How to choose an electronic load

For quite a long time, the simplest solutions were used to test, for example, a power supply under load: power resistors or light bulbs. But with the widespread availability of high-power semiconductor components and the emergence of equally powerful power supplies, it became possible to make this process more convenient by using an electronic load.

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It’s probably worth explaining right away that a resistor load has the advantage of being close to ideal, but it also needs additional cooling, just like other electronic components. Light bulbs present a different problem: the filament’s resistance is very different when cold and hot, so connecting this kind of load can trip the overload protection even on a perfectly good power supply.

In any case, the basic purpose of any load, whether electronic or made from power resistors, is to convert the energy drawn from the source into heat. That’s why most of the unit consists of a power stage and cooling system. The exception is regenerative electronic loads, which return up to 95% of the energy to the grid, but these devices are very expensive and extremely rare.
Everything else affects only measurement accuracy and service features, so the first things you’ll usually see when inspecting one are a large heatsink and powerful fans.

So, when choosing one, you should consider the following:
1. Budget: high-power loads can be expensive.
2. The maximum parameters you need, usually power, current, and voltage.
3. Whether it has a four-wire connection, especially for working with high currents.
4. Whether it can connect to a computer for plotting graphs and control.
5. Its features, both in standalone operation and when connected to a PC.
6. Measurement accuracy and parameter setting accuracy. In some situations, lower accuracy has no effect on the tests, so you can save money here.



Most of the specifications are straightforward when choosing a load, but the maximum voltage deserves a separate mention. The overall measurement circuit includes wires, connectors, current-measuring shunts, and the power stage.
The minimum voltage drop across the transistors depends on their voltage rating. If you buy a load rated for a much higher voltage “just to be safe,” you may find that it can’t deliver its rated current at very low voltages.

For example, when testing batteries, especially LiFePO4 and LTO, the voltage can be below 2 V. The current may initially match the set value, but it will drop toward the end of the discharge. This happens when the load is operating at its maximum current and the source is at its minimum voltage.



Most basic electronic loads operate in constant-current mode: they regulate the current in the circuit of the source connected to them. But this isn’t suitable for testing sources that are themselves current generators, such as chargers. To put it simply, a voltage source (power supply, battery) is loaded with a current regulator, while a current source (charger) is loaded with a voltage regulator; otherwise, they’ll conflict.
There are actually more than two modes, but the four main ones are:
CC, or Constant Current: current regulation
CV, or Constant Voltage: voltage regulation; the load prevents the voltage from rising above the set value by increasing the current.
CP (CW), or Constant Power: power regulation; the device varies the current to draw the set amount of power.
CR, or Constant Resistance: constant resistance; the load current changes automatically according to the input voltage.


Also, while the type of current doesn’t matter for a resistor or light bulb, electronic loads are divided into two classes: DC and AC.
And then there are the service features. Some loads are very basic, with a standard ammeter-voltmeter; more advanced models have a microcontroller and can calculate the capacity that has passed through them. There are also versions that connect to a computer, and, of course, programmable electronic loads that let you set an operating algorithm, emulate a pulsed-current load, combine different modes, perform analysis, and more.

The power stage is most often built around MOSFETs. They’re much easier to control, but more importantly, they can load sources starting at almost zero voltage. In addition, there are electronic loads built around bipolar transistors, which work better in linear mode. A third option is IGBT transistors, used where high power is required.

For a while, Chinese developers even made a hybrid power supply combined with an electronic load function, where the power stage could operate either as a power supply regulator or as a load.



The simplest electronic load, operating in CC mode (and CV mode, for that matter), can be built at home with just a few components: an op-amp, a transistor, and a couple of resistors. It will have its drawbacks, of course, but it will work.
The variable resistor sets the current, while the fixed resistor is used for measurement.



To improve stability, you’ll need to make it a little more complex, but it will still be within reach of a beginner electronics hobbyist. The circuit below is essentially an electronic load circuit.


A similar version is also available ready-made. It can draw up to 10 A from sources with voltages up to 100 V, at power levels up to 75 W. For this board, you only need to buy a heatsink, a low-power power supply, and a variable resistor to adjust the current…


But the circuit designs shown above have drawbacks: low power, and, if you build one entirely from scratch, the need to find and buy individual components, make a circuit board, and so on. So a good option for a beginner electronics hobbyist is to buy a component kit for building an electronic load based on the LM324 op-amp. It includes almost everything you need. - review


Once assembled, all you need to do is find a suitably sized heatsink, and the electronic load is essentially ready. To improve stability, however, it’s recommended that you replace the included 1 nF capacitors with ones in the 22–47 nF range.

The result is a 150 W electronic load (with a suitable heatsink) with CC mode. If you like, you can modify it to work in CV and even CP mode, but that’s a topic for another article.



If you want something more capable, hobbyists should consider “semi-finished” products, or simply ready-made power modules. These already include both the electronics and cooling system, and are usually rated for around 100–300 W. They come in various configurations with different maximum current and voltage ratings.

