The MR-J3-500A is Mitsubishi Electric’s 5 kW MELSERVO-J3 series servo amplifier for 200 V single-phase or three-phase AC power supply with pulse train position command input — a legacy servo amplifier from Mitsubishi’s third-generation MELSERVO platform, providing 5 kW continuous servo control at 23 A for HC-SFS502 and HC-RFS503 series servo motors in active pulse train-commanded servo systems where direct maintenance replacement is required without platform migration. Atlantech Drives holds stock of the MR-J3-500A. Contact us for fast worldwide delivery and competitive pricing.
What Is the MR-J3-500A?
The MR-J3-500A is a MELSERVO-J3 series servo amplifier providing 5 kW (5,000 W) continuous output power for Mitsubishi HC-SFS502, HC-RFS503, and equivalent 5 kW servo motors equipped with the MR-J3’s 17-bit multi-turn absolute encoder. The «A» suffix designates the pulse train input variant — the MR-J3-500A accepts position command pulses from any host controller (Mitsubishi QD75MH4, FX2N-10PG, FX3U-2PG, third-party CNC or motion controller) via open-collector or differential RS-422A pulse input at up to 4 Mpps. The 5 kW power stage provides 23 A continuous output current with 69 A peak (3×), enabling high-torque positioning at the rated capacity for heavy-load machine tool axes, large gantry systems, and high-power industrial servo applications built on the MELSERVO-J3 platform during its active production period (approximately 2004–2013). The MR-J3-500A implements the MELSERVO-J3 three-loop servo control architecture with 2 kHz current loop bandwidth, Advanced Vibration Suppression Control (AVSC, first generation, single notch filter), and auto-tuning via MR Configurator2. The amplifier does not include a built-in STO safety function — the 5 kW power level in a safety-compliant J3 installation requires an external safety contactor rated for the motor’s full operating current.
Key Technical Specifications
- Model: MR-J3-500A
- Rated Output Power: 5 kW (5,000 W)
- Power Supply: 200–240 VAC single-phase or three-phase, 50/60 Hz
- Continuous Output Current: 23.0 A
- Maximum Output Current: 69.0 A (3× continuous peak)
- Compatible Servo Motors: HC-SFS502, HC-RFS503, HG-SR502 (J4 motor, J3 compat. mode)
- Command Interface: Pulse train input (open-collector or differential RS-422A)
- Maximum Input Pulse Frequency: 4 Mpps (differential), 200 kpps (open-collector)
- Encoder Interface: Serial 17-bit absolute encoder (131,072 pulses/rev)
- Safety Function: None built-in (external safety contactor required)
- Regenerative Brake: Built-in, external MR-RB series resistor connectable
- Communication: USB (MR Configurator2), RS-422 (multi-axis)
- Operating Temperature: 0°C to 55°C
- Dimensions (W × H × D): 130 mm × 250 mm × 182 mm
- Weight: Approx. 3.5 kg
Typical Industrial Applications
The MR-J3-500A is found in active service in high-power pulse-train-commanded servo axis applications built during the MR-J3 era. In large horizontal machining centres where the X, Y, and Z feed axes each require 5 kW of continuous servo power, the MR-J3-500A drives these axes under the command of a Mitsubishi QD75MH4 or QD75D4 positioning module — the pulse train interface providing adequate axis synchronisation for 3-axis machining without the tight multi-axis coordination of SSCNET. Large-format router and engraving machines for signage and architectural applications use the MR-J3-500A for gantry axis drives where sustained 5 kW power handles heavy aluminium and composite material cutting forces. In automated waterjet cutting systems, the MR-J3-500A drives the X-axis traverse where the combined gantry mass and water pressure reaction force demands sustained 5 kW at rated traverse speed. Press brake backstop positioning systems with servo backstop axis weights of 50–100 kg use the MR-J3-500A to provide the continuous thrust force required for rapid backstop positioning between consecutive bends. Robotic welding and dispensing gantry systems built with Mitsubishi J3-era motion controllers use the MR-J3-500A for the primary gantry traverse axes where 5 kW provides adequate power for the combination of carriage mass, tool weight, and process reaction forces at the required traverse speeds.
Replacement & Upgrade Notes
The MR-J3-500A has been discontinued from Mitsubishi production and is sourced from aftermarket inventory. For direct maintenance replacement, the MR-J3-500A is specified when the existing HC-SFS502 or HC-RFS503 servo motor is being retained, the pulse train command wiring from the host controller is unchanged, and upgrading to MR-J4 is deferred. The current-generation direct upgrade is the MR-J4-500A, which is physically compatible (same 130 mm housing width and same mounting pattern) and accepts the same HC-series servo motors in J3 motor compatibility mode (PA22 = 1) — enabling amplifier-only upgrade without motor or wiring changes beyond updating the servo parameter settings. Key MR-J4-500A improvements over the MR-J3-500A include 22-bit encoder resolution (versus 17-bit), built-in STO eliminating the external safety contactor, AVSC II dual notch filter (versus single notch AVSC I), and improved auto-tuning convergence. For facilities with multiple MR-J3-500A units across high-value machine tool systems, the risk profile of continued MR-J3-500A operation increases as the amplifier age approaches 15+ years — DC bus capacitor life, cooling fan bearing life, and increasing difficulty sourcing authentic replacement units are the three primary risk factors. A proactive MR-J3-500A-to-MR-J4-500A migration programme during scheduled production maintenance, rather than reactive replacement at failure, reduces unplanned downtime risk and provides the safety function compliance improvement as a concurrent benefit.
Frequently Asked Questions
Q: Can an MR-J3-500A with a failed DC bus capacitor be repaired, or must the complete amplifier be replaced?
A: DC bus capacitor replacement in the MR-J3-500A is technically feasible but requires specialist servo amplifier repair capability — correct capacitor type and voltage rating must be matched, and the repair must include functional testing under load to verify ripple current performance and DC bus voltage regulation before reinstallation. Mitsubishi authorised service centres can perform this repair; independent repair shops with servo drive experience can also perform capacitor replacement if the correct capacitors can be sourced. For machines where extended downtime during repair is acceptable, authorised refurbishment is cost-effective compared to sourcing a replacement MR-J3-500A at aftermarket premium pricing. For machines requiring rapid return to service, a replacement MR-J3-500A from stock — or an MR-J4-500A upgrade — is faster than repair.
Q: What external safety contactor rating is required for the MR-J3-500A at 5 kW?
A: The external safety contactor in the MR-J3-500A’s main circuit must be rated for the servo motor’s maximum operating current — at 5 kW and 200 VAC, the motor’s maximum continuous current is 23 A and the peak current is 69 A. A safety contactor rated for at least 25 A AC-3 duty (contactor category for induction motor switching) at 200 VAC provides adequate continuous current rating, but the 69 A peak inrush on acceleration must also be verified against the contactor’s make current rating. Mitsubishi’s safety sub-function guide for MR-J3 systems recommends specific contactor models — consult the MR-J3 safety sub-function manual for the approved contactor specifications at 5 kW output.
Q: Is the MR-J3-500A compatible with the FX3U-20SSC-H SSCNET III/H adapter?
A: No. The MR-J3-500A is a pulse train input amplifier — it has no SSCNET interface of any kind and cannot connect to the FX3U-20SSC-H. The FX3U-20SSC-H communicates via SSCNET III/H protocol with MR-J4-B series amplifiers only. To control the MR-J3-500A from an FX3U base unit, use the FX3U-2PG pulse output positioning adapter which generates the required pulse train signal at up to 100 kHz for the MR-J3-500A’s pulse input.
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