Cooling Fan
Thermal Management
Moving air multiplies a heatsink's effectiveness several-fold. Modern DC fans are small BLDC motors with built-in drive — some with tach feedback and PWM speed control (the 4-wire PC standard).
What it looks like
Cooling Fan
A typical thermal management — exact shape, colour and markings vary between manufacturers.
Types & variants
Key specs
Size & thickness
mmFrame sizes: 25, 30, 40, 60, 80, 92, 120, 140 mm square; 10/15/25 mm thick. Bigger + slower = quieter for the same airflow.
Voltage
V (DC)5 V (USB projects), 12 V (most common), 24 V (industrial panels), 230 V AC (cabinet fans).
Airflow
CFM / m³/hVolume moved in free air — the headline number, halved or worse once filters and fins resist it.
Static pressure
mmH₂O / PaAbility to push through resistance — what matters on dense heatsinks and filters; blowers excel here.
Noise
dBAUnder ~25 dBA is quiet. Sleeve bearings are quieter but die sooner than ball bearings, especially mounted horizontally.
Bearing type
—Sleeve (cheap, 30k h), ball (durable, 60k+ h), fluid/hydro dynamic (quiet AND durable).
Markings
Label lists size, voltage, current and model; wire colours: red +, black −, yellow/white tach, blue PWM (PC standard). Airflow arrow and rotation arrow are moulded on the frame side.
Standard values
12 V 80×80×25 and 120×25 axial fans dominate; 5 V 30/40 mm for Pi/3D printers; 230 V 4-inch axial for panels; 12 V blowers for 3D printer part cooling.
How to choose
1) Largest, slowest fan that fits — quietest per CFM. 2) Dense fins or filters → prioritise static pressure (or a blower). 3) 4-wire PWM if you want temperature-based speed control without extra hardware. 4) Ball/FDB bearings for 24×7 duty or hot environments. 5) Push air across the sink in the direction the fins run; check the moulded arrows.
Pinout & package
2-pin (JST/bare), 3-pin, or 4-pin PC headers. Tach outputs 2 pulses per revolution (open collector — needs a pull-up). PWM pin expects 25 kHz. Mounting: four corner holes for screws or rubber anti-vibration pins.
Example circuits
- 12 V fan switched by an NPN/MOSFET from a thermostat or MCU pin (flyback diode across the fan)
- PC 4-wire fan: 25 kHz PWM speed control + tach monitoring on an Arduino
- Peltier hot-side sink with a mandatory ball-bearing fan
- Panel cabinet: 230 V fan + filter in, exhaust grille out, thermostat controlled
Common failures
Dry sleeve bearing (rattle at start, seizure later — a drop of oil under the hub sticker buys time), dust-clogged blades (low flow, overheating), dead drive electronics (twitch but no spin), and cracked blades from probing fingers.
How to test
Apply rated voltage: should spin instantly and smoothly. Measure current vs label. Scope/count tach pulses for RPM (pulses/2 × 60). A fan that needs a flick to start has a failing bearing or drive coil. Hold-by-frame only — flexing the hub kills bearings.
Substitutes
Same size/voltage swaps directly; match or exceed CFM and static pressure. A 3-wire fan works on a 4-pin header (voltage control instead of PWM). AC fans and DC fans are not interchangeable without a supply change.