Ease the Load When Testing AC & DC Sources

An electronic load is a versatile and effective measurement tool. It receives electricity from a power source, such as a power supply or battery, and sinks current to ground. It provides insights into how the power source behaves under different load conditions for AC or DC power sources. By keeping an electrical parameter such as voltage, current, power, or resistance fixed, it can measure voltage/current or power/resistance under constant-voltage (CV), constant-current (CC), constant-power (CP), and constant-resistance (CR) conditions. Armed with microprocessors, modern electronic loads are “smart” and can quickly characterize a wide range of AC and DC power sources, often showing clear test results on their own display screens or on an external computer. When an AC or DC supply must be evaluated, during design or even for maintenance, an electronic load provides much needed capabilities.

Electronic loads are often equipped with self-protection functions to protect the user and the test equipment. Protection is typically provided against over-temperature, over-voltage, over-current, and over-power conditions. These features make it safer to use electronic loads, especially during high-power measurements, and can be found in many of the AC, DC, and combination AC/DC electronic loads available from Axiom Test Equipment (don’t miss the earlier blog on electronic loads, “Learn More About Electronic Loads”).

Electronic loads for AC testing are typically built for single-phase and three-phase AC power systems at standard grid voltages, such as 110 or 220 V AC, depending upon region, but may also be capable of measurements at other AC voltages depending upon the test equipment. Measurements are typically performed on units under test (UUTs) such as uninterruptible power supplies (UPS), DC/AC inverters, and AC power supplies. Electronic loads for DC measurements cover wider voltage ranges, testing such UUTs as DC power supplies and supporting circuits, batteries, and solar panels. Finding the best electronic load for an application is usually a matter of matching the load’s limits and capabilities to the needs of the application.

Starting the search for an electronic load usually begins by understanding an application’s requirements, for AC or DC testing. A suitable electronic load should be rated for at least the maximum current, voltage, and power of a UUT. Some margin should be allowed beyond the expected voltage, current, and power upper limits, keeping in mind that greater margins bring greater cost.

In terms of functionality, a DC electronic load will typically support different operating modes, such as CC, CV, CP, and CR modes. A DC electronic load should at least support the operating modes needed for an application of interest, although many currently available electronic loads support all four standard modes. Any DC electronic load being considered for a particular application should provide the required operating voltage range, maximum current rating, and maximum power rating. It may have additional requirements, such as capabilities for static and dynamic measurements, performing measurements on multiple UUTs at one time, and different types of computer interfaces, such as USB or GPIB. Electronic loads for high-power testing must manage electricity dissipated as heat. They should be equipped with some form of cooling mechanism, such as cooling fans, to manage the heat.

Comparing Solutions

A quick summary of currently available AC and DC electronic loads provides a sample of the measurement capabilities of different test equipment. The B&K Precision 8514 is part of the company’s 8500 Series of programmable DC electronic loads. It is compact enough to move around a test bench and easy to use, with large pushbuttons and a clear display screen. It operates in CC, CV, CP, or CR mode and is rated for 1200 W maximum power. The maximum current rating is 240 A for a voltage range of 0.1 to 120.0 V DC. It has a USB port for connection to an external computer but also has enough internal memory to save as many as 25 programmed test setups. It is safe to use, with built-in self-protection for over-temperature, over-voltage, over-current, over-power, and reverse-polarity cases. The DC electronic load is ideal for characterizing DC power sources, DC power supplies, DC-to-DC converters, batteries, fuel cells, and solar cells.

When testing involves higher power levels, the Chroma 63212A-150-1200 DC electronic load performs static and dynamic measurements at power levels as high as 12 kW. It handles current from 0 to 1200 A and voltage from 0 to 150 V DC. In addition to the four standard (CC, CV, CP, CR) operating modes, it provides a constant-impedance (CZ) mode, and an auto mode in which the electronic load automatically switches among the four basic modes, for specialized test applications, such as lithium battery charger testing.

This versatile measurement system includes yet another operating mode, with a sinewave loading function in which a user can set current bias, a loading sinewave, and sinewave frequency (to 50 kHz) for checking fuel cells and DC-internal-resistance (DCIR) testing. The Chroma 63212A-150-1200 features overpower and overcurrent protection and programming/memory for more than 250 load timing functions. In a modular configuration, the Chroma 63600-5 is a DC electronic load mainframe that holds as many as five modules to provide capability as needed. Plug-in modules are available for maximum voltage of 80 V, maximum power of 200, 300, or 400 W, and maximum current of 20, 60, and 80 A. 

Controlling heat is a large part of testing high-power electronic supplies and load banks are designed to efficiently dissipate heat produced as part of high-power supply testing. The Simplex Swift-E Plus Portable Load Bank weighs only 50 lbs. but can handle as much as 15 kW AC power during 2/3-wire, single-phase AC testing. With on-board cooling fans, it is a practical choice for testing high-power sources such as generators. Its control panel includes a digital power meter to facilitate power measurements.

Since AC power sources can be affected by distortion and other nonlinear effects, the NH Research (NHR) 9430-24 is a regenerative four-quadrant current-regulated AC load that allows users to customize power waveforms. It operates to 24 kW and with AC voltages to 350 V rms. It can perform single-phase, three-phase, or split-phase AC testing across a waveform frequency range of 30 to 880 Hz. Nonlinear power testing includes measurements of crest factor and power factor, with a 10% to 90% slew rate of less than 500 μs. The test equipment unit can also function as a DC electronic load to 200 V DC.

For extended functionality from a single test equipment unit, the Elektro-Automatik (EA) EA-PSB11500-60 is a bidirectional DC power supply that packs a programmable power supply and electronic load in a single 4U-high rack-mount enclosure. With maximum positive voltage of 2 kV DC and maximum current rating of 60 A, the power supply can work to power levels as high as 30 kW. The space-saving unit also integrates a software-defined arbitrary waveform generator for creation of custom waveforms.

For more information on these loads and load banks, other test equipment, or to request a rental or sales quote for your next project – visit our homepage www.axiomtest.com. For a “real-time” connection, speak directly with one of our sales reps by calling 760-806-6600 or emailing sales@axiomtest.com. For more Power Testing Equipment resources and equipment, visit our Power Testing Equipment category page.