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Mitsubishi MR-J3BAT | MELSERVO MR-J3 Series Servo Amplifier Battery — 3.6V / 2000mAh / Absolute Encoder Retention

Part Number: MR-J3BAT

Manufacturer: Mitsubishi Electric (Japan)

Product Type: Lithium Battery — Servo Amplifier Spare 

Absolute Encoder Position — Why This Battery Exists

Mitsubishi's MR-J3 series servo amplifiers drive servo motors equipped with absolute encoders. An absolute encoder retains axis position data through power cycles without a homing (reference return) operation. The encoder stores position information in a battery-backed multi-turn counter inside the servo amplifier — the MR-J3BAT is the battery that powers this counter when the machine's main supply is off.

When the MR-J3BAT depletes, the multi-turn absolute position counter loses power during machine off cycles. Position data is lost. At the next power-on, the servo amplifier generates an absolute encoder battery alarm (typically AL.92 on MR-J3 series). The machine cannot resume production until a reference return (homing) is performed to re-establish the axis position datum — which is the same operational requirement as a standard incremental encoder. The absolute position advantage is only maintained while the battery has sufficient charge.

The battery resides in the servo amplifier, not inside the servo motor. This matters for servicing: the motor can be replaced or moved without affecting the absolute position battery, and the battery can be replaced at the amplifier without touching the motor or mechanical connection.

Key Specifications

When to Replace — Before the Alarm Activates

Mitsubishi recommends replacing the MR-J3BAT every 3 to 5 years under normal operating conditions, or when the battery alarm (AL.92) appears. The alarm activates before the battery fully depletes — there is a remaining charge at alarm activation. Do not treat the alarm as a scheduled replacement indicator and then delay weeks before acting. Battery depletion after the alarm produces position data loss at the next power-down.

Replace the battery with the servo amplifier powered on where the installation allows. The amplifier's internal capacitors briefly maintain the multi-turn counter during the battery swap, preventing position data loss during the replacement. Replacing with the amplifier de-energised risks counter data loss if the capacitor charge is insufficient to bridge the replacement time. Work quickly when replacing without power.

FAQ

Q1: The servo amplifier shows AL.92. What does this mean?

AL.92 is the MR-J3 series absolute position battery alarm. It indicates the MR-J3BAT battery voltage has dropped below the warning threshold. The battery is not yet dead — but position data will be lost at the next power-down if the battery is not replaced promptly. Replace the MR-J3BAT and confirm the multi-turn absolute position data is intact after replacement.

Q2: Where is the battery installed — in the motor or the amplifier?

The MR-J3BAT installs in the MR-J3 series servo amplifier, not in the motor. The absolute encoder uses the motor's internal encoder for position detection, but the multi-turn counter (which tracks position across multiple rotations through power cycles) is powered by the battery in the amplifier. Motors with absolute encoders do not contain a battery internally.

Q3: Can the MR-J3BAT be replaced without losing absolute position data?

Yes, if the replacement is performed quickly with the amplifier powered on. The amplifier's internal capacitors briefly sustain the multi-turn counter during the battery swap. Replace the battery with power applied, reconnect the new battery before removing the old one if the connector arrangement allows simultaneous connection, and work within the brief capacitor-supported window. If replaced with power off, re-homing may be required to restore absolute position.

Q4: What is Logistic Class A for the MR-J3BAT?

Logistic Class A is Mitsubishi Electric's classification for recommended stock items — spare parts that should be held on-site as standard maintenance inventory because they are time-limited consumables required for predictable servicing events. The MR-J3BAT is classified Class A because battery replacement is a scheduled maintenance item for all MR-J3 servo systems with absolute encoders, not a conditional event.

Q5: Can the MR-J3BAT be used with other Mitsubishi servo amplifier series besides MR-J3?

The MR-J3BAT is specifically designed for the MR-J3 series amplifier's battery connector and voltage requirements. Other Mitsubishi servo series use different batteries — the MR-J2S series uses a different battery (MR-BAT), and the MR-J4 series uses the MR-BAT6V1SET. Confirm the amplifier series before ordering. Fitting an incorrect battery type risks inadequate voltage, connector incompatibility, or insufficient capacity for the application.