Case 150-190 - Page 17

Specific Gravity Check
The most reliable way to determine the
concentration of sulfuric acid in the elec-
trolyte is to measure the relative weight or
specific gravity of the solution. A hydrom-
eter is used for this, and only enough solu-
tion is removed from a battery cell so the
float is suspended freely and not touching
the top, bottom or sides of the glass tube,
Figure F-2. Always hold the hydrometer at
eye level and in vertical position when taking
a reading. A hydrometer reading is only cor-
rect when the temperature of the solution is
80° F.
/IOTl l\fost hydrometers have a calibrated
thermometer to correct this.
When it is above or below this reading, it
has to be corrected either by adding . 004
gravity points for every 10° above 80°F. or
subtracting .004 gravity points for every 10°
below 80° F., Figure F-3.
\\:hen the specific gravity readings be-
tween the cells show a variation of .025, the
battery should be replaced.
Specific gravity readings will change de-
pending upon climate.
State Specific Gravity Range for
of
Climate Zone
Charg-e
Fri!!id
Temperate Tropical
100%
1.280 1.260
1.225
75%
1.230 1.215
1.180
50%
1.180
1.170 1.135
Discharged
1.080 1.070
1.045
The battery should never be allowed to
drop below 75% charge while not in use.
\\'hen a battery is to be charged, it may be
charged at any rate which does not allow the
battery terminal voltage to exceed 15. 5 volts
(12 volt battery) while charging. The battery
temperature should never exceed 1l0°F.
while charging, if it does reduce charging
rate.
The charger should be left on until the
specific gravity readings stay the same after
three checks of an hour apart.
A fast charge method is used only to give
the batteries a boost for starting. This type
of charge puts out a very high am per age un -
til the battery temperature is up to 1l0°F.,
then it shuts off.
F-3
7
Figure F-1
HOLD HYDROMETER
VERTICALLY STRAIGHT
/
---,-
TAKE READING
AT EYE LEVEL
FLOAT MUST
BE FREE
Figure F-2
TEMPERATURE IN
160
Of OF El EC TROLY TE
150
+
32
GRAVITY POINTS
+
28
TO ADD OR
+ 24 SUBTRACT
+
20
FROM READING
0
- 12
-16
-20
- 24
- 28
- 32
Figure F-3