Discussion on the principle of lithium ion and Ni MH battery charger
Battery charging
A new rechargeable battery or battery pack (a few batteries in a battery group) can't guarantee that it is full of electricity. In fact, they are likely to have been fully discharged. Therefore, first of all, the battery / battery pack should be charged according to the manufacturer's Guide to chemical components.
Each charge should be applied in order of voltage and current in accordance with the chemical composition of the battery. Therefore, the charger and charging algorithm need to meet the different requirements of the chemical components of different batteries. The terms used for battery charging including constant current (CC) for NiCd and NiMH batteries, and constant / constant pressure (CC/CV) for lithium ion and lithium polymer batteries. Now,let's talk about the principle of lithium ion and Ni MH battery charger.
Ni MH battery charging
Although the NiMH charger is similar to the NiCd charger, the NiMH charger uses the delta T/dt method to terminate the charge, which is the best way to charge the NiMH battery at present. The voltage drop at the end of the NiMH battery is smaller, and the low charge rate (lower than 0.5C, which is at the temperature) may not decrease the voltage.
The new NiMH battery will have an early error peak during the charging cycle, which causes the charger to recharge early. In addition, there will be almost sure to be overcharged at the end of the single use - Delta V detection, which leads to the limit of charge and discharge number before the failure of the battery. There seems to be no -dV/dt charging algorithm for NiMH batteries in all conditions (new or old, hot or cold, full or partial discharge). Therefore, unless the NiCd charger uses the dT/dt method to terminate the charge, the NiCd charger can not be used to charge the NiMH battery. Moreover, because the NiMH battery can't absorb the overcharge well, the trickle charge current is smaller than the NiCd battery (about 0.05C).
The slow charge of NiMH battery charger is difficult. Because of the rate of 0.1C to 0.3C, changes in voltage and temperature do not accurately indicate that the battery is full. Therefore, the slow charger must depend on the timer to decide when to end the charge. In order to ensure that the NiMH battery is full, we should charge quickly at the rate approaching to 1C (or battery manufacturer's designated rate), while monitoring voltage (delta V = 0) and temperature (dT/dt) to determine when to end charging.
Li-ion and lithium polymer battery charging
The nickel base battery charger limits the current, while the li-ion battery charger needs to limit the voltage and current at the same time. The initial lithium ion battery charging voltage is limited to the 4.10V/ section. The higher the voltage means the larger the capacity, the 4.20V battery voltage can now be achieved by adding chemical additives. The current lithium ion battery is usually charged to 4.20V, with a tolerance of + 0.05V/.
When the end voltage reaches the voltage threshold and the charging current is reduced to 0.03C (about 3% of Icharge, reference Figure 6), the battery is full. Most li-ion battery chargers have reached full charge for about 3 hours. Although some linear chargers claim that Li-ion battery charging takes only about one hour, such chargers usually terminate charging when the battery terminal voltage reaches 4.2V. This method can only charge the battery to 70% of its capacity.
The above is the brief discussion on the principle of lithium ion and Ni MH battery charger for your reference.