The dog days of summer are upon us: High temperature records have already been broken, from southern California to New England, leaving power outages in their wake. Heat also puts a stress on the UPS and batteries in traffic cabinets, just when they are needed most to handle power brownouts or outages. While the ITS Cabinet Standard specifies operating ranges up to 74° C (165° F), the effect of summertime temperatures in excess of 100° F plus direct sunlight on the cabinet, plus the heat produced by the electrical components themselves can quickly turn a traffic cabinet into an oven, shortening the lives of components and, worst case, leading to system failure.
Unfortunately, high temperatures are going to continue to climb. Numerous U.S. and Canadian cities last year saw days of temperatures ranging from 110° up to 127°F, and the trend is upward. But system designers and builders can mitigate heat problems by choosing UPS technology that is not only more heat tolerant but also generates a minimum of heat as a result of its own operation.
For example, some ITS systems use exclusively double-conversion UPS systems, on the assumption that double conversion is the best way to isolate transportation system components from fluctuations in incoming utility power. But because all the UPS components are under continuous load and there is some power loss with each conversion, a double-conversion UPS also continuously generates extra heat within a traffic cabinet. A cooler alternative is a UPS system with active power supervision, that can run in a more power-efficient, cooler mode during the 97% of the time that incoming power quality falls within acceptable parameters.
The other way to minimize heat-related failures is to look for newer battery technologies that are more efficient and heat-tolerant. Nickel-zinc batteries are now commercially available, with a low heat rise and wide operating range to support cabinet thermal optimization.
During heat waves, traffic system outages can make a bad situation worse, stranding drivers with idling cars adding to the heat and making air quality worse. If traffic system planners plan ahead, choosing technology designed to beat the heat, DOTs and drivers can all breathe easier in the hot years to come.