a. Constant Voltage Chargers
The most common example of a constant voltage charger is the DC power supply of a simple car battery charger, which includes a step-down transformer from the mains and a rectifier to provide DC voltage. Constant voltage chargers are frequently utilized in the lead-acid cells found in cars and back-up power systems. While generally more complex due to additional protective circuitry for both user and battery safety, lithium-ion cells also regularly incorporate constant voltage systems. Known as a voltage-limiting device, the Li ion charger is comparable to the lead-acid system. To distinguish the Li ion charger and from its lead-acid counterpart, simply note the increased voltage per cell, tighter voltage tolerance, and the lack of trickle or float charge when completely charged. Manufacturers of Li ion cells maintain stringent settings on voltage cut-off, as Li ion is unable to accept overcharge, unlike the relative flexibility of lead-acid systems.
b. Constant Current
The voltage of constant current chargers shuts down when the voltage level reaches full charge and resumes automatically when additional voltage is required to maintain constant current flow. Nickel cadmium and nickel-metal hydride cells or batteries frequently utilize this design.
c. Trickle Charge
To account for self-discharge of the battery, trickle charge can provide continuous charge or long-term, constant-current charge for stand-by use. Based on the frequency of discharge, such charge rates may vary.
Those batteries that are susceptible to damage caused by over-charging, such as NiMH and Lithium batteries, are not recommended for trickle charge. Chargers may be designed to switch to trickle charging when the battery completely charged.
d. Float Charge
Permanent connection exists in parallel between the battery and the load across the DC charging source. These are maintained at a constant voltage just below the battery’s upper voltage limit.
Float charge is mainly utilized with lead-acid batteries for emergency back-up power systems.