Mitsubishi HC-SF502BK (HCSF502BK) — 5kW AC Servo Motor, Keyed Shaft + Brake, MELSERVO J2 Series

Product Identification

Part Number: HC-SF502BK

Also Searched As: HCSF502BK, HC-SF-502BK

Series: Mitsubishi MELSERVO HC-SF (J2 Generation)

Motor Type: AC Brushless Servo Motor — Keyed Shaft with Electromagnetic Brake, 2000 rpm

Condition: New In Box, Factory Sealed

Overview

The Mitsubishi HC-SF502BK is a 5kW medium-inertia AC brushless servo motor from the original MELSERVO J2 platform, carrying both features that define its variant: a machined keyway on the drive shaft and a spring-applied electromagnetic brake. At 23.9 Nm continuous and 71.6 Nm peak, it delivers the output capacity that heavy machine tool axes and high-load automation drives require, while the brake ensures that capacity comes with the fail-safe mechanical hold that demanding applications cannot do without.

This specific combination — keyed shaft plus brake at 5kW — appears on a recognisable category of axis. Large CNC machine Z-columns carrying heavy spindle assemblies that need a positive coupling interface and a mechanical hold against gravity. Rotary table drives with keyed gear hubs that must hold index position under power-off conditions. Transfer and shuttle mechanisms where the motor-side coupling requires a keyway and the loaded axis cannot rely solely on servo lock between cycles. The HC-SF502BK is purpose-built for exactly this intersection of requirements.

As a J2-generation motor, the HC-SF502BK carries the 14-bit serial absolute encoder at 16,384 positions per revolution and maintains full compatibility with both the original MR-J2-500 amplifier family and the later MR-J2S-500 platform. That dual-generation amplifier compatibility is one of the most practically useful aspects of the HC-SF series — machines running first-generation MR-J2 hardware can accept this motor without any amplifier change, making it the clean sourcing target for a large installed base of J2-era machine tools.

Technical Specifications

5kW, 23.9 Nm: Where This Motor Gets Specified

Five kilowatts at 2,000 rpm sits in a demanding part of the servo motor capacity range — above the mid-range axes that 2kW and 3.5kW motors handle, below the largest standard capacity at 7kW. The HC-SF502BK is the motor that gets specified when a 3.5kW drive runs into its torque ceiling under production conditions and a 7kW unit would be oversized and harder to justify on panel space and power supply capacity.

The 23.9 Nm continuous rating is what the motor can sustain indefinitely within its thermal limits. Heavy VMC table feeds pushing large workpieces at sustained cutting feedrates, HMC pallet shuttle drives cycling repeatedly under loaded pallet weight, large rotary table axes contouring through multi-face machining programs — these are the operating conditions where the continuous torque figure determines whether the motor runs within its thermal budget or approaches overload over a production shift.

The 71.6 Nm peak — three times continuous — is the amplifier's resource for acceleration. Moving a large, high-inertia load from rest to rapid traverse speed requires a torque impulse considerably above the continuous figure. The peak rating defines the ceiling of that impulse; the duty cycle determines how often the motor can use it without approaching its thermal limits. A well-matched axis application uses the peak capacity during acceleration phases and returns to well within the continuous rating during the cutting or transfer portion of each cycle.

The 7.5 kVA power facility demand governs electrical supply design, panel wiring, and regenerative energy handling. At 25A rated current, cable sizing, fusing, and contactor selection must all be appropriate for this current level. Regeneration from decelerating high-inertia loads — a loaded pallet decelerating at high shuttle speed, a heavy Z-column stopping from rapid traverse — returns energy to the amplifier DC bus. The MR-J2 or MR-J2S-500 amplifier handles this, but regenerative resistor capacity should be confirmed for axes with frequent high-energy deceleration events.

Keyed Shaft at 5kW: Engineering the Connection

Twenty-three point nine Newton-metres at continuous rated torque is a substantial load for a shaft-to-hub coupling interface to handle reliably over years of production service. Seventy-one point six Newton-metres peak is the actual design target: this is what the coupling must transmit without slip under the worst operating condition the axis will encounter — a maximum-acceleration traverse immediately followed by a sharp reversal, a rapid deceleration from full rapid traverse, or a sudden load shock from an interrupted cut.

