6H-8 CHARGING SYSTEM
Hydrometer test
The direct method of checking the battery for state of charge is to
carry out a high rate discharge test, which involves a special pre-
cise voltmeter and an expensive instrument used in the service
shops, but not recommendable to the user of the vehicle.
At 20°C of battery temperature (electrolyte temperature) :
• The battery is in “Fully Charged State” if the electrolyte S.G.
is 1.280.
• The battery is in “Half Charged State” if the S.G. is 1.220.
• The battery is in “Nearly Discharged State” if the S.G. is
1.150 and is in danger of freezing.
As the S.G. varies with the temperature, if battery temperature is
not at 20°C (68°F), you have to correct your S.G. reading (taken
with your hydrometer) to the value at 20°C (68°F) and apply the
corrected S.G. value to the three-point guide stated value.
For the manner of correction, refer to the graph showing the rela-
tion between S.G. value and temperature at the left.
How to use the temperature-corrected state-of-charge graph
Suppose your S.G. reading is 1.28 and the battery temperature is
–5°C (23°F). Locate the intersection of the –5 °C line and the 1.28
S.G. line.
The intersection is within the “A” zone (shaded area in the graph)
and that means “Charged State”.
To know how much the battery is charged, draw a line parallel to
the zone demarcation line and extend it to the right till it meets
with the percentage scale. In the present example, the line meets
at about 85% point on the percentage scale. Therefore, the bat-
tery is charged up to the 85% level.
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