Uninterruptible Power Supplies and Standby Power Systems
Written by two experienced engineers, this book covers rotary UPS systems and battery selection, and offers complete, up-to-date guidance on design, installation, operation, and maintenance.
TABLE OF CONTENTS Uninterruptible Power Supplies and Standby Power Systems
Chapter 7: Batteries
Introduction
It is said 95 percent of UPS problems are induced by battery/human error problems, a sweeping statement, nevertheless one in general vogue at the moment. True, in the early days of development of the popular sealed lead acid battery, now correctly identified as the valve regulated lead acid (VRLA) battery, reliability was not high. Since that time some 20 years ago, there have been constant developments in design resulting in a reliable performance. This chapter therefore goes into some detail on types of VRLA cells available and also covers the flooded-type cells available today.
Types of Cell
Among the variety of secondary (rechargeable) cells available, only two are in use for UPS applications. These are lead acid and nickel-cadmium batteries. Both of these are available in differing types, each type having its own characteristics and qualities affecting choice and application.
Lead Acid
Lead acid cells having a chemical process which in simplistic terms consists of electrodes constructed from lead and lead dioxide in a dilute sulphuric acid solution. If the potential is measured between the two electrodes, an approximate reading of 2 V is apparent.
Chemical Reactions/Basic Design
The chemical reaction that occurs is best illustrated as follows:
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Reaction at the negative plate (pure lead)
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Reaction at the positive plate (lead oxide)
Adding together 1 and 2 the chemical reaction for the cell is:
As the action proceeds and the discharge is complete, the plates are covered in the case of the negative plate with lead sulphate and...
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