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Ni-mh rechargeable batteries, Performance characteristics, 1 general characteristics – Duracell Ni-MH User Manual

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Ni-MH Rechargeable Batteries

5.1 General Characteristics

The discharge characteristics of the nickel-metal

hydride cell are very similar to those of the nickel-
cadmium cell. The charged

open circuit voltage

of both

systems ranges from 1.25 to 1.35 volts per cell. On
discharge, the

nominal voltage

is 1.2 volts per cell and

the typical

end voltage

is 1.0 volt per cell.

Figure 5.1.1 illustrates the discharge character-

istics of nickel-metal hydride and nickel-cadmium
rechargeable cells of the same size. As shown, the volt-
age profile of both types of cells is flat throughout most
of the discharge. The

midpoint voltage

can range from

1.25 to 1.1 volts per cell, depending on the discharge
load. Figure 5.1.1 can also be used to compare the
capacity of the two rechargeable types. Note that the
capacity of the nickel-metal hydride cell is typically up to
40 percent higher than that of a nickel-cadmium cell of
equivalent size.

5.2 Discharge Characteristics: Effect of

Discharge Rate and Temperature

Typical discharge curves for DURACELL nickel-

metal hydride batteries under constant current loads at
various temperatures are shown in Figures 5.2.1 to
5.2.3. Discharge voltage is dependent on discharge
current and discharge temperature.

FIGURE 5.1.1

1.5

1.4

1.3

1.2

1.1

1.0

.9

Voltage (V)

Ampere-Hour Capacity (%)

Comparison of discharge voltage and capacity of
same-size Ni-MH and Ni-Cd cells.

[

Conditions: Charge: C/3 for 5 hours, Temperature: 21

°

C (70

°

F)]

0 20 40 60 80 100 120 140 160

Ni-MH

C/5

C/5

Ni-Cd

5

5

Performance Characteristics

FIGURE 5.2.1

Voltage (V)

Discharge Capacity (Ah)

FIGURE 5.2.2

Discharge Capacity (Ah)

Voltage (V)

C (2.4A)

Voltage (V)

Discharge Capacity (Ah)

8.5

8.0

7.5

7.0

6.5

6.0

5.5

0 0.5 1.0 1.5 2.0 2.5

C/5 (0.48A)

C (2.4A)

C (2.4A)

FIGURE 5.2.3

Voltage and capacity of DURACELL DR30 Ni-MH
batteries at various discharge temperatures
and rates.

[Conditions: Charge: 1C to -

V = 60mV @ 21

°

C (70

°

F)]

Temperature: -20

°

C (-4

°

F)

8.5

8.0

7.5

7.0

6.5

6.0

5.5

0 0.5 1.0 1.5 2.0 2.5

C/5 (0.48A)

C (2.4A)

Temperature: 45

°

C (113

°

F)

8.5

8.0

7.5

7.0

6.5

6.0

5.5

C/5 (0.48A)

C (2.4A)

0 0.5 1.0 1.5 2.0 2.5

Temperature: 21

°

C (70

°

F)

C/5 (0.48A)

Temperature: 0

°

C (32

°

F)

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