The MR-J4-70B is Mitsubishi Electric’s 750 W MELSERVO-J4 series servo amplifier for 200 V single-phase or three-phase AC power supply with SSCNET III/H optical fibre network interface — providing closed-loop servo control at continuous rated output current of 5.0 A for Mitsubishi HG-SR and HG-KR series servo motors in the 750 W frame, covering the mid-range power requirement in multi-axis SSCNET III/H servo systems for machine tool feed axes, packaging machine servo axes, and conveyor positioning systems where 750 W of continuous servo power provides the correct balance of speed and torque for medium-load axis applications. The MR-J4-70B is available through Atlantech Drives — quote within 24-48 hours, worldwide express shipping, 12-month warranty.
What Is the MR-J4-70B?
The MR-J4-70B is a MELSERVO-J4 series servo amplifier providing 750 W (0.75 kW) continuous output power via SSCNET III/H optical fibre, representing the mid-range capacity step between the small-frame 200 W MR-J4-20B and the 1 kW MR-J4-100B in the MR-J4-B SSCNET III/H sub-series. The amplifier is compatible with Mitsubishi HG-SR52 (500 W), HG-SR72 (750 W), HG-KR73, and equivalent servo motors equipped with the standard 22-bit multi-turn absolute encoder. Like all MR-J4-B variants, the MR-J4-70B receives all position and speed commands exclusively via SSCNET III/H optical fibre at 0.888 ms or 0.444 ms cycle time — there is no pulse train input on the B-series amplifiers. The MR-J4-70B’s 55 mm housing width is wider than the 40 mm MR-J4-10B and MR-J4-20B, reflecting the larger power components required for 750 W output — this width difference should be noted when planning a multi-axis panel layout where MR-J4-10B/20B and MR-J4-70B amplifiers are installed side by side. The amplifier includes the full MR-J4 feature set: AVSC II, STO safety function (IEC 61800-5-2 SIL2, EN ISO 13849-1 PLe), fully closed-loop dual encoder support, and MR Configurator2 USB commissioning interface.
Key Technical Specifications
- Model: MR-J4-70B
- Rated Output Power: 750 W (0.75 kW)
- Power Supply: 200–240 VAC single-phase or three-phase, 50/60 Hz
- Continuous Output Current: 5.0 A
- Maximum Output Current: 15.0 A (3× continuous peak)
- Compatible Servo Motors: HG-SR52, HG-SR72, HG-KR73, HG-KR43 and equivalent
- Command Interface: SSCNET III/H optical fibre (150 Mbps full-duplex)
- Communication Cycle: 0.444 ms or 0.888 ms (selectable)
- Encoder Interface: Serial 22-bit absolute encoder (262,144 pulses/rev)
- Safety Function: STO (Safe Torque Off), IEC 61800-5-2 SIL2 / EN ISO 13849-1 PLe
- Regenerative Brake: Built-in, external MR-RB series resistor connectable
- Housing Width: 55 mm
- Operating Temperature: 0°C to 55°C
- Dimensions (W × H × D): 55 mm × 170 mm × 165 mm
- Weight: Approx. 1.4 kg
Typical Industrial Applications
The MR-J4-70B is specified for medium-load servo axes in SSCNET III/H multi-axis machine systems where 750 W of continuous servo power provides the optimum balance of motor frame size, axis speed, and continuous torque capability. In horizontal machining centre 3-axis feed drive systems (X, Y, Z), the MR-J4-70B is frequently specified for the Z-axis (vertical spindle head) where 750 W provides adequate thrust for the spindle head weight plus cutting force reaction, while the longer X and Y axes requiring higher sustained feed forces specify larger MR-J4-B amplifiers. In multi-axis packaging machine drives — where fill station, seal station, and cut station axes each require independent servo positioning — the MR-J4-70B covers the majority of axis power requirements in standard sachet, blister, and flow wrap packaging machinery up to 200 packages per minute. Rotary indexing table drives for multi-station assembly machines commonly specify the MR-J4-70B when the combined table and tooling mass requires 750 W of servo power to achieve the required index time and settling accuracy. In robotics, the MR-J4-70B drives the wrist axes (axes 4, 5, 6) of medium-payload industrial robots in the 20–50 kg payload range, where the wrist axis torque requirements at rated payload and speed fall within the 750 W motor continuous rating.
Replacement & Upgrade Notes
The MR-J4-70B is the direct SSCNET III/H successor to the MR-J3-70B in the same power class — the 750 W SSCNET III/H amplifier for medium-load multi-axis servo systems. The MR-J4-70B provides substantial improvements over the MR-J3-70B: 22-bit encoder resolution versus 17-bit (MR-J3), AVSC II versus AVSC I, STO safety function (eliminating the need for an external safety relay for STO compliance), 0.444 ms minimum communication cycle versus 0.888 ms (MR-J3 minimum), and improved auto-tuning convergence for faster commissioning. MR-J3-compatible HG-SR and HG-KR series motors with 17-bit encoders can continue operating with the MR-J4-70B in a compatibility mode, enabling phased upgrade where the amplifier is replaced first and the motor (with 22-bit absolute encoder) is upgraded in a subsequent maintenance cycle. The MR-J4-70B’s parameter structure is largely compatible with the MR-J3-70B — most servo gain and control parameters have equivalent settings in the MR-J4 parameter set, and MR Configurator2 includes a parameter conversion function that translates MR-J3 parameter files to MR-J4 format as a starting point for MR-J4-70B commissioning. For systems where the MR-J4-70B is being introduced alongside retained MR-J3-70B amplifiers on the same SSCNET III/H chain, note that SSCNET III/H (MR-J4) and SSCNET III (MR-J3) are physically identical fibre connections but use different communication protocols — MR-J3 and MR-J4 amplifiers cannot share the same SSCNET chain.
Frequently Asked Questions
Q: Why is the MR-J4-70B rated at 750 W rather than 700 W, despite the «70» in the model designation?
A: Mitsubishi’s MR-J4 model numbering uses a simplified numeric code that does not directly represent watts — the «70» designates the 750 W power class within the model numbering scheme, consistent with Mitsubishi’s legacy MELSERVO model designation conventions where «70» historically mapped to the 750 W/0.75 kW power class. The continuous output power is 750 W as documented in the MR-J4-70B hardware manual and servo amplifier catalogue.
Q: Can the MR-J4-70B control a servo motor in speed control mode (velocity reference) rather than position control mode via SSCNET III/H?
A: Yes. The motion controller can command the MR-J4-70B in speed control mode via SSCNET III/H by selecting the speed control operating mode in the motion controller’s servo program. In speed control mode, the motion controller sends speed reference values rather than position setpoints to the MR-J4-70B at each communication cycle, and the amplifier’s speed loop maintains the commanded speed. Speed control mode is used for spindle drive applications, winding tension control, and conveyor speed synchronisation where speed regulation rather than position accuracy is the primary control objective.
Q: What is the MR-J4-70B’s built-in regenerative resistor capacity, and when is an external resistor required?
A: The MR-J4-70B’s built-in regenerative resistor has a continuous rated power of approximately 30 W, sufficient for standard 750 W motor decelerations in light-to-medium duty cycle applications. For high-inertia loads (rotary tables, large gantry structures) with frequent deceleration cycles exceeding 30 W average regenerative power, an external MR-RB series resistor connected to the MR-J4-70B’s P and C terminals is required. Calculate the average regenerative power using the application’s deceleration parameters and verify against the 30 W built-in limit before deciding whether an external resistor is needed.
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