Lead Acid and Nickel Cadmium Battery Selection and Sizing
Lead Acid and Nickel Cadmium Batteries are two main types of batteries used for supplying power to stationary backup power systems. Both types have their advantages and disadvantages which has to be evaluated according to the application in which certain battery is to be used. Lead-Acid Batteries and best solutions in some cases and Nickel Cadmium batteries in others. In addition to this, there are different versions of each type which are more suited either to high or low discharge rates. Maintenance free valve regulated lead acid batteries with immobilized electrolyte have become more and more important.
Applications of Batteries:
Some of the applications of the batteries includes:
- Power Stations
- Telecommunication Systems
- Solar power stations
- UPS plant
- Standby emergency lighting
- Radio Link Systems
Battery selection is influenced by the following considerations
From the point of view of installation and space requirements, Ni-cd batteries have a clear advantage over lead-acid batteries for certain power ranges and operating times, since they can almost be mounted in tiers to save space
Lead-acid batteries require less maintenance compared to Ni-Cd batteries. Ni-Cd batteries cannot be left in discharged state for long periods. In standby parallel operation Ni-Cd batteries must be given an equalizing charge several times a year to maintain their full load charging capacity.
Ni-Cd battery is east to assemble since their individual cells are lighter, although there are 40% more cells than in a corresponding lead-acid battery. Small versions of both types are combined into blocks of trays of rated voltages 4 to 12 V
Lead acid and Ni-Cd batteries for very short operating time costs approximately similar, however lead acid batteries are considerably cheaper for extended operation
Lead acid batteries operate in a narrower charge and discharge voltage range than Nickel-Cadmium counterpart
State of Charge:
The state of charge of the lead acid battery can be determined by measuring the acid's specific gravity. With Ni-Cd batteries, particularly attention must be paid to charging procedure and state of charge can be ascertained from discharge tests
Sizing of Batteries:
The minimum data necessary for sizing a battery are: the requisite operating time, the power or discharge current to be supplied, and the permissible voltage range particularly the end point voltage. Other data such as ambient temperature, frequency of mains failures and specific load cycles, may also influence the sizing
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