What Is an Electronic Load? Operating Modes and Selection Criteria
An electronic load is a programmable test instrument that draws energy from a power supply, battery or converter at a set current, voltage, resistance or power to test it under load.
An electronic load is a programmable test instrument that draws energy from the source it is connected to at a set current, voltage, resistance or power, testing the source under real operating conditions. It is used to measure the behaviour of power supplies, adapters, chargers and DC-DC converters under load, and to see the capacity of batteries and cells by discharging them at a specific current. The absorbed energy turns into heat in the instrument; an electronic load cannot power a circuit, which is the job of a laboratory power supply.
Operating modes
- Constant current (CC): Draws the set current from the source. Used for load regulation tests of power supplies and battery discharge tests.
- Constant voltage (CV): Draws as much current as needed to hold the voltage at its terminals constant. Used to test chargers and current-limited sources.
- Constant resistance (CR): Simulates a resistive load.
- Constant power (CP): Holds the drawn power constant even as the voltage changes; used in battery and converter tests.
- Dynamic mode: Switches between two current levels at a set frequency and slope; the source's response to sudden load changes is watched on an oscilloscope.
Verify the modes a model supports in the manufacturer's datasheet.
Selection criteria
- Consider voltage, current and power together: All three limits apply at once; the drawn power (voltage × current) cannot exceed the total power. For example, the UTL8512+ (150 V, 30 A, 300 W) can draw 30 A only up to 10 V and at most 2 A at 150 V. The UTL8513A+ (150 V, 120 A, 600 W) draws 120 A up to 5 V.
- Voltage range: The source's open-circuit voltage must not exceed the load's maximum input voltage. 150 V models suit adapters and low-voltage sources; for high-voltage DC sources the 500 V UTL8512B+ is chosen.
- Minimum operating voltage: An electronic load cannot draw full current at very low voltage. If you will test low-voltage sources such as a single cell, check the minimum operating voltage in the datasheet.
- Dynamic performance: The current slew rate (A/µs) and maximum dynamic frequency determine how fast the load can change during a transient response test. The product data of the catalog models mentions 5, 10 and 50 kHz.
- Interface: Production testing and automated measurement need communication; the product data of the catalog models lists RS232 (with SCPI commands) and, on some, optional RS485.
- Leads and remote sensing: At high current the test lead cross-section must carry the current. To exclude the voltage drop along the leads, connect the remote sense input, where available, to the source terminals.
Common mistakes
- Exceeding the voltage limit: If the open-circuit voltage of a source such as a solar panel or series-connected batteries exceeds the instrument's maximum voltage, the load is damaged.
- Using thin, long leads: The voltage drop distorts the set value in CV, CR and CP modes.
- Not setting a cut-off voltage when discharging a battery: The battery discharges below the voltage the manufacturer allows and is damaged.
Related standard
The safety standard for measurement, control and laboratory equipment is IEC 61010-1; check the model's conformity in the manufacturer's documentation.
Electronic loads in the catalog
The Electronic Load Devices category lists 8 active DC electronic loads from Unit; all are sold on a quote basis.
| Model | Values in the product name |
|---|---|
| UTL8211+ | Single channel |
| UTL8212+ | Compact, high precision |
| UTL8511+ | Programmable |
| UTL8511A+ | 150 V, 30 A, 200 W |
| UTL8512+ | 150 V, 30 A, 300 W |
| UTL8512A+ | 150 V, 30 A, 400 W |
| UTL8512B+ | Programmable, up to 500 V |
| UTL8513A+ | 150 V, 120 A, 600 W |
For the voltage, current and power limits of models whose name does not state them, see the technical data on the product page. High-current test leads (UNI-T UT-L0615-OO 60 A, UT-L0312-UU 30 A) are in the Measuring Instrument Accessories category.
Frequently asked questions
What is the difference between an electronic load and a power resistor?
A power resistor has a fixed value; the current it draws changes with voltage. An electronic load holds current, voltage, resistance or power at the set value, measures it and can change it by program.
How is battery capacity measured with an electronic load?
The battery is discharged in CC mode at a constant current down to the cut-off voltage given by its manufacturer. Current multiplied by the elapsed time gives the capacity (Ah).
How do I get the price of these models?
All models in the category are sold on a quote basis; request a quote on the product page for price and delivery time.