The MR-J3-70A is a 700 W servo amplifier from Mitsubishi Electric, part of the MELSERVO-J3 series with general-purpose AC interface, designed for high-accuracy positioning and speed control in factory automation applications. In stock at Atlantech Drives. Request your quote within 24–48 hours with worldwide shipping and 12-month warranty.
What Is the Mitsubishi MR-J3-70A?
The MR-J3-70A is the 700 W model of the MELSERVO-J3 -A sub-series, which uses analogue/pulse train command interface (as opposed to the -B suffix SSCNET III fibre-optic network interface). It accepts ±10 V DC analogue speed or torque commands, or pulse train position commands from a controller or motion CPU, making it compatible with a wide range of positioning controllers, including third-party systems. The J3 series uses a 262,144-pulse/rev (18-bit) absolute encoder as standard, delivering high positioning resolution without the need for an additional encoder option. The MR-J3-70A is suitable for pairing with HG-SR, HG-MR, and HC-LP series servo motors at the 700 W rating.
Key Technical Specifications
- Rated output: 700 W
- Rated voltage: 200–230 V AC, 1-phase or 3-phase, 50/60 Hz
- Rated current: 5.0 A (3-phase input)
- Command interface: Analogue (±10 V), pulse train (open collector / differential)
- Encoder compatibility: 18-bit absolute encoder (262,144 pulses/rev)
- Control modes: Position, speed, torque, position/speed switching
- Max. torque: 300% instantaneous
- Regenerative option: Built-in regenerative resistor; external option available
- Communication: RS-422 (MR Configurator, MR-J3-D01 option for CC-Link)
- Dynamic brake: Built-in
- Enclosure: Open chassis (IP00), panel-mount
- Operating temperature: 0 to 55°C
- Dimensions (W × H × D): 55 × 170 × 168 mm
Compatibility & System Integration
The MR-J3-70A interfaces directly with Mitsubishi positioning controllers including the QD75MH, LD75MH, and FX3U-20SSC-H via pulse train output. For analogue speed control from a MELSEC-Q or iQ-R analog output module, connect the speed command to VC and SG terminals and select speed control mode via CN1 input signals. Compatible servo motors at 700 W include the HC-LP72, HG-SR72, and HG-MR73 — always verify the specific motor-amplifier combination in the MELSERVO-J3 catalogue before ordering, as encoder wiring and brake specifications differ between motor families. For multi-axis systems requiring synchronised motion, the MR-J3-70A can be connected to an MR-J3-D01 option card to enable CC-Link communication, allowing speed and torque references to be issued over the network rather than via hardwired analogue signals. Integration with third-party controllers via pulse train is straightforward using the CN1 differential pulse input (PP, NP, PG pins), which accepts open collector or line driver signals up to 4 Mpps.
Troubleshooting Guide
- AL.16 (Encoder error 1): Typically caused by a damaged or incorrectly wired encoder cable. Inspect the CN2 encoder connector for bent pins, and verify that the encoder cable shield is connected at the amplifier end only. Measure encoder cable continuity with the motor stationary — intermittent faults often only appear under mechanical load.
- AL.24 (Ground fault): Indicates current leakage between the motor phase windings and the motor frame. Disconnect the motor cable at CN2 and measure insulation resistance between each U/V/W phase and PE with a 500 V megohmmeter — readings below 1 MΩ indicate motor insulation degradation. Also check for damaged motor cable insulation.
- AL.52 (Error excessive): The position error counter has exceeded the in-position tolerance set in parameter Pr.10. For pulse train positioning systems, verify that the command pulse frequency does not exceed the amplifier’s rated input of 4 Mpps. For analogue systems, check that the speed command signal is within ±10 V — overvoltage on VC can cause runaway and trigger this alarm.
- Communication loss to MR Configurator: The MR-J3-70A uses RS-422 on the CN3 connector, not RS-232. Ensure you are using an RS-422-to-USB converter (Mitsubishi MR-J3USBCBL3M or compatible) and that the correct COM port is selected in MR Configurator. RS-232 direct connection will not work.
Frequently Asked Questions
Q: Can the MR-J3-70A be used with MR-J4 series servo motors?
A: No. MELSERVO-J3 and J4 series use different encoder interfaces and connector pinouts that are not cross-compatible. MR-J4 motors with their 22-bit encoder cannot be driven by MR-J3 amplifiers. Use MR-J3-compatible motors (HG-MR, HG-SR, HC-LP series) with the MR-J3-70A.
Q: Does the MR-J3-70A support absolute position detection without a battery?
A: No. Absolute position retention requires an MR-J3BAT battery unit connected to the CN4 connector. Without the battery, the encoder operates in incremental mode and a homing (zero return) operation is required at every power-up cycle.
Q: What is the maximum cable length between the MR-J3-70A and the servo motor?
A: The maximum encoder cable length is 50 m using Mitsubishi standard encoder cables. The maximum power cable length is also 50 m, though for cables exceeding 10 m it is advisable to check the voltage drop against motor rated voltage and to use cable with the correct conductor cross-section specified in the MR-J3 instruction manual.
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