BATTERY VOLTAGES – CHARGED AND DISCHARGED CONDITIONS
The cell voltage of a battery depends upon the temperature of the battery and has a negative
temperature coefficient – the voltage level increases at lower temperature and decreases at
higher temperature. The voltages are normally specified at 80º F (26.7º C).
On a 12 volt battery, the no load battery voltage is between 11.4 VDC (fully discharged) and
12.9-13.0 VDC (fully charged). On a 24 volt battery, the no load battery voltage is between
22.8 VDC (fully discharged) and 25.8 -26.0 VDC (fully charged).
CHARGING STAGES - I, Uo, U
The charger is preset to charge in 3 stages as described in the succeeding paragraphs. The
charger is called “IUoU Charger” based on the DIN designation of the charging stages – “I”
Phase, “Uo” Phase and “U” Phase. Please refer to the charging curve given at Figure 1 for
understanding the 3 charging stages.
NOTE:
The charging voltages indicated below pertain to battery temperature of 80º F.
Stage 1 - Constant Current, Bulk Charge Mode (I Phase):
When the charger is first
connected to a battery, the battery will start drawing current proportional to the discharged
condition of the battery. When the battery is deeply discharged, it will initially try to draw
a very large current. If this initial current draw is more than 45 A (SEC-1245A) or more than
25A (SEC-2425A), the charger will enter Stage 1 – The Bulk Charge Mode (“I” Phase).
During this period, SEC-1245A will deliver a constant current “I” = 45 A and SEC-2425A
will deliver a constant current “I” = 25 A. The charger will be operating under current limit
condition and the voltage at the charging terminal will be same as the actual voltage of the
discharged battery. The voltage of the battery will slowly start rising and when the battery
voltage approaches voltage U = 13.8 V (SEC-1245A) or voltage U = 27.6 V (SEC-2425A),
the current drawn by the battery will reduce below the current limit value of 45 A (SEC-
1245A) and 25 A (SEC-2425A). The charger will exit current limit condition and will now
output constant voltage of U = 13.8 V (SEC-1245A) or constant voltage U = 27.6 V (SEC-
2425A). The battery will continue to charge at this constant voltage and its charging current
draw will reduce further. When the charging current drawn by the battery reduces below 80%
of the charger capacity “I” i.e. 36 A (for SEC-1245A) or 20 A (for SEC-2425A), the charger
will automatically switch over to Stage 2 – Constant Over-voltage, Timed Absorption /
Boost Charge Stage (“Uo” Phase).
During this Stage, following LED indications are provided:
•
Charging Indicator LED (4) on the front panel turns red
•
Red LED under “I Phase” is lighted on the Remote
Panel (15) ( Optional accessory)
NOTE:
When “Half Power Mode” is selected (See under “Half Power Mode / Reduction of
Maximum Charging Capacity”), the maximum charging capacity (current limit value) of the
charger is reduced as follows:
•
Current limit of SEC-1245A is reduced to 22.5 A +/- 1 A instead of 45 A
•
Current limit of SEC-2425A is reduced to 12.5 A +/- 1 A instead of 25 A
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