SamplexPower SEC-1250UL Mode D'emploi page 11

seCtIOn 4 |
StAGe 1- BUlK cHARGe StAGe ("i" PHASe)
In this stage SEC-1250UL outputs voltage of 13.5 VDC and SEC-2425A outputs 27V.
The following explanation is for SEC-1250UL. Explanation for SEC-2415UL will be
same but the voltage values will be 2 times and current values will be half as compared
to SeC-1250UL.
note: For explanation purpose, it is assumed that the battery is deeply discharged
to around 10.5 / 21V when charging is initiated.
When the charger is switched on, the battery will try to draw very large current =
(13.5V- 10.5V) ÷ Internal resistance (0.02 Ω) = 150A which will be much higher than the
current limit value of 50A. The charger will enter current limit condition (point A2),
its internal voltage will try to drop but will be clamped to the terminal voltage of the
battery i.e. 10.5V (point A1). The battery starts charging at constant current of 50A (Sec-
tion A2-B2) and its intrinsic voltage starts rising almost linearly (Section A1-B1). When
its intrinsic voltage approaches 13.5V, the current drawn by the battery will reduce to
< 50A. At this point (B2), the charger will exit current limit and will output a constant
voltage of 13.5V (point B1). As the battery charges further under constant voltage of
13.5V (Section B1 – C1), its intrinsic voltage rises further and its current starts to taper
down (Section B2 – C2). The current tapers down because the intrinsic battery voltage is
rising and the differential voltage between 13.5V of the charger and intrinsic voltage of
the battery is reducing thereby, lesser current is driven into the battery. Tapering charge
is provided at this transition to reduce surface charge effect to ensure that the charge
slowly diffuses to the internal thickness of the plates and prevents overcharging. When
the charging current tapers down to 80% of the rated capacity of the charger (40A for
SEC-1250UL and 20A for SEC-2425UL) at point "B2", the charger transitions to the next
Stage 2 - Absorption Boost Stage ("U
charging characteristics during this Stage Are As Follows:
• Battery voltage rises slowly and almost linearly (it will start rising sharply at
the beginning of the next Absorption Stage 2).
• The entire charging current is used to convert Lead Sulfate to Sponge Lead at
the Negative plates and to Lead Dioxide at the Positive plates.
• There is no gassing and the charging efficiency is high - around 91%.
• The restored capacity in this stage is inversely proportional to the charging rate
(due to Peukert Effect). This means that as the charging rate is increased, the
capacity restored reduces. This stage restores 60% of capacity at charging rate
of C/5, 70% to 75% capacity at charging rate of C/10 and 85% to 90% of
capacity at charging rate of C/20
• Red LED marked "I Phase" will be lit on the optional Remote Control
Model 900-RC
Principle of Operation
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