What is the correct way to charge a nickel-cadmium battery

Nickel-cadmium battery is operated by the reaction of chemical substances, and chemical materials tend to consume themselves. In the environment with high temperature, self-consumption will be more serious, the capacity will be reduced, and there may be leakage and rust. Charging and discharging at high temperature will cause damage to the battery and reduce its life. Cadmium nickel battery can work stable temperature range is very wide, charging about 0 ~ 45 ℃, the discharge of about 20 ~ 60 ℃, save about 30 ~ 45 ℃, normally the best preserved in cold but not humid place. Temperature for the life of the battery and charging and discharging characteristics influence is very big, the charge and discharge if the environment temperature is higher, the material of the battery is damaged, a version of the function of the active material to reduce reduce capacity, isolation between anode cathode isolation editions of insulation to reduce cause short circuit, and temperature have also become low voltage of the battery, charge and discharge efficiency to reduce a lot of, the battery capacity is greatly reduced. Therefore, unless the nickel-cadmium battery is heat-resistant, please pay attention to the temperature of the battery when charging and discharging. Do not use too much current to avoid excessive temperature.

overcharge

In the process of charging the battery voltage will be increased gradually along with the increase of the storage battery, when the battery storage capacity is saturated electrode materials cannot continue charging, if continue to charging the electrolyte will electrolysis, and at the anode produce oxygen, hydrogen at the cathode, so can cause internal pressure rise inside the sealed battery, battery internal structure can be damaged. This phenomenon is called overcharging.

In order to avoid a rechargeable batteries have been damaged, will usually cathode anode large capacity, the capacity of production better than anode will be saturated so when overcharge and produce oxygen, and the cathode is unsaturated and won't produce hydrogen, oxygen diffusion anode produce after the cathode can react with a charge of metal cadmium to absorb oxygen, and the reaction rate and the speed of the metal cadmium to produce balance, thus effectively avoid the pressure rise of the battery. However, if the charging current is too large (when using fast charging), the battery will lose its balance, and the battery's internal pressure will push the battery's safety valve away. Hydrogen and oxygen will leak to the outside of the battery, and the battery will not be sealed again until the pressure is reduced and the safety valve closes the battery. But gas leaks have reduced the amount of chemical material inside, resulting in shorter battery life.

Change in charging voltage

When the battery is overcharged, because the oxygen generated by the anode reacts with the cathode to generate heat, the battery temperature will rise and the shell will become hot. As the higher the temperature is, the lower the charging voltage of the battery will be, so the battery voltage will continue to rise during charging until the overcharging, the battery temperature will rise suddenly and rapidly, and the voltage will no longer rise but start to decline from the peak.

Nominal voltage

When nickel-cadmium batteries are discharged under standard discharge conditions, the voltage will slowly drop until the discharge is almost finished, and the voltage will drop significantly. This voltage value is called the nominal voltage. The nominal voltage of general nickel-cadmium batteries is 1.2v, which is the same meaning as the 1.5v marked on general dry batteries and is marked on the battery shell. As long as the voltage value of nickel-cadmium battery must be at least above the nominal voltage of 1.2v, the more electricity stored, the higher the voltage.

Discharge termination voltage

When the battery is discharging, its voltage will gradually decrease with the reduction of battery power. When the voltage drops to the required level, it will not continue to discharge, which is called discharge termination, and this voltage level is called discharge termination voltage. Generally, the discharge termination voltage recommended by the manufacturer is about 0.9v ~ 1.1v. When the voltage is discharged to this level, the electric quantity has almost been released. This condition is called complete discharge. If the nickel-cadmium battery is completely discharged without removing the load and it continues to discharge, then it is overdischarged and the voltage drops sharply until it reaches 0V. If the discharge is stopped before the voltage drops to about 0V, the battery voltage will automatically and quickly return to the nominal voltage of about 1.2v.

Excessive discharge

The fatal flaw of nickel-cadmium batteries is that they are over-discharged. Setting the discharge termination voltage at this condition will not only drive the load without power, but also cause damage to the battery life. And once the voltage continues to drop to almost 0V accidentally, even if you want to stop the discharge and remove the load, I'm afraid it is too late. The voltage of the battery can't recover automatically, and the general charger can't charge the battery again. Its voltage will remain fixed at 0V. At the moment it is like a stroke like paralysis over there, not to mention the longevity, it is often a life SOB sad zai can no longer be used.

Definition of battery capacity

The capacity of a battery is the amount of discharge charge that can be obtained by discharging the battery until the voltage drops to the terminal voltage. If the specified current and temperature and other standard discharge conditions, the full charge of the battery discharge until the discharge terminates, the resulting capacity is called rated capacity (or nominal capacity). The capacity of the electrode depends on the amount of active material consumed, and the standard discharge conditions are determined according to the type of battery. Capacity is defined according to the discharge reaction of the battery, rather than the charging reaction. Therefore, the capacity of the battery we often say is the amount of accumulated discharge charge that can be obtained during the discharge, rather than the amount of charge that flows in during the charge.

