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Q
What is a fan operating point, and why is it different from free-air CFM?
AA fan operating point is the intersection between the fan P-Q curve and the system impedance curve. Free-air CFM is measured at zero static pressure, while installed airflow depends on filters, heat sinks, ducts, guards, and enclosure openings. For defense electronics cooling, selection should be based on the required airflow at the expected pressure drop, not on free-air airflow alone.
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Q
Should I select a cooling fan by static pressure, total pressure, or airflow?
AStart with the required heat removal and installed airflow, then check whether the fan can provide that airflow at the system pressure drop. Static pressure is usually the practical value used to overcome restrictions such as fin stacks, filters, ducts, and compact VPX or avionics enclosures. Total pressure may be reviewed in formal test reports, but product selection should confirm the full operating point.
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Q
Where should axial and centrifugal fans operate on a P-Q curve?
AThe preferred operating region depends on the fan type and system impedance. Axial fans are commonly selected away from stall-prone low-flow regions and should be checked against the actual enclosure resistance. Centrifugal blowers are often used when the system needs higher static pressure through ducts, filters, or dense heat sinks. Final selection should be verified with the model-specific P-Q curve.
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Q
How should replacement fan selection start when only a competitor model is known?
ABegin with the public datasheet or measured sample data for the existing fan: frame size, mounting pattern, voltage range, current, speed, airflow, static pressure, acoustic limit, connector or lead interface, PWM logic, and FG/RD output type. The replacement should then be checked against the system operating point, environmental requirements, and qualification plan rather than by size match alone.
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Q
What motor commutation and PWM frequencies matter for EMI troubleshooting?
ATwo frequency families matter. Motor commutation frequency depends on pole count and RPM; for example, a 4-pole motor at 6,000 RPM produces a 400 Hz commutation frequency. PWM gate-drive or speed-control switching may sit much higher; selected Perseus BLDC fans use a 15.625 kHz internal switching frequency during startup or speed-controlled operation. EMI troubleshooting should look at both the low-frequency commutation components and the higher-frequency switching components on the power and signal harness.
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Q
Why do high-impedance ducts or fin stacks need static-pressure-focused fan selection?
AFree-air CFM is measured at zero static pressure and is not the airflow delivered inside a dense enclosure. Heat sinks, filters, louvers, long ducts, and tight VPX/CPCI card cages create system resistance. The real airflow is the intersection of the fan P-Q curve and the system impedance curve. Centrifugal fans are often a better fit for high-impedance paths because they maintain pressure through narrow or redirected airflow channels, while axial fans are better for lower-resistance, direct-through cooling.
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Q
When should I choose a 400Hz AC fan instead of a 28VDC BLDC fan?
AChoose a 400Hz AC fan when the platform already provides 115V phase / 200V line, 3-phase aircraft or shipboard power and the replacement target is tied to that legacy electrical interface. The Titan PCG67JFZY722-63G-AA reference model is a 400Hz AC platform with 22,000 RPM rated speed, at least 140 CFM airflow, and at least 79 mmH2O static pressure. Choose 28VDC BLDC when the system needs PWM speed control, FG/RD feedback, lower-voltage power distribution, or easier integration with digital thermal controllers.
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Q
Which fan materials are best for salt fog, cleanrooms, and airborne weight targets?
AMaterial choice should follow the failure mode. Aluminum alloy housings improve rigidity, heat spreading, and vibration resistance for airborne, naval, and tracked-vehicle systems. PPO or engineered polymer configurations reduce weight and support corrosion resistance where the mechanical load is lower. For salt fog, specify coating, fastener material, bearing sealing, and MIL-STD-810H Method 509.7 exposure. For cleanroom equipment, review particle shedding, lubricant volatility, and surface treatment rather than choosing only by frame material.
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Q
How long do Perseus fans last in high-temperature duty?
AService life depends on bearing load, speed, temperature, humidity, vibration, and contamination. Representative Perseus DC fan models list L10 life of 50,000 hours at 40°C, while the Titan 400Hz AC reference model lists L10 life of 13,000 hours at 40°C. For semiconductor or furnace-adjacent duty, review lubricant temperature limit, bearing type, airflow path cleanliness, and the actual chamber-side ambient before using any catalog life value.
AA fan operating point is the intersection between the fan P-Q curve and the system impedance curve. Free-air CFM is measured at zero static pressure, while installed airflow depends on filters, heat sinks, ducts, guards, and enclosure openings. For defense electronics cooling, selection should be based on the required airflow at the expected pressure drop, not on free-air airflow alone.
