Part Number: HC-SFS81K
Manufacturer: Mitsubishi Electric (Japan)
Series: MELSERVO J2-Super — HC-SFS
Rated Output: 850 W (0.85 kW)
Power equals torque times angular velocity. Fix the power at 850W and halve the speed to 1,000 rpm, and the rated torque doubles compared to what the same wattage produces at 2,000 rpm. The HC-SFS81K delivers 8.12 Nm continuously — roughly double what a comparable 850W motor produces at 2,000 rpm. This is the reason the 1,000 rpm family gets specified: not for shaft speed, but for sustained torque at moderate velocities.
The applications that naturally land here — winding drives, rotary indexing tables, slow conveyor axes, direct-drive mechanisms, CNC lathe turret drives — all share a common requirement: genuine torque authority at low shaft speed, without forcing a high gear ratio between motor and load. A 1,000 rpm motor often reduces the gearing required, which means lower backlash, better efficiency, and a simpler drive train. In some cases, it makes direct coupling viable.
The 24.4 Nm peak (3× continuous) handles acceleration and deceleration transients without pushing the motor toward its thermal limit during motion phases.
At 8.12 Nm continuous and 24.4 Nm peak, the shaft coupling carries real mechanical load. Timing belt drives, chain sprockets, gear hub connections, and worm gear inputs all generate cyclic and reversing torque at the motor shaft — exactly the conditions that gradually induce fretting and micro-slip in friction-clamp hubs over production service life.
The keyway changes the mechanism. Torque flows through the key in shear, not through surface friction. A correctly fitted keyed connection degrades far more slowly under reversing loads, and its eventual failure mode (visible key or keyway wear) is usually detectable — unlike the insidious, symptom-free micro-slip that friction interfaces can develop.
Hub installation: Use the shaft-end threaded hole and a drawbolt to pull the hub axially into position. Never hammer or press. At this frame size, axial impact during fitting travels through the shaft directly to the encoder at the motor's rear. The damage typically does not produce an immediate fault — it appears weeks later as intermittent position errors under vibration.
| Parameter | Value |
|---|---|
| Rated Output | 850 W |
| Rated Torque | 8.12 Nm |
| Peak Torque | 24.4 Nm |
| Speed | 1,000 rpm (max 1,500 rpm) |
| Encoder | 17-bit absolute, 131,072 ppr |
| Flange | 130 × 130 mm |
| Protection | IP65 + oil seal |
| Amplifier | MR-J2S-100A / B / CP |
Requires MR-J2S-100 (J2-Super). Not compatible with original MR-J2-100 amplifiers (cannot read 17-bit encoder). MR-J3 and MR-J4 require a renewal adapter kit. For machines running MR-J2-100, source the HC-SF81K (14-bit encoder, same mechanical specification).
Q1: What amplifiers are compatible?
MR-J2S-100A, -100B, or -100CP. Not compatible with original MR-J2-100, MR-J3, or MR-J4 without adapter. For MR-J2-100 machines, use HC-SF81K (J2 generation, 14-bit encoder).
Q2: HC-SFS81K vs HC-SFS102K — what is the difference?
Same amplifier class (MR-J2S-100), same flange (130 × 130 mm), same encoder. Different operating points: HC-SFS81K = 8.12 Nm at 1,000 rpm; HC-SFS102K = 4.78 Nm at 2,000 rpm. Same wattage class, different torque-speed balance. Use 81K where sustained torque at low speed matters; use 102K where higher shaft speed at moderate torque suits the application.
Q3: Why does an 850W motor use the same MR-J2S-100 as a 1kW motor?
The MR-J2S-100 is rated at 1kW and covers both the 850W HC-SFS81 and 1kW HC-SFS102 within its capacity envelope. The HC-SFS81K runs comfortably within the amplifier's current and power ratings, and this pairing is confirmed in Mitsubishi's J2-Super compatibility documentation.
Q4: Where is the encoder backup battery, and when does it need replacing?
The A6BAT lithium battery is in the MR-J2S-100 servo amplifier, not in the motor. Replace it when the amplifier displays a low-battery alarm. A fully depleted battery resets the multi-turn counter — a reference-return cycle is then required before production can resume.
Q5: Is a key supplied with the HC-SFS81K?
The keyway is machined into the shaft, but the key itself is not typically included in Mitsubishi's standard motor packaging. Verify keyway dimensions from the HC-SFS81 series instruction manual and source the appropriate key for the hub bore and torque requirement.
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