SINAMICS S120 Brake Resistor Configuration PM340 Crane Hoist

1. Application Overview

A SINAMICS S120 multi-axis servo drive in crane hoist service must dissipate the regenerative energy that appears on the DC link whenever the hoist lowers a load or decelerates a heavy suspended mass. With Active Line Modules (ALM) or when the line is unable to absorb the regenerated energy, an external braking resistor (chopper resistor) is required across terminals DCP/R1 (or DCP/DCN, depending on the Power Module family) of the Power Module. For the PM340 frame FSD used in this reference, the chopper is integrated inside the Power Module — no external braking module is required — only the external resistor.

The drive family automatically activates a connected brake resistor when the DC link voltage exceeds the chopper turn-on threshold. However, several parameters must be set correctly so that the chopper engages reliably, the thermal model is monitored, and the regenerative controller (Vdc-min for kinetic buffering or Vdc-max for chopper use) does not fight the resistor.

2. Hardware Identification

Before touching any parameter, confirm the exact hardware on the nameplate. Mis-sized resistors (in ohms, peak power, or continuous power) are the single most common root cause of chopper faults (F7860, F7861) and DC-link over-voltage (F30002).

PM340 Power Modules up to frame FSE include an internal chopper. From frame FSF (90 kW and above) the chopper is removed and an external Braking Module (e.g. 6SL3760-1BE32-2AA0) is required. The FSD used here has the chopper built in, so the only addition is the resistor itself, wired between the DCP and R1 terminals of the PM340 power block.

3. Brake Resistor Sizing for Crane Hoist

Crane hoist duty is intermittent heavy regenerative. The energy to dissipate when lowering a load E_reg is:

E_reg = m · g · h · (1 - η_mech) · (1/η_motor)

where m = load mass, h = lowering height, η_mech = gearbox + sheave efficiency, η_motor = motor efficiency. The peak power is then:

P_peak = E_reg / t_brake

with t_brake the controlled lowering time. The peak power must be below the resistor's P_peak,20s rating, and the average power over one hoist cycle must be below the resistor's continuous (P_N) rating. For an FSD PM340, the matching resistor (≈ 17 Ω, 6.8 kW cont., 25 kW peak) accepts regenerative peaks typical of crane hoist, but always verify against the actual load case. Refer to Siemens FAQ 109781580 for the canonical sizing procedure.

4. Electrical Connection

1. Connect the brake resistor between terminals DCP (positive DC link) and R1 (chopper output) on the PM340 terminal block. Never connect across DCN; that is the DC bus return, not the chopper output.
2. Use a shielded, twisted-pair cable; ground the shield at both ends via EMC clips. Refer to the EMC installation guidelines in the S120 Equipment Manual.
3. If the resistor has a built-in thermal switch (PTC/NC contact), wire it to a free digital input on the CU310-2 (e.g. DI 0 on X122) and route it into p3665[0] = r0722.x. Configure p3666[0] for the fault response (typically OFF2).
4. Tighten terminal screws to the torque specified on the PM nameplate (typically 6 Nm for FSD power terminals).

5. Required Parameter Changes

The resistor itself does not need parameter changes to operate — the chopper turns on automatically when the DC-link voltage exceeds the threshold — but the thermal model, the converter protection, and the Vdc controllers must be set so the resistor is recognized, monitored, and not bypassed by the Vdc-max controller.

6. The Vdc Controller Conflict (Root Cause of "Not Working")

The original field report is a classic S120 issue. Both the Vdc-min controller (kinetic buffering, p1240) and the Vdc-max controller (p1241) regulate the DC link by adjusting the speed setpoint. When either controller is enabled, it clamps the DC-link voltage below the chopper threshold by bleeding energy back into the motor (motor-generator mode). The external resistor never sees a voltage high enough to turn on, so it appears "dead."

Symptoms match the field report exactly:

• Chopper status r3681.0 = 0 (chopper off) during a controlled lower.
• DC link r0070 hovering at ≈ 760 V (kinetic buffering active) instead of climbing to 773 V.
• Resistor cold and the line supply absorbing all the regen — fine for testing, catastrophic for a crane without a regenerative line module.

Correct configuration for an Active Line Module (ALM) or a non-regenerative line:

1. Set p1240 = 0 (Vdc-min controller disabled) unless the application specifically calls for kinetic buffering to ride through a mains dip — a crane hoist almost never needs it because gravity provides the energy buffer.
2. Set p1241 = 0 (Vdc-max controller disabled). The chopper and resistor will now control the DC link during regen.
3. Set p0219 = 2 so the firmware knows an external resistor is fitted and monitors its thermal model.
4. If the resistor overheats after a few seconds at low speed, the problem is either (a) too-small continuous power rating, or (b) the Vdc-min controller is still being implicitly enabled by some Safety Integrated or technology object. Verify by reading r0050.0 and r0050.1 (status of Vdc controllers).

