The increasingly developed portable electronic products have higher and higher requirements on the performance of rechargeable batteries such as capacity and cycle life. There are four types of commonly used batteries, nickel-cadmium batteries and lead-acid maintenance-free batteries (SLA for short) in the last century. It has been widely promoted in the 1960s, and the two categories of nickel-metal hydride batteries and lithium-ion batteries (lithium-polymer batteries) have only been commercialized in the past ten years. These four categories of batteries have their own strengths, and the following table shows A basic reference, the specific values of different battery manufacturers may be quite different, consult the manufacturer when using, the data in the table is only for comparison and reference (C in the table is the nominal capacity of the battery, the unit is AH (Amp hour) , A represents the charging constant current.)
Comparison Items Lead-Acid Maintenance-Free Batteries Nickel-Cadmium Batteries (NICD) NiMH Batteries (NIMH) Lithium-Ion Batteries (LI-ION)
Energy density (Wh/kg)304060100
Cycle life (times) 300800500800
Operating temperature (°C)0~350~450~400~50
Maximum charging current (A) 0.25C2C1C1C
Charging method after constant current constant voltage after constant current constant current constant current after constant voltage
Charging time (hours)C/A + 2 hoursC/A + 20%C/A + 20%C/A × 2
Of course, people hope that the charger can be charged in a short time, but due to the large current and difficult control, this has a certain degree of cost in terms of cost and technology. If the use conditions permit, choose the one with the end of charging in about 10~14 hours. The night-time slow-charging charger will have the advantages of low price and small size.
For SLA batteries used in parallel online, it is recommended to use 2.27V/unit (corresponding to 13.7V for 12V batteries) constant voltage charging. This solution will not overcharge the battery, but also help stabilize the voltage of the device. When using SLA battery for charging and discharging, you should use the "three-stage" charging method of 0.2C constant current, then 2.45V/unit constant voltage, and the battery will enter 2.27V/unit constant voltage immediately after charging. The entire charging time is about 8 to 10 hours.
The NICD battery allows overcharging with a certain current, so it is economical to use a simple constant current source charger with a current of 0.1C.
NIMH batteries are more sensitive to overcharging. Even if the current is 0.1C, if the battery is charged for more than 14 hours or the already charged battery is charged for a few more hours, the life of the battery will be greatly damaged. It is very important to turn off the current in time or reduce the charging current to below 0.02C, even for 0.1C nighttime slow-charging NIMH chargers.
There have been many successful cases of smart fast chargers with a maximum charging current of about 2C. Such chargers generally must monitor battery voltage, temperature and other parameters at any time during the charging process, and automatically reduce the charging current when the battery is about to be fully charged. This can minimize the risk of over-temperature and over-voltage caused by battery overcharging.
The charging characteristics of NICD and NIMH batteries are very similar, except that NIMH batteries generate more heat and less peak voltage during charging. These two types of batteries use one of the following conditions as the fast charging termination condition during fast charging: including the voltage rising slope (dV/dt), the negative voltage increase (-dV) and the battery temperature rising slope (dT/dt) . There are also three conditions that are set to operate under abnormal protection conditions: maximum battery temperature, maximum battery voltage, and the built-in timer of the charger. To achieve these monitoring and intelligent switching actions, the cost of the charger will definitely increase, but without these measures, the battery will face potential safety hazards such as reduced capacity, reduced cycle life, and even leakage and explosion.
The charging methods of LI-ION and SLA batteries are similar, and both require constant current and then constant voltage. The difference is that lithium-ion batteries require higher voltage accuracy (<1%) in the constant voltage stage of charging. Since the safety of lithium batteries is a fatal hazard, special care is required in end-of-charge control and protection. For different applications, lithium-ion battery packs will have built-in corresponding charge and discharge protection circuits, so as to more safely protect the battery from happening.
