Cooling Fan FAQ Deep-Dives
The questions behind 45 short engineering answers, each written around the numbers, limits and pass/fail criteria a cooling engineer needs in a design review. Start from the quick FAQ, or go straight to a deep-dive below.
Fan Selection ＆ Operating Point
How does altitude change fan selection?Air density falls with altitude: about 0.90 at 1000 m, 0.82 at 2000 m, 0.74 at 3000 m (ISA). What that does to
How do I convert CFM to m³/h (and back)?Exact conversion factors between CFM, m³/h and m³/s with a quick table, plus the trap of comparing values meas
How do I estimate required airflow from heat load?The energy-balance method Q = P/(ρ·cp·ΔT) with a worked 500 W example, realistic margin factors, and why the c
What do the fan laws tell me about changing fan speed?The three fan laws with worked numbers: flow scales with speed, pressure with speed squared, power with speed
Do two fans in parallel double the airflow?Parallel and series fan arrays explained: combined curves, real gains, reverse-flow risks and how to validate
How should I select a fan for a high-ambient product?What changes at 60–85°C ambient: electrolytics and lubricants, L10 life, current derating, plastics and how to
How do I read a fan P-Q curve?A practical walkthrough of fan P-Q curves: free-air point, maximum pressure, stall region, system curve inters
Replacement ＆ Cross-Reference
What connector details must match in a fan replacement?Pin pitch, pinout order, latch type, wire gauge and mating connector part numbers to verify before approving a
How do I cross-reference a competitor fan to your product?A method to map a Sanyo Denki, SUNON, Delta, NMB or ebm-papst part number to a candidate: what to extract from
Does a replacement fan's start-up current matter?Why start-up current exceeds steady-state current, typical magnitudes, how to measure it, and how to size the
Why does the replacement fan report a different speed (RPM)?Tach pulses-per-revolution differences, PWM duty-map shifts and real speed differences — how to tell which one
Are PWM, FG and RD signals interchangeable between fan brands?What PWM frequency and duty conventions, tach pulses-per-revolution and RD alarm logic you must verify when sw
What should a fan replacement qualification checklist cover?A complete checklist for qualifying a replacement cooling fan: mechanical, electrical, signals, acoustics, the
Is a same-size fan an equivalent replacement?Why matching frame size and bolt pattern is only step one: P-Q curve, voltage window, PWM/FG/RD behaviour, con
Airflow ＆ Pressure Measurement
How does air temperature affect fan performance?Density falls as air heats up: what that does to fan pressure, mass flow, cooling and current — with the corre
Why does my anemometer give different readings every time?Common anemometer mistakes in enclosure airflow work — placement, swirl, averaging, blocking the inlet — and h
How does a loading filter change the fan's operating point?Filter pressure drop rises with dust load, pushing the operating point up the resistance curve — installed flo
How do I measure static pressure inside an enclosure?How to measure the static pressure a fan works against: differential tap placement, gauge choice, typical magn
What are recirculation and bypass losses in an enclosure?Short-circuit flows inside enclosures: recirculation back through the fan and bypass around the heat source, t
How can I verify the airflow a fan actually delivers in my product?Four practical ways to verify installed airflow — ΔT energy balance, pressure-flow inference, flow bench, and
Control ＆ Signals
Why does my fan control loop hunt (oscillate)?Why temperature-driven fan control loops oscillate: sensor placement, thermal lag, hysteresis, steep duty maps
Why does my fan stall or stop at low PWM duty?The stall floor explained: why DC fans stop or run rough below a minimum duty (commonly 10–20%), what happens
Is fan speed proportional to PWM duty cycle?Duty-to-speed maps are monotonic but not linear, flatten near maximum and have a stall floor — how to measure
What PWM frequency should I use for DC cooling fans?Why 20–30 kHz (25 kHz typical) is the standard PWM frequency window for 4-wire DC fans, what goes wrong at low
What does the RD (rotation detect) signal indicate?What RD outputs assert (and when), open-drain wiring and pull-ups, behaviour at locked rotor versus slow rotat
How does the fan tach (FG) signal work?Tach output mechanics: pulses per revolution, the RPM = 60·f/PPR conversion, open-collector wiring, pull-up si
Noise ＆ Vibration
What is blade-pass frequency and why does my fan whistle?BPF = blade count × revolutions per second. Worked examples, why some installations amplify it, and design lev
What is the difference between dB(A) and sones in fan noise specs?dB(A) is logarithmic, sones linear in loudness: why doubling sones means doubling perceived loudness, how the
How do fan imbalance and mounting affect vibration?Rotor imbalance, mounting stiffness and structure-borne noise: how imbalance grades work, why soft vs hard mou
Why does a fan get louder over time?Dust imbalance, lubricant depletion, loosening mounts and wear-in: the four mechanisms behind rising fan noise
Why does my fan emit a high-pitched whine, and how do I fix it?Tracking down whine sources: audible PWM frequency, current ripple, duty-region interactions and wiring — with
Life ＆ Reliability
How can I detect a cooling fan failing before it stops?The signals that precede fan failure — current drift, tach jitter, noise growth, RD events — how to instrument
How should fans be stored, and does storage age them?Storage conditions for DC fans (temperature, humidity, packaging), why lubricant settling makes long-stored fa
What does L10 bearing life actually mean for my product?L10 is the hours by which 90% of an identical fan batch still runs — at stated speed, load and temperature. Wh
What is the difference between MTBF and L10 for fans?MTBF (population mean time between failures, usually electronics-driven) vs L10 (bearing life by which 90% sur
Should I choose a sleeve or ball bearing fan?Sleeve, ball and hydraulic bearing systems compared by cost, noise, life, orientation sensitivity and temperat
Environment ＆ Protection
Do humid and condensing environments affect cooling fans?How humidity cycles attack fans: condensation on cold soak, leakage currents, bearing lubricant wash-out conce
How often should enclosure fans and filters be cleaned?Why there is no universal cleaning interval, how to set one from data (filter ΔP trend, current trend, inspect
Do cooling fans cause EMI or EMC problems?EMC reality for DC fans: the fan is mostly a victim and a coupling path, not a major emitter; where emissions
Do I need an IP-rated fan for my enclosure?What IP ratings mean for fans specifically, why sealing a fan costs airflow and noise, and why the enclosure's
How do I protect cooling fans in coastal or corrosive environments?Salt attack on fans: mechanisms, protection layers (coatings, materials, drainage), relevant test methods (IEC
Custom ＆ Buying Process
What drives the cost of a custom cooling fan?The six factors that set custom fan cost: motor and bearing class, environmental protection, interface and con
What information should I send to request a custom cooling fan?The exact information set that makes a custom fan RFQ answerable in one pass: operating point, electrical inte
How does the custom fan sample process work?The stages of a custom fan project: specification review, selection or design, sample build, validation on the
What is the minimum order for custom cooling fans?Why MOQ depends on customization depth rather than one number: standard-frame samples, light custom variants,
Send it with your operating condition — airflow and static pressure, voltage, size limit and environment — and MEGA Tech will answer it with selection data and, where it helps, a sample plan.
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