Refer to the official Siemens FAQ 109781580 — "How do I activate an external brake resistor on a single axle system?" and the cross-reference 109771795 for the canonical parameterization sequence.

7. Pre-Load Test Procedure

Before any load is suspended, validate the brake resistor without the hoisting gearbox loaded. The goal is to prove the chopper fires and the resistor's thermal model tracks its energy.

7.1 Static Verification (no motor movement)

1. Power on the drive; confirm CU310-2 DP is in RUN (green LED, no F-class faults).
2. In STARTER / Startdrive / TIA Portal, go online to the CU310-2 and open the expert list.
3. Read p0219 — must equal 2. Read p0212 — must equal the resistor's continuous rating in watts. Read p1240, p1241 — both must equal 0.
4. Open the control panel. With the drive in Ready to Power-On state, set p1990 = 1 only if motor ID is required first; otherwise skip.

7.2 Dynamic Verification (no-load motor run)

1. Disable the mechanical brake on the hoist (or run the motor uncoupled) so the load is just inertia.
2. Command a moderate speed (e.g. 20 % of rated). Monitor the trace r0070 (DC-link voltage).
3. Command a fast stop (OFF1, OFF3, or setpoint 0). The drive decelerates the motor, acting as a generator.
4. Watch r0070 rise to 773 V. At that instant, r3681.0 (chopper active) must toggle to 1 and the resistor's surface temperature (or the r3682 thermal-model load %) must begin to climb.
5. After the stop, read r0999 for any new fault entries. A clean stop yields no F7860/F7861.

7.3 Trace Setup for the Acceptance Test

Record the following signals in a STARTER trace or TIA trace, sample at 1 ms for the duration of the dynamic test:

7.4 Acceptance Criteria

• DC-link voltage never exceeds 800 V during the dynamic test.
• Chopper status r3681.0 = 1 for the duration of the regenerative phase.
• Thermal-model load r3682 < 100 % at the end of the test (otherwise the resistor is undersized).
• No F7860 (overtemperature), F7861 (I²t), F30002 (DC-link over-voltage) during or after the test.

8. Fault Codes Specific to the Brake Resistor

9. Troubleshooting Matrix

10. Crane-Specific Considerations

• Mechanical brake interlocks. On a hoist, the mechanical holding brake is the primary safety device. The brake resistor is only for the electrical regen path. The brake must close on OFF1/OFF2, not on a mains dip. Test the brake-resistor function only after the mechanical brake has been verified.
• Long lowering distances. A 20 m lowering of a 10 t load dissipates ≈ 200 kJ. The 6.8 kW continuous resistor can absorb that in ≈ 30 s at 100 % duty; the 25 kW peak rating covers the controlled-lowering transient. Anything beyond that requires a resistor upgrade or a regenerative Active Line Module (6SL3130-7TE…).
• Safety Integrated. If the drive runs in SINUMERIK/SIMOTION with SINUMERIK Safety Integrated, the STO/SS1/SBC signals do not interact with the chopper, but a power loss still forces a regen event. The chopper must be sized for the worst-case uncontrolled gravity drop, or the load must be arrested by a back-up mechanical brake.
• Re-power cycle after a change. SINAMICS stores brake-resistor parameters in the EEPROM but the chopper enable latch is set on first RUN transition. After changing p0219 or p0212, power the CU310-2 off, wait for the display to go blank, and re-apply 24 V.

11. Verification Checklist Before Load Test

1. ☐ p0219 = 2; p0212 matches resistor nameplate; p0213 = 1.
2. ☐ p1240 = 0; p1241 = 0 (unless kinetic buffering explicitly required).
3. ☐ p1531 is set to a value that allows full regen (typically −0.3 · p0207 to −0.5 · p0207).
4. ☐ No thermal input wired → set p3665[0] = 0 and p3666[0] = 0; otherwise wire to the resistor's NC contact.
5. ☐ Mechanical brake released and back to test mode.
6. ☐ No-load dynamic test run; chopper r3681.0 = 1; DC link clamped at 773 V; r3682 < 100 %; no faults in r0947/r2121.
7. ☐ Save the parameter set to the CF card on the CU310-2 (Menu "Copy RAM to ROM").

Only after this checklist is complete should the hoist be commissioned with a suspended load. The first loaded lower should use a calibrated test mass, with the trace of r0070, r3681, and r3682 recorded and stored with the commissioning report.