Choosing the Perfect Electronic Load

Like a programmable power supply in reverse, an electronic load simulates load conditions and measures power consumption.

As end-users demand increasingly efficient devices and longer battery run times, designers increasingly depend on electronic loads. According to MarketsAndMarkets, sales of electronic loads are expected to grow 6.3% per year and reach $4 billion in 2024.

The challenge is that today’s electronic loads have numerous features. The wide range of capabilities poses a challenge in selecting a cost-effective tool. There are numerous questions to consider:

·       How much power must the electronic load absorb?

·       What types of devices will the electronic load be testing?

·       Do I need a regenerative load?

·       What building facilities are needed to power and cool the load?

·       How will the electronic load be controlled?

·       What safety features does the electronic load have?

·       What software will connect the electronic load?

With advancements constantly reshaping the landscape of electronic loads, it can be challenging to identify a cost-effective solution that meets both current and future application requirements. This article may save engineers valuable time and help them avoid mistakes by outlining the key parameters to consider when choosing an electronic load.

Determine Load Power Requirements

Start by determining the power your load needs to absorb. Consider the total power, maximum voltage, and maximum current that your device-under-test (DUT) can supply. It’s not enough to know the maximum kilowatts you need. Remember that power is a product of current and voltage, so your chosen electronic load should also have voltage and current input ratings that match or exceed the output parameters of your DUT. By ensuring compatibility in power requirements, you can effectively test your devices and avoid any limitations or performance issues.

Review Input Range

While power, voltage, and current requirements are straightforward, it's worth considering how the load's input characteristic can maximize flexibility and potentially lead to cost savings. Some electronic loads offer an autoranging input characteristic. This feature allows operators to test at full power over a wide range of current and voltage values.

A conventional electronic load can sink maximum power only at its maximum rated voltage and current. In contrast, an electronic load with autoranging can absorb full power down to 33% of the rated voltage. This means that in some applications, a lower-power electronic load can be used, resulting in reduced cooling requirements, capital costs, and annual operating costs. In other cases, a single electronic load can replace two (one used for low-power testing and one used for high-power testing). Furthermore, autoranging electronic loads offer adaptability to future requirements compared to electronic loads with conventional input characteristics.

Identify Needed Control Parameters

Electronic loads can control power, voltage, current, and resistance as needed for testing. Some electronic loads offer additional control capabilities, ensuring the flexibility to test a wide range of devices. Ensure that the selected load can control all the parameters necessary for testing your DUT.

For instance, testing a power source typically requires a constant current mode to assess performance under different load conditions. Similarly, testing a charging device may require voltage control to analyze the charger's response to changing voltage levels. If your test protocol involves assessing how your DUT performs over a wide range of load resistances, then you will need an electronic load that can control resistance.

Additionally, if your test protocol involves testing a DUT's output, and that output is under low voltage, then verify that the electronic load can control at the needed voltage while sinking the necessary current. Check the datasheet for the lowest voltage an electronic load can control while sinking the maximum rated current. The specification to look for is called minimum control voltage and is usually expressed as VMin at IMax.

Identify the Various Types of Test Methods Needed

Consider whether your testing requires dynamic conditions, such as fast load changes, or disturbances, such as noise simulation. If you are testing batteries, battery chargers, fuel cells, or solar panels, you will want to simulate various operating conditions to assess the device's performance. Dynamic load conditions must be added by a function generator.

A function generator allows engineers to create custom waveforms and simulate various load conditions to stress the DUT. A function generator can simulate I-V (current-voltage) curves and produce ramp and pulse loads to test the DUT's response to dynamic load changes. Additionally, DC sine waves can simulate and test the response of a DUT to noise, a test commonly performed on power supplies.

Integrating a high-power electronic load with a low-power function generator adds complexity to the test setup. Consider whether you want an electronic load that includes a built-in function generator. The manufacturer may include a library of tests that include the needed functions.

