SINAMICS V20 Fault F2 — Overvoltage

Overview

The F2 (Overvoltage) fault on a Siemens SINAMICS V20 variable frequency drive (VFD) indicates that the DC-link voltage has exceeded the drive's internal safety threshold. This trip acts as a hardware protection mechanism to prevent catastrophic failure of the drive's internal capacitors and IGBT logic switches. For a standard 400V three-phase unit, this critical threshold is typically around 820 V DC, while on a 230V single or three-phase unit, it is approximately 410 V DC.

Symptoms

When a SINAMICS V20 drive experiences an F2 fault, it exhibits several recognizable operational symptoms:

• Instantaneous Stop: The drive stops sending output frequency to the motor, triggering a coast-to-stop (OFF2 state).
• Fault Display: The basic operator panel (BOP) displays a flashing F2 alphanumeric message.
• LED Indication: The drive status LED transitions to red, signaling a critical system fault.
• Repetitive Tripping During Deceleration: The fault most commonly manifests near the end of a process cycle when the motor is commanded to ramp down.
• Intermittent Stoppages: Systems operating on unstable, dirty power distribution networks or near heavy industrial machinery may experience random trips even when the motor is running at a constant speed or when idle.

Possible Causes

To effectively isolate the source of the F2 fault, look for these common mechanical and electrical issues:

• Rapid Deceleration Rate: The deceleration ramp time (configured by parameter P1121) is too short for the inertia of the connected load.
• Regenerative Load (Overhauling): The physical application (such as an inclined conveyor, hoist, high-inertia fan, or centrifugal separator) forces the motor shaft to rotate faster than the synchronous speed outputted by the VFD, turning the motor into a generator.
• Input Line Voltage Spikes: Transient overvoltage spikes or surges on the mains supply line, often caused by power-factor correction capacitor switching, lightning, or nearby heavy inductive loads cycling down.
• Disabled or Misconfigured Vdc Controller: The drive's internal DC bus voltage regulator parameter (P1240) is disabled or set incorrectly, preventing the VFD from dynamically managing deceleration rates.
• Faulty Dynamic Braking Setup: Missing, undersized, or damaged external dynamic braking resistors, or an improperly programmed dynamic braking parameter (P1237).
• Incorrect Drive Sizing: The drive's thermal capacity or internal DC-link capacitance is too small to handle the kinetic energy feedback from the system.
• Internal Hardware Failure: Damaged DC link voltage-sensing circuit boards or physical decay in the drive's main capacitor bank.

Step-by-Step Troubleshooting

Follow this structured sequence to identify and correct the cause of the F2 overvoltage condition.

Step 1: Measure and Verify Safety Limits

First, isolate the drive and verify the incoming supply. Use a high-quality, calibrated true-RMS multimeter to measure the phase-to-phase AC voltage at the input terminals (L1-L2-L3 or L1-N for single-phase units).

• Ensure the input voltage does not exceed the drive's nominal rating plate tolerances (+10% maximum continuous allowance).
• Inspect the line for balance; unbalanced phases can generate abnormal currents that manifest as voltage instability on the internal DC bus.

Step 2: Read live DC-Link Voltage

Keep your hands clear of live components. Power up the drive and use the BOP to view the active, unlogged parameter r0026 (DC Link Voltage value).

• At standstill, r0026 should equal your line voltage multiplied by approximately 1.35 to 1.41 (e.g., a balanced 400V line will show roughly 540 to 565V DC on the bus).
• Run the motor and watch r0026 closely during deceleration. If the reading spikes toward 800V just before the F2 trip occur, the issue is regenerative energy rather than input mains instability.

Step 3: Extend Deceleration Ramp Times

If the V20 trips exclusively during motor ramp-down, the rate at which kinetic energy is being pulled from the rotor is too high.

• Navigate to parameter P1121 (Deceleration Time #1).
• Incrementally increase the value in seconds (e.g., from 5 seconds to 15 seconds).
• If your process requires a fast stop, do not simply extend this parameter indefinitely; instead, see Step 5 and Step 6 to deal with dynamic braking.

Step 4: Configure the Vdc Max Controller

The SINAMICS V20 possesses an automated utility to avoid overvoltage faults by actively altering the deceleration rate dynamically if the DC link voltage exceeds safety thresholds.

