Resolving SINAMICS S120 ON/OFF1 Startup Delay: P0346, Brake, and DC-Link

Engineer field notes for diagnosing and reducing the 1000–1800 ms quiescent period between the leading edge of STW1.0 (ON/OFF1) and the first mechanical motion of a SINAMICS S120-driven induction motor. Applies to Active Line Module (ALM) + Motor Module chassis configurations and to Active Interface Module (AIM) chassis with internal line contactor. Covers parameter P0346 (magnetization time), P1215–P1218 (mechanical brake control), P0861/P0862 (line contactor pre-charge), control-word sequencing, and trace-based verification on STARTER / Startdrive.

1. Problem Definition

A SINAMICS S120 drive configured with an Active Line Module (ALM) or with a chassis-format Active Interface Module (AIM) shows a 1000–1800 ms delay between the leading edge of control word bit 0 (STW1.0, ON/OFF1) and the first measurable mechanical movement of the motor shaft. All enable signals are present, the ramp-function generator is enabled, the brake is commanded to open, no faults are queued, and the DC link is already charged to the regulated 600 V level.

Trace recordings (function generator via STARTER trace or Startdrive trace) show that the drive advances from internal state "Ready" to "Controller enable / pulses enabled" only after a measurable quiescent period during which neither pulse pattern nor output current is present. The magnetizing current then rises for the duration of P0346 before the setpoint is finally released. The issue has been reproduced on 55 kW cage-induction motor modules in both crane-hoisting and indexing-axis applications. It is reproducible only on chassis hardware; Booksize units in equivalent applications do not exhibit the same delay.

1.1 Typical symptoms

• ON/OFF1 (STW1.0) is set high; the drive does not enter state S4 (Operation) for 1.2 to 1.8 seconds.
• Trace r0899 (status word ZSW1) shows the bit pattern advancing through S2 (Ready for switching on) → S3 (Ready for operation) → S4 (Operation) with a visible gap at the S3 → S4 transition.
• r0046.27 (Missing enable) drops at the trailing edge of the delay; no drive-side fault is latched.
• Output current ramps from 0 to magnetizing current over the value of P0346; current setpoint is not released until after the gap.
• Mechanical brake command r1229.1 (command "close brake / open brake") toggles at the end of the gap, not at the leading edge of ON/OFF1.

1.2 Acceptable target

For crane-hoisting, conveyor, and indexing axes on most SINAMICS S120 applications the accepted targets are:

• 250–350 ms from ON/OFF1 leading edge to first torque production.
• 0–150 ms from ON/OFF1 leading edge to first mechanical motion once the brake has been released (i.e. the delay attributed solely to the S120 drive itself should be below 200 ms in steady-state operation).

2. Anatomy of the SINAMICS S120 Startup Sequence

The S120 control sequence advances through five distinct internal states before the first mechanical torque is produced. The delay between any two adjacent states is a function of hardware settling, software debounce, parameter-set values, and the external enable signals configured in p0852, p0854, p0855, p0856, p0858, and p0860. The function chart 2440 (control sequence / state machine) in the SINAMICS S120/S150 List Manual documents these transitions; the description in the SINAMICS S120 product documentation should be treated as the source of truth.

Reading the table bottom-up: most of the 1000–1800 ms delay on chassis hardware is concentrated in the S3 → S4 transition and the S3 dwell time. The first two transitions (S1 and S2) account for only 150–300 ms in a well-configured system.

3. Root Cause Analysis — Four Controllable Delay Sources

The 1.0–1.8 s delay is the sum of four independent, partially overlapping contributions. Each is controllable and each has a different remedy.

3.1 Magnetization time P0346

P0346 sets the time the drive leaves the rotor free to build up flux before a torque-producing setpoint is released. For an induction motor, the rotor must be magnetized to approximately rated flux before any meaningful torque is produced; an unmagnetized motor started under load will stall or pull excessive current.

Default behavior: P0346 is calculated automatically from the motor data during initial commissioning (P0340 = 1 or 2) and typically lands in the 1.0–3.0 s range for a 55 kW motor. The default is conservative because it assumes cold motor, full-load inertia, and a worst-case rotor time constant.

