Battery Testing with an Electronic Load

As the electronics industry continues to grow, so does the need for better batteries, and battery technology that reduces their size, improves their reliability, and increases their capacity.  Engineers require an instrument that is capable of testing batteries to ensure they can meet the requirements of their product.  An electronic load is used to test batteries’ reliability and capacity.  Batteries can be tested under a variety of static and dynamic conditions, including by absorbing a constant current, voltage, and power level as well as dynamically being able to change how the instrument absorbs current, voltage, and power based on preprogrammed test cases.  These can include testing the battery’s rated capacity, capacity retention, and life cycle performance. 

To test batteries’ rated capacity, capacity retention and lifecycle performance, RIGOL has created the DL3000 Series Programmable DC Electronic Load.  An electronic load is meant to absorb power from a power supply, battery, or other power sources. This particular model includes a built-in battery testing and list application which allow the instrument to perform rated capacity, capacity retention, and lifecycle performance testing on batteries.  These three tests are critical for engineers to determine how a battery will perform throughout its intended lifetime.

Let’s dive deeper into one of these key battery tests. The capacity retention test will help determine how well the battery will retain its maximum capacity over time. To demonstrate the capacity retention test, we have performed this test on two different 18-volt tool batteries that are about the same age, and have about the same number of charge and discharge cycles between them.  The first is a Nickel Metal Hydride battery and the second is a Lithium Ion battery. We expect that over time the Lithium Ion battery will retain the ability to store more of its original capacity than the Nickel Metal Hydride battery.

We examined these batteries under a number of different conditions to determine their capacity retention by comparing their actual effective capacity to their original specified capacity.  To perform this test, we used RIGOL’s DL3000 Series which allowed us to easily test a number of static current draw conditions.  We would have the instrument draw constant current from the batteries between 0.5 amps to 3 amps for an extended period, with the instrument stopping the test when the batteries were discharged enough that their output voltage level was 9 volts, half of their original voltage of 18 volts (Figure 1).

Our tests demonstrated that the batteries are meant to operate between 1 to 2 amps of a constant current load, as the test showed similar operating conditions for each.  The Lithium Ion battery (Figure 2) performed better and had a more consistent discharge curve than the Nickel Metal Hydride battery (Figure 3) operating under similar conditions, which indicates that the Lithium Ion battery will be able to retain more of its initial capacity compared to the Nickle Metal Hydride battery.

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Figure 2 – Lithium Ion Battery Discharge Curve

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Figure 3 – Nickel Metal Hydride Battery Discharge Curve

Based on a comparison of the test data against the two batteries’ original typical discharge curves, the Nickle Metal Hydride battery was operating at about 15% of specified capacity (Figure 4) and the load level was nominal, so the capacity loss is likely the result of age, usage, and the charging process.  Generally, Nickel Metal Hydride batteries respond poorly to being left charging for long periods of time, as it can limit their capacity.   

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Figure 4 – Nickel Metal Hydride Battery Capacity Comparison

The Lithium Ion battery was found to be operating at about 75% of the specified capacity and again the load values were nominal.  The Lithium Ion batteries hold capacity better as they age, and respond better to a long-term trickle charge. 

The DL3000 series enables engineers to easily test a battery’s rated capacity, capacity retention, and lifecycle performance, allowing them to predict how long the battery they are using will last in their product.  This capability plays a vital role as the electronic industry continues to drive demand for smaller, more reliable, and longer-lasting batteries.
 

Rigol Technologies

www.rigolna.com