A backup battery can remain connected to a charger for a long time. But does keeping it at one fixed voltage really meet its charging requirements?
For backup power systems used in power utilities, rail transit and telecommunications, batteries need to remain adequately charged while avoiding prolonged overcharging. This is why industrial battery chargers distinguish between two important charging modes: float charging and equalization charging.
Although both modes are used to charge batteries, they serve different purposes. Understanding when and how to use each mode helps ensure that the charging strategy matches the actual condition and requirements of the battery.
Float charging maintains a battery's charge after it has been substantially charged. It uses a lower, stable voltage to compensate for self-discharge and small losses while the battery remains connected to the charger.
Equalization charging uses a higher voltage for a controlled period. It can be used to restore capacity after deep discharge or, for battery types that permit it, help address differences between individual cells.
In simple terms:
The two modes have different purposes and should be applied according to the battery manufacturer's recommendations and the actual operating conditions.
In backup power applications, batteries may remain connected to a charger for extended periods. Once the battery is substantially charged, continuously using a higher charging voltage is not appropriate.
Float charging addresses this requirement.
Float charging uses a relatively low and stable voltage to compensate for battery self-discharge and small losses while the battery remains connected to the charging system.
Its purpose is to maintain the battery's charged state during standby.
However, the float voltage needs to be appropriate:
Therefore, float voltage should be configured according to the battery manufacturer's recommendations and operating conditions.
For lead-acid batteries, float voltage is related to temperature.
When the temperature rises, an excessively high float voltage may accelerate water loss and corrosion. At lower temperatures, an excessively low float voltage may prevent the battery from becoming fully charged over time.
Temperature compensation can help adjust the target voltage according to battery temperature.
This allows the charging system to account for temperature changes rather than relying on one fixed voltage under all operating conditions.
Float charging maintains the battery during standby, while equalization charging serves a different purpose.
It may be used after deep discharge to restore battery capacity. For battery systems that permit equalization charging, it can also help improve differences in individual cell conditions.
Equalization charging applies a higher voltage for a controlled period.
Unlike float charging, it is not intended to operate continuously during normal standby. Once the required conditions are met, the charger should exit equalization mode and return to float charging.
The transition from equalization to float charging can be based on different conditions, including:
Some advanced systems can also incorporate temperature compensation into their charging strategy.
Equalization charging is not necessarily better when applied more frequently.
Frequent manual equalization charging may increase temperature rise and gassing. This is particularly important for sealed lead-acid batteries.
Whether equalization charging is necessary, and how long it should last, should follow the battery manufacturer's recommendations and the actual condition of the battery.
An automatic equalization strategy should also avoid unconditional time-based activation. It can take factors such as discharge depth, float charging duration, temperature and manufacturer recommendations into account.
For battery systems that do not require frequent equalization charging, this function can be disabled.
An industrial battery charger needs more than a choice between two charging voltages. It should provide configurable charging parameters and appropriate control functions to support the required charging strategy.
Important functions include:
When connected to a Battery Management System (BMS), the charger can also adjust its strategy according to the charging current and voltage permitted by the BMS.
After deep discharge, battery voltage may be relatively low.
If a higher equalization voltage is applied directly without reasonable current limitation, the initial charging current may become excessive.
Therefore, the charger needs to control both voltage and current. When a BMS is involved, the charger should follow the maximum charging current permitted by the BMS.
When a charger switches from automatic float charging to equalization charging and then back to float charging, the system should record relevant information.
This includes:
These records help users trace the charging process and understand why the charging mode changed.
Charging parameters such as equalization voltage, charging duration and current limitation should be managed appropriately.
Parameter access management helps prevent unauthorized or arbitrary changes to important settings during on-site operation.
Float charging and equalization charging should not be treated as identical requirements for every battery type.
Lead-acid, nickel-cadmium (Ni-Cd) and lithium batteries have different charging characteristics.
|
Battery type |
Charging considerations |
|
Lead-acid batteries |
Some systems use float charging together with controlled equalization charging. |
|
Ni-Cd batteries |
Their charging voltage ranges may differ from those of lead-acid batteries. |
|
Lithium batteries |
Charging depends more on the voltage and current permitted by the BMS. |
For industrial battery chargers supporting multiple battery types, charging parameters and control logic need to be configurable according to the selected battery system.
The charging strategy should not rely on one fixed set of parameters for all batteries.
For battery systems connected to a BMS, charging control can take battery information into account rather than relying only on fixed voltage settings.
Relevant feedback may include:
This information can help the charger adjust its charging strategy according to the battery's actual condition.
The battery's safety limits should always take priority over fixed voltage settings.
Float charging and equalization charging perform different tasks in industrial backup power systems.
Float charging maintains the battery during long-term standby, while equalization charging supports recovery after deep discharge or helps address cell differences where the battery system permits it.
The key is not simply to provide both modes, but to configure and manage them according to battery type, operating conditions and manufacturer recommendations.
For industrial battery chargers, configurable voltage settings, current limitation, appropriate mode switching and BMS coordination all contribute to a charging strategy that better matches the battery's requirements.
EverExceed is a manufacturer of customized AC/DC power solutions, with more than 20 years of battery manufacturing experience and over 10 years of power system integration experience. Its product portfolio includes industrial batteries, industrial battery chargers, UPS systems, telecom power systems and energy storage solutions. With in-house R&D and manufacturing capabilities, EverExceed provides customized power solutions for different industrial applications.
Float charging maintains the battery's charge during standby by compensating for self-discharge and small losses. Equalization charging applies a higher voltage for a controlled period to support recovery after deep discharge or address cell differences where applicable.
Not necessarily. Frequent manual equalization charging may increase temperature rise and gassing, particularly for sealed lead-acid batteries. Its necessity and duration should follow the battery manufacturer's recommendations and the actual battery condition.
Lead-acid battery float voltage is related to temperature. Temperature compensation adjusts the target voltage according to battery temperature.
After deep discharge, applying a higher equalization voltage without reasonable current limitation may result in excessive initial charging current. Therefore, both voltage and current need to be controlled.
Yes. Lead-acid, Ni-Cd and lithium batteries have different charging characteristics. Charging parameters and control logic should be configured according to the battery type.
A BMS can provide information such as temperature, SOC, individual cell voltage limits and permitted charging current. This information can help the charger adjust its charging strategy according to the battery's condition.
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