Adaptive Charging: Principles Adaptive Charging (Part 3 of 4)
This article originally appeared in the 2Q17 edition of Battery Power Magazine. The article is published on our blog in 4 parts. You can access the full article here.
Principles of Adaptive Charging
The basic principle of Adaptive Charging is to minimize the amount of time batteries spend on float while maintaining full charge for backup applications. This is executed by cycling the batteries through an automated testing regimen that intelligently decides after every test whether the batteries need to be charged.
Figure 3: Adaptive Charge Management regimen shown as a flow chart.
Batteries are maintained in a standby (off charge) mode by isolating them from the rectifier bus via Servato’s proprietary technology. The VRLAs are charged about 20 percent of the time and at rest about 80 percent and are still kept at full capacity. Limiting the oxygen recombination reaction that causes degradation significantly increases battery life. In this standby mode, batteries are still available for instantaneous discharge in case of a power outage.
While the batteries are at rest they are monitored at periodic intervals multiple times per day. Servato uses OCV and Temperature to indicate state of charge. State of Health is determined by evaluating several parameters including DC Resistance, charge efficiency, and self-discharge rates, among others. All battery data is parsed for any trends that may indicate existing or developing battery issues.
The measurements are collected and analyzed automatically and compared to a library of battery data accumulated through more than 5 million battery-operating hours. If stable, the batteries are allowed to remain in the standby mode for a period of time when they will be tested again. If the data show changes greater than embedded set points a charge is initiated.
If and only if charging is necessary, the batteries are put on the rectifier bus until they are fully charged to the dv/dt charge termination point. This replaces energy lost through self-discharge and any short-term discharges that may have occurred. As soon as the full charge criteria are satisfied the batteries are again isolated from the rectifier. If the batteries have been discharged for more than a preset time during the standby period they are immediately connected to the rectifier for charging to eliminate any possibility of standing in a partially discharged condition.
In a multi-string application, the strings are charged sequentially to assure string-to-string equalization. Each string is brought to full charge independent of the other strings in the system. This reduces the adverse affects caused by random inter-string variation. Following any charge event the battery strings are given a State of Health test. A short discharge is applied to the batteries. Voltage and time characteristics are recorded and used to calculate the internal resistance.
Adaptive charging assures that the batteries are charged whenever the data trends indicate that a charge is necessary and not anymore, and it automatically compensates for normal temperature-dependent phenomena such as self-discharge. Compared to continuous float charging or intermittent charging, Adaptive Charging offers a way to improve battery service life and reliability.
Figure 4: Comparison of Adaptive Charging to continuous float in an accelerated life test.
This battery life extension is not just a theory. Laboratory and field data confirms the ability of Adaptive Charging to extend battery life. An independent test laboratory was used to compare the capacities of VRLA batteries over time when they were on continuous float and when subjected to an Adaptive Charging regimen. Tests were carried out according to the Time Warner Accelerated life test protocol. Four strings of batteries were tested, battery capacities were measured at approximately three-month intervals and averaged and charted as shown in Figure 4.
Part 4 of 4 of the article will be published soon.
Headquartered in New Orleans, LA, Servato is a leading provider of active battery management solutions to telecom, power, transportation, and solar companies. Servato’s solutions allow leading companies and infrastructure operators to reduce CapEx and OpEx by extending battery life, reducing maintenance costs and streamlining operations. Utilizing highly accurate data, proprietary algorithms, adaptive charging and cloud-based visualization software, Servato provides unprecedented insight and control over distributed DC power assets in industrial settings. To learn more, please visit: www.servatocorp.com
