Battery Charging Characteristics

Battery charging features
when a constant current into the discharge is finished just charge the battery when the battery internal resistance as the pressure drop generated, so the battery voltage rapidly increased (A point). Since then, the battery charge start, the battery voltage to a lower rate continued to rise. In this range (AB between),Anything as long as the heart, just do not be afra, the electrochemical reaction to generate a certain rate of oxygen, while oxygen is also the same rate and hydrogen compounds, therefore, the battery internal temperature and gas pressure are very low.
battery charging process, the resulting compound of oxygen than oxygen, the battery internal pressure increased. * Normal pressure within the battery about 1 pound force / inch 2. Been charged, according to the charging rate, the battery internal pressure will soon rise to 100 lbf / inch 2 or higher.
of the various battery charging method, nickel-cadmium batteries to generate the gas is an important issue. Gathered at the surface of the bubble plate, the plate will reduce the surface area involved in chemical reactions and increase the battery's internal resistance. Overcharge, the battery to generate a large number of gas, if not quickly compound, the battery internal pressure will increase significantly, this will damage the battery. In addition, the pressure is too large, sealed battery will play open pores, so that electrolyte dispersion. If the electrolyte has repeatedly put holes through the oven, the electrolyte viscosity increased, and plate transfer between the ions become difficult, so the battery's internal resistance to increase, decrease of capacity.
after a certain time (C points), the electrolyte begins to produce bubbles, these bubbles gather in the plate surface, so that the effective area of the plate decreases, so the battery's internal resistance increases, the battery voltage began to rise rapidly. This is close enough electrical signal.
fully charged, the rechargeable battery into the battery current is not converted to energy storage, but the oxygen in the cathode plate produces super potential. Oxygen is generated as the electrolyte electrolysis is not due to cadmium hydroxide, cadmium reduction generated. Potassium hydroxide and water in the composition of the electrolyte, the hydrogen ion into oxygen, water and free electrons, reaction is
4OH? → O2 ↑ +2 H2O +4 e? Although the electrolyte of oxygen can quickly produce electrolyte in the negative electrode surface compound, but remained significantly increased battery temperature. Furthermore, since the charging current used to produce oxygen, so increasing the pressure within the battery.
as from a large number of hydrogen ions than hydroxide, cadmium from the little easier to decompose in the oxygen, so the rapid rise in temperature inside the battery, so that the battery voltage drops. Therefore the battery voltage curve peak (D point).
electrolyte, oxygen generation and recombination is the exothermic reaction, battery charging (E point), constantly produce oxygen, so that the temperature and pressure within the battery increases. If the mandatory discharge of gas, will cause the electrolyte to reduce the battery capacity decline and damage the battery. If the gas can not be quickly discharged, the battery will explode.
low rate constant current trickle charging, the battery will produce within the dendrite. These dendrites can spread through the partition between the plates. The proliferation of more serious cases, these dendritic cells can cause some or all of the short circuit.
NiMH rechargeable battery nickel-cadmium batteries with similar characteristics, both the voltage during charging, the temperature curve shown in Figure 1-2 and Figure 1-3. Can be seen, charge termination, nickel-cadmium battery voltage drop is much greater than the nickel-metal hydride batteries. When the battery capacity of up to 80% of rated capacity before, nickel-cadmium batteries slowly rising temperature, when the battery capacity of up to 90% after the nickel-cadmium battery temperature was rapidly rising. When the battery is fully charged when the basic, Ni-Cd / Ni-MH battery is basically the same rate of temperature rise.

charging method and charging the battery charging process can generally be divided into pre-charge, fast charge, top-up charge, trickle charge four stages.
long-term need or a new battery, the first on the use of fast charging, it will affect battery life. Therefore, this battery should be used to trickle charging, charging them to meet certain conditions, this stage is called pre-charge.
fast charge is to use high current charging, the battery power quickly restored. Fast charge rate is generally more than 1C, fast charge time of battery capacity and charge rate by the decision.
order to avoid over charging, the charger uses a number of small current charge. Nickel-cadmium battery normal charge, you can accept the C/10 charge rate or lower, so charging time to more than 10h. Use of small current charge, the battery will not produce too much gas, the battery temperature is not too high. Received as long as the battery charger, the low rate constant current battery charger can provide a small trickle charge current. Rechargeable battery with low current when the heat generated within the battery can naturally disperse.
trickle charger is charging the main problem is too slow, for example, 1Ah battery capacity using the C/10 charge rate, the charging time to more than 10h. In addition, the battery low charging rate repeatedly charged, will produce dendrite. Most of the trickle charger, do not have any voltage or temperature feedback control, and therefore can not guarantee that the battery is fully charged, immediately turn off the charger.
fast charge constant current charging and pulse charging points are two constant-current charge is a constant current to the current charging, pulse charging is the first use of pulse current charging the battery. Then let the battery discharge, so the cycle. Great battery pulse amplitude, width very narrow. Discharge pulse amplitude usually charge pulse 3 times. Although the discharge pulse amplitude and the battery capacity, but, with the ratio of charge current amplitude remained unchanged.
charging process, the nickel-cadmium batteries in nickel hydroxide reduced to nickel hydroxide, cadmium hydroxide to cadmium reduction. In the process, bubbles, gathered at the plate on both sides, this will reduce the effective area of the plate, so that the internal resistance of the plate increases. Since the effective area of smaller plates, filled all of the time required to increase capacity.
join the discharge pulse, the bubble plate and leave the board with the negative oxygen compound. This polarization process to reduce the battery's internal pressure, temperature and resistance. At the same time, filled most of the battery charge is converted to chemical energy, which does not turn into gas and heat.
charge and discharge pulse width should be chosen to ensure the restoration of the original crystal structure of the plate, eliminating the memory effect. Depolarization by discharge measures, can improve the charging efficiency and allows high current fast charge.
with some of the fast charge only the law, after the termination of fast charge, the battery is not fully charged. To ensure 100% of capacity filled, make up the charging process should be added. Complement the charging rate of not more than 0.3C. In the complementary process of charging, the temperature will continue to rise, when the temperature exceeds the limit, the charger into trickle charge state.
deposited, the nickel-cadmium battery will discharge rate of C/30 to C/50 reduced to compensate for battery self-discharge due to the loss of power, make up after charging, the charger should automatically transferred to the trickle power process. Trickle charging, also known as maintenance charge. According to self-discharge characteristics of the battery, trickle charge rates are generally low. As long as the battery connected to a charger and charger plugged in, in the maintenance of state of charge, the charger, a charging rate will be added to the battery charge, it will give the battery is fully charged state of the total.


