This article is about how NiCd batteries work and how to repair them. By reading this article, you can better understand how NiCd batteries work and how to repair NiCd batteries and put these principles and methods into practice correctly.
NiCd battery is the earliest type of battery used in mobile phones, laptops, and other equipment, it has good high current discharge characteristics, strong resistance to overcharge and discharge, and simple maintenance, generally using the following reaction discharge:
Cd+2NiO(OH)+2H2O=2Ni(OH)2+Cd(OH)2 The reaction is reversed when charging.
The active substance on the positive electrode plate of a NiCd battery consists of nickel oxide powder and graphite powder, graphite does not participate in the chemical reaction and its main function is to enhance the electrical conductivity. The active substance on the negative electrode plate consists of cadmium oxide powder and iron oxide powder, the role of iron oxide powder is to make the cadmium oxide powder have a high diffusivity, prevent clumping and increase the capacity of the electrode plate. The active substances are wrapped in perforated steel strips, pressed into shape, and then become the battery's positive and negative electrode plates. The plates are separated by alkali-resistant hard rubber insulating sticks or perforated PVC corrugated sheets. The electrolyte is usually a potassium hydroxide solution.
Compared to other batteries, NiCd batteries have a moderate self-discharge rate (i.e. the rate at which the battery loses its charge when not in use). If a NiCd battery is not fully discharged and recharged during use, the next time it is discharged, it will not be able to discharge the full charge. For example, if the battery is fully charged again after 80% discharge, the battery can only discharge 80% of its charge.
This is the so-called memory effect. Of course, a few complete discharge/charge cycles will bring the NiCd battery back to normal operation. Due to the memory effect of NiCd batteries, if not fully discharged, each cell should be discharged to below 1V before recharging.
NiCd batteries are packaged in two types of packaging, a positive convex head for retail use and a positive flat head for assembly, with no difference in capacity. Charging is done using 1.6 times the voltage in the charging circuit. Normally, NiCd batteries are charged 300 to 800 times, with the capacity dropping to approximately 80% after 500 charges and discharges. The memory effect of NiCd batteries is more severe than that of NiMH batteries. Therefore, they must be recharged only when completely dead to ensure long service life.
Charge NiCd batteries at a constant current in the range of 0.05C to greater than 1C. Some low-cost chargers use absolute temperature termination of charge. Although simple and inexpensive, this method of charge termination is imprecise. A better method is to terminate charging by detecting a voltage dip when the battery is full. The -ΔV method is most effective for NiCd cells with charge rates of 0.5C or higher. -ΔV charge termination detection should be combined with cell temperature detection, as aging cells and mismatched cells may reduce ΔV.
A more accurate full charge detection can be achieved by detecting the temperature rise rate (dT/dt) and this full charge detection is better for the cell than a fixed temperature termination. A charge termination method based on a combination of ΔT/dt and -ΔV avoids overcharging the battery and extends battery life.
Fast charging improves charging efficiency. At a charge rate of 1C, the efficiency can be close to 1.1 (91%) and the time to fill an empty battery is a little over 1 hour. When charged at 0.1C, the efficiency drops to 1.4 (71%) and the charge time is around 14 hours.
Because NiCd batteries receive close to 100% of the electrical energy, almost all of the energy is absorbed during the 70% of the charge start time and the battery remains unheated. The ultra-fast charger takes advantage of this feature to charge the battery to 70% in a few minutes, charging at a few C without heat generation. Once charged to 70%, the battery then continues to charge at a lower rate until the battery is fully charged. Finally, the charge ends with a trickle of 0.02C to 0.1C.
The cadmium (Cd) in the negative electrode and the hydroxide ion (OH-) in a sodium hydroxide (NaOH) are synthesized into cadmium hydroxide, which attaches to the anode and emits electrons. The electrons travel along the wire to the cathode where they react with the water in the sodium hydroxide solution to form nickel hydroxide and hydroxide ions, which attach to the anode and return to the sodium hydroxide solution.
Discharge reaction equation.
Negative reaction: Cd+2OH-→Cd(OH)2+2e-
Positive reaction: 2e-+NiO2+2H2O→Ni(OH)2+2OH-
Total reaction: Cd+NiO2+2H2O→Cd(OH)2+Ni(OH)2
Charge reaction equation.
Positive reaction: Ni(OH)2+2OH-→ 2e-+NiO2+2H2O
Negative reaction: Cd(OH)2+2e-→ Cd+2OH-
Total reaction: Cd(OH)2+Ni(OH)2→ Cd+NiO2+2H2O
For the charge/discharge reaction equations of other types of batteries, please refer to the other articles in the battery chip list on the Quarktwin website.
Advantages: NiCd batteries can be charged quickly at high currents and can provide high currents for loads, and the voltage changes are minimal when discharging, but they have low charging efficiency and severe memory effects. NiCd batteries can withstand overcharging or over-discharging, are easy to operate, and will not deteriorate over a long period.
Disadvantages: The cadmium in NiCd batteries is toxic, thus NiCd batteries are not conducive to the protection of the ecological environment, and the many disadvantages make NiCd batteries have been eliminated from the range of applications of digital equipment batteries.
Step 1, the normal voltage of the nickel-cadmium battery is 1.2 V, available 12 V voltage to its "hit", with a single desktop computer switch power supply,
a: First green wire end, and black wire end short, so that the switch power supply turns on the output of 12 V voltage. The black wire end of the lead wire is then battery negative, with the yellow wire end of the lead wire touching the positive terminal of the battery a;
b: As an action on the 12V power supply equivalent to a short circuit, the switching power supply will start a short circuit protection, the 12V power supply disappeared; the green wire end and the black wire end of the short wire pull out and then short, the output 12V voltage.
Repeat the a and b processes until the battery has a voltage of a few volts with a multimeter, then set it aside. Activate the other end-of-life batteries.
Step 2, Use the mobile phone charger to charge 3 NiCd batteries, the output of the charger is 5V, charge the 3 batteries for about 8 hours to charge each battery to more than 1.2V, when charging often use a multimeter to measure each battery to see if the voltage of each battery is about the same high or low, if there is a particularly low, you can use step 1 "hit" again to activate it. " to activate it. Click to reload
Step 3, Use sufficient batteries first until they are used up, then measure each battery with a multimeter to see if the voltage of each battery is about the same high or low, if there are particularly low ones, or if the voltage drops to zero, you can use it again with step one "hit" to make it activate completely. Repeat the above steps several times to restore the rechargeable NiCd battery.
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