• Locate parameter P1240 (Configuration of Vdc Controller).
• Ensure it is set to 1 (Enable Vdc_max controller).
• Note: If your system requires tightly synchronized machine timing, enabling this controller can extend deceleration times beyond what is programmed in P1121. If precise timing is required, you must disable this parameter (P1240 = 0) and install a dynamic braking resistor.

Step 5: Audit the Dynamic Braking Module and Resistor

Check the configuration of your external dynamic braking system. Note that SINAMICS V20 Frame Sizes D to F have built-in braking choppers, while Frame Sizes A to C require an external companion Dynamic Braking Module (DBM).

• If your framework includes a resistor, measure its terminal resistance with the system powered down and disconnected. Ensure the Ohm rating aligns with the minimum allowable resistance specified inside the Siemens V20 manual for your drive size.
• Verify that parameter P1237 (Dynamic Braking Duty Cycle) is configured correctly. Set it to a value matching your application load profile (values 1 to 5 map to 5% to 50% duty cycles, respectively).

Step 6: Test Voltage Sensing Circuit Isolation

If the drive trips on F2 immediately upon power-up, even before the run command is issued and the motor is stationary, the problem is likely internal.

• Power off the unit, wait at least 5 minutes for the DC link capacitors to discharge fully, and disconnect the wires from terminals U, V, W and L1, L2, L3.
• Perform a standard diode test across the input rectifier bridge and IGBT elements with a multimeter. If any internal diodes show a short circuit (0.00V), the drive internal power circuitry is compromised and will require replacement.

Recommended Actions

To prevent the F2 fault from occurring again, apply the following preventative upgrades to your control cabinet layout:

1. Enable S-Curve Smoothing: Set your acceleration/deceleration smoothing parameter P1130 to a low, stable value (e.g., 0.5 to 1.5 seconds). This softens the transition at the beginning and end of ramps, heavily suppressing rapid, system-jarring energy regeneration spikes.
2. Install a Line Choke / Reactor: If your power system is susceptible to transients from nearby power factors capacitor switching, install a Siemens line choke in series on the input supply side. This attenuates voltage spikes before they hit the V20's diode bridge.
3. Deploy Dynamic Braking Components: For rapid start-stop tasks (conveyors, packers, winders), matching the V20 drive with a compatible dynamic braking resistor is highly recommended to redirect surplus DC energy out of the drive as heat.

Recommended Replacement Parts

If diagnostic checks indicate damaged hardware, replace the faulty components with these OEM-grade parts:

Related Articles

• How to Clean and Inspect VFD DC Link Capacitors
• Siemens SINAMICS V20 Dynamic Braking Resistor Selection Guide
• Sizing External AC Line Reactors for Siemens Industrial Drives

FAQ

Q: Can I run my motor without a dynamic braking resistor if I get intermittent F2 faults?

Yes, but only if your application can tolerate longer ramp-down times. By increasing parameter P1121 (Deceleration Time) or activating the default P1240 Vdc_max dynamic controller, you can slow the motor down gradually enough to keep the DC-link voltage beneath the trip ceiling without needing a dynamic braking resistor.

Q: Why does the F2 fault occur immediately when the motor begins ramping down?

This behavior occurs due to regenerative braking. A running motor possesses kinetic energy stored in its rotor and the coupled mechanical load. When the VFD drops its output frequency faster than the rotor naturally slows down due to friction, the rotor slips past the synchronous field speed. The motor temporarily functions as an AC generator, pumping power back through the drive's output transistors and raising the voltage of the DC-link capacitor bank.

Q: Do all Siemens SINAMICS V20 drives support dynamic braking resistors directly?

No. This is a critical engineering distinction on the V20 line. Only the larger Frame Sizes (D, E, and F) contain integrated dynamic braking choppers allowing a direct terminal connection to a resistor. The smaller Frame Sizes (A, B, and C) lack an internal chopper circuit; to use a braking resistor with these frames, you must install an intermediate external Siemens Dynamic Braking Module (DBM).

Q: What is the normal operating DC bus voltage for a standard 400V SINAMICS V20?

When sitting idle on a standard, balanced 400V system, the internal DC bus voltage (read in r0026) sits around 540V to 565V DC. During normal motoring action, this value will fluctuate slightly. The safety threshold that triggers an F2 overvoltage fault is 820V DC. If parameter r0026 shows an idle value above 600V DC, your main utility line may be over-voltage or operating with unstable harmonics.