Configuring SINAMICS G120 PM240-2 Brake Chopper to Clear F07400

Problem Description: F07400 on a High-Inertia Sand Sieve Application

A SINAMICS G120 PM240-2 power module paired with a CU240E-2 PN-F control unit is driving a sand sieve machine at a continuous throughput of roughly 300 tonnes per hour. The drive is sized for a 30 kW induction motor. After commissioning, the operator reported fault F07400 "Drive: DC link voltage maximum controller active" approximately every 250 ms while the sieve was running under load and decelerating. Because the fault was cyclic and tied directly to the machine run profile, the issue was traced to regenerative energy feeding back into the DC link during every braking phase of the sieve mechanism.

Fault F07400 is not a hardware trip in the conventional sense; it is the Vdc-max controller reporting that the DC link voltage has reached its upper intervention threshold and that the controller is actively extending the ramp-down time to keep the link within limits. The drive is still running, but it is doing so by overriding the configured deceleration ramp. If the regenerative energy exceeds the controller's absorption capability, the drive will eventually trip with F30002 "DC link overvoltage" and shut the motor down.

Root Cause: Why F07400 Recurs on a 30 kW Sieve Drive

The PM240-2 has a built-in brake chopper, but the chopper is inactive until a braking resistor is wired to terminals DCP/R1 and R2 and the relevant parameters are configured. With no resistor present, the only sink for regenerative energy is the Vdc-max controller, which works by stretching the deceleration ramp. On a high-inertia sieve with a stiff load, the controller cannot lengthen the ramp enough to keep up with the energy being returned, so the link voltage hits the threshold every deceleration event — in this case, every 250 ms.

Two diagnostic checks to confirm regen-limited behaviour before installing hardware:

1. Read r0026 (actual DC link voltage) and r1242 (Vdc-max controller output) in trace. If r0026 approaches the chopper threshold on every deceleration and r1242 saturates, the issue is regen-limited, not supply-limited.
2. Read the actual motor speed ramp and compare it to the configured ramp-down time (p1121). If the actual ramp is much slower than configured, the Vdc-max controller is actively stretching the ramp.

Once regen is confirmed, the correct remedy on a PM240-2 is to wire the matching JJY braking resistor and configure the brake chopper parameters, not to alter p1121 alone. Lengthening the ramp only delays the energy return; the kinetic energy is still there to dissipate.

Hardware Identification and Catalog Numbers

Use the following catalog numbers to match the field installation before any parameter work begins. Substituting an incorrect resistor value will either trip the chopper on overcurrent or fail to dissipate the regen energy.

Verify the actual kilowatt rating and frame size on the rating plate of each component before commissioning. The 15 Ω resistor value is the standard match for this PM240-2 power level. The PM240-2 chopper IGBT and the JJY resistor are sized as a pair — do not substitute a lower ohm value (excessive current) or a higher ohm value (chopper cannot pull the link down fast enough).

PM240-2 Brake Chopper Architecture

The PM240-2 differs from the older PM240 in that the brake chopper IGBT is integrated into the power module. There is no separate brake chopper module to order; the chopper is the upper IGBT in the inverter bridge, and terminals DCP/R1 and R2 are brought out to the top of the unit specifically to connect the external braking resistor in series with that IGBT.

Operation sequence:

1. During normal motoring, the chopper IGBT is held off and the resistor is electrically isolated.
2. When the DC link voltage rises to the chopper threshold, the chopper IGBT turns on, connecting the resistor across the DC link.
3. Regenerative current flows from the link through the resistor to R2, dissipating the energy as heat.
4. When the link voltage falls back below the hysteresis threshold, the chopper turns off.

For the chopper to operate, the drive firmware must know the resistor's continuous power rating. On CU240E-2 PN-F firmware V4.6 and later this is parameter P219 (braking resistor power in kW). On pre-V4.6 firmware the same role is played by P1237 (braking load duty cycle). The value is used for thermal modelling and to prevent the resistor from being overloaded during sustained braking.

Wiring the Braking Resistor to DCP/R1 and R2

Mechanical and electrical steps:

1. De-energize the drive, lock out the line disconnect, and wait at least 5 minutes for the DC link capacitors to discharge below 50 V. Verify with a meter at DCP and DCN before touching any conductor.
2. Remove the two rubber seals on the top of the PM240-2. These cover the DCP/R1 and R2 terminals. Do not discard the seals — they are re-used as strain relief and IP21 protection.
3. Route the resistor cables through the rubber seals. The seals must close around the cable jacket to maintain the IP21 rating.
4. Terminate one resistor lead to DCP/R1 (positive DC bus + brake resistor terminal) and the other lead to R2 (brake resistor return). Torque to the value printed on the terminal label of the specific PM240-2 frame.
5. Mount the resistor itself on a heat-resistant surface with the supplied brackets. Maintain the clearances given in the hardware installation manual. The resistor body can reach high temperatures during sustained braking — the convection clearance around the housing is part of the thermal design.
6. Wire the resistor's integrated temperature switch (PTC or bimetallic) to a free digital input on the CU240E-2. This is required for safe operation; the drive must be able to shut down if the resistor overheats.

