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Section 3 |
battery backup application using 12V, 40-100 ah battery
This Battery Backup Unit has been preset for battery backup application for a 12V
battery of approximately 40 to 100 Ah capacity with the maximum charging current
limited to approximately 4A (At power supply voltage set at 14.0V and battery
discharged to 11.1V).
battery backup application using 24V, 40-100 ah battery
When using this unit in the preset condition for 24V, 40-100 Ah battery backup
application, the charging current will increase approx. two times to 8A (At power supply
voltage set at 27.6V and battery discharged to 22.3V).
calculating Maximum battery charging current
Maximum battery charging current ib = {(Vp – Vd) – Vb} divided by rs.......... equation 1
Vp = Output voltage of the power supply (14V for 12V battery and 27.6V for 24V battery)
Vd = Forward voltage drop across Schottky Diode D1 (up to 0.5V)
Vb = Battery voltage
rs = E quivalent series resistance. In this case, R1 (1.2 Ohm) and R2 (1.2 Ohm) in
parallel = 0.6 Ohm (See Fig 3.1).
Assuming the voltages of fully discharged 12 V and 24 V batteries to be 11.1V and 22.3V
respectively (at Discharge Rate of around C/10 (0.1C) Amps), the maximum charging
currents will be as follows as per equation 1:
For 12 V battery backup = (14V – 0.5V – 11.1V) divided by 0.6 Ohm = 4a
For 24 V battery backup = (27.6V – 0.5V – 22.3V) divided by 0.6 Ohm = 8a
Section 4 |
4.1 instaLLation DiagraM anD DiMensions
Fig 3.1 shows the installation diagram. Dimensional details are given at Fig 2.3.
4.2 cabLe siZing, terMination anD Fusing
The size of the cables used to connect the power supply, the battery and the load to
this unit will depend upon the maximum value of the current flow and the length of
the cable run. Current flowing through a cable will produce an undesirable voltage
drop along the length of the cable. The voltage drop is proportional to the resistance of
the cable. Higher resistance produces higher voltage drop. The resistance of the cable
increases as the cable becomes thinner. Similarly, the resistance increases with the length
of the cable. It is desirable to limit the voltage drop to 2% which will be 0.24V for 12V
battery and 0.48V for 24V battery.
Description and Principle of operation
installation
SAMLEX AMERICA INC. | 7
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