Samlex America SAM-3000-12 - Manual (Page 14)

12 | SAMLEX AMERICA INC. SAMLEX AMERICA INC. | 13
An example of this calculation for a 12V inverter is given below:
Let us say that the total continuous ac Watts delivered by the 12V inverter = 1500W.
Then, using Formula 2 above, the DC current to be delivered by the 12V batteries =
1500W ÷10 = 150 Amperes.
next, the energy required by the load in ampere Hours (ah) is determined:
For example, if the load is to operate for 3 Hours, then as per Formula 3 above, the energy
to be delivered by the 12V batteries = 150 Amperes × 3 Hours = 450 Ampere Hours (Ah).
finally, as per rule of thumb at formula 4, the ah capacity of the batteries should be
twice the energy required by the load in ah = 450 Ah x 2 = 900 Ah.
Dc input power terminals
Custom made DC input terminals using M9 Nut / Bolt arrangement have been provided
for connecting DC input cables (10, 11 in Fig 3.1 to 3.3). The terminals are protected by
plastic covers.
important Wiring/cabling information
Although wires and cables are good conductors of electric current, they do have some
resistance, which is directly proportional to the length and inversely proportional to the
thickness (diameter) i.e. resistance increases in thinner and longer wires. Current flowing
through resistance produces heat. Cables and wires are covered with insulating material
that can withstand a specified temperature of the conductor under specified conditions.
To ensure that the insulation is not damaged due to excessive overheating, each wire size
has a maximum allowable current carrying capacity called "Ampacity" which is specified
by NEC Table 31.15 (B) (17). Further, NEC also specifies that wire size should be based on
Ampacity - 1.25 times the rated current flow.
Resistance of wires and cables produces another undesirable effect of voltage drop. Volt-
age drop is directly proportional to the resistance and the value of current flow. Voltage
drop produces loss of power in the form of heat. In addition, excessive voltage drop from
the battery to the inverter may prematurely shut down the inverter due to activation of
the Low Input Voltage Protection Circuitry of the inverter (10.5 ± 0.3V). DC cables should
be sized to ensure maximum voltage drop is limited to less than 5%.
effects of low voltage on common electrical loads are given below:
Lighting circuits – incandescent and Quartz/Halogen: Loss in light output 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 an early proportional drop in
light output.
ac induction motors: These are commonly found in power tools, appliances, etc. They
exhibit very high surge demands when starting. Significant voltage drop in these circuits
may cause failure to start and possible motor damage.
SECTION 4 | Installation
11002-SAM-1000-1500-2000-3000-12-0814.indd 14 14-08-12 9:59 AM