Every piece of complex electrical equipment comes with its own power supply, from your TV to your personal computer, because such sensitive systems require a constant supply of consistent electrical power to function. In an office or factory this equipment is on larger scale of complexity, but the same reason applies for its existence. Standard electricity supplied by the national grid is high voltage AC current, while home electronics and automated industrial machinery both require a stable DC current to function, so the electricity supplied by the country's power plants has to be converted to a lower voltage, direct current supply.
These units are called regulated DC Power Supplies and function on two basic principles; switch-mode conversion, and the older linear style of conversion which downgrades the power input through successive components. Linear converters generate more heat but less noise, while switch-mode converters are noisier but more efficient. There is also a third option, an unregulated power supply, that can supply reliable high current at low cost. These units can be used in rugged inductive applications where regulation of the output voltage is not critical, such as indicator lamps, relays, solenoids and DC motors.
The lighter and more compact switching units convert commercial AC current input to stable high frequency DC current output, via high speed switched semiconductors. They can be operated on a variety of input voltages and output capacities, and offer several operating methods. These include series or parallel operation to increase the power supply's voltage or capacity if necessary, and a backup to ensure that the supply continues uninterrupted. Other functions are often included, such as protection against excess voltage or current overload.
Choosing an industrial power supply is relatively simple, and for modern applications switched mode power supplies are the most popular. Most of them are only 25% as big as an equivalent linear supply, but 25% more efficient, with a universal input voltage that can take from 85-264V AC and a frequency range of 47-63 Hz. The output voltage is generally adjustable and many power supplies have built-in sensors to determine what voltage is applied, together with an over-voltage protector, though under-voltage can sometimes also be a problem. It's important to identify, from each device that will be connected to the power supply, what its DC input requirements are, and, if necessary, calculate the exact amount of power required for each item drawing power from the supply to ensure that it will be sufficient. If in doubt, always over-estimate the output volume, and add an extra 25% to be on the safe side.
The complex assemblages of items that require mounting in modern automated systems have given rise to a new form of connector, the DIN rail mounting. This architecture allows combinations of modular components to be simply snapped on to a mounting strip, including power supplies, although some compatibility checks are required. DIN rails come in three different formats and sizes, so it's important to make sure that all your components are of the same size and format as the mounting rail. DIN rail architecture is also commonly attached to a back plate and enclosed in a housing to protect components from the environment, so heat generation and operating temperature of the power supply must also be taken into consideration. If your system requires a dense assemblage of components in a small housing, a power supply with 89% or more efficiency, and a no-load power consumption of less than 0.1W will prevent excess heat dissipation which could cause damage.
Power supplies for industrial machinery come in many shapes and sizes, according to their applications, and Rowse Automation has a great (and expanding) selection of items to fit your exact specifications.