The modules made by Sousim stand out in particular. They’re available at different power ratings, and some can even be controlled over RS485. But even the basic models, with adjustment via a variable resistor, can operate not only in CC mode but also in CV mode. They also have an onboard microcontroller that monitors overloads and temperature, and controls the installed fans based on both temperature and power.
Review




Add a small power supply and an ammeter-voltmeter to these modules, and you can easily build a DC electronic load that’s simple yet quite functional. The example in the photo is rated for 300 W, 40 A, and up to 150 V, with CC and CV modes (at half power) and battery capacity measurement.


The next step up is devices that include not only a power stage but also a control unit. Depending on the size of the heatsink, they’re most often rated for 150 or 180 W. However, it should be noted that this is the maximum power, and it also depends heavily on the source voltage. For example, the load can work more easily at 12 V, 10 A than at 120 V, 1 A, even though the power dissipated is the same in both cases. This is due to the characteristics of the power transistors.


There are similar models that can be connected to a computer and have a nicer display, but their other specifications are similar to those of the previous models.


The TEC40K series of electronic loads deserves a separate mention. These devices come in three versions rated at 400, 800, and 1600 W, and can draw up to 45 A.


The devices have their own control panel, but can also be controlled from a computer and used to plot discharge curves. Despite their unremarkable appearance, they are in a fairly high class.



If you don't repair power supplies but occasionally need to measure a battery's capacity, there are more specialized boards. In principle, they can also work as ordinary electronic loads, but they're much better suited to battery testing. In this case, the battery is first charged with any suitable charger, then discharged using the load.
ZB206+ (left) has a maximum voltage of 8.5 V, which is suitable for testing two Li-Ion batteries connected in series. Its maximum current is 2.6 A and its power is up to 12 W. - review
ZPB30A1 (right) is considerably more powerful, rated at up to 60 W, 10 A, and 30 V.

Both also support four-wire connections and can measure a battery's internal resistance.


If you want a reliable device with plenty of features and don't want to do any soldering, take a look at the wide range of ZKEtech electronic loads. This Chinese company specializes in just this kind of equipment.
Their products fall into two main categories:
EBD - electronic loads only.
EBC - electronic loads combined with a charger, essentially battery testers.
They also vary in power, current, and maximum voltage.

Before moving on to a general overview of the models, though, it's worth mentioning some key features of this company's devices.

1. All of the company's devices support connection to a computer. This is needed both to control them and to plot current/voltage and power graphs. EBC series models can also run programmed tests.
What's more, if you have several electronic loads from this company, you can control them all at once from a single software window. They appear in additional tabs in the upper-left corner of the window.


This feature isn't just useful for monitoring; it also makes it easy to create combined graphs, with up to 9 curves overlaid.


2. All the loads also have four-wire connections, which immediately solves the problem of measurement accuracy.


That's why the loads have four terminals: two for the power connection and two for measurement.


For connections, people most often use either leads with alligator clips or a dedicated battery holder.


The simplest model is the EBD-M05. It has no charger and is rated at just 35 W, with a maximum voltage of 19.5 V and current of 5 A, but otherwise retains the capabilities of the higher-end models. Its distinguishing features include highly accurate voltage measurement and current setting, and, of course, a four-wire connection—properly professional.


EBC-A05+ is more versatile because it includes a charger. It is rated at up to 60 W, with a maximum voltage of 30 V and current of 5 A. It also comes in an enclosure and includes a power supply and a cable for connecting to a computer. This load is well suited to measuring the capacity of batteries designed for low currents, such as those in mobile phones, tablets, smartphones, and laptops.
There is also a very similar-looking device, the EBC-A01. It is rated at just 30 W and up to 1 A, but its key advantage is that it can work with low currents, starting at 1 mA. This feature is important when testing very low-capacity batteries, where ordinary testers would be too “coarse” and therefore have a high measurement error.


If you need to test batteries with a high discharge current, the EBC-A20 is a better choice. It also has a built-in charger, but its maximum current is 20 A. Keep in mind that its maximum power is only 85 W, so at that current it can only load a battery down to 4.25 V.
At the same time, EBC-A20 also supports operation with an input voltage of up to 30 V, with the current decreasing proportionally.
This model is also a good fit for charging and testing lead-acid batteries: it can charge them at up to 5 A and discharge them at up to 6 A. As with other loads, it uses a four-wire connection, with each pair of wires joined directly at the alligator clips. - review


For a more versatile solution—for example, for testing power supplies, measuring battery capacity, and charging batteries—you could consider the EBC-A10H. It can provide a load current of up to 10 A and a charging current of up to 5 A, while its maximum power dissipation is 150 W, noticeably higher than the previous models. It is controlled with a push-button encoder, making standalone operation a little more convenient than with the previous models, although it can also be connected to a computer. - review


If you need to test both power supplies and batteries, and want a current of up to 20 A along with substantial power, there is the EBD-A20. It is essentially a hybrid of the EBC-A20 and EBC-A10H, with a maximum current of 20 A, power of 200 W, and maximum voltage of 30 V. Keep in mind, though, that it has no charger (like all models in the EBD series), so you will have to charge batteries separately before testing them. Also, program-controlled operation is unavailable, since that feature also relies on the charger.