On a plain straight shaft at this capacity, the friction-clamp coupling hub must be sized and installed with significant clamping force to guarantee no slip at 71.6 Nm. The margin is workable but not generous, and it depends on consistent installation torque, clean shaft surfaces, and a hub bore tolerance that achieves the specified interference. Any deviation — a slightly oversized bore, contaminated shaft surface, undertorqued clamping fasteners — reduces the margin, and on a 5kW axis with a heavy load, a slip event means position loss on a significant piece of machinery.

The keyway on the HC-SF502BK removes that dependency. The torque path runs through the key's shear cross-section, not through surface friction. Under the cyclic, reversing, and shock loads that characterise production machine tool operation, a properly fitted keyed connection does not develop micro-slip. The coupling's clamp still contributes to the joint's axial retention and overall stiffness, but the torque transmission is mechanically guaranteed by the key.

The keyway serves driven-side designs that specifically require it. Gear hubs on worm-gear rotary table drives, timing belt pulleys on large ball-screw axes, sprocket drives on pallet transfer chains, and precision coupling hubs on direct-coupled mechanisms — all of these either require or are better served by a keyed shaft. If the driven-side hub has a keyway machined in it, the motor shaft needs one too, and the HC-SF502BK is the specification.

Installation guidance: use the shaft-end threaded hole to draw the coupling hub axially onto the shaft using a drawbolt and washer rather than pressing or driving it on by impact. At this frame size, any axial impact during installation travels through the shaft to the encoder disc and bearing assembly at the motor's rear. The damage that results may not cause an immediate fault — it often appears weeks or months later as intermittent encoder errors that are extremely difficult to trace back to installation. The drawbolt method takes thirty seconds longer than a mallet. It is always worth the time.

Electromagnetic Brake: Fail-Safe Hold at 5kW

The spring-applied brake on the HC-SF502BK is a fail-safe device. The spring engages when 24V DC is removed — the shaft is clamped mechanically, independent of amplifier state, control power, or any software condition. This characteristic is what makes it genuinely fail-safe rather than merely electrically held: the default state is locked.

At 5kW, the load consequences of an unbraked axis losing servo control scale accordingly. A 5kW servo motor driving a large VMC Z-column carries the full weight of the machine's spindle head — potentially several hundred kilograms of steel positioned above the workpiece and fixturing. When the amplifier trips, servo current drops to zero in milliseconds. On a braked motor, the spring engages and the column holds. On an unbraked motor, the column follows gravity until the amplifier's dynamic brake function or mechanical friction brings it to rest — and the distance it travels before stopping is not negligible.

The brake is also relevant during planned machine shutdowns. Modern CNC machines cycle through many more planned stops per shift than emergency events — tool changes, programme pauses, shift-end shutdowns. On each of these, the Z-axis is parked at a known height. The brake holds it there without servo current, without consuming amplifier power, and without any risk of the column drifting if the servo loop relaxes or an amplifier fault occurs during the stop.

Three installation requirements that apply specifically at this capacity level:

Use the MR-J2 or MR-J2S amplifier's MBR (electromagnetic brake interlock) output to control the brake relay. The MBR signal times the brake engagement to occur only after the amplifier has decelerated the motor to a complete stop. At 5kW, engaging the spring against a rotating shaft generates a significant shock load — the kind that damages brake friction surfaces rapidly and shortens brake service life from years to weeks in severe cases.

Fit a surge absorber directly across the brake coil terminals. The coil is an inductive load; switching off 24V DC without suppression generates a voltage spike that can damage the relay output or other components in the brake circuit. The absorber must be positioned at the coil, not at the relay — distance along the cable reduces its effectiveness.

For vertical axes, Mitsubishi's published guidance places the recommended maximum static unbalanced torque at 70% or less of the motor's rated torque — approximately 16.7 Nm at the motor shaft for the HC-SF502BK. Axes with higher gravitational unbalance should include supplemental counterbalancing such as a pneumatic balance cylinder rather than relying on the servo torque and brake alone.

