The **MEH74XBX-R** is a high-performance, industrial-grade axial cooling fan manufactured by **Sanyo Denki** (San Ace). It is part of the high-static pressure series designed for dense electronic environments. ### 1. Key Technical Specifications The model number encodes specific electrical and physical properties: | Feature | Specification | | :--- | :--- | | **Dimensions** | 70mm x 70mm x 38mm | | **Rated Voltage** | 48V DC | | **Operating Voltage Range** | 36V to 72V DC | | **Rated Current** | 1.15 A | | **Rated Input** | 55.2 W | | **Rated Speed** | 16,300 RPM | | **Max Airflow** | 102.4 CFM (2.9 m³/min) | | **Max Static Pressure** | 1000 Pa (4.02 inchH2O) | | **Noise Level** | 68 dB(A) | --- ### 2. Electronic Components & Features The internal circuitry of the MEH74XBX-R consists of several sophisticated control systems: #### A. Brushless DC (BLDC) Motor Driver The fan utilizes a 3-phase brushless motor design. This eliminates the mechanical wear of brushes, increasing the lifespan (MTBF) significantly. The driver IC handles electronic commutation based on internal Hall effect sensors that detect the rotor position. #### B. PWM Control (Speed Regulation) The "-R" suffix typically denotes specific control options or environmental protections. This model supports **Pulse Width Modulation (PWM)**, allowing an external controller to adjust the fan speed dynamically based on the thermal load. This saves energy and reduces noise when full cooling capacity is not required. #### C. Tachometer (Pulse Sensor) Output It features a dedicated wire for a frequency generator (FG) signal. The electronic circuit outputs two pulses per revolution, allowing the system's BIOS or controller to monitor the actual RPM and trigger an alarm if the fan stalls. #### D. Protection Circuitry * **Locked Rotor Protection:** If the blades are physically obstructed, the internal circuitry cuts power to the motor coils to prevent overheating and circuit burnout. It periodically attempts a "soft start" to resume operation. * **Reverse Polarity Protection:** Protects the internal electronics if the positive and negative leads are accidentally swapped. --- ### 3. Pinout Configuration Typically, this 4-wire high-performance fan follows this color-coding convention: 1. **Black:** Ground (GND) 2. **Red:** Power (+48V) 3. **Yellow:** Tachometer / Sensor Output 4. **Brown/Blue:** PWM Control Input