Direct Current Power Systems 163
Applications of Primary Cells
There are many types of primary cells available today, with unlimited
applications. The carbon-zinc (or Lechanche) cell, discussed previously, is
the most often used type of dry cell. This cell has a low initial cost and is
available in a variety of sizes. It is used primarily for portable equipment
or instruments. For uses that require a higher voltage or current than one
cell can deliver, manufacturers combine several cells in series, parallel, or
series-parallel arrangements to form batteries suitable for specialized ap-
plications. Carbon-zinc batteries can be obtained in voltage ratings from 1.5
volts, at over I-ampere capability, up to about 3000 volts.
Mer cury Cells—Another type of primary cell is the mercury or zinc-
mercuric oxide cell, shown in Figure 7-4. This cell was developed as an im-
provement of the carbon-zinc cell. The mercury cell has a more constant
voltage output, a longer active service time, and a smaller physical size.
However, the mercury cell is more expensive and produces a voltage of
1.35 volts, which is lower than that of the carbon-zinc cell.
Alkaline Cells—An alkaline or zinc-magnesium dioxide cell, shown in
Figure 7-5, is another type of primary cell. These cells have very low in-
ternal resistance and a voltage per cell of 1.5 volts. Because of their low
internal resistance, alkaline cells will supply higher currents to the electri-
cal loads connected to them. Alkaline cells are capable of a much longer
service life than the equivalent carbon-zinc cells.
Nuclear Cells—A ecent source of DC power that has been developed rFigure 7-4. Cutaway drawing of a mercury primary cell