How Does Altitude Affect AC-DC Power Supplies?

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Most AC-DC power provides that meet the protection requirements per UL/EN 60950-1 for ITE (Data Expertise Tools) purposes are designed to function at typical workplace and manufacturing unit altitudes, which might differ from barely above sea stage to as high as 2,000 meters (6,562 toes). And, many power provide producers present models which are designed and rated for operation at greater altitudes, as much as 3,000 meters (9,843 toes) so their provides can be utilized in main cities positioned at greater elevations (e.g., Denver, Santa Fe, Mexico Metropolis, Bogota). Many broadcasting/communications stations/towers are positioned at altitudes as much as 3,000 meters or greater with the intention to maximize their vary.

Altitude impacts the design of power provides since ‘air’ is used as an electrical insulating medium (aka, dielectric) within the building of power provides, in addition to most digital units. The density and dielectric power (insulating property) of air is excellent at sea stage, however at greater altitudes, the thinner air loses a few of its dielectric power, which must be compensated for. Switchmode power provides function off of high voltages (inputs of 90 to 265Vac) and internally generate even greater voltages (400Vdc or extra), which must be insulated and contained to stop high voltage arcing or breakdown inside the provide, and to guard the end-equipment and working personnel.

The drawing beneath reveals a cross part of a typical printed circuit board (PCB), which is comprised of copper electrical conduction paths that our chemically etched on an insulated (dielectric) fiber board materials (e.g., FR4, woven fiberglass fabric with epoxy resin), plus digital elements that aren't proven on this drawing. As may be seen, the fiber board and air, mixed with the distances between the etched conductive traces are the primary insulation mediums for the circuit board.

Drawing Credit: Mammano B, ‘Security Concerns in Power Provide Design, Underwriters Laboratory / TI
  • The time period ‘Clearance’ refers to scarcity path between the 2 conductive components (circuit traces, elements, and so on.), measured via air.
  • The time period ‘Creepage’ refers back to the scarcity path between two conductive components measured alongside the floor of the insulation (PCB, insulating supplies/obstacles, and so on.).

What does this should do with altitude? Since ‘air’ will get thinner (diminished barometric stress) at greater altitudes and turns into much less of an insulator, the PCB and element layouts should be designed with ample security spacing distances to stop high voltage arcs or breakdowns between conductors and/or digital elements.

For instance, typical power provide design apply might permit 8 mm spacing distance between primary and secondary circuits and 4 mm spacing distance between primary and floor. These spacing distances will differ relying upon the voltage ranges between conductors and elements and the anticipated humidity, temperatures, air pollution ranges, and attitudes.

For these power merchandise that have to be accredited per the Chinese language CCC group (required to export provides into China), the new Chinese language Security Normal GB 4943.1-2011, which is analogous to UL/EN 60950, requires strict specs for creepage and clearance distances. As of December 1, 2012, the primary-to-secondary clearances should enhance by an element of 1.48 to qualify the availability for operation as much as 5,000 meters, since many areas in China are positioned at high altitudes. The choice for CCC licensed power provides is that they have to clearly marked with a warning label that states that the power provide have to be used beneath 2,000 meters (see desk beneath).

The bottom design altitude for ITE power provides is 2,000 meters. Nevertheless, as talked about earlier than, because the altitude will increase, the air turns into a poorer insulator and the spacing distances should be elevated per the next desk (assuming an 8 mm clearance at 2000m).

Altitude (meters) Barometric Stress (kPa) Multiplication Issue for Clearance Ensuing Clearance (mm)
2000 80.0 1.00 8.00
3000 70.0 1,14 9.12
4000 62.0 1.29 10.32
5000 54.0 1.48 11.84

As may be seen from this desk, if a power provide is to be operated at 5,000 meters, its conductor/elements clearances have to be elevated by 48% in comparison with a provide designed for 2,000 meters.

The opposite main impact of high altitudes on power provides is that the much less dense air doesn't conduct warmth as nicely. To compensate for greater altitudes, power provides must be derated, or make use of bigger warmth sinks, or have elevated pressured air circulation, or a mix of those to insure correct cooling. As well as, the power provide have to be designed with the correct conductor and element clearances as mentioned above.

In abstract, every time an application requires power provide should function at altitudes above 2,000 meters (6,562 toes), at all times examine with the producer to find out if that is acceptable, or if an alternate mannequin that's designed for greater altitudes is required.