Electrical Power Systems Technology

Direct Current Power Systems 165

clear cell shown in Figure 7-6 has air removed through the center tube

to form the vacuum inside it that isolates the positive and negative elec-

trodes. The DC output produced by this cell is extracted through termi-

nals connected to the tritium source (negative) and to the carbon connec-

tor (positive). The output of this cell is dependent upon the nuclear energy

generated by the tritium source; therefore, the voltage output decreases as

the cell ages.

CHARACTERISTICS OF SECONDARY CELLS

Regardless of the type of primary cell used, its usable time is limited.

When its chemicals are expended, it becomes useless. This disadvantage is

overcome by secondary cells. The chemicals of a secondary cell may be reac-

tivated by a charging process. Secondary cells are also called storage cells.

The most common types of secondary cells are the lead-acid cell, nickel-iron

(Edison) cell, and nickel-cadmium cell

The Lead-acid Cell

The widely used lead-acid cell is one type of secondary cell. The elec-

trodes of the lead-acid cell are made of lead and lead peroxide. The positive

plate is lead peroxide (PbO 2 ), and the negative plate is (Pb). lead The electro-

lyte is dilute sulfuric acid (H 2 SO 4 ). When the lead-acid cell supplies cur-

Figure 7-6. Cutaway drawing of a nuclear cell