Parameter Configuration

The following parameter set activates the integrated brake chopper and deactivates the Vdc-max controller. Both changes are required: leaving the Vdc controller active while a brake chopper is in use creates a control conflict, because both subsystems will try to manage the link voltage at the same time.

To enter the JJY:023424020001 continuous power value into P219, read the rating from the resistor's data plate and enter the value in kilowatts. Do not enter peak power; enter the continuous power rating. The firmware uses this value to model resistor heating and to clamp the chopper duty cycle.

Commissioning with SINAMICS STARTER

SINAMICS STARTER (or TIA Portal with the SINAMICS Startdrive plug-in) is the recommended commissioning tool for this parameter work. The Operator Panel BOP-2 can be used, but the Expert List path is faster.

Procedure in STARTER:

1. Connect to the drive via PROFINET, PROFIBUS, or the USB port on the CU240E-2 and bring the drive online.
2. Open the project, select the drive, and switch to the Expert List view.
3. Filter the parameter list for P1280, P219 (or P1237 on pre-V4.6 firmware), and P2106.
4. Set P1280 = 0 and write to the drive (RAM only first).
5. Set P219 to the continuous power (in kW) from the resistor data plate and write to the drive.
6. If the resistor's overtemperature switch is wired to a digital input, set P2106 to the bit address of that input. For DI 3 the value is 722.3.
7. Confirm the settings by reading the parameters back.
8. Save the parameters to the non-volatile memory of the CU240E-2 with Copy RAM to ROM.
9. Perform a brief load test, then observe r0026 (DC link voltage) and r1239[0] (chopper ON time) in trace. With the chopper working, r0026 rises during deceleration but is held just below the threshold by the chopper, and r1239[0] shows a duty cycle that matches the deceleration duty of the sieve.

Temperature Fault Wiring via Digital Input

Many Siemens braking resistors, including the JJY series, include an integrated temperature switch. The switch is normally closed and opens when the resistor body exceeds its rated temperature. Wiring this switch to a CU240E-2 digital input and assigning it as an external fault source gives a hard stop if the resistor overheats.

For a CU240E-2 PN-F with the temperature switch wired to DI 3, the parameter is P2106 = 722.3. This tells the drive to monitor bit 3 of the digital input status word r0722, and to trigger external fault 1 if that bit goes low (i.e., the switch opens).

For redundancy, P2107 can be used for external fault 2 with a second digital input, and P2108 / P2109 / P2112 for additional sources if the application has multiple temperature switches (e.g., on a resistor array).

Verification and Field-Proven Results

After commissioning, the installation described here ran for approximately 2.5 days continuously without F07400 or any related faults. The verification points below were used to confirm correct operation:

1. Trace r0026 during a deceleration event. With the chopper active, the link voltage rises, the chopper IGBT pulses to clamp it, and the voltage stays below the threshold. A clean trace shows a brief overshoot followed by a flat top under the threshold.
2. Trace r1239[0] / r1239[1]. The chopper duty cycle reading should be non-zero only during braking events and zero during motoring.
3. Check resistor body temperature. The JJY resistor will be warm after a deceleration cycle but should cool back to ambient within the next motoring cycle. Persistent high temperature indicates either an under-sized resistor or excessive braking duty.
4. Check the operator panel fault buffer. After at least 30 minutes of normal operation, the fault buffer should be empty of F07400 and F30002 entries.
5. Inspect for F7452 / overtemperature events. If the resistor temperature switch fires, the drive will record an external fault 1 event with a timestamp; absence of this event confirms the resistor is operating within thermal limits.

For a permanent record, save the trace to a STARTER project file. This becomes part of the site's commissioning documentation and provides a baseline for future maintenance.

Troubleshooting Matrix

Related Parameters for Deep Diagnostics

For engineers who want to verify chopper behaviour at signal level beyond the basic r0026 / r1239 readouts, the following parameters are useful during commissioning:

Commissioning Checklist

1. Confirm hardware: CU240E-2 PN-F (6SL3244-0BB13-1FA0), PM240-2 (6SL3210-1PE26-0AL0), braking resistor JJY:023424020001 (15 Ω).
2. De-energize the drive, wait for DC link discharge, and verify with a meter.
3. Wire the resistor from DCP/R1 to R2 through the rubber seals. Torque to the terminal label value.
4. Wire the resistor's overtemperature switch to a free digital input (DI 3 used in this installation).
5. Connect STARTER to the drive via PROFINET or USB and bring the drive online.
6. Set P1280 = 0 (inhibit Vdc-max controller).
7. Set P219 to the continuous kW rating from the resistor data plate.
8. Set P2106 = 722.3 (DI 3 routed to external fault 1).
9. Copy RAM to ROM.
10. Run a controlled deceleration test, trace r0026 and r1239, and confirm the chopper clamps the link below the threshold.
11. Check the fault buffer after 30 minutes — must be free of F07400 and F30002.
12. Save the STARTER trace to the project file for site documentation.

Frequently Asked Questions