[NH Research] Approaches for Charger Testing
IntroductionChargers manage voltage and current to refill, or recharge a battery according to the manufacturer’s specifications. While simple in concept, a charger may be required to change its output characteristics, detect and test batteries before or during charge, or even require communication with the battery or the utility company. Chargers range from a simple charger which provides only a constant current (CC), constant power (CP), or constant voltage (CV) output all the way up to a grid-managed charger which changes how it charges the battery based on utility, battery, and additional conditions. This application note provides a basic description for testing each type of charger.Always On Chargers Always on chargers typically provide a fixed output. For example, a lead acid trickle charger provides only a small constant current (CC) output. This type of charger can be verified by using an electric load ith either constant voltage (CV) or constant resistance (CR).In rare cases, this type of charger may provide either CC or CV during the charge profile. In this case, the electronic load can still be used by using a constant resistance (CR) loading.All NH Research (NHR) loads support CC, CV, CP, and CR allowing maximum flexibility in evaluating always on chargers.Waking up a ChargerBattery chargers may not provide an output voltage or current until it first detects the voltage from the battery, an external interlock is closed, or both. The charger may even use these battery detection conditions in order to determine how to safely start charging the battery. For example, the charge profile may wait until the temperature reaches an acceptable level or contain additional pre-charge steps to recover deeply discharged batteries.In these cases, the test fixture may contain a small power supply, diodes, or relays needed to “wake-up” the charger. All NHR air-cooled loads provide digital I/O allowing additional test fixture devices to be managed by the load.We provide connections that allow a turn-on signal to be used for a charger or a small power supply. Or control a relay/switch to connect the power supply to the charger to start it up then disconnect it later.Chargers that “Test” the Battery During ChargeChargers may “test” the battery during charge by reducing or even drawing power from the battery itself. Some types of batteries require these “tests” for the charge to be properly accepted, to reduce internal pressure, or to re-absorb chemicals within the battery itself. Alternatively, some chargers do these “tests” in order to safely charge the battery, to determine the health of the battery, or for self-calibration of the charger itself. How the charger “tests” the battery and what the charger expects to see in a normal battery determine the approach used in validation.Combining an NHR load with a power supply along with a control application on a PC is a very cost effective solution for low power chargers (