Why the delay is visible: if the controller issues ON/OFF1 and a setpoint simultaneously, the drive performs magnetization while the brake is still closed. The user perceives this as a delay because no mechanical motion occurs during magnetization. The magnetizing current itself rises over P0346, not instantaneously.

3.2 Mechanical brake release

When a holding brake is configured (P1215 ≠ 0), the brake release sequence runs after the magnetization has stabilized. The sequence is:

1. Output current exceeds the brake opening threshold P1220 (default 0 A on speed-controlled axes, configurable).
2. Brake open command issued on r1229.1; output stage toggles the brake output or the Safe Brake Relay / Safe Brake Adapter.
3. Brake physically releases after P1216 (brake opening time, default 100 ms; manufacturer-stated values 50–500 ms).
4. Setpoint released; ramp-function generator begins to accelerate the motor.

If the brake opening time P1216 is conservatively set to 250 ms and the brake opening threshold is set to 50 % of rated torque, the combined delay is 250–500 ms on top of the magnetization time.

3.3 DC-link pre-charge and line contactor

The DC-link pre-charge path differs sharply between infeed topologies:

• Active Line Module (ALM): pre-charge is performed by the active IGBT bridge; the DC link reaches the regulated 600 V level within 100–500 ms of line power. Once the ALM is in state "Operation" the DC link is held at 600 V indefinitely, including during the OFF state. Subsequent ON commands do not retrigger pre-charge.
• Basic Line Module (BLM): pre-charge is passive through a resistor; takes 0.5–5 s depending on DC link capacitance. Re-pre-charges on every line-side disconnect.
• Active Interface Module (AIM) chassis: contains an internal pre-charge path and line contactor. The contactor closes on line power; pre-charge takes 1–5 s; once the contactor is closed the DC link remains charged as long as line power is present.

If the user's drive uses an ALM and the ALM is already in state "Operation", pre-charge should not contribute to the delay. If, however, the line contactor to the AIM/BLM is being closed by the same ON command that closes the line contactor, the delay will include the pre-charge interval.

3.4 Chassis vs Booksize hardware timing

Chassis Motor Modules (≥ 250 kW) and chassis ALM/AIM modules execute the state-machine transition with a 100–200 ms additional latency compared to Booksize modules. This is documented in the S120 List Manual function chart 2440 footnote and is related to the optical-fiber communication debounce between the Control Unit and the Motor Module. Booksize units use a faster internal bus, so the same control sequence completes ~150 ms sooner.

This is a hardware-fixed contribution; it can only be masked by overlapping other delays (e.g. issuing the ON/OFF1 in advance, as described in §6.1).

4. Parameter Reference

All parameters below are described in the SINAMICS S120/S150 List Manual. Default values shown are for firmware V5.2 SP3; consult the List Manual for your firmware version, as defaults can shift between releases.

5. Diagnostic Procedure — Trace r0899, r0046, and r1229

A four-channel trace on STARTER or Startdrive resolves the cause in under five minutes. Use a 1 kHz sample rate, a 4 s pre-trigger, and the following signals:

• r0899.0 — ZSW1.0 (Ready for switching on)
• r0899.1 — ZSW1.1 (Ready for operation)
• r0899.2 — ZSW1.2 (Operation enabled)
• r0899.6 — ZSW1.6 (Switching on inhibited / Missing enable acknowledged)
• r0046.27 — Missing enable signal (latched bit)
• r1229.1 — "Open brake" command to the brake output stage
• r0063 — Actual speed (filtered; useful to confirm the moment of mechanical motion)

Reading the trace from left to right:

1. STW1.0 rising edge: ON command accepted.
2. ZSW1.0 = 1 within 5 ms (no missing enable).
3. ZSW1.1 = 1 within 50–100 ms (pulses can be enabled).
4. ZSW1.2 = 1 — this is the transition you must time-stamp. The interval between STW1.0 rising and ZSW1.2 = 1 is the measured startup delay.
5. r1229.1 toggles high shortly after ZSW1.2 = 1; r0063 begins to rise P1216 ms later.

