The MR-J3-20B is Mitsubishi Electric’s 200 W MELSERVO-J3 series servo amplifier for 200 V single-phase or three-phase AC power supply with SSCNET III optical fibre network interface — the entry-level SSCNET III model in the MR-J3-B sub-series, providing closed-loop servo control at continuous rated output current of 1.5 A for Mitsubishi HC-KFS23 and HC-MFS23 series 200 W servo motors in active multi-axis SSCNET III servo systems managed by MELSEC-Q Q172DSCPU or Q173DSCPU motion controllers. In stock at Atlantech Drives. Request your quote within 24-48 hours with worldwide shipping and 12-month warranty.
What Is the MR-J3-20B?
The MR-J3-20B is a MELSERVO-J3 series servo amplifier providing 200 W (0.2 kW) continuous output power via SSCNET III optical fibre — the SSCNET III network-commanded variant of the MR-J3-20A pulse train model, sharing the identical 200 W power stage but receiving all position and speed commands exclusively via SSCNET III plastic optical fibre at 0.888 ms communication cycle from a compatible Q-series motion controller. The MR-J3-20B is compatible with Mitsubishi HC-KFS23, HC-MFS23, and equivalent 200 W servo motors equipped with the MR-J3’s 17-bit multi-turn absolute encoder (131,072 pulses/rev). As a SSCNET III amplifier, the MR-J3-20B has no pulse train input — it cannot be operated without a connected SSCNET III motion controller. The compact 40 mm housing width makes the MR-J3-20B suitable for dense multi-axis panel installations where many low-power axes must fit within a constrained panel width. Like all MR-J3-B amplifiers, the MR-J3-20B does not include a built-in STO safety function, relying on external safety contactors for IEC 62061 / EN ISO 13849 safety compliance — a key distinction from the current-generation MR-J4-20B which includes dual-channel STO as standard.
Key Technical Specifications
- Model: MR-J3-20B
- Rated Output Power: 200 W (0.2 kW)
- Power Supply: 200–240 VAC single-phase or three-phase, 50/60 Hz
- Continuous Output Current: 1.5 A
- Maximum Output Current: 4.5 A (3× continuous peak)
- Compatible Servo Motors: HC-KFS23, HC-MFS23, HG-KR23 (J4 motor, J3 compat. mode)
- Command Interface: SSCNET III optical fibre (10 Mbps)
- Communication Cycle: 0.888 ms
- Encoder Interface: Serial 17-bit absolute encoder (131,072 pulses/rev)
- Safety Function: None built-in (external safety contactor required)
- Regenerative Brake: Built-in
- Communication: USB (MR Configurator2), RS-422 (parameter cascade)
- Operating Temperature: 0°C to 55°C
- Dimensions (W × H × D): 40 mm × 150 mm × 138 mm
- Weight: Approx. 0.8 kg
Series Comparison & Selection Guide
Within the MR-J3-B SSCNET III sub-series, the MR-J3-20B is the smallest power model alongside the MR-J3-10B (100 W) — both share the same 40 mm compact housing and are specified for light-load precision axes in multi-axis SSCNET III systems. The MR-J3-20B provides twice the continuous output of the MR-J3-10B, making it appropriate for slightly heavier axis loads — rotary indexer axes, lead screw-driven cross-slides with moderate load, and wrist axes on light-payload robots. When comparing to the current-generation equivalent, the MR-J4-20B provides the same 200 W power with 22-bit encoder resolution (versus 17-bit), built-in dual-channel STO (versus external contactor requirement), AVSC II (versus AVSC I), and 0.444 ms minimum communication cycle option (versus 0.888 ms fixed for MR-J3). For maintenance replacement in active MR-J3 SSCNET III systems where the motion controller (Q172DSCPU, Q173DSCPU) is being retained, the MR-J3-20B direct replacement is the appropriate specification. For systems where the motion controller is simultaneously being upgraded to iQ-R (RD77MS), the MR-J4-20B must replace the MR-J3-20B as the iQ-R motion module uses SSCNET III/H and cannot communicate with MR-J3 amplifiers. The MR-J3-20B is discontinued from production and available from aftermarket inventory only — plan procurement lead times accordingly for maintenance replacement scenarios.
Installation Advice
The MR-J3-20B’s SSCNET III fibre connections (CN1A input, CN1B output) use standard plastic optical fibre (POF) with push-pull connectors — the same connectors and cable type used by MR-J4-B SSCNET III/H amplifiers, enabling existing POF cable infrastructure to be reused if the system is later upgraded from MR-J3 to MR-J4. When installing a replacement MR-J3-20B in an existing SSCNET III chain, power down the complete system before removing or inserting SSCNET III fibre connections — inserting or removing POF connectors while the SSCNET III system is powered can generate optical transients that cause communication errors on adjacent amplifiers in the chain, potentially triggering servo alarms across the system. After installing the replacement MR-J3-20B and reconnecting all cables, write the correct machine-specific servo parameters to the new amplifier using MR Configurator2 via USB before enabling servo operation — the replacement unit ships with factory default parameters that will not match the original machine’s tuned servo gains. For the 200 W MR-J3-20B, the servo parameter set is typically small (10–15 key parameters) compared to higher-power models, but all gain parameters (PG1, VG1, VIC, VG2) must be correctly set before the first servo-on command to avoid mechanical oscillation or AL.50 overload on light-load 200 W axes. Keep a printed or digital copy of the replaced unit’s MR Configurator2 parameter file in the machine maintenance documentation to enable rapid parameter recovery without relying on memory or calculation.
Frequently Asked Questions
Q: Can the MR-J3-20B operate as a standalone servo amplifier for JOG testing without a SSCNET III motion controller connected?
A: No. The MR-J3-20B receives all motion commands exclusively via SSCNET III — without a connected Q172DSCPU or Q173DSCPU motion controller, no servo motion commands can be issued. For JOG testing without a motion controller, MR Configurator2’s JOG operation function can command the motor via USB connection to the amplifier — this provides basic position, speed, and JOG commands for commissioning and test purposes without requiring the motion controller to be online.
Q: Is the MR-J3-20B compatible with the Q170MCPU compact motion controller?
A: Yes. The Q170MCPU is a MELSEC-Q compact module that integrates a motion CPU with SSCNET III interface (up to 8 axes), and the MR-J3-20B is fully compatible as a SSCNET III slave amplifier on a Q170MCPU-managed chain. The Q170MCPU provides the same SSCNET III communication as the Q172DSCPU and Q173DSCPU for the amplifiers it manages — no special configuration is required on the MR-J3-20B to switch between these motion controllers.
Q: Does the MR-J3-20B support fully closed-loop control with a separate load-side encoder?
A: The MR-J3-20B supports a limited dual encoder function via the CN2L connector for load-side encoder feedback, enabling fully closed-loop position control that compensates for ball screw backlash and mechanical compliance. The fully closed-loop function in MR-J3 amplifiers is less sophisticated than the MR-J4 implementation — verify the specific closed-loop configuration requirements against the MR-J3-20B hardware manual before specifying this option for precision applications.
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