Effect of temperature on run times of uninterruptible power supply systems for signalized intersections

Traffic signal failures due to power outage can significantly impact the safety and efficiency of intersection traffic operation. Uninterruptible Power Supply (UPS) systems are used to power traffic signals in the event of a power outage. The performance of these UPS systems under different temperature conditions has not been studied. Four different UPS systems were evaluated at sub-zero temperatures, room temperature, and hot temperatures (from -25 °C to +72 °C). All the UPS systems showed longer run times as the temperature increased and drastically shorter run times as the temperature decreased. For +72 °C condition, the percentage change relative to room temperature ranged from +6% to +26%. The percentage change at -25 °C condition ranged from -32% to -80%. The increase in duration of flashing compared to duration of solid operation ranged from 89% to 158%. The increase in combination of solid and flashing duration compared to solid operation duration ranged from 35% to 81%. It is recommended to switch to flashing or a combination of solid and flashing mode of operation in cold temperatures to increase the run time. It was also found that a UPS with a greater battery capacity may not yield greater run times under all temperature conditions.