Enabling Reverse Command on Siemens SIMOREG 6RA70 1Q Drive

Overview

The Siemens SIMOREG DC-MASTER 6RA70 in a single-quadrant (1Q) configuration can only deliver armature current in one polarity. To obtain a reverse (REV) command without changing the drive variant, the field current polarity must be physically reversed while the armature bridge remains in its single-quadrant topology. This is implemented by switching the field winding through two mechanically interlocked DC contactors commanded from binary outputs of the drive. The SIMOREG 6RA70 then supervises direction through its binector/connector logic, exposed on terminal strip X171, and routed through parameters P671 and P672 to the internal command word.

This article documents the field-reversal topology, the binary I/O wiring at X171:37 (FWD) and X171:38 (REV), the binector mapping (B0012, B0014), and the function diagrams (G110 for wiring, G200 for field reversal) that must be read in conjunction with chapter 9.18 of the 6RA70 parameter manual.

Prerequisites

• SIMOREG 6RA70 firmware installed (verify on parameter r060 or the rating-plate firmware label); the 6RA70 series covers firmware 1.x through 3.x — field reversal via contactors is supported across all firmware revisions of the 1Q variant.
• 6RA70 parameter list / function diagram manual (Compendium, order number 6RX1700-0AD74 or the matching edition for the firmware loaded).
• Two DC-rated contactors rated for the motor field current (typically 110 V or 310 V DC coil, depending on the field supply) with mechanical and electrical interlocks so that both contactors cannot pick up simultaneously.
• Two free binary outputs on the drive (terminal strip X172) for FWD/REV coil drive, or external interposing relays if the on-board outputs cannot source the contactor coil current.
• 24 V DC control supply for the binary inputs and the contactor coils.
• Field supply connection at the drive's XU1/XV1/XW1 or equivalent terminal block (verify against the as-built wiring diagram).

Quadrant Configurations: 1Q vs 2Q vs 4Q

Before commissioning, confirm the drive variant. The 6RA70 is ordered as a single-quadrant (1Q), two-quadrant (2Q), or four-quadrant (4Q) unit. Each variant has a different power section and a different parameter default set.

If the rating plate shows a single thyristor bridge and a single armature current sensor, the unit is 1Q. Field reversal is the only legitimate reverse path on a 1Q drive — do not attempt to swap armature leads, because the armature converter cannot regenerate and the drive will fault on overcurrent or commutation failure.

Hardware Topology: Field Reversal Contactors

The field winding is connected through two DC contactors arranged so that only one can be closed at any time. Polarity at the field terminals is therefore reversed between the two contactors.

The contactor coils are driven from binary outputs of the 6RA70. Configure these as "FWD command" and "REV command" indicators using parameters P770 / P771 (or the equivalent binary-output routing parameter for the firmware revision; see the function diagram G110 sheet in the manual). Alternatively, derive the coil drive from the FWD/REV command bits that the drive passes to its own logic.

Binary Input Wiring on X171

The binary inputs of the 6RA70 are wired to terminal strip X171. For forward and reverse commands, the relevant terminals are:

The exact binector-to-terminal mapping must be verified against the function diagram sheet G110 in the 6RA70 manual for the firmware revision installed; some firmware revisions use a different binector index for the same terminal. The mapping in the table is the canonical mapping referenced in the chapter covering 1Q field reversal.

Wire the binary inputs as 24 V sourcing inputs:

1. Bring a 24 V DC control supply to a common terminal (typically X171:1 or X171:2 — see the manual's wiring sheet).
2. Wire X171:37 through a normally-open FWD pushbutton or PLC output contact to 24 V.
3. Wire X171:38 through a normally-open REV pushbutton or PLC output contact to 24 V.
4. If the drive is being commanded from a PLC, do not parallel-wired the inputs without isolating them; use one PLC output per terminal.

Binector Assignment: B0012 and B0014

Binectors are single-bit logic signals inside the 6RA70 used to combine digital conditions. B0012 and B0014 are the two binectors that carry the FWD and REV commands from the input terminals to the parameter layer.

To verify which terminal is wired to which binector:

1. Open the DriveMonitor / SIMOVIS commissioning tool, or use the optional OP1S operator panel.
2. Navigate to menu Parameter > Binector / Connector > Display.
3. Enter binector B0012 and confirm the source terminal (should be X171:37).
4. Enter binector B0014 and confirm the source terminal (should be X171:38).

If a binector is mapped to a different terminal than the wiring sheet indicates, change the routing parameter for that input (the parameter number depends on firmware; in the canonical mapping it is indexed under the input assignment parameter block).

