Basic knowledge of various rechargeable batteries and chargers

The increasingly developed portable electronic products have higher and higher requirements for the capacity and cycle life of rechargeable batteries. At present, there are four commonly used categories, nickel cadmium batteries and lead-acid maintenance free batteries (SLA), which have been widely promoted in the 1960s, nickel hydrogen batteries and lithium-ion batteries (lithium-containing polymer batteries) These two types of batteries have only been commercialized in recent ten years. These four types of batteries have their own advantages. The following table gives a basic reference. The detailed values of different battery manufacturers may vary greatly. Consult the manufacturer when using. The data in the table are only for comparison and use (C in the table is the nominal capacity of the battery, the unit is ah (ampere hour), and a indicates the charging constant current.) Comparison item lead acid maintenance free battery nickel cadmium battery (NiCd) nickel hydrogen battery (NIMH) lithium ion battery (Li-Ion) energy density (WH / kg) 304060100

Cycle life (Times) 300800500800

Operating temperature (° C) 0 ~ 350 ~ 450 ~ 400 ~ 50

Maximum charging current (a) 0.25c2c1c

Charging method: constant voltage after constant current constant current constant voltage after constant current

Charging time (hours) C / A + 2 hours C / A + 20% C / A + 20% C / A ×  Of course, people expect the charger to complete charging in a short time, but because the current is large and difficult to operate, it has a certain cost in terms of cost and skills. If the application conditions allow, choosing a slow charging charger at night after charging in about 10 ~ 14 hours will have the advantages of low price, small volume and so on

For SLA batteries used in parallel on-line, it is recommended that 2.27v/cell (13.7v for 12V batteries) be used for constant voltage charging. This scheme will not overcharge the battery, but also help to stabilize the equipment voltage. For occasions where SLA batteries are often used for off-line charging and discharging, 0.2C constant current and then 2.45v/cell constant voltage should be used. After the battery is charged, the "Three-stage" mode of 2.27v/cell constant voltage should be immediately entered Charging method. The whole charging time is about 8 to 10 hours.

There have been many successful examples of intelligent fast chargers with a maximum charging current of about 2C. Generally, such chargers must monitor the battery voltage, temperature and other parameters at all stages of the charging process, and actively reduce the charging current rate when the battery is about to be fully charged, so as to minimize the risk of over temperature and over voltage caused by battery overcharge.

The charging characteristics of NiCd and NiMH batteries are very similar. Only NiMH batteries generate more heat during charging and the peak voltage is less obvious. Both types of batteries adopt one of the following conditions as the conditions for stopping fast charging: voltage rise slope (DV / DT), negative voltage growth (- DV) and battery temperature rise slope (DT / DT). Three other conditions are set for lifting action under abnormal maintenance conditions: the maximum battery temperature, the maximum battery voltage and the built-in timer of the charger. To realize these monitoring and intelligent switching actions, it must increase the cost of the charger. However, without these measures, the battery will face safety problems such as reduced capacity, reduced cycle life and even liquid leakage explosion DANGER.

The charging methods of Li-ion and SLA batteries are similar, requiring constant current and then constant voltage. The difference is that lithium-ion batteries require high voltage accuracy (< 1%) in the charging constant voltage stage. Because the safety of lithium batteries is a risk of death, there are requirements for handling and maintenance after charging.