BU-909: Battery Test Equipment

The energy a battery holds can be measured with a battery analyzer by applying a full discharge. The battery is first charged and then discharged at a controlled current while measuring the time to reach the end-of-discharge point(See BU-402: What is the C-rate?) A capacity of 100 percent delivers the specified Ah; 50 percent is shown if the discharge time is cut in half.

Measuring capacity by discharge gives the most reliable assessment, a method that is most effective with portable batteries. A periodic analysis ensures that the batteries are kept within an acceptable performance range and prompts replacement if the capacity is below a required target threshold and can no longer be raised. Larger batteries are normally not cycled as this is time-consuming and stresses the battery. That’s where non-invasive test methods come in(See BU-904: How to Measure Capacity)

Progress is being made with rapid-testing but this only provides estimated state-of-health results and the accuracies vary with the technology used. While older rapid-test methods measured the internal battery resistance, advanced rapid-test methods look at diffusion, charge transfer and migration that are present in Li-ion and lead acid batteries(See BU-907: Testing Lithium-based Batteries)

Technicians are most comfortable testing a battery with a voltmeter, anything further goes beyond the routine for many. Chemistry, voltage and Ah markings on the battery are often not well understood, nor are maintenance folks sure what to look for in a battery. Many portable packs have multiple connections with unclear markings. Hesitation is understandable as batteries come in many chemistries and vary in size from a coin to installations filling an entire building. A voltage reading gives instant results by showing that something is alive and a brief loading verifies power, but this does not assure sustained delivery that is so critical in a battery.

Battery Analyzer

Battery analyzers became popular in the 1980s and 1990s to restore nickel-cadmium batteries that were affected by “memory.” Today these workhorses are used to analyze a broad range of batteries as part of fleet management and assuring system integrity. Periodic battery analysis is needed because batteries tend to have a shorter life than the host it powers. Battery analyzers act as gatekeepers to retire packs when they fall below a set performance criteria.

Figure 1 illustrates a Cadex C7x00 C-Series battery analyzer that accommodates lead-, nickel- and lithium-based batteries. The instrument features automated service programs and operates in stand-alone mode or with PC software.

Four-station analyzers services batteries from 1.2 to 36V and 6A charge and discharge currents. The batteries interface with custom Battery Adapters that configure the analyzer to the correct setting.

The most common program is Auto that charges a battery, applies a discharge to measure capacity and completes the program with a final charge. Other programs include Custom to put the battery through a unique choice of charge, discharge, wait and repeat. The Lifecycle program cycles the battery until the capacity has dropped to the preset target capacity while counting the cycles. This program is used to evaluate battery durability. OhmTest measures the internal battery resistance and Runtime discharges a battery at three different current levels to simulate unique usage pattern. QuickSort™ sorts lithium-ion batteries into Good, Low and Poor in 30 seconds, and Boost reactivates packs that have fallen asleep due to over-discharge. Further programs include Self-Discharge to test losses and Prime that cycles a battery until the maximum capacity is reached. Prime also verifies the spare capacity before charge.

Connecting various shapes of batteries to an analyzer has always been a challenge and folks have designed fancy contraptions with springs and levers so complicated that only the inventor can operate. There are no simple ways to connect a battery, especially when servicing small packs with tiny surface contacts or smart batteries with numerous blade contacts.

Cadex solved the battery interface with SnapLock™ adapters. These custom-made adapters are easy to use as they are designed for a given battery type; they only go in one way. Each adapter stores up to 10 codes (C-codes) that configures the analyzer to the correct settings. The user can edit the parameters with the analyzer’s menu function or with the PC-BatteryShop™ software. The universal adapters interface to specialty packs, such as mobile phone batteries; larger batteries connect by the user-programmable Smart Cable.

PC Software

A battery analyzer would not be complete without intuitive software. PC-BatteryShop™ provides a simple yet powerful PC-interface to control and monitor Cadex C7x00 C-Series Battery Analyzers. With software, the PC becomes the command center and displays charge and discharge characteristics in real time. Clicking the mouse on any of the 3,000 batteries listed in the database or swiping the bar code on the battery label configures the analyzer. Figure 2 demonstrates such a system.

Running on software, the PC takes over the control of the battery analyzer. Programming is by clicking on a battery in the database or scanning the battery label.

Smart batteries enable a new level of battery analysis by reading the battery serial number, model, type and age, as well as the digital equivalent of the capacity that reflects battery state-of-health without applying a full discharge. A full discharge will still be needed occasionally to verify and calibrate the battery(See BU-604: How to Process Data from a “Smart” Battery)

Battery Test Systems

While battery analyzers check batteries in service and predict replacement, battery test systems provide multi-purpose test functions for research laboratories. Typical applications are life-cycle testing to simulate battery loading and verifying durability in the field, as well as checking cell balance of a multi-cell pack in field simulation. These tests can be fully automated with a custom program that the user composes.

Figure 3 illustrates the Cadex C8000, a battery test system that captures load signatures of mobile phones, laptops and power tools, and then applies the simulated loads to verify battery runtime as if used in real life situations. The device is capable of monitoring individual cells with the help of floating analog inputs. The Dual Power Port Cable extends the discharge current from 10A per station to 20A by parallel function. Higher wattage is possible by connecting the C8000 to an external load bank. The system also manages environmental chambers and reads SMBus batteries while being in full control of all functions from one central point.

Four independent channels provide up to 10A each and 36V nominal. Maximum charge power is 400W, discharge is 320W. The discharge power can be enhanced with external load banks.

Being digital provides advantages over analog by offering a large test range in a compact housing. This eliminates the need to buy extra modules to perform low and high voltage and current measurements. Another advantage is ultimate immunity from neighboring channels. The limitation is the inability to measure extremely low voltage and current that would be possible with specialty modules. The C8000 works as a stand-alone or with PC-BatteryLab™ operating up to eight C8000 analyzers servicing 32 batteries independently (with most PCs).

A battery test system, such as the Cadex C8000, includes many redundant safety algorithms that identify a faulty battery and terminate a service before an unwanted event could occur. Such security may not be available when using a programmable power supply and a programmable load to test batteries. Although an open platform offers great flexibility, it requires careful programming to prevent stress to the battery inflicting possible damage or fire if an anomaly occurs. For destructive tests the safeguards of the C8000 can be overridden.