Case 580SR Service Manual page 992

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164
TEST CHARGING
This test is designed only for batteries that have
failed the previous capacity test.
1. Attach the battery starter (high rate discharge
tester) positive leads to the battery positive ter-
minal and the negative leads to the battery neg-
ative terminal.
2. Connect the battery charger positive lead to the
battery positive terminal and the negative lead
to the battery negative terminal.
3. Turn the charger timer past a "3 minutes" charge
indication and then back to the "3 minutes"
mark.
4. Set the charging rate as close as possible to 40
amperes.
5. After 3 minutes at this fast charge take the volt-
meter reading.
Z If the total voltage is over 15.5 volts the battery is
unsatisfactory and is probably sulphated or worn
out and should be replaced.
NOTE: a mildly sulphated battery can be recovered
by using a multiple battery type charger, with an
open circuit upper voltage limit of 50 V.
Owing to the high resistance of a sulphated battery,
it will primarily require a high voltage setting to over-
come the resistance of the sulphation initially there
may be no visible acceptance of the charge. After a
few minutes of inactivity a small charge will be ap-
parent, followed by a rapid increase in the charge
rate. The charge rate must not exceed 14.0 am-
peres or the electrolyte temperature 50 °C.
When the ampere rate is stable, reset the volts until
the charge ampere rate is a steady 5 A.
Continue at this rate until the electrolyte specific
gravity stops rising at approximately 1.275 - 1.280 at
20 °C, this can take up to 48 hours of charging.
Stand the battery for 24 hours and then conduct the
capacity test detailed previously.
Z If the total voltage is under 15.5 volts, test the spe-
cific gravity of each cell and re-charge the battery
to the following scale:
Specific Gravity
1.150 or less
1.151 to 1.175
1.176 to 1.200
1.201 to 1.225
NOTE: when battery problems are experienced the
fan belt tension and the complete charging system
should be checked.
SECTION 55 - ELECTRICAL SYSTEM
Fast charge up to:
60 minutes
45 minutes
30 minutes
15 minutes
(Slow charge only)
COMMON CAUSES OF BATTERY FAILURES
Z Internal open circuit.
Z Internal short circuit.
Z Loss of electrolyte.
Z Separation of active materials from grids.
Z Accumulation of sulphate crystals too large to dis-
perse.
These failures are normally caused by the following:
Z Failure of inter cell components.
Z Excessive crystal growth may puncture the sepa-
rators and cause short circuits.
Z Excessive over charging (charging system mal-
function, boost/recovery techniques with high volt-
age, operation in very high temperatures).
Z Freezing of electrolyte. A fully charged battery
does not freeze until -65 °C. A 50% charged bat-
tery freezes between -17 °C and -27 °C. Fully
discharged electrolyte freezes at -3 °C to -11°C.
Excessively high boost charging and gassing will
also cause separation of active materials from
the grids. Separation destroys the chemical
function of the battery.
Z Crystal growth occurs whenever batteries are left
discharged. High temperatures and extended dis-
charged periods increase this condition.
At room temperature after one week the battery is
unlikely to recover on the vehicle.
Recharge will require a higher constant voltage.
After 3 weeks the battery will have suffered perma-
nent degradation and the procedure detailed previ-
ously for charging a "Deeply Discharged" battery
should be followed.
When fully charged, batteries have a long shelf life.
The lead calcium type battery self discharges at 3%
per month. This means that it will take 16 months to
lower to 50% charged. On the loader backhoe the
quiescent load is about 50 mA. To predict rundown
on a static vehicle this should be added as approxi-
mately 8 Ah per week.
It is worth stressing that when cranking, if a battery
starts to fade, it is beneficial to stop and allow two
minutes for the battery to recover. The recovery time
should be increased as the temperature decreases.
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