The balanced charging of lead-acid batteries (commonly known as "balanced charging") is a key operation to restore battery consistency through a specific charging process, in response to issues such as uneven cell voltage and capacity deviation that occur during long-term float charging or cyclic use of the battery pack. The operation must strictly follow safety regulations and battery characteristics. The specific steps are as follows, suitable for industrial energy storage UPS、 Lead acid battery packs for electric vehicles and other scenarios (with a typical cell voltage of 2V/6V/12V).
1、 Preparation before Charging: Safety and Basic Inspection
The inspection before uniform charging is a prerequisite for avoiding safety accidents (such as leakage, bulging, short circuit) and ensuring charging effectiveness. The core needs to confirm the safety of "personnel, equipment, and battery" in three aspects:
Environment and personnel preparation
Choose a site with good ventilation, no open flames, and away from flammable and explosive materials (charging lead-acid batteries can produce hydrogen gas, which may explode when exposed to open flames), and turn on the exhaust fan if necessary.
Personnel should wear insulated gloves, goggles, and insulated shoes; Prepare emergency tools (such as dry powder fire extinguishers, absorbent cotton, alkaline neutralizers, to deal with leaks or small-scale fires).
Equipment and tool inspection
Confirm the parameters of the balanced charger: It needs to support three-stage charging of "constant current constant voltage float charging" (or dedicated equalization charging mode), and the output voltage and current need to match the specifications of the battery pack (for example, the average charging voltage of a 12V single battery is usually 14.4-14.8V, and the average charging voltage of a 2V single battery is 2.35-2.4V, depending on the battery manufacturer's parameters).
Check whether the charger output line and plug are damaged or short circuited, and whether the alligator clip or wiring terminal is secure; Calibrate the voltage/current display of the charger with a multimeter to avoid errors.
Battery pack status check
Appearance: Check each individual battery for leakage, bulging, shell cracking, and pole corrosion (if any, the corrosive material needs to be treated first or the faulty battery needs to be replaced, and direct charging is not allowed).
Voltage measurement: Use a DC voltmeter (with an accuracy of ≥ 0.01V) to measure the open circuit voltage of each individual battery cell (after disconnecting the load and standing still for more than 2 hours), and record the deviation value - if the voltage difference between individual cells exceeds 0.1V (2V cell) or 0.3V (12V cell), equalization charging is required; If the voltage of a single unit is lower than 1.8V (2V) or 10.8V (12V), it may indicate severe power loss. A small current pre charge (below 0.1C) should be added to 1.9V/11.4V or above before entering equalization charging.
Connection: Confirm that the series/parallel connections of the battery pack are secure, without looseness or virtual connections (virtual connections can cause local heating and burn out the terminal posts).
2、 Core operating steps: three-stage equalization charging process
Balanced charging should be carried out in three stages: constant current charging → constant voltage charging → float charging to normal. The key is to control the charging voltage, current, and duration to avoid overcharging causing battery dehydration and plate softening. Taking the common "12V single cell battery pack (such as 3 12Vs connected in series to form 36V)" as an example, the parameters need to be adjusted based on the battery capacity (C, unit Ah):
Stage 1: Wiring and starting constant current charging (eliminating capacity deviation)
Correct wiring
Disconnect the battery pack from the load/inverter and ensure that the battery pack is in a 'no-load' state.
The charger output terminal should be connected to the positive terminal of the battery and the negative terminal of the battery (reverse connection is absolutely prohibited! Reverse connection will instantly burn the charger and battery poles). When wiring, connect the positive terminal first and then the negative terminal; If using a crocodile clip, the pole should be clamped tightly to avoid poor contact.
Recheck the polarity of the wiring: Use a multimeter to measure the polarity between the charger output terminal and both ends of the battery pack, confirm consistency, and then turn on the power.
Set constant current parameters and start
The constant current is controlled between 0.1C-0.2C (e.g. 100Ah battery, current set to 10-20A). If the current is too high, it will cause the battery to heat up too quickly, and if it is too low, the charging efficiency will be low.
Start the charger, enter constant current mode, and observe the voltage changes of the battery pack: during this stage, the voltage will gradually increase, but the current will remain stable. Continue charging until the "total voltage of the battery pack reaches the uniform charging constant voltage value" (for example, the uniform charging constant voltage of a 12V unit is 14.4V, and if three units are connected in series, the total voltage needs to reach 43.2V).
Check every 30 minutes during the process: the temperature of the battery casing (≤ 45 ℃, if exceeded, reduce the current or pause), and whether the wiring is heating up (if heating up, power off and re tighten).
Stage 2: Switching to constant voltage charging (restoring cell consistency)
Automatic/manual switching of constant voltage mode
When the total voltage of the battery pack reaches the preset "uniform charging constant voltage value" (such as 14.4V for a 12V cell), the charger will automatically switch from "constant current" to "constant voltage" (if it is a manual charger, the voltage needs to be manually adjusted to the constant voltage value, and the current will naturally decrease).
The core of the constant voltage stage is to maintain a stable voltage at a constant recharge and gradually reduce the current - at this time, the "lagging cells" inside the battery will continue to be recharged, gradually narrowing the voltage difference with other cells.
Constant voltage stage duration control
Continuously charge at constant voltage until the charging current drops to 0.02C-0.05C (for example, for a 100Ah battery, the current drops to 2-5A), which is the key criterion for completing equalization charging (if the current is too low, the battery is basically fully charged, and continuing to charge will cause dehydration).
If the current still does not drop below 0.05C after 2-3 hours of constant voltage, it is necessary to check whether the individual battery has severe sulfurization (you can try adding "de sulfurization charging", but professional operation is required), or if the charger parameters are set incorrectly.
Stage 3: Floating Charge Transition and Charging End
Switch float charging mode (protect battery)
When the charging current drops to 0.02C-0.05C, switch the charger to "float charging mode", set the float charging voltage to 13.5-13.8V/12V (lower than the average charging voltage to avoid overcharging), and continue float charging for 1-2 hours to stabilize the battery voltage at the float charging level and allow the internal electrolyte to fully react.
Power outage and closure
After the float charging is completed, disconnect the charger power first, and then remove the wiring (sequence: remove the negative pole first, then remove the positive pole to avoid sparks during wiring).
Measure the open circuit voltage of all individual batteries again (after 1 hour of standing): if the voltage difference between the individual batteries is ≤ 0.05V (2V individual battery) or 0.15V (12V individual battery), it indicates successful equalization charging; If the deviation is still large, the equalization process needs to be repeated 1-2 times (but not more than 3 times to avoid overcharging).
Clean the battery pole: If there is residual electrolyte (white powder), wipe it with warm water and baking soda solution, and then dry it with a dry cloth to prevent pole corrosion.