fast charge termination control method using fast charging method, charging current for the conventional charge current of a few times. Fully charged, if not promptly stop fast charging, the battery temperature and internal pressure will increase rapidly. Internal pressure is too large, sealed battery will play open pores, so that electrolyte dispersion, resulting in electrolyte viscosity increased, and the battery internal resistance increases, the capacity decrease.
from fast charge characteristics of nickel-cadmium batteries can be seen, fully charged, the battery voltage began to decline, the battery temperature and internal pressure rising rapidly, in order to ensure the battery is fully charged, but they charge, you can use timing control, voltage control and temperature control to be a number of ways.
(1) time control charging rate of 1.25C
use, the battery may be sufficient 1h; when using 2.5C charge rate, 30min may be sufficient. Thus, according to battery capacity and charge current, it is easy to determine the required charge time. This simple control method, but due to the initial battery charge state is not exactly the same, and some lack of battery charge, and some battery charging, so only when the charging rate of less than 0.3C, this approach allowed.
(2) voltage control
in the voltage control method, the most easy to detect the battery's maximum voltage. Voltage control method commonly used are:
maximum voltage (Vmax) can be seen from the charge curve, the battery voltage reaches the maximum when the battery is fully charged. Charging process, when the battery voltage reaches the specified value, it should immediately stop fast charging. This control method has the disadvantage: the maximum voltage of the battery is fully charged with the ambient temperature, charge rate and variable, and each single cell battery maximum charge pressure is also a difference, so this approach can very accurately determine the battery is enough to charge.
voltage negative incremental (-ΔV) as a negative battery voltage increment and the absolute voltage of the battery pack is not related to ambient temperature and the charging rate and other factors, it can accurately determine the battery is fully charged. Drawback of this control method is: the battery voltage negative increment, the battery has been charged, the battery temperature is high. In addition, Ni-MH battery is fully charged, the battery voltage to go through a longer period of time before a negative increment, than the more serious charge. Therefore, this control method is mainly applied to nickel-cadmium battery
voltage zero incremental (0ΔV) Ni-MH battery charger, in order to avoid the negative when there is a voltage increment of the time too long and damage the battery, usually 0ΔV Control Act . Disadvantage of this approach are: fully charged before the battery voltage in a small period of time may change, resulting in premature stop the fast charge. For this reason, most of the existing Ni-MH Battery Quick Charger are detected by sensitive-0ΔV, when the battery voltage is slightly lower, the immediate cessation of fast charging.
(3) temperature control
in order to avoid damage to the battery, the battery temperature is too low can not start fast charging, the battery temperature rises to the specified value, you must immediately stop the fast charge. Commonly used method of temperature control:
maximum temperature (Tmax) during the charging process, usually when the battery temperature reaches 55 ℃, it should immediately stop fast charging. Battery and battery temperature can be fitted with a thermistor to detect. Disadvantage of this approach is the thermistor response time longer, the temperature detection have a certain lag, while the maximum battery temperature and environmental temperature. When the ambient temperature is too low, the fully charged, the battery's temperature reach 55 ℃.
temperature rise (ΔT) in order to eliminate the environmental impact, temperature control method can be used. When the cells reach the required temperature value, the immediate cessation of fast charging. In order to achieve temperature control, must use two thermistors were used to detect the battery temperature and ambient temperature.
temperature change rate (ΔT / Δt) nickel metal hydride and nickel cadmium battery is fully charged, the battery temperature rose rapidly, and the increased rate ΔT / Δt is basically the same, when the battery temperature rise 1 ℃ per minute, it shall immediately terminate the fast charge This charge control method is widely used in recent years. It should be explained, since the thermistor resistance and temperature relationship is nonlinear, therefore, in order to improve accuracy to reduce the thermal resistance should be non-linear effects.
minimum temperature (Tmin) When the battery temperature is below 10 ℃, using high-current fast charging, it will affect battery life. In this case, the charger should automatically be transferred to trickle charge until the battery temperature rises to 10 ℃, then transferred to fast charge.
(4) integrated control
the advantages and disadvantages of various control methods. In order to ensure that in any case, can accurately and reliably control the battery charge status, the current rapid charger typically includes timing control, voltage control and temperature control of the integrated control method.