Basic Working Principle of Charging and Discharging for Battery Charge and Discharge Testing Equipment

Basic Working Principle of Charging and Discharging for Battery Charge and Discharge Testing Equipment

Charging Process

Charge and discharge testers can implement various forms of charging processes, such as constant voltage charging, constant current charging, constant current followed by constant voltage charging, forward pulse charging, positive and negative pulse charging, etc. The charging process can be customized based on the battery's performance needs.

1. Constant Voltage Charging: The charge and discharge equipment is set to constant voltage mode. Since the set charging voltage is near the fully charged voltage of the battery, the charging current is at its highest at the beginning of the charging process. As the battery's terminal voltage increases, the voltage difference between the charger and the battery decreases, and the charging current gradually decreases. When the charging current reduces to a certain level, the charging ends. In constant voltage charging, the initial charging current is relatively large, which may be detrimental to the battery cells' lifespan.

2. Constant Current Charging: The charge and discharge equipment is set to constant current mode, where the current remains constant throughout the charging process. The battery's terminal voltage gradually rises over time until it reaches the cut-off voltage, at which point the charging process ends. In constant current charging, if the current is set too low, it will result in a longer charging time. If the current is too high, it can cause significant battery polarization, leading to a notable voltage drop when the charging circuit is removed.

3. Constant Current Followed by Constant Voltage Charging: This method combines the advantages of both constant current and constant voltage charging. Initially, a relatively large current is set for constant current charging to improve charging efficiency. When the charge reaches a certain level, it switches to constant voltage charging, and the charging current gradually decreases, allowing the battery to absorb more charge.

4. Pulse Charging: In this method, large current charging is applied for a period, followed by a zero-current interval. During this interval, the battery can undergo partial depolarization, reducing energy loss during the charging process and allowing for more charge to be stored.

Pulse charging can take various forms, such as variable current pulse charging, variable voltage pulse charging, and positive-negative pulse charging. For example, in variable current pulse charging, the current remains constant over equal time intervals and is interrupted by a brief pause, after which the constant current charging resumes, repeating in cycles. The overall trend follows a gradual reduction in current. Variable voltage pulse charging is similar to variable current pulse charging, except that voltage is the control variable. In this case, the current decreases following a pattern, while the voltage increases. In positive-negative pulse charging, the zero-current interval is replaced by a reverse current, supposedly for better depolarization.

Discharge Process

The charge and discharge tester is used to assess the discharge performance of batteries, mainly for various scenarios such as lifespan testing, working condition simulation testing, capacity testing, consistency screening, as well as other battery parameter and safety tests. The different testing objectives determine the variations in current and voltage during the discharge process. The desired current and voltage can be input through the upper computer, and the tester adjusts the power output according to the control system's requirements.

1. Lifespan Testing: Cycle life is one of the most important battery testing items. Based on different experimental purposes, the same battery is tested repeatedly under charging and discharging conditions until its capacity decreases to 80% of its original value, at which point the number of cycles can be calculated. Cycle life testing is used to evaluate battery performance or to define suitable operating conditions.

   
   

2. Working Condition Simulation Testing: Working conditions refer to the operational state of equipment under conditions directly related to its performance. If the data on voltage and current changes in the battery pack during equipment operation can be obtained and then simulated in real time, such as switching between different charging and discharging currents and cycling through them, the battery's real dynamic performance during operation can be replicated. This allows testing of whether the battery meets the equipment’s operational requirements.

   
   

3. Capacity Testing: Battery capacity is obtained by integrating current over time, from the start of charging or discharging until the cut-off conditions are met. By comparing results, performance differences between various products can be analyzed. Common testing items include current rate and temperature characteristics tests. The higher the accuracy of current and voltage measurements and the faster the sampling rate, the more precisely battery cell capacity differences can be detected.

   
   

4. Consistency Screening: Inconsistency between batteries can cause the performance of the battery system to be much worse than that of individual cells, significantly reducing the overall battery pack's lifespan. Lithium battery consistency screening indicators include capacity consistency, internal resistance consistency, constant current ratio consistency, discharge platform consistency, voltage consistency, and batch consistency. Consistency screening methods include static screening and dynamic screening. Traditionally, static screening is more commonly used. "Static" refers to cell parameters that are independent of working conditions. Parameters typically used for static screening include battery capacity, open-circuit voltage, and internal resistance. Dynamic screening, on the other hand, is a method of grouping based on differences in cell parameters during charging and discharging operations.