Siemens 1FK7 Servo Motor Replacement Guide

Overview

The Siemens SIMOTICS S-1FK7 is a highly versatile, permanent-magnet synchronous servo motor that has served as the backbone of industrial motion control for over two decades. Famously paired with SINAMICS S120, S150, and master drives, the 1FK7 family has been widely deployed in high-performance applications including packaging machines, machine tools, plastics processing, winders, and assembly lines.

With the Siemens product lifecycle moving downstream, the 1FK7 series has reached phase-out status (milestone PM400/PM410). Finding direct replacements, migrating to the newer generation SIMOTICS S-1FT2/1FK2 lines, or sourcing high-quality refurbished stock has become a critical operational priority for maintenance teams globally. Repairing or replacing these legacy units correctly prevents costly production downtime and maintains the precise dynamic response of your automated systems.

Legacy Product Information

The Siemens 1FK7 range is characterized by its high overload capability, exceptional dynamic performance, and integrated DRIVE-CLiQ interface option, which allows plug-and-play identification by SINAMICS control units.

The 1FK7 was offered in two main technical designs:

• SIMOTICS S-1FK7 HD (High Dynamic): Designed for low rotor inertia to achieve extremely rapid accelerations and short cycle times.
• SIMOTICS S-1FK7 CT (Compact): Optimized for high torque-to-size ratios, offering a space-saving footprint with a higher rotor inertia suited for stable control under fluctuating load ratios.

Motor MLFB Part Number Breakdown

Siemens uses a machine-readable 16-character Machine Readable Product Code (MLFB). Matching these characters is crucial to identifying key specifications. A typical part number looks like: 1FK7063-5AH71-1AA0.

• 1FK7 (Characters 1–4): Family type (Synchronous Servo Motor).
• 063 (Characters 5–7): Shaft Height (e.g., 03 = SH36, 04 = SH48, 06 = SH63, 08 = SH80, 10 = SH100).
• 3 (Character 8): Length designator (e.g., 0, 3, 4, 5).
• 5 (Character 9): Cooling classification (e.g., 5 = Natural cooling IP65, 2 = Natural cooling IP64).
• A (Character 10): Rated Input Voltage and Speed (e.g., A = 600V DC link, F = 3000 RPM, H = 4500 RPM).
• H (Character 11): Shaft extension and holding brake type (e.g., A = plain shaft, no brake; H = keyway, with 24VDC holding brake).
• 7 (Character 12): Integrated Encoder Type (e.g., 1 = Incremental encoder, A = DRIVE-CLiQ absolute encoder AM20DQI, E = Resolver).
• 1 (Character 13): Structural design / mounting style (e.g., 1 = IM B5 flange).
• A-Z (Characters 14-16): Technical variation, connector exit direction, or special options.

Lifecycle Status

The 1FK7 series is currently in the active phase-out and discontinuation phase. While new custom builds are restricted or carry heavy price premiums from the OEM, component-level spare parts, refurbished units, and surplus stocks remain the most cost-effective path to preserving legacy infrastructure.

Recommended Replacements

When a 1FK7 motor fails, you have three primary paths: direct-fit exact legacy replacement, moving to the direct functional successor (SIMOTICS S-1FT2), or shifting to the cost-optimized modern successor (SIMOTICS S-1FK2).

Compatibility Considerations

1. Mechanical Footprints & Flanges

Siemens designed the successor series (specifically the SIMOTICS S-1FT2) to match standard IEC mounting flanges. For example, a 1FK7 with Shaft Height 63 (1FK706x) aligns closely with a 1FT206x counterpart. However, you must verify:

• Shaft Diameters: Smooth vs. Keyed shafts (standardized DIN 42955 tolerances). Ensure the keyway depth and width match your existing coupling.
• Overall Length: Modern motors are often shorter due to superior magnetic material density. Ensure your machine has enough clearance for the mechanical coupling to close the gap.

