Mitsubishi QM25TB-2HB BKO-C2115H02 CNC Power Module – BKO-C2115 Series

QM25TB-2HB BKO-C2115H02: DC Bus Power Distribution in Mitsubishi CNC Servo Architecture

The Mitsubishi QM25TB-2HB (factory reference code BKO-C2115H02) is a dedicated power module within the Mitsubishi CNC servo drive ecosystem. Its primary function is to condition, distribute, and protect the DC bus voltage that feeds downstream servo amplifier axes in multi-axis machining center configurations. Unlike a generic power supply, this module operates as an active participant in the CNC control loop — it interfaces directly with the CNC controller’s power management bus, enabling coordinated charge/discharge sequencing across the servo network.

In a typical Mitsubishi CNC cabinet (M70, M80, or C70 series), the QM25TB-2HB sits between the main AC input rectifier stage and the individual axis servo amplifier units. It handles inrush current suppression during spindle and axis motor startup, regenerative energy absorption during deceleration, and DC bus voltage clamping to protect downstream IGBT modules from overvoltage transients. The BKO-C2115H02 reference designates the second hardware revision of the BKO-C2115 family, incorporating updated gate drive circuitry and improved thermal management over the original BKO-C2115H01.

For maintenance engineers managing a fleet of Mitsubishi CNC machines, sourcing a verified QM25TB-2HB is a precision procurement decision. A counterfeit or mismatched power module will not merely underperform — it will corrupt the DC bus voltage profile, triggering cascading servo alarms (AL.30, AL.31 series on Mitsubishi MR-J4 amplifiers) and potentially damaging the servo amplifier’s input capacitor bank. This page provides the engineering data needed to confirm fitment and make an informed procurement decision.

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Technical Parameters

Hardware Logical Analysis

The QM25TB-2HB is built around a three-stage power conditioning architecture that addresses the three principal failure modes of servo bus power systems: inrush transients, regenerative overvoltage, and EMC-induced bus noise.

Inrush Suppression Circuit: At power-on, the AC input passes through a series NTC thermistor (cold resistance ~10 Ω) that limits the capacitor bank charging current to a safe level. After approximately 200 ms, an internal bypass relay closes, shorting the thermistor and eliminating its resistive loss during normal operation. This two-stage approach avoids the thermal fatigue that plagues single-relay designs operating at high cycle rates — a common failure point in older BKO-C2115H01 units.

Regenerative Energy Management: During axis deceleration, servo motors act as generators, pumping energy back into the DC bus. The QM25TB-2HB monitors bus voltage via an internal comparator. When bus voltage exceeds the clamping threshold (~360 V DC), the module activates the internal braking resistor circuit. For high-inertia applications (large rotary tables, heavy gantry axes), an external braking resistor can be connected to the DB terminal pair, extending the module’s regenerative absorption capacity proportionally to the external resistor’s wattage rating.

EMC Design: The module incorporates a common-mode choke on the AC input lines and a differential-mode LC filter on the DC bus output. These passive components attenuate high-frequency switching noise generated by the downstream servo amplifier IGBTs, preventing conducted emissions from propagating back into the facility’s power distribution network. The chassis ground connection uses a low-impedance copper strap rather than a wire bond, reducing ground loop inductance at frequencies above 1 MHz — a design detail that directly impacts compliance with EN 61800-3 Category C2 EMC requirements.

Thermal Architecture: The power stage components (rectifier bridge, bus capacitor bank, braking IGBT) are mounted on an aluminum heat spreader plate with direct contact to the forced-air cooling channel. The internal fan operates at a fixed speed, providing consistent airflow regardless of load — a deliberate design choice that simplifies thermal modeling in cabinet layout calculations. Thermal resistance from junction to ambient for the braking IGBT is rated at 1.2 °C/W, supporting sustained braking duty cycles without derating.

System Integration Benefits

• Deterministic Bus Voltage Regulation: The QM25TB-2HB maintains DC bus voltage within ±5% of nominal under dynamic load transitions, ensuring servo amplifier PWM calculations remain accurate and axis positioning repeatability is not degraded by bus voltage droop.
• Coordinated Power-On Sequencing: The module’s ready signal (MCON output) is read by the CNC controller before enabling servo axis excitation. This hardware interlock prevents axis enable commands from being issued while the bus is still charging — eliminating a class of startup faults that occur when power modules are replaced with non-OEM equivalents lacking this signal.
• Alarm Transparency: The module outputs discrete fault signals for overvoltage, undervoltage, and overtemperature conditions. These signals map directly to Mitsubishi CNC alarm codes, allowing maintenance personnel to diagnose power module faults from the CNC operator panel without opening the cabinet.
• Regenerative Energy Recovery: By absorbing deceleration energy internally rather than dissipating it through axis brake resistors, the module reduces thermal load on the cabinet and extends the service life of mechanical braking components on high-cycle applications.
• Scalable Multi-Axis Support: A single QM25TB-2HB can supply the DC bus for up to four MR-J4-B servo amplifier axes in a shared-bus configuration, reducing cabinet wiring complexity and the number of AC input circuit breakers required.
• Direct Drop-In Replacement: The BKO-C2115H02 revision maintains full mechanical and electrical compatibility with BKO-C2115H01 mounting positions, connector pinouts, and signal interfaces. No firmware changes or parameter adjustments are required on the CNC controller after replacement.
• Reduced Unplanned Downtime: Stocking a verified QM25TB-2HB as a spare reduces mean time to repair (MTTR) for DC bus faults from days (sourcing lead time) to hours (swap and restart). For high-utilization machining centers, this translates directly to measurable OEE improvement.
• Compliance with Mitsubishi Maintenance Protocols: Using the OEM part number ensures compatibility with Mitsubishi’s predictive maintenance data — the CNC controller’s internal power module health monitoring accumulates operating hours and fault event counts against the OEM part’s expected service life curve.

Quality Assurance & Global Logistics

Every QM25TB-2HB BKO-C2115H02 unit dispatched from our Xiamen facility is a genuine Mitsubishi Electric component procured through verified industrial supply channels. Each unit undergoes a three-point inspection protocol before packaging: label and serial number authentication against Mitsubishi’s part marking standards, visual inspection of connector contacts and housing integrity, and a DC bus output voltage verification test under a resistive load.

Units are packaged in anti-static PE bags, placed in custom-cut EPE foam inserts, and shipped in double-wall corrugated cartons rated for international air freight handling. For fragile or high-value orders, wooden crating is available on request.

From Xiamen, we dispatch via DHL Express, FedEx International Priority, and UPS Worldwide Express — typical transit times are 3–5 business days to Europe, 2–4 business days to Southeast Asia, and 4–7 business days to the Americas. A commercial invoice, packing list, and certificate of origin are included with every shipment to facilitate customs clearance. Export compliance documentation (ECCN classification, country of origin certificate) is available upon request for regulated procurement environments.

All units are covered by a 12-month warranty from the dispatch date. Warranty claims are handled directly by our technical team — no third-party RMA routing. Defective units are replaced or credited within 10 business days of receipt and inspection.

Contact Information

Email: [email protected]
WhatsApp: +86 18359268345
Web: siemensplc.com
Location: Xiamen, China
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