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Q
How much can fan noise be reduced by speed control?
ASpeed control is the most effective lever for reducing acoustic noise: reducing fan speed by 50%, 40%, 30% and 20% lowers noise by approximately 15, 11, 8 and 5 dBA respectively, based on Perseus acoustic measurements in our semi-anechoic chamber. Low-noise blade options and vibration-isolated mounting are also available. Final acoustic levels depend on the system installation; contact us for configuration-specific guidance.
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Q
Can Perseus fans operate at extreme low temperatures below -55°C?
AFor very low temperature environments, Perseus fans can be configured with internal heaters and temperature sensors for continuous operation below -55°C. Standard operating range is -55°C to +85°C; extended temperature variants are configuration-specific. In representative cold-environment testing, an evaluated configuration started and operated reliably under defined conditions. Confirm your temperature profile with our engineering team for a configuration review.
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Q
Can Perseus fans meet both MIL-STD-461G emissions and MIL-STD-810H vibration limits?
APerseus fans are designed with integrated EMI filtering and mechanical isolation. In representative testing, evaluated configurations have been measured against conducted and radiated emission limits (RE102/CE102, 10 kHz - 18 GHz) and tested at vibration levels representative of fighter platforms (25 g RMS for 10 hours). Because test setups vary by platform, review applicable data for your specific environment with our engineering team.
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Q
Can one PWM signal control multiple BLDC cooling fans?
AOne PWM command can often be shared by multiple compatible fans when the control reference is correct and the controller can support the electrical interface. The PWM reference should normally be tied to the fan negative return unless an isolated interface is specified. The design should also check pull-up behavior, signal voltage, cable length, and noise immunity before release.
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Q
Can FG or RD feedback outputs from multiple fans be connected in parallel?
AFG and RD feedback outputs should normally be routed separately to the controller. These outputs are commonly open-collector or open-drain style signals, and parallel wiring can hide an individual fan fault or distort the tachometer reading. For redundant cooling trays or multi-fan avionics modules, each fan feedback line should be reviewed as an independent status or speed signal.
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Q
Can a fan feedback wire be used as the PWM ground reference?
ANo. A feedback output such as FG or RD is not a ground return. It may be pulled low, floating, or switching depending on fan status and the external pull-up circuit. Using it as a PWM ground reference can cause unstable speed control, false fault detection, and poor noise immunity. The PWM reference should use the defined fan negative return or an approved isolated interface.
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Q
Why can PWM speed control fail even when the fan is powered correctly?
ACommon causes include an incorrect PWM reference ground, reversed signal wiring, incompatible control voltage, an unintended external voltage divider, excessive cable noise, or a missing isolation strategy between digital ground and power return. In avionics or RF equipment, PWM wiring should be checked together with EMC planning, cable routing, and controller input protection.
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Q
What should be checked when fan noise increases after installation?
ANoise after installation can increase because of inlet restriction, outlet obstruction, grille turbulence, structural resonance, incorrect mounting torque, unexpected PWM duty cycle, or operation near an unstable point on the P-Q curve. The review should compare free-air data with installed airflow, pressure drop, vibration path, and the actual mounting structure.
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Q
What PWM and feedback signals do 28VDC BLDC fans use?
APWM control and FG/RD feedback signals should be reviewed with the correct reference ground. The PWM control reference is normally tied to the fan negative return, and interface errors can cause unstable speed control, false fault feedback, or signal noise. FG feedback is used to monitor fan speed through pulse frequency, while RD feedback is used to monitor run or fault status. FG/RD outputs should normally be wired individually when independent fan monitoring is required.
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Q
How does altitude affect fan cooling performance?
AAt low pressure, volumetric airflow and cooling capacity should not be treated as the same value. Reduced air density lowers heat capacity per unit volume and changes pressure performance, so high-altitude fan selection should be reviewed by operating point, air density, thermal load, enclosure resistance, and model-specific speed behavior. For airborne or high-altitude electronics, low-pressure review may reference MIL-STD-810H Method 500.6 when the qualification plan requires altitude or low-pressure testing.
ASpeed control is the most effective lever for reducing acoustic noise: reducing fan speed by 50%, 40%, 30% and 20% lowers noise by approximately 15, 11, 8 and 5 dBA respectively, based on Perseus acoustic measurements in our semi-anechoic chamber. Low-noise blade options and vibration-isolated mounting are also available. Final acoustic levels depend on the system installation; contact us for configuration-specific guidance.
