DC fast chargers in the 60–180 kW class dissipate roughly 6–9% of their throughput as heat inside the power cabinet — that's a steady 4–16 kW of waste heat that has to leave the enclosure. The default solution is a fixed-speed cooling fan rated for worst-case ambient and worst-case load, running 100% duty all the time. It works, but it wastes 35–50% of the fan energy across a typical operating year.
Why fixed-speed is so wasteful
A field study across 240 outdoor chargers in temperate climates showed that the cabinet only requires 100% cooling airflow during 8% of operating hours. For 62% of the time, 40% airflow would meet the thermal target. The remaining 30% of the time fits between those two extremes. Yet a fixed-speed fan delivers 100% airflow for 100% of the time.
PWM control with two temperature inputs
The simplest effective scheme uses two NTC thermistors — one on the IGBT heatsink, one on the inlet ambient — feeding a 4–20 mA PWM signal to an EC fan. Below 35°C heatsink, fan runs at 30%. Linear ramp from 30% to 100% between 35°C and 65°C heatsink. Above 65°C, fan locks at 100% and the system raises an over-temperature warning.
Energy savings — three field cases
| Site | Climate | Fan kWh/yr (fixed) | Fan kWh/yr (PWM) | Savings |
|---|---|---|---|---|
| Norwegian highway hub | Cold | 1,260 | 584 | 54% |
| German urban depot | Temperate | 1,260 | 732 | 42% |
| Spanish coastal site | Hot | 1,260 | 868 | 31% |
PWM also extends fan life. At 40% average duty, the bearing L10 life roughly doubles compared to 100% continuous operation. A 60,000-hour rated fan now exceeds the 10-year warranty period of the charger itself.
Ambient cut-out logic for cold climates
Below 5°C ambient, natural convection plus the airflow generated by the rectifier transformer's own induced thermals is often enough to cool a charger at <40% load. A second logic layer that holds the fan at 0% when ambient < 5°C AND charger output < 40 kW captures another 4–8% of annual fan energy on top of the PWM baseline.
Specifying the right fan
EC axial fans in the 200–280 mm class with integrated PWM input are the sweet spot for cabinet cooling — IP54 minimum, IP66 for coastal sites, and an operating range that covers 0–100% without falling below the controller's minimum stable speed. TTTIGER's EC-220 and EC-280 series ship with 0–10V and PWM inputs as standard and have been deployed on >18,000 chargers across Europe and Asia.
