Summary
Many pieces of electronic equipment include a power supply unit (often abbreviated to PSU) to convert the raw electrical power from the mains or a battery to the form needed. An example would be in your laptop computer or phone charger. A phone charger takes 120V AC power from your electrical socket and converts it to 5V DC for the phone to use. This conversion prevents the electrical components of the phone from damage as they are only designed to use 5V DC power.
Primary selection criteria for a power supply
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.
Calculate total wattage needed
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. This should be at least 20% greater than what is required. See an example of sizing a power supply below
