Samlex Power PST-150-12 Manuel Du Propriétaire page 33

SECTION 8 |
The DC input circuit is required to handle very large DC currents and hence, the size of
cables and connectors should be selected to ensure minimum voltage drop between
the battery and the inverter. Thinner cables and loose connections will result in poor in-
verter performance and will produce abnormal heating leading to risk of insulation melt
down and fire. Normally, the thickness of the cable should be such that the voltage drop
due to the current & the resistance of the length of the cable should be less than 2% to
5%. Use oil resistant, multi- stranded copper wire cables rated at 105ºC minimum. Do
not use aluminum cable as it has higher resistance per unit length. Cables can be bought
at a marine / welding supply store.
Effects of low voltage on common electrical loads are given below:
- Lighting circuits - Incandescent and Quartz Halogen: A 5% voltage drop causes an
approximate 10% loss in light output. This is because the bulb not only receives less
power, but the cooler filament drops from white-hot towards red-hot, emitting much
less visible light.
- Lighting circuits - Fluorescent: Voltage drop causes a nearly proportional drop in
light output.
- AC induction motors: These are commonly found in power tools, appliances, well
pumps etc. They exhibit very high surge demands when starting. Significant voltage
drop in these circuits may cause failure to start and possible motor damage.
- PV battery charging circuits: These are critical because voltage drop can cause a dis-
proportionate loss of charge current to charge a battery. A voltage drop greater than
5% can reduce charge current to the battery by a much greater percentage.
8.4.4 Fuse Protection In Battery Circuit
A battery is an unlimited source of current. Under short circuit conditions, a battery can
supply thousands of Amperes of current. If there is a short circuit along the length of the
cables that connects the battery to the inverter, thousands of Amperes of current can flow
from the battery to the point of shorting and that section of the cable will become red-hot,
the insulation will melt and the cable will ultimately break. This interruption of very high
current will generate a hazardous, high temperature, high-energy arc with accompanying
high-pressure wave that may cause fire, damage nearby objects and cause injury. To prevent
occurrence of hazardous conditions under short circuit conditions, an appropriate fuse with
Interrupting Capacity ≥ 1000A should be used in the battery circuit. The fuse should be
installed as close as possible to the battery preferably within 7". Automotive blade type of
fuses may be used e.g. Type ATO by Littel Fuse.
WARNING!
Use of an appropriately sized external fuse as described above is mandatory to
provide safety against fire hazard due to accidental short circuit in the battery
wires. Please note that the DC side fuse inside the unit (20A for PST-150-12 and
10A for PST-150-24) is designed to provide protection to the internal compo-
nents of the inverter. This internal fuse will NOT blow if there is a short circuit
along the length of cables connecting the battery and the inverter.
Installation
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