12
As stated previously, the bulk charge brings the bank to an 80% charging level.
The remaining 20% of the capacity is a function of time and current. The charger will
maintain current level until the bulk set point has been reached, then the charger
switches to the absorption timer. The current levels start decreasing as the internal
resistance in the battery increases. Assume over the time of the absorption charge that
50% of your maximum charge current will be available (this is factored into the equation).
0.42 = (20%/50%) + 5%. 5% is added due to losses.
ABSORPTION CHARGE TIME
Where : T = 0.42 x C /I
T = ABSORPTION CHARGE TIME
C = 20 hr RATED CAPACITY (of the Bank)
I = Charging Current ( 10% of C20 max)
0.42 = ( 20%/50%) + 5% (5% is added due to losses)
EXAMPLE
2 Banks of 6 V S-530 models
20 hr rate = 400 x (2 strings) = 800 ah
I = 10% of 800ah = 80 amps. If charger is 60 amps max, 60 is used
T = 0.42 x 800/80 = 4.2 hrs OR T = 0.42 x 800/60 = 5.6 hrs
FLOAT CHARGE
The batteries require a certain amount of voltage in order to maintain full charge when
no load is applied. The power supply keeps the batteries at a constant full state of
charge. In order to prolong battery life, the float settings on the power supply should be
adjusted to the voltage indicated in Table 2.
EQUALIZATION - PREVENTATIVE
Individual cells will vary slightly in specific gravity after a charging cycle. Equalization
or a “controlled overcharge” is required to bring each battery plate to a fully charged
condition. This will reduce stratification and sulfating, two circumstances that shorten
battery life. Equalization of the battery bank is recommended every 30 to 180 days,
depending on the usage of the individual system. To equalize the cells, charge the
batteries until the voltage elevates to the “Equalization” voltage shown in Table 2. Charge
parameters and maintain for 2 to 3 hours per bank. A constant SG for 30 minutes is a
good indication of cell equalization. It is recommended to water the battery cells half way
through the equalization. This will assure the water is mixed with the electrolyte.
FREQUENCY
It is recommended to balance charge the batteries before usage. Corrective equalization
needs to be performed if symptoms arise such as a constantly running generator (low
capacity) or the battery bank will “not hold a charge”. These symptoms are typical of
a heavily sulfated battery. If a battery is not being fully charged on a regular basis or
limited equalization is performed using a generator, sulfating will occur from “deficit”
cycling. This undercharge condition can take months before it becomes a major and
noticeable problem.
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