2. Feedback Systems & DRIVE-CLiQ

Older 1FK7 motors utilized standard Resolver feedback, Sin/Cos encoders, or absolute encoders with dedicated encoder cables. Many models featured DRIVE-CLiQ (DQ)—the Siemens proprietary digital interface that integrates encoder signals and thermal protection onto a single serial link.

• If replacing a 1FK7 DRIVE-CLiQ motor with an 1FT2 equivalent, verify the encoder configuration (e.g., absolute multi-turn 24-bit).
• Modern replacements utilize M17/M23 Speed-Connect or OCC single-cable configurations rather than the historic dual-cable (power + signal) structure. Adaptor cables or new prep assemblies are often necessary.

3. Electrical Characteristics

To ensure the drive system operates without high-frequency feedback loops or tracking errors, the electrical properties must align closely:

• Stall Torque ($M_0$): Must be equal to or greater than the original unit.
• Rotor Inertia ($J$): A motor with significantly lower rotor inertia (e.g., migrating from 1FK7 CT to a very light 1FT2) may cause control loop instability if the load ratio is high. Tuning parameters must be recalculated.
• Rated Current ($I_N$) and Max Current ($I_{max}$): Must fall within the output capabilities of the existing SINAMICS Motor Module.

Upgrade Benefits

If you choose to migrate to the modern SIMOTICS S-1FT2 or 1FK2 lines instead of sourcing an exact 1FK7 replacement, your system stands to gain several technical advantages:

• Higher Encoder Resolution: Modern encoders feature up to 24-bit resolution (over 16 million increments per revolution) compared to the older 20-bit designs, leading to exceptional positioning accuracy and ultra-smooth surface finishes in CNC machining.
• Lower Thermal Losses: Advanced winding insulation and cooling geometry reduce heat generation, prolonging bearing and winding lifecsyclex.
• One Cable Connection (OCC): Reduced installation footprint and simplified design by combining power and feedback lines into a single, highly shielded dynamic cable.
• Higher Maximum Speeds: Improved rotor dynamics enable higher maximum rotational velocities ($n_{max}$), potentially shortening overall cycle times.

Common Migration Challenges

• Firmware Limitations: If you install a newer 1FT2 or 1FK2 motor on an older SINAMICS S120 drive running a legacy firmware version (e.g., below V4.8), the drive database will not contain the electronic rating plate ID of the new motor. This requires a firmware upgrade or manual motor parameter entry using Siemens STARTER.
• Connector Redesigns: Legacy 1FK7 motors often used heavy threaded M23 power and M17 encoder connections. Modern iterations use Speed-Connect push-and-twist connectors or specific metric variants, meaning your current cables will not plug directly into the new motor.
• Brake Power Requirements: Modern holding brakes may have different current draws. Check that your 24VDC brake supply channel (integrated into the motor module or external) is capable of supplying the correct holding currents.

Step-by-Step Replacement Procedure

Follow these steps to safely swap a compromised 1FK7 motor with a replacement unit:

Step 1: Pre-Demolition Backups & Safety

1. Isolate all electrical sources in accordance with standard Lockout/Tagout (LOTO) procedures. Disconnect both main AC line inputs to the drive system and the auxiliary 24V DC auxiliary power supplies.
2. Ensure the axis is mechanically locked if it is a vertical or loaded axis subject to gravity drop.
3. Using STARTER or TIA Portal, execute a full upload of the drive parameters. Save the .ap1x or project files as a backup.

Step 2: Mechanical Decoupling & Dismounting

1. Disconnect the power and encoder/DRIVE-CLiQ cables. Store these cables in a dry area free from machine coolant.
2. Loosen and remove the mechanical coupling connecting the motor shaft to the gearbox or ball screw.
3. Support the weight of the motor (use a hoist for larger shaft heights like SH80 and SH100). Unbolt the flange mounting bolts and systematically extract the motor.