If the gap between ZSW1.1 = 1 and ZSW1.2 = 1 is approximately equal to P0346, the magnetizing time is the dominant contributor. If the gap is approximately equal to P1216, the brake release time is the dominant contributor. If the gap is approximately equal to P0861+P0862, pre-charge is the dominant contributor. If all three are short and a residual 150–200 ms remains, chassis hardware debounce is the dominant contributor.

6. Solutions and Optimization

The remedies below are ordered from most effective to least. Apply them in order, re-measuring between each, until the target delay is met.

6.1 Reorder the enable sequence — "ON first, then Run"

This is the single highest-impact change and the one most often missed in the field. The principle: the magnetization dwell (P0346) and the chassis hardware debounce (~150 ms) can be done in advance, so that the leading edge of STW1.0 is not the leading edge of "first time we need torque".

Implementation:

1. Issue STW1.0 (ON/OFF1) and STW1.3 (pulse enable) before the moment torque is needed. For a crane, this is typically at the moment the operator selects "hoist" or "lower"; for a conveyor, it is at the moment the upstream process signals "ready".
2. Hold the ramp-function generator at zero (STW1.4 = 0, STW1.5 = 0, STW1.6 = 0) until the motion is requested.
3. When motion is needed, raise STW1.4 (enable speed controller), STW1.5 (RFG start) and STW1.6 (setpoint enable) only. The drive is already in S4 / pulses-enabled / magnetized. The brake opens within P1216 ms and motion begins.

Result: residual delay from "Run" command to first mechanical motion is reduced to the brake opening time P1216 (50–250 ms typical) plus the chassis debounce already absorbed in step 1. The 1000–1800 ms gap is eliminated because the gap is filled with idle time before the motion command, not after.

6.2 Reduce P0346

The value of P0346 should be ≥ 3 × rotor time constant Tr. For a 55 kW 4-pole cage motor, Tr is typically 200–500 ms; a safe P0346 is 600–1500 ms. The default 1500 ms is conservative.

1. Read the actual rotor time constant from p0623 (motor equivalent circuit diagram, rotor time constant). Confirm the unit and verify against the motor data sheet.
2. Set p0346 = max(50, 3 × p0623). For a motor with Tr = 300 ms, this gives 900 ms — a 600 ms reduction.
3. Verify with a no-load start that the magnetization completes within the new p0346 by tracing r0331 (smoothed magnetizing current / flux actual value).
4. Verify under load that the motor does not stall or pull excessive current during the first 200 ms of setpoint release. A short stall period indicates P0346 is too short.

6.3 Pre-magnetize during standstill with zero setpoint

For applications where the user is willing to draw magnetizing current continuously while the drive is at standstill, configure the drive so that the rotor is magnetized whenever the system is "ready" (e.g. crane in cabin, conveyor in standby, hoist not moving). The drive is in S4 with r0063 = 0, drawing magnetizing current at no-load losses.

Implementation:

• Keep STW1.0 = 1, STW1.3 = 1, STW1.4 = 1 throughout the standby period.
• Set the setpoint to 0 (or use a freeze-setpoint bit).
• Make sure the motor is force-cooled if the duty cycle in standby is high; a magnetized standstill motor relies on the integrated fan for cooling, and rotor losses can accumulate.
• Reduce P1310 (continuous boost) before applying this technique — a continuous boost of 50 % at standstill can cause 30–40 % of rated current to flow, which can overheat the motor if the standby is long.

Result: "first motion after standby" is immediate (only P1216 + brake debounce, ~150–250 ms). The penalty is continuous magnetizing current (~30 % of rated, depending on P1310) and reduced thermal headroom.

6.4 Optimize brake timing

Three parameters dominate brake timing:

• P1216 (release time): set to the manufacturer-stated release time of the actual brake, not to a conservative default. A 100 ms value is fine for a millisecond-class industrial disc brake; setting P1216 = 500 ms is overkill and adds 400 ms to the delay.
• P1218 (torque threshold): on a vertical axis, set to a value that ensures torque is established before the brake releases. Typical: 5–10 % of rated torque for a hoist, 0–2 % for a horizontal axis.
• P1220 (current threshold): for safety, do not set to 0 — set to a low value (e.g. 5 % of rated) so that the drive confirms it is producing current before commanding the brake open.

