Page 224 - Lindens Handbook of Batteries

9.18 PRIMARY BATTERIES

FIGURE 9.11 Typical discharge curves for general-purpose Leclanché and zinc chloride D-size batteries, dis-
charged 2 h/day at 20°C. Solid line: Zinc chloride; broken line: Leclanché.

Typical discharge curves for general-purpose D-size Leclanché and zinc chloride batteries,
of equivalent capacity, discharged 2 h per day at 20°C, are shown in Fig. 9.11. These curves are
characterized by a sloping discharge and a substantial reduction in voltage with increasing current.
The zinc chloride construction shows a higher voltage characteristic and more service at the higher
current levels. On the 50 mA drain, both constructions provide nearly equivalent performance. This
is the result of the depletion of manganese dioxide at the low discharge rates, as most zinc-carbon
batteries are cathode limited.

9.6.3 Effect of Intermittent Discharge

Performance of zinc-carbon batteries varies depending upon the type of discharge. The performance
of Leclanché batteries is significantly better when used under intermittent compared to continuous
discharge conditions, because (1) a chemical recuperation reaction replaces a small portion of active
ingredients during the rest periods, and (2) transport phenomena redistribute reaction products. 5
Zinc chloride batteries can support heavier drains and respond to intermittent discharges with lon-
ger discharge cycles. This system relies upon its improved transport mechanism to support heavier
drains and to redistribute reaction product. (Fig. 9.12) illustrates the general effects of intermittency
and discharge rate on the capacity of a general-purpose D-size battery. On extremely low-current
discharges, the benefit of intermittent rest and discharge is minimal for both systems. It is likely that
the reaction rate proceeds more slowly than the diffusion rate and results in a balanced condition
even during discharge. Under conditions of extremely low rate of discharge, factors such as age
will reduce the total delivered capacity. Most applications fall in the moderate- (radio) to high-rate
(flashlight) categories, and for these the energy delivered can more than triple when the cell is used
intermittently as compared with continuous usage.
The standard flashlight current drains are 300 mA (3.9 Ω per cell) and 500 mA (2.2 Ω per cell),
which correspond to two-cell flashlights using PR2 and PR6 lamps, respectively, or three-cell flash-
lights using PR3 and PR7 lamps, respectively. The beneficial effects of intermittent discharge are
clearly shown in Figs. 9.13 and 9.14 which compare Leclanché general-purpose D-size batteries
on four different discharge regimens: continuous, light intermittent flashlight, heavy intermittent
flashlight, and a 1 h/day cassette simulation test. Table 9.5 lists the ANSI application tests currently
being used to evaluate both cell systems.