One key difference between commercial and military power supplies is the range of environments in which they are built to operate. As you may have guessed, military power supplies operate in a wider range of environments than commercial power supplies. That is because power supplies used in military applications are expected to operate in a variety of environments, from the depths of space to the depths of the ocean and from the tropics to the Arctic. With that in mind, here are two key temperature-related factors that exemplify the environmental challenges of power supplies:
Temperature range: Commercial power supplies can operate well in average temperature environments – for example, temperatures that can be expected from various weather conditions on land. But military power supplies must accommodate temperatures that range from -40 degrees Celsius (-40 degrees Fahrenheit) to +85 degrees C (185 degrees Fahrenheit).
Temperatures on earth seldom reach -40 or +185 degrees. But a military power supply might be required to withstand the higher or lower temperatures present in space or in direct sun on concrete or metal as well. It must also be able to withstand overheating, and have overheating protections in place. During the manufacturing process, a military power supply undergoes testing to ensure that it can endure this broad temperature range.
Temperature changes: Sudden temperature changes can cause many electronic systems, including commercial power supplies, to experience thermal shock. Examples include space operations, aircraft, and systems that are stored in a heated enclosure but when required to operate, immediately move to hot or cold environments. This could result in the system shutting down or being damaged, which could be catastrophic and cost billions of dollars (think Mars rovers).
The military standards (MIL-STD) that specify the testing which military power supplies must undergo to prove they can handle required temperature variations are MIL-STD-202, MIL-STD-750, MIL-STD-810, and MIL-STD-883. These MIL-STDs provides a number of test regimens for cycling an assembly or component (a power supply system or a part of the power supply system) through rapidly changing temperatures. Typical test cycles for military power supplies range from 0° to 100° C, but can reach maximums of -65° to +150° C or more, with recommended intervals of exposure.
Temperature handling represents only one set of challenges for military power supplies, but it is an important factor that separates electrical systems approved for military use from their civilian counterparts. From the heat of the Sahara to the cold of Siberia, a military power supply must be able to operate flawlessly in any temperature it may experience during operation.