

• Mechanical Jam: A physical obstruction in the machinery, a seized bearing, or a brake that hasn't released.

• Excessive Load: The machine is being asked to move more weight than the motor's torque profile allows.

• Incorrect Parameterization: The ramp-up times (p1120) are too short, or the torque limits are set too low for the application.

• Encoder Issues: If the drive is getting "garbage" data about how fast the motor is spinning, it might think it's stalled when it isn't.

• Phase Loss: A power issue between the drive and the motor.

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💡 How to Troubleshoot and Fix It

Before you start swapping out hardware, try these steps:

Step	Action	What to Check
1	Check Mechanics	Can you rotate the motor shaft by hand (with power off)? Check for jammed belts or gears.
2	Verify Brakes	Ensure the motor brake is receiving the signal to open and is physically releasing.
3	Check p2175 & p2177	Increase the "Motor Blocked" threshold (p2175) or the delay time (p2177) if your application has a very heavy start-up.
4	Ramp Times	Increase the acceleration time (p1120). Sometimes the drive just needs more time to get a heavy load up to speed.
5	Current Limits	Check if the current/torque limits are set too low for the actual work required.