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1.4.3 BATTERY CHARGING STAGES:

General descriptions of 4 stages of battery charging are given at Sections 1.4.3.1 to 1.4.3.4. Depending upon the
type of battery and its application, different Charging Profiles can be created using appropriate charging stages.

NOTE:

7 types of Charging Profiles are available in EVO

Series through programming parameter "CHARGING PROFILE".

Refer to Section 5.6 for details.

1.4.3.1 Stage 1 - Constant Current Bulk Charge Stage

: In the first stage, known as the Bulk Charge Stage,

the charger delivers a constant, maximum charging current that can be safely handled as specified by the battery
manufacturer. The value of the Bulk Charge Current depends upon the total Ampere Hour (

) capacity of the

battery or bank of batteries. A battery should never be charged at very high charging current as very high rate of
charging will not return the full 100% capacity as the Gassing Voltage rises with higher charging current due to
“Peukert Effect”. Also, very high charging current produces higher temperature in the active material of the plates
resulting in loss of cohesion and shedding of the active material that settles on the bottom of the plates. Shedding of
the active material results in loss of capacity. If the quantity of the shedded active material at the bottom of the plates
rises, it may short the cells.. As a general thumb rule, the Bulk Charging Current should be limited to 10% to 13%
of the Ah capacity of the battery (

20 Hour discharge rate

). Higher charging current may be used if permitted by the

battery manufacturer. This current is delivered to the batteries until the battery voltage approaches its Gassing Voltage
of around 2.4 V per cell at 77º F / 25º C or (i) 14.4V for 12V Battery Pack/ Bank or, (ii) 28.8V for 24V Battery Bank or,
(iii) 57.6V for 48V Battery Bank. The Bulk Charge Stage restores about 75% of the battery's capacity. The Gassing
Voltage is the voltage at which the electrolyte in the battery begins to break down into Hydrogen and Oxygen gases.
Under normal circumstances, a battery should not be charged at a voltage above its Gassing Voltage (except during
Equalization Stage) since this will cause the battery to lose electrolyte and dry out over time. Once the Gassing Voltage
is approached, the charger transfers to the next stage, known as the Absorption Stage.

INFO

As the Bulk Charge Stage is a constant current stage, the charger does not control the voltage and the
voltage seen at the output terminals of the charger will be the actual battery voltage (

this will rise slowly

towards the Gassing Voltage under the influence of the constant charging current

1.4.3.2 Stage 2 - Constant Voltage Absorption Stage

During the Absorption Stage, the charger changes from

constant current to constant voltage charging. The charging voltage is held constant near the Gassing Voltage to
ensure that the battery is further charged to the full capacity without overcharging. The Absorption Stage feeds
additional 40% of the capacity that adds up to a total charged capacity of around 115% to take care of around
15% loss of charging efficiency. As the output voltage of the charger is held constant, the battery absorbs the charge
slowly and the current reduces gradually till all of the soft Lead Sulfate (

PbSO

) crystals have been converted to Lead

Dioxide (

PbO

) on the Positive Plates and Sponge Lead (

Pb)

on the Negative Plates. The time the charger is held in the

Absorption Stage before it transitions to the next Float Stage is determined in one or more of the following conditions:

By a fixed timer (e.g. 4 to 8 Hours)

. This may result in overcharging of almost fully charged batteries.

When charge current drops to specified threshold

: Switching over to the Float Stage when the charge