The Q35B is Mitsubishi Electric’s 5-slot main base unit for the MELSEC-Q programmable controller series — the compact 5-slot backplane providing one power supply slot, one CPU slot, and three I/O or intelligent function module slots for building MELSEC-Q control systems with moderate module requirements in a space-efficient panel footprint. In stock at Atlantech Drives. Request your quote within 24-48 hours with worldwide shipping and 12-month warranty.
What Is the Q35B?
The Q35B is a MELSEC-Q series main base unit (backplane) providing 5 total slots — one power supply slot (leftmost, for Q61P, Q62P, or Q63P power supply module), one CPU slot (slot 0, for Q02UCPU, Q03UDECPU, Q04UDEHCPU, or other Q-series CPU), and three module slots (slots 1, 2, 3) for Q-series I/O modules (QX80, QY40P, etc.) and intelligent function modules (QJ71E71-100 Ethernet, QD75MH4 positioning, QJ71PB92D PROFIBUS, etc.). The «5» in the model designation indicates the 5-slot total capacity, with 3 usable module slots after accounting for the dedicated power supply and CPU slots. The Q35B is the smallest main base unit in the standard MELSEC-Q base unit range — the Q38B (8-slot) and Q312B (12-slot) provide more module slots for larger systems — making the Q35B appropriate for compact MELSEC-Q systems where the control requirement fits within 3 intelligent/I/O module slots. The Q35B includes an extension base unit connector on its right side, enabling an unlimited number of Q6□B extension base units to be added to the system when more than 3 module slots are required — the Q35B’s 3 main base module slots combined with one or more Q68B (8-slot extension) or Q612B (12-slot extension) extension base units can address large MELSEC-Q system requirements while retaining the compact Q35B main base footprint.
Key Technical Specifications
- Model: Q35B
- Total Slots: 5 (1 power supply + 1 CPU + 3 module slots)
- Module Slots: 3 (slots 1, 2, 3 — I/O and intelligent function modules)
- Compatible Power Supply: Q61P, Q62P, Q63P, Q64P
- Compatible CPUs: All Q-series CPU modules (Universal, High Performance, Process, Safety, Motion)
- Extension Connector: Right-side extension bus connector (for Q6□B, Q6DB extension base units)
- Module Slot Width: 27.4 mm per slot (standard Q-series module width)
- Bus Standard: Q-series internal bus (proprietary Mitsubishi backplane bus)
- Operating Temperature: 0°C to 55°C
- Dimensions (W × H × D): 245 mm × 98 mm × 44.1 mm
- Weight: Approx. 0.47 kg
Series Comparison & Selection Guide
The MELSEC-Q main base unit range spans four slot counts: Q33B (3 slots, 1 module slot), Q35B (5 slots, 3 module slots), Q38B (8 slots, 6 module slots), and Q312B (12 slots, 10 module slots). The Q35B is selected when the complete MELSEC-Q system fits within 3 module slots — a common configuration for single-function dedicated controllers such as a single-axis servo positioning system (Q02UCPU + QD75MH4 positioning + QJ71E71-100 Ethernet in slots 1, 2, 3), a compact SCADA node (Q02UCPU + QJ71E71-100 Ethernet + QX80 input in slots 1, 2, 3), or a basic stand-alone machine controller (Q02UCPU + QX80 input + QY40P output in slots 1, 2, 3). For systems requiring 4–6 module slots, the Q38B is typically specified to avoid the complexity of extension base unit wiring. For systems requiring more than 6 module slots in the main base, the Q312B (10 module slots) avoids the need for extension bases in large-module-count systems. When comparing Q35B to building a Q38B system: the Q35B’s smaller footprint reduces panel space consumption, but adding a Q68B extension base for additional modules adds cost and the extension bus cable. If 4–6 modules are anticipated in the system’s lifecycle, specifying the Q38B from the outset avoids the future cost of adding an extension base. The Q35B is the most cost-effective choice when 3 module slots definitively meets the application’s requirements with no planned expansion.
Installation Advice
The Q35B installs on a standard 35 mm DIN rail using the two DIN rail mounting clips integrated into the base unit’s rear panel — press the base unit onto the DIN rail until both mounting clips engage with positive clicks confirming secure retention. Alternatively, the Q35B can be directly screw-mounted to a flat panel surface using the four M4 screw holes in the base unit’s mounting flange — screw mounting provides more secure retention in high-vibration environments compared to DIN rail mounting. Install the Q35B with the module insertion direction facing outward from the panel (away from the panel backplate) — the module connector engagement direction and the module front-panel LED indicators must be accessible from the panel front for commissioning and maintenance access. Maintain a minimum 40 mm clearance above and below the Q35B for forced-air cooling convection — the MELSEC-Q modules dissipate heat primarily upward through natural convection, and insufficient clearance above the modules causes elevated operating temperature that reduces module lifespan. For the Q35B’s extension bus connector, use only Mitsubishi’s QC05B (0.45 m), QC06B (0.6 m), or QC12B (1.2 m) extension bus cables for connecting extension base units — third-party extension cables are not compatible with the Q-series internal bus electrical specification and can cause intermittent module communication errors or permanent base unit damage.
Frequently Asked Questions
Q: Can a motion CPU (Q172DSCPU) be installed in the Q35B alongside a sequence CPU (Q02UCPU) for a multi-CPU configuration?
A: Yes. The Q35B supports multi-CPU configuration with up to 4 CPU modules when the base unit has sufficient CPU slots — however, the Q35B has only one CPU slot (slot 0), limiting it to single-CPU operation. For multi-CPU systems (Q02UCPU sequence CPU + Q172DSCPU motion CPU), the Q38B or Q312B (which provide multiple CPU-capable slots) must be used. The Q35B’s single CPU slot is a fundamental architectural constraint that cannot be overcome by software or module selection.
Q: Is the Q35B compatible with MELSEC-Q modules from all generations, including older Q02CPU-era modules?
A: Yes. The Q35B uses the standard Q-series internal bus that is backward compatible with all MELSEC-Q module generations — Q-series I/O modules and intelligent function modules from the Q02CPU era (Basic model CPU generation) through the current Universal CPU generation can be installed in the Q35B. However, some module combinations may have functional restrictions when paired with specific CPU generations — verify module compatibility with the specific Q-series CPU model in the GX Works2 module compatibility list.
Q: Can the Q35B be used as an extension base unit for a larger MELSEC-Q system with a Q38B or Q312B main base?
A: No. The Q35B is a main base unit — it includes the CPU slot and power supply slot required for main base operation. Extension base units (Q6□B, Q6DB series) are separate product models designed specifically for extension use without a CPU slot. The Q35B cannot function as an extension base — it must always be the main base unit of the MELSEC-Q system, with Q6□B or Q6DB extension bases added to its right-side extension connector for additional module slots.
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