Yanmar YM155d Service Manual page 70

of a battery: by i t s 'Ampere Hour' electrical
capacity (AH) or i t s 'Watt Hour' electrical capac-
ity
(WH). Generally speaking, the 'Ampere
Hour Capacity'
is
used.
Electrical capacity (AH) = discharge current
(A) x hours of dis-
charge (H) required
for battery t o reach
discharged terminal
voltage
The capacity of a battery will vary according t o
i t s discharge current rate, the ambient tempera-
ture during discharge, and the time and manner
i n which the battery
is
used.
The capacity will also vary according t o the
temperature of the electrolyte during discharge.
The higher the temperature, the larger the capac-
ity; and the lower the temperature, the lower the
capacity.
-
When starting the engine, the battery discharges
at a very high current flow rate. Accordingly, it
can be readily understood that starting
is
more
difficult when the ambient temperature is very
low, because the capacity of the battery is lower-
ed. I n addition, the viscosity of the engine oil
also increases as the temperature drops.
(3) Inspection of the Battery
a) Electrolyte Capacity
The water content of the electrolyte will
evaporate during use, or will be reduced in
volume because of electrolysis. I f there
is
in-
sufficient electrolyte, the battery i s liable t o
sustain damage, and it there is too much, the
electrolyte will overflow and damage the body
and other parts of the tractor.
According1y;the level of the electrolyte in the
battery should be inspected regularly, and re-
plenished with distilled water when insuffi-
cient. The level of the electrolyte should be
M
,
sufficient so that the separators of the plates
are not exposed.
If the plates are exposed t o the atmosphere,
sulfation will ensue, and
it
will no longer be
possible t o recharge the battery.
Too
low & r r m level OMrfilled
b) Specific Gravity
The specific gravity of the electrolyte of a bat-
tery varies according t o the temperature.
The specific gravity should be adjusted t o the
specific gravity at
68°F
120°C).
Use a hydrometer t o get the specific gravity
reading:
Specific
gravity
1.260
1.220
1.160
1.090
1.080'
1.050
Usable ar
it.
Recharge
immediately.
Condition
100%
75
50
25
10
0
Charged condition
Usable limit
Discharged
Fully discharged