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We all know that AC input voltage when unstable can be dangerous. That’s why you use power supplies to convert AC voltage into safe, consistent and constant DC output voltage. But the question is, what do you have to think about when selecting a power supply? In today’s episode we will explore key considerations for selecting the right one for your application.
When choosing a power supply that’s right for you, the primary selection criteria are the input voltage, the output voltage, and the output power capacity. Your typical input voltage choices will be either 120–240 V single-phase (the most common), or 230–480 V three-phase. The misapplication of the input voltage may cause the power supply to fail. The typical output voltages are 12 V or 24 V, with 24 V being the most common. The misapplication of output voltage could potentially damage your sensitive and expensive devices such as PLCs.
To select the proper power rating of your power supply, add up the current ratings of the devices you will run with the power supply and multiply it by the output voltage of the power supply. This will give you the total wattage needed to run your system. You always want to select a power supply wattage that is slightly larger than what is required to run the system. An undersized power supply will not run the system properly, causing potential shutdowns and damage to the equipment connected to the power supply.
It’s also important to understand where the power supply is going to be installed and who will have access to the panel in the facility. Are simple screw terminal power supplies acceptable? Or is a greater level of worker protection required for an IP20 rated finger-safe terminal power supply?
There are also applications that go beyond simply providing stable power. The first potential need is for a buffer module, which will work in conjunction with the power supply to provide power to the load during brief line power failures. This will provide backup via a capacitor for instances where total power is lost for a short time (250 ms @ 240 V, 5s at 24 V). The other option is a redundancy module, which allows you to use multiple power supplies in a redundant fashion to keep the load powered in the event of a device failure.
The final factors to consider are the space available, the environment for the panel’s location in the facility, and the geography of the facility. These will impact the form and fit that you select for space, whether you need a device that is rated for fire and shock risk areas, and whether the power supply that you select meets North American and/or global application standards.
