Zinc-carbon batteries voltage

R n in battery voltage sources varies from about 35 in a 9-V zinc-carbon battery to less than 6 in a lead-acid cell. Electronically controlled sources produce very low an important point to which we will return. 

A common dry cell battery is the zinc-carbon battery, using dry Leclanche cell, with a nominal voltage of 1.5 volts. 

Closed-Circuit Voltage. The closed-circuit voltage (CCV), or working voltage, of the zinc-carbon battery is a function of the load or current drain the cell is required to deliver. The heavier the load or the smaller the circuit resistance, the lower the closed-circuit voltage. Table 8.4 illustrates the effect of load resistance on the closed-circuit voltage for D-size batteries in both the Leclanche and zinc-chloride systems. 

TABLE 8.4 Initial Closed-Qrcuit Voltage of a Typical D-size Zinc-Carbon Battery as a Function of Load Resistance at 20 C... 

The theoretical potential of the battery is greater than 2.8 V, but this voltage is not realized in practice. The observed values are decreased by about 1.1 V, giving an open-circuit voltage of 1.9-2.0 V, still higher than for the zinc-carbon battery. 

Primary Zinc/carbon (Leclanche) 2Mn02 + H20 + 2e —> Mn203 + 20H Zn— Zn2+ + 2e NH4Cl/ZnCl2/ Mn02/damp C powder Graphite Zn 1.55 Portable voltage sources (dry batteries)... 

In the zinc-carbon dry cell, a spacer made of a porous material and damp from the liquid in the paste separates the paste from the zinc anode. The spacer acts as a salt bridge to allow the transfer of ions, much like the model voltaic cell you studied in Section 20.1. The zinc-carbon dry cell produces a voltage of 1.5 V until the reduction product, ammonia, comes out of its aqueous solution as a gas. At that point, the voltage drops to a level that makes the battery useless. 

The standard carbon-zinc Leclanche battery is expected to remain one of the most widely used dry primary batteries in the future beeause of its low cost and reliable performance. This type of battery is manufaetured in many styles by many companies-one company alone manufaetures over 100 versions with voltages varying from 1.5 V to approximately 500 V and with various shapes, sizes and terminal arrangements. 

Table 54.2 Estimated average service life at 21 °C for a selection of Union Carbide Eveready carbon- zinc Leclanche dry cells and batteries, voltage range 1.5-9V... 

Types of activated carbon which have electrical conductivity can be used instead of manganese dioxide as a depolarizer in dry-cell batteries.77 Powdered activated carbon is treated with ammonium chloride and pressed into a porous cylindrical shape that is placed in a zinc container forming the outer electrode. If provision is made for a sufficient. supply of air, the effect of the activated carbon cylinder is similar to that of"manganese dibxide. The potential of the activated carbon batter is 0.1 volt lower than that of the manganese dioxide type, but the voltage is steadier and is practically constant throughout the life of the battery. 

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