Parameter Configuration: P671 and P672

Parameters P671 and P672 select the binector source for two of the drive's internal command signals. The exact semantic of each parameter is firmware-revision-dependent, so consult the parameter list shipped with the unit. The standard mapping in the 1Q field-reversal application is:

In addition to P671 / P672, the following parameters commonly need verification on a 1Q field-reversal conversion:

Function Diagram Reference: G110 and G200

The function diagrams are the definitive reference for any 6RA70 logic configuration. For field reversal in a 1Q drive, two sheets are mandatory reading:

Chapter 9.18 of the parameter manual covers field reversal in 1Q operation end-to-end. Read it in full before commissioning; it includes the commutation timing required between FWD and REV transitions, the field-economy behavior, and the conditions under which the drive inhibits a direction change (typically: armature current not zero, speed not below threshold, or field current not yet established).

Commissioning Procedure

1. Verify the drive is the 1Q variant (rating plate, parameter r006 or hardware code per manual).
2. Power down, lock out, and verify zero energy on the armature bus, field bus, and 24 V control.
3. Install K-FWD and K-REV contactors between the drive's field output terminals and the motor field terminals. Wire mechanical and electrical interlocks.
4. Wire the contactor coils to two binary outputs of the 6RA70 (X172 outputs routed by the parameters indicated in function diagram G110) or to external interposing relays driven from those outputs.
5. Wire X171:37 to the FWD command source and X171:38 to the REV command source.
6. Power up control only. Using DriveMonitor or OP1S, verify that B0012 follows X171:37 and B0014 follows X171:38.
7. Set P671 and P672 per the table above. Save to the drive's non-volatile memory.
8. Set the field parameters (P082, P083) to motor nameplate values.
9. Disable the armature enable (set the relevant enable-source parameter to a state that will not command the armature). Drive the field only to verify contactor sequencing.
10. Command FWD. Verify K-FWD picks up, K-REV is released, and the field voltmeter at the motor terminals shows the expected polarity (use a DC voltmeter on the field leads before they go to the motor — observe polarity).
11. Command REV. Verify K-REV picks up after K-FWD releases, polarity at the motor field reverses.
12. Re-enable armature enable, command FWD with a small setpoint, verify rotation. Bring the setpoint to zero, command REV, verify rotation reverses.
13. Run the drive through the full speed range in both directions and record the field current, armature current, and speed for the commissioning report.

Verification and Diagnostics

After commissioning, validate the reverse path with the following checks:

• Direction bit state: Read the relevant status parameter (e.g., r035 or the firmware-equivalent) and confirm it toggles between FWD and REV correctly.
• Field current direction: Place a DC ammeter in the F1 lead and verify that the sign of current reverses between FWD and REV. The 6RA70 displays field current on parameter r084 as a signed or unsigned value depending on the parameter list; if the display is unsigned, mechanical measurement at the field leads is the only reliable indicator.
• Armature current: Verify that armature current does not surge during the field-reversal transition. A momentary inrush is normal because the field is collapsing and re-establishing; values above the rated armature current indicate a transition timing problem.
• Fault memory: Read r047 (fault buffer) and r049 (alarm buffer) for any F001–F0xx field faults. Refer to the official diagnostics compendium for a complete fault-code listing.

The Siemens technical support portal hosts an official 6RA70 diagnostics PDF that covers fault localization, parameter dump procedure, and reset sequence. It is recommended to bookmark it during commissioning: SIMOREG 6RA70 fault diagnostics FAQ.

Safety and Interlocking Requirements

• Provide a hardwired mechanical interlock between K-FWD and K-REV contactors so that a controller fault cannot close both simultaneously.
• Use a make-before-break overlap only if the field supply can tolerate a momentary short; on most 6RA70 1Q field supplies this is not acceptable. Use break-before-make with a delay at least equal to 5× the field time constant.
• Wire an auxiliary contact from each contactor back to a binary input of the drive (X171 terminal) so the drive can confirm which contactor is actually closed. This is the field-contactor feedback loop and is a recommended practice on critical applications.
• Do not command REV while the motor is rotating in FWD at high speed. The 6RA70 firmware inhibits reversal under some conditions; verify the inhibit behavior on the installed firmware and add an external zero-speed permissive in the PLC if necessary.
• When the drive is off, the field contactors must be released. The 6RA70 will drop the binary outputs on power-down; do not bypass this.
• Ensure the field economy function (P258 / P259 area, firmware-dependent) is configured so that idle field does not hold the wrong contactor closed.

Troubleshooting Matrix

FAQ