Industry News
Basic knowledge of rechargeable batteries and chargers
2020-09-12
With the development of portable electronic products, the capacity and cycle life of rechargeable batteries are required to be higher and higher. At present, there are four common types of rechargeable batteries: nickel cadmium batteries and lead-acid maintenance free batteries (SLA), Ni MH battery and Li ion battery (including lithium polymer battery) have been widely used in recent ten years. These four types of batteries have their own advantages. The table below gives a basic reference. The specific values of different battery manufacturers may vary greatly. Consult the manufacturer when using. The data in the table are only for comparison and reference (C in the table is the nominal capacity of the battery, The unit is ah (ampere hour), and a is the constant current of charging.)
Comparison items:
Lead acid maintenance free battery nickel cadmium battery (NiCd) nickel hydrogen battery (NIMH) lithium ion battery (Li ion)
Energy density (WH / kg) 30 40 60 100
Cycle life (Times) 300 800 500 800
Working temperature (℃) 0 ~ 350 ~ 450 ~ 400 ~ 50
Maximum charging current (a) 0.25c 2C 1C 1C
Charging mode constant voltage constant current constant current constant voltage constant current constant voltage after constant current
Charging time (hours) C / A + 2 hours C / A + 20% C / A + 20% C / a × 2
Of course, people hope that the charger can be completed in a short time, but due to the large current and difficult control, this has a certain degree of cost and technology to pay. If the use conditions permit, choose 10 ~ 14 hours or so of charging end of the night slow charging charger will have low price, small size and other advantages
For the on-line parallel connected SLA Battery, it is recommended to use 2.27v/cell (13.7v corresponding to 12V battery) constant voltage charging. This scheme will not overcharge the battery, but also help to stabilize the equipment voltage. For the occasion where SLA batteries are often used for off-line charging and discharging, the first 0.2C constant current and then 2.45v/cell constant voltage should be used, After the battery is charged, it will enter the "Three-stage" charging method with constant voltage of 2.27v/cell. The whole charging time is about 8 to 10 hours
A simple constant current source charger with a current of 0.1C can be used economically for NiCd batteries. NiMH batteries are sensitive to overcharge, that is, using a current of 0.1C. If the battery is charged for more than 14 hours or the battery is charged for a few more hours, it is economical to select a simple constant current source charger with a current of 0.1C, It is very important to turn off the current or reduce the charging current to below 0.02c when the battery is charged, even for 0.1C slow charging NIMH charger at night
There are many successful cases of intelligent fast charger whose maximum charging current is about 2C. This kind of charger must monitor battery voltage, temperature and other parameters at all stages of charging process at any time. When the battery is about to be fully charged, it will automatically reduce the charging current rate, 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, but the NiMH batteries have more heating and less peak voltage during charging. One of the following conditions is used as the fast charging termination condition for these two types of batteries: voltage rise slope (DV / DT), negative voltage growth (- DV) and battery temperature rise slope (DT / DT). There are also three conditions that are set to operate under abnormal protection conditions: maximum battery temperature, maximum battery voltage and charger built-in timer. In order to realize these monitoring and intelligent switching actions, the cost of charger will certainly rise. But without these measures, the battery will face potential safety risks such as capacity reduction, cycle life reduction and even leakage explosion. Li-ion and SLA batteries have similar charging methods, both of which require constant current and then constant voltage. The difference is that lithium-ion batteries require higher voltage accuracy (< 1%) at the constant voltage stage. As the safety of lithium batteries is a fatal hazard, special care should be taken in the control and protection of charging end. For different applications, lithium-ion battery pack will be built-in corresponding charge and discharge protection circuit, so as to more safely protect the battery from happening
Comparison items:
Lead acid maintenance free battery nickel cadmium battery (NiCd) nickel hydrogen battery (NIMH) lithium ion battery (Li ion)
Energy density (WH / kg) 30 40 60 100
Cycle life (Times) 300 800 500 800
Working temperature (℃) 0 ~ 350 ~ 450 ~ 400 ~ 50
Maximum charging current (a) 0.25c 2C 1C 1C
Charging mode constant voltage constant current constant current constant voltage constant current constant voltage after constant current
Charging time (hours) C / A + 2 hours C / A + 20% C / A + 20% C / a × 2
Of course, people hope that the charger can be completed in a short time, but due to the large current and difficult control, this has a certain degree of cost and technology to pay. If the use conditions permit, choose 10 ~ 14 hours or so of charging end of the night slow charging charger will have low price, small size and other advantages
For the on-line parallel connected SLA Battery, it is recommended to use 2.27v/cell (13.7v corresponding to 12V battery) constant voltage charging. This scheme will not overcharge the battery, but also help to stabilize the equipment voltage. For the occasion where SLA batteries are often used for off-line charging and discharging, the first 0.2C constant current and then 2.45v/cell constant voltage should be used, After the battery is charged, it will enter the "Three-stage" charging method with constant voltage of 2.27v/cell. The whole charging time is about 8 to 10 hours
A simple constant current source charger with a current of 0.1C can be used economically for NiCd batteries. NiMH batteries are sensitive to overcharge, that is, using a current of 0.1C. If the battery is charged for more than 14 hours or the battery is charged for a few more hours, it is economical to select a simple constant current source charger with a current of 0.1C, It is very important to turn off the current or reduce the charging current to below 0.02c when the battery is charged, even for 0.1C slow charging NIMH charger at night
There are many successful cases of intelligent fast charger whose maximum charging current is about 2C. This kind of charger must monitor battery voltage, temperature and other parameters at all stages of charging process at any time. When the battery is about to be fully charged, it will automatically reduce the charging current rate, 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, but the NiMH batteries have more heating and less peak voltage during charging. One of the following conditions is used as the fast charging termination condition for these two types of batteries: voltage rise slope (DV / DT), negative voltage growth (- DV) and battery temperature rise slope (DT / DT). There are also three conditions that are set to operate under abnormal protection conditions: maximum battery temperature, maximum battery voltage and charger built-in timer. In order to realize these monitoring and intelligent switching actions, the cost of charger will certainly rise. But without these measures, the battery will face potential safety risks such as capacity reduction, cycle life reduction and even leakage explosion. Li-ion and SLA batteries have similar charging methods, both of which require constant current and then constant voltage. The difference is that lithium-ion batteries require higher voltage accuracy (< 1%) at the constant voltage stage. As the safety of lithium batteries is a fatal hazard, special care should be taken in the control and protection of charging end. For different applications, lithium-ion battery pack will be built-in corresponding charge and discharge protection circuit, so as to more safely protect the battery from happening