Consider the Energy Costs

Conventional electronic loads absorb power and dissipate it in the form of heat. This is not a problem for benchtop testing at low power. However, at higher power, particularly for production testing that is almost continuous, the heat is a significant source of wasted energy. For these applications, a good choice is an electronic load with regenerative capability, which means it converts the absorbed DC power into an AC waveform and returns it to the power grid.

Click image to enlarge

Figure 2. The Series ELR from EA Elektro-Automatik is an example of a regenerative electronic load that returns up to 96% of absorbed energy to the grid

While regenerative electronic loads may have a higher initial cost compared to conventional electronic loads, the long-term energy savings outweigh the initial investment. In addition to consuming less power, air conditioning costs are greatly reduced, further lowering the utility bill. In some cases, such as production testing of EV batteries, the energy cost savings are enough to recoup the investment in new test equipment. Also, by efficiently returning energy to the grid, regenerative electronic loads contribute to corporate sustainability goals.

Determine Infrastructure Needs

Electronic loads come in various power capacities, and the utility requirements differ accordingly. In general, electronic loads with power capacities of up to 3 kW can operate on single-phase power. Loads ranging from 5 kW to 15 kW likely require three-phase power.

Most electronic loads maintain a safe internal operating temperature using forced air cooling. For higher power electronic loads, water cooling options are available. The space for this equipment needs to be considered, especially on a production floor where space is dear.

Check Safety Features

Given the substantial power, voltage, and current involved, the safety of an electronic load is paramount. It is crucial to ensure that the electronic load provides adequate protection mechanisms to safeguard both the load and the testing environment. Overtemperature protection is essential to shut down the load if the internal temperature reaches a dangerous level. Similarly, overcurrent, overvoltage, and overpower protection are crucial to prevent damage to the load and ensure safe operation. While all electronic loads have protection devices, not all include all four protection modes.

Determine How You Want to Interface with the Electronic Load

Consider the control interface options offered by the electronic load. The interface plays a vital role in how test engineers interact with and control the load. Common interfaces include USB and Ethernet, offering convenient connectivity to PCs and other devices.

In addition to the standard interfaces, some electronic loads offer optional field-installable interfaces that enhance flexibility and allow users to easily add new interfaces for future applications. RS-232 interface compatibility offers the use of standard SCPI commands.

For industrial applications, where integration with a programmable logic controller (PLC) is necessary, some electronic loads support the Modbus command language. Interfaces such as CAN, CANopen, EtherCAT, Profibus, and Profinet enable seamless integration into PLC-based control systems. Additionally, some electronic loads can be controlled via an isolated analog signal, ensuring effective control in industrial environments with high-noise grounds.

Plan to Expand

In many applications, the power demand may exceed the capacity of a single electronic load. In such cases, it is crucial to select a load that allows convenient and safe paralleling of multiple loads. Some electronic loads offer a master-auxiliary operating mode, where one master load can control a set of loads effectively.

Moreover, some electronic loads can distribute the incoming power equally among all connected loads. This sharing mechanism prevents individual loads from absorbing an excessive quantity of power and safeguards the loads from potential damage. Using these strategies, managers can scale up if test power levels increase in the future into the megawatt range.

Define the Software Environment

For automated testing, select an electronic load that is compatible with your software environment. Most electronic loads support standard programming languages such as C or Python, as well as graphical programming languages like National Instruments' LabView. These software environments enable easy and efficient programming and control of the loads, streamlining automated testing processes.

In case coding is not the preferred approach, many electronic loads include dedicated software that enables easy load control, creation of control sequences, and execution of test schemes for various applications such as battery testing, fuel cell testing, automotive standards tests, and solar panel tests. Using the software, operators can quickly develop automated control programs, reducing the time and effort required for test system development.

Equipped with these considerations, you are ready to select the ideal electronic load or loads that suit your requirements. By carefully evaluating the parameters discussed in this article and by leveraging the supplier’s expertise, you can confidently choose an electronic load that ensures accurate testing, optimal performance, and cost-effective operations.

EA Elektro-Automatik