Mitsubishi HC-SFS502B (HCSFS502B) — 5kW AC Servo Motor with Electromagnetic Brake, MELSERVO-J2S Series

Product Identification

Part Number: HC-SFS502B

Also Searched As: HCSFS502B, HC-SFS-502B

Series: Mitsubishi MELSERVO HC-SFS Series (J2S / J2-Super Generation)

Motor Type: AC Brushless Servo Motor with Electromagnetic Brake

Condition: New In Box

Overview

The Mitsubishi HC-SFS502B is a 5kW medium-inertia AC servo motor from the MELSERVO-J2S (J2-Super) platform — the generation that succeeded the original HC-SF series and redefined what the 5kW class could deliver in terms of positioning resolution and low-speed stability.

Rated at 2,000 rpm with 23.9 Nm of continuous torque, it occupies the top of the standard HC-SFS 2000 rpm range and pairs with the MR-J2S-500 class amplifiers. The nameplate reads 3-phase AC input at 133V / 26A; output is 5kW. The "B" suffix means this variant carries a spring-applied, fail-safe electromagnetic holding brake — the version chosen whenever a powered-off axis cannot be trusted to stay in place on its own.

What separates the HC-SFS502B from its predecessor the HC-SF502B is straightforward: a 17-bit serial absolute encoder delivering 131,072 pulses per revolution, compared to the 14-bit (16,384 ppr) device in the older HC-SF series. That eight-fold increase in resolution doesn't just improve fine-positioning accuracy — it allows the J2S amplifier's speed loop to run at significantly higher bandwidth, which translates into noticeably tighter velocity control at low speed and better disturbance rejection during cutting.

Technical Specifications

The HC-SFS Series — A Step Up from the Original HC-SF

Mitsubishi's naming convention is precise enough that the difference between HC-SF and HC-SFS is easy to read once you know it: the SFS designation marks the J2-Super generation upgrade. Mechanically, the two families share flange dimensions, shaft size, and IP rating — an HC-SFS502B drops into the same mounting position as an HC-SF502B without mechanical modification. What changed is the electronics.

The J2S platform was built around a high-performance CPU and a new high-resolution encoder standard. Speed frequency response on the MR-J2S amplifier reaches 550 Hz or higher, more than double what the original J2 series achieved. The 17-bit absolute encoder in the HC-SFS motor is the enabling hardware for that improvement. With 131,072 distinct positions per revolution, the amplifier's velocity estimator has far more data per unit time, which smooths out low-speed torque ripple and makes the system genuinely more rigid against process disturbances.

For machine tool applications where the HC-SF series performed adequately but not brilliantly — particularly at very low feed rates, or in tapping cycles where the axis must reverse cleanly without dwell — the HC-SFS502B makes a practical and measurable difference.

Electromagnetic Brake: Spring-Applied, Fail-Safe

The holding brake built into the HC-SFS502B is a passive safety device, not a dynamic braking resistor. It works on the de-energise-to-engage principle: 24V DC holds the brake open and allows the shaft to rotate; cut the voltage and the spring immediately clamps the brake disc.

This matters most on vertical axes. A Z-column or quill head on a machining centre carries the full weight of the spindle assembly — typically a substantial fraction of a tonne on a mid-size VMC. When the servo amplifier is de-energised, motor torque drops to zero instantly. Without a holding brake, that load falls. The HC-SFS502B's brake stops that from happening by locking the shaft the moment 24V DC is removed, regardless of whether the removal was planned (normal shutdown) or not (power failure, amplifier fault).

The same principle applies to any axis with significant unbalanced load — pallet columns on HMCs, press back-gauges, gantry Z-axes on portal machines, and clamp mechanisms that need to hold position during processing.

Wiring note: The brake coil is an inductive load. A surge absorber must be fitted across the brake coil terminals to suppress the voltage spike at brake release and engagement. Skipping this step risks damage to relay contacts and amplifier I/O circuits over time. The MR-J2S amplifier's MBR (electromagnetic brake interlock) output provides the correct engagement timing — always route brake control through this signal rather than wiring directly from an e-stop contact.

Absolute Encoder: What It Means in Practice

Absolute encoders remember position. When a machine with HC-SFS502B motors loses power and then restores it, the amplifier reads the current absolute position from the encoder as soon as the control comes up. No homing cycle. No search for reference marks. The axis simply knows where it is.

The 17-bit serial encoder in the HC-SFS502B achieves this with battery backup in the amplifier (the A6BAT lithium cell used across the J2S family). The battery keeps the encoder's position memory alive during power-off. As long as the battery is healthy, the machine can resume from an exact known position after a power interruption.

Battery condition should be checked at regular maintenance intervals. The J2S amplifier displays a battery warning alarm before full depletion; that warning is the prompt to replace the battery before the next planned shutdown, not after.

