IEC 62973-2-2020 Railway applications – Rolling stock – Batteries for auxiliary power supply systems – Part 2: Nickel Cadmium (NiCd) batteries.
The plate stacks are surrounded by alkaline electrolyte, an aqueous solution mainly of potassium hydroxide (KOH)， and distilled or deionized water. The electrolyte does not participate in the electrochemical reaction, which takes place in the cell, but only acts as an ion-carrying medium with its specific gravity remaining fairly constant allowing for large electrolyte reserves to be used. The electrolyte does not chemically change or degrade due to charge/ discharge cycles. Due to NiCd electrochemistry technology, some abuse conditions can be tolerated at the cell level, e.g. overcharging will cause water electrolysis, but only water is consumed. Since there is no chemical change or degradation of electrolyte, it is not necessary to add complex control systems to handle such cases.
4.2.2 Sintered/PBE plate/electrode technology The sintered positive plate/ electrode is obtained by chemical impregnation of nickel hydroxide into a porous nickel sinter coated thin steel strip that is previously perforated and nickel-plated. The negative plastic bonded electrode (PBE) is obtained by the coating of slurry consisting of cadmium oxide mixed with a plastic binder onto a nickel-plated thin perforated steel strip.
4.2.3 Sintered/sintered plate/electrode technology The sintered positive and negative plate/electrode is obtained by chemical impregnation of nickel hydroxide and cadmium oxide into a porous nickel sinter coated thin steel strip that is previously perforated and nickel-plated.
4.2.4 Fiber plate/electrode technology Both the positive and negative plates/electrodes consist of non-woven fibers of nickel or nickel-plated plastic fibers of high porosity.
4.2.5 Pocket plate/electrode technology Both the positive and negative plates/electrodes consist of several flat, perforated metal pockets made from perforated steel strips linked together encapsulating the active materials.
4.3 Environmental conditions NiCd cells/ batteries can perform at extreme temperatures: below -25。C or above +40 °C. Especially when at one extreme temperature is specified, deviations for the opposite extreme temperature may be agreed between end user and/ or system integrator and cell/ battery manufacturer.
4.4 System requirements
4.4.1 System voltage The charging voltage for the NiCd battery is dependent on the number of cells, temperature, and its plate/electrode technology. Although the nominal battery voltage is set by Table 1 of IEC 62973- 1:2018, the number of cells can vary due to the cell charging requirements by their plate/electrode technology.
Due to higher cell charging voltage required by the fiber or pocket plate technology, a lower number of cells can be used in series with a higher capacity. While due to lower charging voltage of sintered/PBE or sintered/sintered plate technology, more cells can be used in series with a lower capacity. Less cells with a higher capacity or more cells withI lower capacity would provide similar energy. The optimised number of cells in a NiCd battery calculated by the battery manufacturer shall allow to operate between the minimum and maximum equipment operating voltage range considering the operating conditions and battery load profile. Then the operational battery charging voltage at 20 °C shall be set considering the calculated number of cells and individual cell charging characteristics. Refer to Table 2.
The NiCd battery nominal voltages and the discharge voltages are different. Figure 2 shows typical discharges of a NiCd cell at different constant discharging currents (shown in multiples of Cn or multiples of In, Cn and In are related, e.g. 0,2 C5 is equivalent to Ig) that vary by battery discharge rate designation (e.g. L, M, H per IEC 60623:2017). This discharge curve (discharge voltages relative to discharge capacities based on constant current discharges) shall be available at different temperatures.IEC 62973-2 pdf download.