- Jan 10, 2018 -
Fast charging termination control method
When the fast charging method is used, the charging current is several times that of the conventional charging current. After sufficient electricity, if the fast charging is not stopped in time, the temperature and internal pressure of the battery will rise rapidly. The internal pressure, sealing the battery will open the pores, so that the electrolyte caused by viscous dissipation, increasing the electrolyte, the battery internal resistance increases, the capacity decreased.
Fast charging characteristics from nickel cadmium batteries can be seen after charging, the battery voltage begins to drop, rapid rise in the temperature of the battery and internal pressure, in order to ensure adequate electric battery and charging can be used but, timing control, voltage control and temperature control for a variety of methods.
(1) timing control
When the 1.25C charging rate is used, the battery 1H is sufficient, and the 30min is sufficient when the 2.5C charging rate is adopted. Therefore, it is easy to determine the required charging time according to the capacity of the battery and the charging current. This control method is the simplest. However, because the initial charging state of the battery is not the same, some batteries are insufficient and some batteries are overcharged, so only when the charging rate is less than 0.3C is it allowed to adopt this method.
(2) voltage control
In the voltage control method, the most easy to detect is the maximum voltage of the battery. The common voltage control methods are:
The maximum voltage (Vmax) can be seen from the charging characteristic curve, when the battery voltage reaches the maximum, the battery is sufficient electricity. In the process of charging, the fast charging should be stopped immediately when the battery voltage reaches the specified value. The disadvantage of this control method is that the highest voltage of the battery is changed with the ambient temperature and charging rate, and the maximum charging pressure of each battery in the battery group is also different. Therefore, it is impossible to accurately and accurately judge that the battery is fully charged.
Negative voltage increment (- Delta V), because the negative increment of battery voltage is independent of the absolute voltage of battery pack, and it is not influenced by environmental temperature and charging rate, it can accurately judge that the battery has enough electricity. The disadvantage of this control method is that the battery has been overcharged after the negative increment of the battery voltage, so the temperature of the battery is higher. In addition, after the nickel hydrogen battery is sufficient, the battery voltage will take a long time, only the negative increment is appeared, and the overcharge is more serious. Therefore, this control method is mainly applied to Ni Cd battery.
In the zero voltage increment (0 Delta V) Ni MH battery charger, the 0 Delta V control is usually used to avoid damaging the battery for too long time. The disadvantage of this method is that before sufficient electricity is sufficient, the battery voltage may change very small for a certain period of time, resulting in a premature stop for fast charging. For this reason, most of the fast charger of Ni MH battery uses high sensitivity 0 Delta V detection. When the battery voltage is slightly lower, fast charging is stopped immediately.
(3) temperature control
In order to avoid damage to the battery, the battery can not start fast charging when the temperature is too low, and the fast charge must be stopped immediately after the battery temperature rises to the specified value. The commonly used methods of temperature control are:
When the maximum temperature (Tmax) is charged, the fast charge should be stopped immediately when the temperature of the battery reaches 45 degrees C. The temperature of the battery can be detected by the thermistor that is installed together with the battery. The disadvantage of this method is that the response time of thermistor is long, and the temperature detection is lagged behind. At the same time, the highest working temperature of the battery is related to the ambient temperature. When the temperature of the environment is too low, the temperature of the battery is less than 45.
In order to eliminate the environmental impact, temperature rise control method can be used to control the temperature rise (T). When the temperature rise of the battery reaches the specified value, the fast charging is stopped immediately. In order to control the temperature rise, two thermosensitive resistors must be used to detect the temperature of the battery and the temperature of the environment.
The temperature change rate (T/ T) NIMH and NiCd battery fully charged, the battery temperature increases rapidly, and the rising rate of delta T/ delta T is basically the same, when the battery temperature rise every minute 1 DEG C, shall immediately terminate the fast charging, the charging control method has been widely used in recent years. It should be noted that because the relationship between resistance and temperature of the thermistor is nonlinear, therefore, in order to improve the detection accuracy, we should try to reduce the influence of the nonlinearity of the thermistor.
The minimum temperature (Tmin) when the temperature of the battery is below 10 degrees centigrade, the use of large current and fast charging will affect the battery life. In this case, the charger should be automatically turned into a trickle charge, and then the battery's temperature rises to 10 degrees C and then turns into a fast charge.
(4) comprehensive control
The above control methods have their own advantages and disadvantages. In order to ensure that the charging state of the battery can be accurately and reliably controlled in any case, the current fast charger usually includes timing control and voltage.