Where This Motor Is Typically Used

VMC Z-axis and quill. The high-capacity Z-axis on a vertical machining centre needs sustained torque for heavy-duty face milling, the brake for safe servo-off, and the absolute encoder to resume after any power interruption without disturbing the workpiece setup.

HMC W-axis and pallet drive. Horizontal machining centres use the W-axis for facing-head depth positioning and pallet shuttles for workpiece transfer. Both require a combination of high torque, brake hold, and reliable absolute position across shift changes.

CNC lathe turret indexing. Large turning centres with servo-driven turrets benefit from the 5kW output for rapid index cycles, and the brake holds the turret firmly at each index position while the clamp mechanism engages.

Transfer and pallet-changing systems. Multi-station transfer lines moving heavy fixtures use servo drives at this capacity range for the combination of speed and load capability. Between stations, the brake holds the pallet index position while fixturing or processing occurs.

Large-format handling and gantry systems. Gantry-style loading systems with significant Z-height and heavy end-effectors use brake-equipped motors on vertical axes for the same fail-safe hold reasons as machine tool Z-columns.

HC-SFS Series — 2000 rpm Family Reference

All models in this table share the 200V AC class input, 2,000 rpm rated speed, 17-bit serial absolute encoder (131,072 ppr), IP65 protection, oil-sealed shaft, and straight-shaft configuration. The 352 and 502 models use the larger 176 × 176 mm flange frame.

New-In-Box: What That Condition Actually Guarantees

A factory-sealed Mitsubishi servo motor has never been wired, mounted, or powered. It arrives in original Mitsubishi packaging — inner foam cradle, carton, protective shaft and connector covers intact. Every specification listed above applies exactly as manufactured. There is no accumulated run-time, no thermal history, and no installation stress on any bearing, coupling interface, or connector.

For machine builders sourcing components for new builds, or maintenance departments building strategic spare stock, new-in-box is the only condition that provides a genuine like-for-like replacement of a factory motor without unknowns. Refurbished or repaired motors may have replaced bearings, re-potted encoder assemblies, or rewound stators — none of which are visible without disassembly. New-in-box has none of those variables.

For storage: motors stored in cool, dry, vibration-free conditions retain full specification for multiple years. If storage exceeds five years, periodic slow rotation of the shaft is advisable to redistribute bearing grease before installation.

Frequently Asked Questions

Q1: Which servo amplifiers are compatible with the HC-SFS502B?

The HC-SFS502B requires a MR-J2S-500 class amplifier. Compatible models include the MR-J2S-500A (general-purpose pulse/analog interface), MR-J2S-500B (SSCNET bus interface), MR-J2S-500CP (built-in positioning function), and MR-J2S-500CL (CC-Link interface). It is not compatible with MR-J2 (first-generation) amplifiers, which use a different encoder protocol, nor with MR-J3 or MR-J4 series amplifiers without a conversion kit.

Q2: What is the key difference between the HC-SFS502B and the HC-SF502B?

Both motors are mechanically interchangeable at the mounting flange and shaft. The critical difference is the encoder: the HC-SFS502B uses a 17-bit absolute encoder (131,072 ppr), while the older HC-SF502B uses a 14-bit encoder (16,384 ppr). The higher resolution enables the MR-J2S amplifier's faster speed loop and improves low-speed smoothness and positioning accuracy. The HC-SFS502B also requires a J2S-series amplifier; the HC-SF502B pairs with J2 or J2S amplifiers.

Q3: How should the electromagnetic brake be controlled in the machine circuit?

Use the servo amplifier's MBR (brake interlock) output signal to control the brake relay — this ensures the brake engages only after the motor has decelerated to a stop, preventing shock loading on the brake disc. The brake coil operates on 24V DC; fit a surge absorber directly across the coil terminals to suppress inductive voltage spikes. Never wire the brake directly from an emergency-stop contact without the MBR interlock in the signal path.

Q4: Does the 17-bit encoder require a battery, and what battery is used?

Yes. The serial absolute encoder requires battery backup to retain position data during power-off. The standard battery is the Mitsubishi A6BAT lithium cell, installed in the MR-J2S servo amplifier (not in the motor body). Battery life is typically several years under normal use; the amplifier will display a low-battery warning alarm before depletion. Replace the battery during a planned maintenance window when the warning appears — do not wait until the alarm forces an unplanned outage.

Q5: Can the HC-SFS502B be used to replace an HC-SF502B in an existing machine without other changes?

The mounting dimensions are compatible, but the encoder interface is different. The HC-SFS502B cannot be used as a direct drop-in replacement for an HC-SF502B on a machine running original MR-J2 amplifiers — the J2 amplifier cannot read the J2S motor's 17-bit serial encoder. The replacement would require changing the amplifier to the MR-J2S-500 series at the same time. If the machine already runs MR-J2S amplifiers, the swap is straightforward; confirm parameter settings via MR Configurator before returning the axis to production.