Representation of battery capacity

The capacity of the battery can be expressed by the value of [(discharge current)x(the discharge time after the voltage drops to the discharge termination voltage)] after calculation. Before the introduction, the basic formula of electricity power for the current x time, unit is the coulomb (Q), battery if the battery capacity to say how much the coulomb, is likely to be more, so the capacity of the battery is the current value of x time, directly to the C = IT (unit in mAh or Ah), where C is the capacity (meaning) with coulomb's, I is current, A is the ampere, mA said the current size of Ann (one over one thousand amp, A), h (hour), on behalf of the hour that is one hour to one over one thousand amperes of current discharge accumulated by the power of 1 mAh. So C is equal to IxT is equal to how much mAh, which is the coulomb equivalent. Usually the battery case package will be marked with the battery rated capacity, used to indicate the maximum capacity of the battery. The capacity of the new nickel-cadmium battery can reach the rated capacity in the first charge and discharge, but the capacity will decrease with the increase of charge and discharge times.

Example: if it takes 2 hours to discharge the battery at 1 ampere, the battery capacity is about 2000mAh. If the battery capacity is expressed in coulombs, then C=IxT=1Ax7200sec=7200 coulombs. Do you also find that 2000mah is less empty and clearer than 7200 coulombs?

The expressions of C

In addition to charging and discharging current in amperes (or milliamperes), the battery also USES the English letter C(capacity) as the current portion of the rated capacity (current x time), which is used as the unit to measure the current. For example, for a battery with a rated capacity of 600mAh, C means 600mA, so current 1C means 600mA, current 2C means 1.2ma, and current 0.1c means 60mA. If you can't find the amperage of charge and discharge current on the specification when you buy the battery in the future, please don't worry, and don't forget to look for how much C is written on it.

Charge and discharge rate

The so-called charge (discharge) rate is the charge (charge) all the capacity of the required time to complete (charge), as the standard speed of charge (discharge). Generally used to explain the discharge (charge) of the speed is how much, such as two hours rate of discharge, is to use 0.5c current, in two hours of time to put the battery full capacity. The 20-minute rate indicates that the rated power of the battery will be fully discharged within 20 minutes with the 3C current. In the battery specification of the manufacturer above, also often use the hour rate to express the standard discharge time, as long as according to the rated capacity to convert to know how much is the standard discharge current. Manufacturers usually provide the specifications of the top rated capacity with temperature 20 ℃, and the discharge is a 5 hour rate 0.2 C conditions to measure.

Charging efficiency

A battery cannot store as much power as it charges, it must wear out, and materials cannot store all of it impossibly, except for the insulator leakage between the anode and cathode. The ratio of the amount of electricity taken out when the battery is discharged to the amount of electricity flowing into the battery when it is charged is called charging efficiency.

Generally, battery manufacturers recommend charging 1.5 times the rated capacity to fully charge the battery. That is to say, it takes 15 hours to charge at the current of 0.1c and half an hour to charge at the current of 3C. Although the theoretical filling amount is 1.5 times of the rated capacity, the actual filling amount is just about the rated capacity.

utilization

Although the rated capacity of the battery is large in theory, in fact, the amount of electricity that can be obtained when the battery is fully charged and then discharged is often less than the theoretical capacity, indicating that the actual storage capacity that the battery can store is not so large. The ratio of the actual capacity to the theoretical capacity is called utilization rate. Usually, the higher the discharge current of the battery, or the lower the ambient temperature, the lower the utilization rate.

The depth of discharge

The ratio of the amount of charge discharged to the amount of charge stored when the battery is discharged is called the depth of discharge, expressed as a percentage. For example, the discharge depth of 20% represents the degree of discharge to the remaining 80% of electricity.

Cycle life

Nickel-cadmium batteries are usually used in the application of repeated charging and discharging periodic work, the life of the battery is limited, the capacity can not be maintained without decline, in a certain working condition after repeated charging and discharging, the capacity of the battery will drop to 80% of the rated capacity (or defined in 60%). This number of repeated charge and discharge is called cycle life. The higher the cycle life is, the longer the battery life will be. The reference specifications for some batteries will indicate the charge and discharge cycles, the number of cycles per discharge depth, and the intended cycle life. With the different charging and discharging current, discharge depth and other charging and discharging conditions, the cycle life also changes, especially when using large current charging and discharging, there will be a phenomenon of shortened life. Currently nickel-cadmium batteries can be used more than 500 times as long as they are normally used according to the instructions attached by the manufacturer at the time of purchase.

Battery internal resistance and voltage

A battery is a voltage source with internal resistance and can be considered as an ideal voltage source (without internal resistance) with a resistor output in series. When the battery is externally connected to the load, the load and the internal resistance are connected in series to the ideal voltage source. Therefore, the partial voltage obtained on the load is the terminal voltage of the battery, which is less than the voltage of the ideal voltage source, and it is called the closed voltage. The higher the internal resistance of the battery, the smaller the load can be divided into voltage, so the ideal battery is no internal resistance.

Nickel-cadmium battery internal resistance is very low, generally only a few milliohms to tens of milliohms, so the external size of the load is different when the discharge voltage is very stable, discharge current curve is very flat, can be used for large current discharge. In general, the internal resistance of dry batteries is often several ohms, and the discharge voltage is unstable and the discharge current curve is not flat.

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