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How to charge the battery without a smart charger

by:dcfpower     2021-03-14

For charging the battery without specifying a charger, we recommend manual charging. Charging the battery is a technical task, and it is safer to charge it under human supervision. If it is not smart charging, we recommend manually charging lead and lithium batteries.

1. About the charging method of lead-acid batteries

Before connecting the batteries, calculate the charging voltage according to the number of batteries in series, and then set the required voltage and current limits. To charge a 12-volt lead-acid battery (six cells) to the voltage limit of 2.40V, set the voltage to 14.40V (6 x 2.40). Choose the charging current according to the battery size. For lead acid, this is 10% to 30% of the rated capacity. A 10Ah battery, 30% of the power is about 3A; the percentage can be lower. The 80A starter battery can be charged at 8A. (A 10% charge rate is equal to 0.1C.)

When charging, also pay attention to the battery temperature, voltage and current. Be sure to charge in a well-ventilated room. Once the battery is fully charged and the current drops to 3% of the rated Ah, the charging is complete. Disconnect charging. If the current has bottomed out and cannot be reduced, disconnect the charging after 16-24 hours; high self-discharge (soft short circuit) can prevent the battery from reaching a low saturation level. But you can also use the power supply to balance the lead-acid battery by setting the charging voltage to 10% higher than the recommended value. The overcharge time is very important and must be carefully observed. The power supply can also reverse sulfation. Set the charging voltage higher than the recommended level, adjust the current limit to the lowest actual value and observe the battery voltage. Fully sulfated lead acid can first draw a very small current, and as the sulfated layer dissolves, the current will gradually increase. Raising the temperature and placing the battery on an ultrasonic vibrator may also help the process. If the battery does not accept charging after 24 hours, it is unlikely to recover.

Second, about the charging method of lithium ion batteries

Lithium ion charge is similar to lead acid. We can also use the power supply, but we must be very careful. Check the full charge voltage, which is usually 4.20V/battery, and set the threshold accordingly. Ensure that none of the batteries connected in series exceed this voltage. (The protection circuit in the commercial battery pack does this.) When the battery reaches 4.20V/battery voltage and the current drops to 3% of the rated current, or has bottomed out and cannot drop further, a full charge is reached. After fully charging, disconnect the battery. Never allow the battery to stay at 4.20V for more than a few hours, otherwise there is a danger of explosion.

Note that not all lithium-ion batteries are charged to the 4.20V/battery voltage threshold. Lithium iron phosphate is usually charged to 3.65V/cell's cut-off voltage and lithium titanate to 2.85V/cell. Some energy batteries can accept 4.30V/cell and higher. It is important to observe these voltage limits.

3. Nickel-cadmium batteries (NiCd) and nickel-metal hydride batteries (NiMH)

Using power to charge nickel-based batteries is challenging because the root of full charge detection lies in the voltage characteristics that vary with the applied charging current . If you must use a regulated power supply to charge nickel-cadmium batteries (NiCd) and nickel-metal hydride batteries (NiMH), please use the temperature rise during fast charging at 0.3-1C as an indication of full charge. When charging at low current, estimate the remaining power and calculate the charging time. The dead 2Ah NiMH will charge in about 3 hours at 750-1,000mA. Trickle charging, also called maintenance charging, must be reduced to 0.05C.

Related information: How to use lithium battery pack for the first time-detailed explanation of charging algorithm for rechargeable lithium ion battery! The working principle of lithium battery pack charger chip


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