J2 Generation Encoder and Amplifier Compatibility

The HC-SF502BK uses the original J2 platform's 14-bit serial absolute encoder at 16,384 ppr. The serial absolute design transmits a digital position word to the amplifier at each sample interval and maintains a multi-turn absolute counter through power-off via battery backup. No incremental counting, no reference return required, and no position uncertainty after power events — as long as the battery is healthy.

The A6BAT lithium battery lives in the servo amplifier, not in the motor body. It is replaced at the amplifier as part of planned maintenance, independent of any work on the motor. The amplifier's battery alarm triggers when cell voltage falls below the safe threshold; replacing the A6BAT before full depletion preserves the absolute position data. A depleted battery means the absolute counter is reset and the machine requires a reference return cycle before production resumes.

Amplifier compatibility is the J2 generation's practical strength for machines currently in service. The 14-bit HC-SF encoder is readable by both generation of Mitsubishi 500-class servo amplifiers:

• MR-J2-500A / MR-J2-500B — Original J2-generation amplifiers. Full compatibility, no restrictions.
• MR-J2S-500A / MR-J2S-500B / MR-J2S-500CP — J2-Super amplifiers, fully backward-compatible with the J2 encoder.

The later HC-SFS502BK with 17-bit encoder runs exclusively on MR-J2S-500 amplifiers. For the large installed base of machines running original MR-J2-500 hardware, the HC-SF502BK is the only correct motor for a like-for-like replacement — the HC-SFS502BK will fault on encoder error without an amplifier upgrade.

HC-SF502BK vs HC-SFS502BK: The Replacement Decision

Output performance is identical. Mounting is identical. The encoder generation and resulting amplifier requirement is the only operative difference. Check the amplifier model before sourcing: MR-J2-500 (without S) means HC-SF502BK; MR-J2S-500 means either motor works, with the HC-SFS502BK offering higher encoder resolution where the application can use it.

HC-SF 2000 rpm Range — Where 5kW Sits

The HC-SF502BK shares the 176 × 176 mm flange with every motor from 2kW to 7kW in the HC-SF 2000 rpm range. Suffix combinations follow a consistent pattern across the whole family: no suffix = straight shaft, no brake; B = straight shaft with brake; K = keyed shaft, no brake; BK = keyed shaft with brake. The HC-SF502BK is the keyed-plus-brake variant at 5kW.

Typical Applications

VMC Z-axis on large vertical machining centres. The Z-column carrying a full-size spindle head is the application that makes the BK suffix specification almost automatic. The column is gravity-loaded; the motor needs a mechanical hold when servo is off; and the coupling interface to the ballscrew is typically a rigid coupling with a keyed bore that requires a keyed motor shaft. The HC-SF502BK covers all three requirements cleanly.

HMC W-axis and deep-bore quill drives. Horizontal machining centre W-axis stroke and quill extension axes move heavy spindle and tooling assemblies. At 5kW with 23.9 Nm continuous, the HC-SF502BK handles the sustained feed force of large-diameter boring operations, and the brake holds the quill in position during tool changes and machine stops.

Large rotary table index drives. Rotary table indexing axes on machining centres and transfer lines use gear-driven servo inputs where the motor-side gear hub is keyed to the shaft. The index position must be held mechanically between cuts — the brake provides that hold at every station — and the absolute encoder confirms exact angular position on every restart without a reference return cycle.

Pallet shuttle and transfer systems on HMCs. Pallet changers on medium-to-large horizontal machining centres transfer pallets weighing several hundred kilograms. The repeated start-stop duty under loaded conditions suits the HC-SF502BK's continuous torque rating, the keyed shaft handles the positive coupling drive design typical of pallet shuttle mechanisms, and the brake secures the pallet at each station against any movement during clamping and machining.

