Page 378 - Battery Reference Book

Stationary type or standby power batteries 32f5

Table 32.1 Application of various types of lead-acid battery
Plant6 Flat plate Flat plate Tubular Marine
YMCflH FNFC R range

Telephone exchanges 0
Mobile telephone exchanges
Generating stations and substations 0
Obsolescent generating stations (short-term)
Emergency lighting 0
Alarms *
Computer emergency power 0
Engine starting 0
Oil rigs 0
Marine %

32.1.2 Selection of suitable stationary or the use of car batteries may also invalidate the specifi-
standby power batteries for the application cations of equipment makers and insurance companies.
Initial savings from incorrectly chosen batteries can
When someone who needs standby power has to select evaporate rapidly in the face of short life, especially
a battery, four questions arise: if the wrong size of battery is chosen as well as the
wrong type. And the failure of an emergency lighting
1. What is the probability of power failure? or fire alarm system can result in danger to human life
2. What is the likely duration of the failure? or legal action. Expert opinion on whether the system
3. What damage could power failure do to people, is the right one for the job will be an important factor in
equipment and production? deciding where the responsibility lies. The battery must
4. What regulations have to be complied with? therefore be selected from a range specifically designed
for the purpose. A very important aspect involved in
It is generally accepted that lead-acid batteries are the selection of standby power batteries is to ascertain
ideal for standby power systems, because they are reli- what is known as the load profile for the proposed
able and relatively low-cost. When it comes to selec- application.
tion, the choice is between the kinds of battery referred To be able to advise on this the battery manufacturer
to earlier. Batteries are tailor-made for specific standby needs to know what is required in terns of current
applications, and Table 32.2 gives a rough guide to the output, voltage and frequency of operation. If only one
suitability of different batteries for different jobs. continuous load is to be supplied, sizing the battery
can be simple. For example, an emergency lighting
system drawing 20 A for 3 h on battery power would
Table 32.2
require a 60Ah battery at the 3 h rate. Since standby
Life Publication Cell type batteries are conventionally rated at the 10 h rate, this
expectancy No. range is equivalent to a 75 Ah battery at the 10 h rate.
(years)
Load projib I (Figure 32.4(a))
Plant6 25 SPuKlI2 YANCTYH
Flat plate 10-12 SPuK3 FA/FC A battery is like an athlete who can be just as exhausted
Flat plate 5-6 SPUKs R range after running 100m as after 10000; the difference is
Tubular 10-12 SPUQ - in the rate at which energy is used up.
Marine 10-12 M4 - Most industrial standby power systems now tend to
be more complex because their total load is the product
(Courtesy of Chloride Power Storage Ltd, Swinton, UK) of many varied and intermittent loads. One battery may
serve different purposes within the same building.
There is an all-too-common idea that ‘a battery is a
battery’ and this sometimes leads to car batteries being Load pmjile 2 (Figure 32.4(b))
used to supply standby power. Although this usually If a battery’s duty cycle can be arranged so that
results in low initial cost, it has serious drawbacks. Car any high-current loads occur early, a battery of a
batteries are designed to supply high currents for short smaller capacity can be used than if heavy currents are
periods and are not intended to cany industrial type required at the end. This is because a piece of electrical
loads for any significant periods. Their life expectancy equipment demands not only a certain current, but also
in standby applications is very low compared to that of a minimum voltage. If loads are likely to occur at
Plant6 and other industrial batteries. More important, any time in the work cycle a special approach will