Tech Talk Blog

What’s the best AC input for your DC power supply?

August 02, 2021 | Topics: Electronic Loads

What’s an AC Input?

An AC input, short for Alternating Current input, is a vital component of a DC power supply system. Unlike Direct Current (DC), which flows in one direction continuously, Alternating Current alternates direction periodically. AC inputs are used to supply the necessary electrical energy to power DC power supplies, enabling them to convert the alternating current into the desired direct current output.

In essence, the AC input serves as the source of power for the DC power supply, providing the electrical energy needed for the conversion process. Understanding the characteristics and specifications of the AC input is crucial for selecting the best-suited input for your specific DC power supply requirements.

In the upcoming sections of this blog, we’ll delve deeper into the considerations for choosing the best AC input for your DC power supply, exploring factors such as voltage requirements, frequency compatibility, input power quality, and more.

AC Inputs and DC Power Supplies

The first step in choosing a DC power supply is determining how much output power you will need. Once you have figured that out, the next decision revolves around how you are going to power the power supply. In other words, you have to identify the best AC input for your DC power supply.

Most DC power supplies rated at 1000 W or less will work just fine on a single-phase, 120 VAC circuit. You cannot, however, simply plug higher power supplies into a 120 VAC wall socket. Most DC power supplies rated at 1,500 W or more will require 240 VAC single-phase power.

Power supplies capable of supplying 3 kW or more will, as a general rule, require some form of three-phase AC power input. Depending on your region and your facility, you may need to connect your EA power supply to three-phase 208 VAC, 380 VAC, 400 VAC or 480 VAC.

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208 VAC input

In the US, 208 VAC connections are common. Our US208V models have a 5-pole AC connector on the rear of the unit as shown in Figure 1. When connecting the 3-phase AC supply, use the labeling next to the plug (filter housing) to ensure that you connect the phases properly.

Connect a 208 VAC 3-phase cable to an EA power supply

Figure 1: This figure shows how to connect a 208 VAC, 3-phase cable to an EA power supply. The cable shown uses the U.S. color code.

The following connections are required:

Rated Power Inputs on AC plug Supply type Configuration
15 kW L1, L2, L3, (N), PE Three-phase (3P) Delta

The PE conductor is necessary and must always be connected! The N conductor, if present in the cable, can be connected to the free position of the AC connector. For a 15 kW power supply, we suggest using a cable with AWG 8 conductors. AWG 8 conductors can handle currents up to 56 A. The AC connector can accommodate loose/soldered conductors up to 16 mm2 (AWG 6).

380 VAC or more

If your installation requires an input voltage of 380 VAC or more, EA offers what we call Wide Range, or WR, input for most of our high-power, programmable DC power supplies and loads. Power supplies with this feature can accept voltages between 380-480 VAC +/- 10%, making it easier to use these power supplies anywhere around the world. This is very important as most power supply designs do not allow for reconfiguring to different input voltages.

To ensure that you don’t run into problems when installing your EA DC power supply, consult with your facilities management personnel to see what input power is available in your lab or production area before purchasing the supply. Be sure to ask the following questions:

  • What AC input voltages are currently available? It’s always less costly if you can use the AC circuits that you already have in your facility.
  • Is single-phase and three-phase power available? Remember that power supplies rated at 3 kW or more will generally require three-phase power.
  • What type of power outlets are currently installed and where are they located? This could be an important consideration in planning your test facility. If you can locate power supplies where you already have power outlets, you can save on installation costs.
  • Do the power outlets available have the appropriate wire gauges required? That is to say can that circuit handle the input current that the power supply will require?
  • What options are available for cooling the supply? This isn’t strictly an issue for choosing the correct AC input for your power supply, but it is an important installation consideration.

When you have the answers to these questions, you will be able to purchase a power supply with the right input power configuration. A good practice is to download the operating manual for the power supplies that you are considering before purchasing them to ensure that you know all the details. This could prevent costly delays in getting your test facility up and running. Operating guides for all EA DC power supplies are available on our website.

Before purchasing an EA product, please feel free to contact us for advice on selecting the right power supplies and electronic loads for your application and how best to install it in your facility. You can visit the EA website, send an e-mail to, or call us at 858-836-1300.

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