Step 3: Shaft Alignment & Installation

1. Clean the machine mounting flange and couplings. Inspect for wear or thermal scoring on the coupling interfaces.
2. Mount the replacement motor onto the mounting flange. Secure the flange bolts using a calibrated torque wrench according to Siemens structural torque limits.
3. Precisely align the shaft coupling. Incorrect radial or axial alignment leads to accelerated bearing wear and high-frequency vibrations.

Step 4: Electrical Connection

1. Clean the contact pins of your cable plugs.
2. Screw on or lock the power and feedback connectors. Ensure the O-ring seals on the connectors are fully seated to prevent ingress of oils or moisture (standard IP65 compliance).
3. Connect any auxiliary grounding straps to the motor housing.

Step 5: Commencing Operation & Parameterization

1. Power up the 24V bus of the SINAMICS system while keeping high voltage (line) disabled.
2. Access the commissioning software (STARTER, Startdrive, or SimoCom U).
3. If using an exact replacement 1FK7 with DRIVE-CLiQ, verify that the drive automatically recognizes the motor's Electronic Rating Plate.
4. If migrating to an upgraded model, modify the offline drive configuration with the new motor MLFB, load the configuration, and download it to the target Control Unit.
5. Perform a "pole position identification" (magnetic alignment) if required by the control technique.
6. Conduct low-speed jogging in manual mode to verify rotation direction and brake operation before running regular production cycles.

Frequently Asked Questions

Q1: Can I replace a 1FK7 containing an absolute encoder with a resolver-based version?

No. Reservers rely on analog sin/cos variations generated by electromagnetic coils, requiring completely different interface cards (like Siemens SMC10 or SMC20 modules) compared to digital absolute encoders using DRIVE-CLiQ. The control parameters must be radically redesigned, and extra hardware modules are needed on the SINAMICS drive side.

Q2: What is the differences between 1FK7 Compact (CT) and High Dynamic (HD) motors?

The HD variant utilizes a much thinner, longer rotor design containing high-remanence permanent magnets, resulting in minimal rotational inertia. This is reserved for rapid-start-stop axes. The CT version has a wider, shorter rotor giving it higher rotor inertia. This makes tuning simpler for systems with fluctuating load inertia.

Q3: How can I tell if my 1FK7 motor's holding brake has failed?

If the drive regularly throws faults like "Motor blocked" or overcurrent during startup, the 24VDC brake might not be opening. Perform a static torque test by supplying 24VDC manually to the brake pins (adhering to polarity) and attempts to turn the shaft by hand. If it remains locked or exhibits significant drag, the internal brake pad or spring assembly has failed.

Q4: Are original cables compatible with modern replacement 1FT2 motors?

Not without modifications. Older 1FK7 motors utilize discrete power and encoder run cables. Modern replacements like the 1FT2 use either unified One Cable Connections (OCC) or updated Speed-Connect connectors. You will need to order corresponding adaptor cables or replace the cable run with modern MOTION-CONNECT 500 or 800-series options.

Related Products & Families

To complete your motion control modernization or maintain active lines, consider these related system components:

• SINAMICS S120 Drive Modules (Booksize & Blocksize): Power units that driving 1FK7 and successor motors.
• MOTION-CONNECT Cables (6FX5002 & 6FX8002): Siemens' high-flex power and encoder signal cables designed to handle torsional stress in cable tracks.
• SIMOTICS S-1FT2 & S-1FK2: The modern industrial servo lines serving as direct technical successors.
• Sensor Modules (SMC20, SMC30, SME120): Necessary for interfacing legacy resolver or absolute feedback signals into the DRIVE-CLiQ network.

Need Help?

Navigating motor migrations, interpreting Siemens MLFB options, or finding direct replacements can be complex. Palm Parts Solution specializes in supplying a wide range of new, high-quality refurbished, and hard-to-find surplus Siemens components, including the SIMOTICS S-1FK7 servo series. Every part we sell comes backed by a comprehensive warranty, giving you peace of mind and protecting your production lines from unnecessary downtime. Get in touch with our engineering support team today to locate your direct-fit replacement motor or transition legacy components efficiently.