It looks very similar to the EBC-A10H; the only differences are the terminals and the fan mounted on the side.


The company also makes other models for more specialized applications, with different maximum currents, voltages, and power ratings. What they have in common is that almost all of them use the same software, which is genuinely convenient.


There are also even more specialized devices: the multichannel EBC-X series testers.
They are designed for battery “aging” tests—or, more accurately, cycle-life testing—to determine how many cycles it takes for battery capacity to fall below a specified level.
There are three models for different discharge and charge currents: 1/1 A, 10/5 A, and 10/10 A. They also differ in design: some connect to external holders that fit into special trays, while others have built-in holders, which are more convenient for testing batteries of the same length.


These testers use their own dedicated software, specifically designed for cycle-life testing.


But that’s not all: there is an adapter that lets you combine up to 8 loads into an EBC-X equivalent. However, it only works with two loads: the EBC-A40L (low-voltage, 40 A) and the EBC-B20H (high-voltage, 20 A). In the EBC-X software, they appear as a single multichannel tester. - review


If you mainly plan to use an electronic load for testing switching power supplies, with battery testing as more of an extra, it is worth considering the following pair of devices.

These two models have a lot in common: power up to 400 W, voltage up to 150 V, maximum load current up to 40 A, CC, CV, CP, and CR modes, and even roughly comparable prices. However, they differ in their additional features.

For example, the KUNKIN KP184 has a basic display, a computer connection, four-wire connections, a dynamic power supply test function (10 kHz), and measurements of battery capacity and internal resistance. This makes it a better fit for those who want to test not only power supplies but also batteries with voltages up to 150 V.


The East Tester ET5410, on the other hand, has a more informative display and noticeably more features. Its dynamic test is not limited to a single frequency; you can flexibly choose the parameters. It also offers combined CC + CV and CR + CV load modes, resistance, voltage, and current measurement modes, and a keyboard connection for more convenient control. It can be used to test batteries, but it has a two-wire connection and cannot communicate with a computer.


Above, I mentioned the dynamic testing function. This mode can be important when testing power supplies under pulsed loads and current fluctuations. Sometimes a power supply that works normally with a steady load current starts to "go crazy" when connected to loads with pulsed power consumption. Dynamic load mode is designed for tests like these: the current draw changes at a set frequency and duty cycle.


If you need near-maximum accuracy and functionality, it’s better to look at devices from more established manufacturers. Keep in mind, though, that they’re often rated for less power than the models shown above, or their prices can rise significantly.

For example, the programmable load ITECH IT8511A+: 150 V, 150 W, 30 A, with CC, CV, CP, and CR modes, dynamic load, a full set of necessary protections, list-based operation (a programmable equivalent of dynamic mode), short-circuit testing for power sources, direct parameter entry, computer connectivity, and a "warm, old-school" VFD display.


The next step up could be the RIGOL DL3021, rated for 200 W, up to 40 A, and the same 150 V. It has all the features listed above, plus a large screen, digital inputs and outputs, computer connectivity via both USB and a local network, and operation according to a user-defined program.


Having covered loads ranging from inexpensive kits to professional solutions, I can’t leave out lab-grade equipment, such as the ITECH IT8615.
Here, the power rating is 1800 W, the voltage is 420 V, and the current goes up to 20 A. But that’s not the key point: this load is designed to work with AC as well as DC, and in addition to the usual operating modes, it offers adjustable crest factor and power factor.
But if you take a look at the back, you’ll see that "deep down" it’s still the same device for turning electrical energy into heat—just a very smart one.


The manufacturer equipped this device not only with a large screen, but also with a built-in oscilloscope, so you can watch the test in real time and see how the device under test responds. The load can also measure harmonic distortion up to the 50th harmonic.


And if 1800 W isn’t enough, it supports parallel operation and three-phase operation in both delta and star configurations. The total power therefore increases in proportion to the number of connected devices.


To make choosing easier, here’s a quick summary:
1. If you’re a beginner hobbyist and don’t plan to spend much, you can consider a DIY option, such as a kit based on the LM324. It can save you money while giving you a powerful load, albeit a very basic one.
2. If you’ve already "found your calling" and plan to repair power supplies, and can spend a little more, you can look at ready-made modules such as the Sousim or TGEC40k, as well as entry-level factory-made models like the East Tester ET5410. The first option is cheaper; the second is considerably more functional.
3. Battery testers with built-in electronic loads are a category of their own. Most electronic loads can test batteries, but ZKEtech EBC-series devices can do more than just run tests automatically, alternating charge and discharge cycles and plotting the results: they can also perform battery life-cycle tests.
4. Professionals will probably be interested in branded loads that offer not only extensive functionality and high accuracy, but also operating modes unavailable on simpler models. Note, though, that if you also need high power, the price can be substantial. Then again, good things are rarely cheap.
5. It’s hard to recommend anything to users of lab-grade equipment, since they usually know what they need and choose their tools for specific tasks.