Switch mode power conversion technology dominates nearly every segment of the economy, including demanding aerospace and military power systems that impose requirements more demanding than those imposed by power utilities or industry. Switch mode converters are, for example, successfully hardened against the effects of frequent lightning strikes on aircraft, against the effects of nuclear electromagnetic pulse in war fighting applications, and against the effects of severe vibration and ionizing radiation in launch vehicles and spacecraft. Success in these applications demonstrates two things: first, there is no fundamental impediment to employing switch mode technology in any application; second, that application success depends on the ability of the manufacturer to understand, document, design, and manufacture the product to survive the environmental and performance requirements of the customer’s application.

In industrial and power utility applications the reasons for the slow pace of adoption of switch mode chargers seem to include:

• Incompatibility of most switch mode chargers with 480-volt 3-phase AC supplies

• Failure in many cases to sufficiently harden switch mode chargers against AC-borne overvoltage stresses

• Real and perceived problems related to forced, versus convection, cooling

Industrial and power utility facilities often drive large battery chargers with 480 volt, 3-phase electrical service. Most switch mode battery chargers, however, are designed to operate from single phase, 208-240 VAC supplies. Some switch mode chargers are rated for AC input up to 320 volts, potentially enabling them to be employed in a 277/480-volt system by connecting phase to neutral. Switch mode chargers are now becoming available with 480 VAC input that does not require the neutral conductor, and which are compatible with all common 3-phase Delta grounding schemes.

Switch mode converters are inherently more vulnerable to mains-borne electrical transients than line frequency converters. This is because power semiconductors in switch mode converters are located upstream of the converter’s power transformer, versus downstream of the transformer in most line frequency designs. This vulnerability can be addressed in switch mode converters by employing the same strategy as that used in aerospace and military systems: multiple layers of defense.

Forced air cooling boosts packaging density and cuts weight and cost in electronic devices. Even with a conversion efficiency of 95% a 7 kW power converter creates 368 watts of waste heat that must be transported from internal components to the environment. Because fans typically fail before power electronics, fans are perceived as an Achilles heel of power converters. The solution employed for years in nearly all higher power UPS and power supplies is to provide redundant fans equipped with failure alarms.

Conventional fan cooling is effective at transferring heat out of densely packaged electronics. The unintended consequence of moving lots of air, however, is the deposition of airborne contaminants onto electronic components and circuit card traces. These contaminants contribute to premature electronics failure. A new method of cooling is presented that reduces the vulnerability of force-cooled electronics to premature failure from atmospheric contamination.

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