Servo-driven press feed and material handling axes. Coil feed servo drives on mechanical presses and servo-controlled material handling axes with vertical or inclined movement components combine the need for substantial torque, positive shaft coupling, and reliable mechanical hold between feed strokes. The HC-SF502BK addresses all three in the J2-compatible package that the original machine's amplifier hardware requires.

New In Box, Factory Sealed

Factory sealed means original Mitsubishi packaging — outer carton intact, inner foam cradle undisturbed, all protective covers in place. The shaft keyway and key slot are protected by the shaft-end cap; encoder and power connector ports remain covered; the IP65 oil seal is in as-manufactured condition. No prior installation, no thermal history, no mechanical wear.

For a production machine stopped waiting on this motor, in-stock new-in-box removes repair turnaround time from the recovery path entirely. For planned maintenance spares inventory — particularly on multi-machine operations where this capacity and configuration appears on multiple axes — factory-sealed stock provides known-condition units that can be commissioned directly.

At the weight typical of this frame class with brake assembly, the HC-SF502BK ships in robust packaging suited to its mass. Stored under stable temperature and low-humidity conditions away from vibration, factory-sealed stock maintains full specification over several years. Beyond five years, a slow shaft rotation as part of the pre-commissioning inspection redistributes bearing grease before first power-up.

Frequently Asked Questions

Q1: Which amplifiers are compatible with the HC-SF502BK?

The HC-SF502BK is compatible with both J2-generation and J2-Super (J2S) amplifiers at the 500 class. Confirmed compatible models are MR-J2-500A and MR-J2-500B (original J2 generation), and MR-J2S-500A, MR-J2S-500B, and MR-J2S-500CP (J2-Super generation). The 14-bit J2 encoder is fully readable by both amplifier platforms. The HC-SF502BK is not compatible with MR-J3 or MR-J4 amplifiers.

Q2: What is the difference between the HC-SF502BK and the HC-SFS502BK?

Both motors deliver 23.9 Nm continuously and 71.6 Nm peak on a 176 × 176 mm flange with a keyed shaft and electromagnetic brake — physically interchangeable at the mount. The distinction is the encoder: the HC-SF502BK uses a 14-bit encoder (16,384 ppr) and works with MR-J2 and MR-J2S amplifiers. The HC-SFS502BK uses a 17-bit encoder (131,072 ppr) and requires MR-J2S amplifiers only. If the machine currently runs MR-J2-500 amplifiers, the HC-SF502BK is the only correct sourcing option. If MR-J2S-500 amplifiers are installed, either motor is compatible.

Q3: How does the electromagnetic brake work, and what is the correct wiring practice?

The brake is spring-applied and fail-safe: 24V DC holds the brake disc clear, allowing free shaft rotation. Remove the 24V and the spring immediately clamps the shaft. It is a holding device only — it must engage only after the amplifier has stopped the motor. Always use the MR-J2 or MR-J2S amplifier's MBR (brake interlock) output to control the brake relay, timing engagement to occur after motor deceleration is complete. Fit a surge absorber across the brake coil terminals to protect against inductive voltage spikes at switch-off.

Q4: Where is the absolute encoder battery, and when should it be replaced?

The Mitsubishi A6BAT lithium battery that backs the 14-bit absolute encoder is installed inside the servo amplifier — not in the motor. It retains the multi-turn absolute position counter through any power interruption, eliminating homing cycles on restart. Replace the A6BAT when the amplifier displays its low-battery warning alarm. Do not wait for full depletion: a completely discharged A6BAT causes the absolute position counter to reset, requiring a reference return cycle before the machine can resume production.

Q5: What is the correct procedure for fitting a coupling hub onto the keyed shaft?

Use the threaded hole at the shaft end to draw the hub axially onto the shaft — a drawbolt, washer, and nut against the hub face applies axial force that seats the hub cleanly without impact. Do not hammer or press the hub onto the shaft. At this motor's frame size, impact loads during hub fitting transmit through the shaft to the encoder assembly at the rear of the motor, causing damage that may not produce an immediate fault but can result in intermittent encoder errors under vibration. The drawbolt method takes slightly longer but protects the encoder reliably.