6.5 Consider a Booksize unit

If the application is not bound to chassis hardware by power level, a Booksize Motor Module has measurably faster state-machine transitions on the order of 100–150 ms less delay. The user with a 55 kW hoist cannot replace the chassis ALM with a Booksize ALM at the same power level; however, the same application on a different motor at lower power can benefit from this. This option is more a hardware-design recommendation than a field fix.

7. Worked Example — 55 kW Crane Hoisting

Use case: 55 kW induction motor on a SINAMICS S120 chassis ALM with an external 24 V holding brake. Original configuration:

• P0346 = 1500 ms (auto-calculated at commissioning)
• P1215 = 1 (brake with torque proving)
• P1216 = 100 ms
• P1218 = 10 %
• P1220 = 5 %
• STW1.0 = ON command from operator pendant
• STW1.3 = same source
• Setpoint from joystick

Measured delay from joystick press to first motion: 1300 ms. Trace shows a 1100 ms gap between ZSW1.1 = 1 and ZSW1.2 = 1 — i.e. P0346 (1500 ms) minus the magnetizing current rise time (≈ 400 ms in this motor) = 1100 ms, plus 200 ms chassis debounce.

Application of §6.1 (reorder): wire the operator "hoist selected" bit to STW1.0 + STW1.3, and the joystick to STW1.4/1.5/1.6. New measured delay: 180 ms (P1216 + 80 ms debounce). Magnetization is done while the operator is choosing direction; the moment the joystick moves, motion begins.

For users who cannot modify the operator interface: apply §6.2 with p0346 = 800 ms (verified by no-load test). New measured delay: 700 ms — still useful, but §6.1 is preferred where feasible.

8. Safety and Side-Effects

• Reduced P0346 with load present: A motor starting under full load with insufficient magnetization will pull 2–3 × rated current for 100–300 ms, then either stall (F07902) or accelerate jerkily. Always test P0346 with the worst-case load attached.
• Continuous pre-magnetization (§6.3): A magnetized standstill motor draws magnetizing current continuously. If the standby duty cycle exceeds 30 % of the time, fit forced cooling or limit the standby to avoid thermal overload. Verify with r0037 (motor temperature model) or with an external PT100.
• Brake pre-torque threshold (P1218): On a vertical axis, an aggressive threshold (e.g. 0 %) opens the brake before torque is established, which causes the load to "droop" by the slack in the gearbox. Use 5–10 % of rated torque for a hoist; use 0 % only for horizontal axes with no vertical load.
• Reordering ON/OFF1 (§6.1): This requires the upstream PLC to manage the state. Make sure the safety circuit (STO, SS1, SBC) still triggers on STW1.3 / pulse-disable; the enable state should not be latched in a way that defeats the safety function.

9. Verification Procedure

After any parameter change, repeat the trace from §5 and confirm:

1. STW1.0 → ZSW1.2 ≤ 200 ms (drive-side residual) for a crane or 350 ms absolute for an indexing axis.
2. ZSW1.2 = 1 → r1229.1 = 1 ≤ 10 ms (no spurious dwell).
3. r1229.1 = 1 → r0063 > 1 rpm within P1216 + 50 ms (brake release is the dominant delay).
4. No F07902 (motor stalled) within the first 2 s of motion.
5. No overcurrent trip (F30001 / F30002) within the first 2 s of motion.
6. Thermal model r0037 remains below 100 % during a 10-minute loaded-cycle test simulating the application duty cycle.

10. Troubleshooting Matrix

11. Common Misconfigurations

• P1215 = 0 with a brake physically present: the drive never issues a brake open command. The motor may still be energized, but the brake stays closed and the drive reports motion incorrectly.
• P0346 = 0: disables the magnetization dwell. The drive releases the setpoint before flux is built. Result: a 2–3 × current spike at brake release and possible F07902.
• STW1.3 wired to the same source as STW1.0 with no independent enable: the reordering in §6.1 cannot be applied because the controller cannot separate "ON" from "pulse enable".
• P1310 left at default 50 % with continuous pre-magnetization: the magnetizing current at standstill is excessive; the motor overheats in long standby. Reduce P1310 to 0–20 % before applying §6.3.

12. Frequently Asked Questions