HF-KP43 Wiring Guide: Mitsubishi Low Inertia Servo Motor Setup

Overview

The HF-KP43 is a 400W low-inertia AC servo motor from the Mitsubishi HF-KP family, built to run on a matched MELSERVO drive as one closed-loop axis. Small packaging machines, pick-and-place units, indexing tables, and labeling heads are the kind of equipment that carries it. Its low inertia rotor spins up and stops fast, which is what small, quick axes need. You replace it when the bearings turn noisy under load, when the drive starts logging encoder faults, or after mechanical damage to the shaft or housing.

The catalog number reads in three parts. HF-KP is the series mark for the low-inertia, small-capacity family in the MELSERVO range, so the letters describe the frame class and the inertia behavior of the rotor. The digits 43 are the capacity code, and in this family they correspond to the 400W class; the rated torque, speed, and current for your exact unit belong to the datasheet and the nameplate. Letters after the digits mark options, with the brake being the common one, and the encoder and shaft variants of the family are listed in the MELSERVO catalog, so copy the full number from the label when you order.

Key specifications

The values below are family-level and catalog-level facts. Anything that varies by option suffix or drive generation is marked "see datasheet", and the nameplate on the unit in hand is the final reference. Where doubt remains, the printed manual for the unit wins over any summary.

Pairing the motor with the drive

Three things have to agree before an HF-KP motor will run. The drive capacity class must suit the 400W motor, the drive must list the motor's encoder on its compatibility tables, and the axis parameters must have been written for the pair. The MR-J4 generation and the earlier J2S generation each carry their own tables, and a motor listed for one generation is not automatically listed for the other, so read the drive manual instead of judging by flange size.

Keep the pairing inside the MELSERVO system. A drive sized for an HF-KP43 will not automatically accept a medium-inertia frame or a different capacity code, and a cable that fits the connector may not signal the same way. Drive capacity classes, encoder support, and firmware revisions all appear in those tables. When you commission a new motor on an old axis, run the drive's auto-tuning with the real load attached, save the parameters, and record the drive and motor identities together in the machine file so the next swap starts from facts instead of memory.

Care points on moving axes

Bearings, encoder connectors, and encoder cables are the three parts that fail first on machine axes, and each leaves a tell you can catch early. A bearing announces itself as a noise that rises with speed and changes under radial load. A connector shows up as intermittent encoder faults after transport, after washdown, or after a crash. A cable flex failure appears as drift or faults that return only on long program cycles with full travel.

Two habits prevent most of it. Add strain relief at every moving joint, so the flex happens in the designed cable length rather than at the connector shell. And on a replacement install, torque the flange bolts evenly, seat the connectors until they latch, and dress the cables along the original routing rather than the shortest path. A photo taken before the old cable comes off makes the original dressing easy to repeat.

Common issues and troubleshooting

Work the axis in this order when a drive faults or the position drifts. Each step either clears the symptom or points to the next one. The order matters, because it finds most faults with the fewest disassembly steps.

Warning: a servo axis can move the instant power returns, and drive bus capacitors hold charge after shutdown. Apply lockout and tagout before opening connectors, wait the discharge interval the drive manual specifies, and measure the bus terminals before touching them.

1. Read the alarm on the drive display and write it down with the axis number before touching anything. The alarm type sorts the rest of the flow into a feedback path, a power path, or a tuning path.
2. Power down and lock out, then inspect the encoder connector at the motor end and the drive end. Reseat both and check the pins under a light. A fault that clears and stays cleared usually ends here.
3. Swap in a known-good encoder cable between the same motor and drive. If the intermittent fault disappears, the cable was the culprit, and its flex section is the wear point to watch on the next unit.
4. Listen to the motor at low speed with the covers off, then again under load. A noise that rises with speed and deepens under load points to bearing wear, and the motor should come off while the machine is already down.
5. Re-run the drive auto-tuning with the real load attached and compare the measured inertia ratio against the range in the drive manual. A ratio outside the expected band explains vibration and overheat complaints that wiring checks never find.
6. Look at the mechanics the old motor lived with before reordering parts: coupling condition, pulley alignment, mounting feet. A replacement dropped onto worn mechanics inherits the same symptoms within weeks.

FAQ

Is the HF-KP43 a 400W motor?

Yes, the 43 capacity code corresponds to the 400W class in the HF-KP family. Rated torque, rated speed, and current belong to the datasheet for your exact option suffix, so check those figures before sizing a drive or a mechanical load.

Can I run an HF-KP43 on a drive from another servo family?

No. The pairing is defined inside the MELSERVO system, where the drive supports the encoder protocol and capacity class of the motors on its list. Check the drive manual's compatibility tables for your exact suffix instead of relying on connector shape. Ask for the compatibility confirmation in writing before the motor ships.

What is the difference between HF-KP43 and HF-KP43B?

The B suffix marks the brake option in this family, which holds the axis against backdrive when the drive is off. The brake adds hardware at the rear of the frame and its own leads, so the two units do not interchange blindly on every machine.