ELECTRICAL SYSTEMS - HOUSE — 8
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20 08 CONTESSA
for short durations, without depleting battery
reserves. Commercial type batteries bridge
the gap of deep cycle and engine batteries.
Commercial batteries release medium amounts
of current over a longer period of time but they
are not designed to cycle their charge capacity.
The working range of a deep cycle battery is
between 50 and 100% state of charge (SOC).
Deep cycle batteries should not be cycled below
50% state of charge. Discharging a deep cycle
battery below 50% state of charge shortens the
life of the battery. Deep cycle batteries use an
amp hour rating which is usually calculated over
a 20 hour discharge interval. For example: A
deep cycle battery with a rated capacity of 100
Ahrs. is designed to release current at the rate of
5 Amps per hour. Multiply a 5 Amp load over
a 20 hour discharge period equals the rated 100
Ahr. capacity.
These discharge gures are calculated with
the battery starting at 100% state of charge
with the battery at 80º F. when the discharge
cycle begins. However, increasing the discharge
load applied to the battery from 5 Amps to
10 Amps on a 100 Ahr battery does not yield
ten hours of discharge time. This is due to the
internal reactions which occur when a battery is
discharging. Actual discharge time for a 10 Amp
load may be closer to eight hours of discharge
time. Increasing the load applied to the battery
to 20 Amps will not yield ve hours discharge
time but may be less than three hours. It might
be understood as a point of diminishing return.
Calculating applied loads to an inverter to
approximate run time from the battery amp
hours available is not an equal trade up when
voltage is inverted and amperage is calculated.
When the inverter is used to operate an AC
load it uses approximately ten times the DC
current needed from the battery when inverting
12 Volts DC to operate the 120 Volt AC item.
There is also a small efciency loss of about
10% when inverting. For example: When using
the inverter to operate an AC electrical item,
which has a current draw rating of 2 Amps, the
inverter will use over 20 Amps DC power from
the batteries.
Determining Current Consumption:
First determine the amount of current used
by an AC item. For example: The television is
rated at 200 watts at 120 Volts AC. Calculate
watts to amps. Divide 200 watts by the operating
voltage of 120, this equals 1.6 Amps. Multiply
1.6 Amps AC current by a factor of ten the
inverter will use, this equals 16 Amps DC
battery current. Add the revised 10% efciency
loss gure, this calculates to a total of 17.6
Amps DC. If the battery bank capacity is rated at
500 Ahrs., actual elapsed time to the suggested
50% state of charge would net viewing time for
the television at approximately 13 hours in ideal
conditions.
The run time gure will vary greatly with
the actual state of charge of the battery bank
when the discharge process begins. Ambient
temperature combined with other working
loads, such as lights and parasitic loads applied
to batteries, affect run times. Calculating the
exact run time is not precise due to all the
variables and equations involved; however,
an approximate time gure can be obtained.
Proper battery maintenance and charge cycles
affect battery performance. Observe the
battery condition with hydrometer and voltage
readings. Use only distilled water when lling
batteries. To achieve the highest quality of
battery performance and longevity maintain the
batteries in their proper operating range.
SOLAR PANEL (Optional)
The solar power system consists of a 100 watt
solar panel and a charge controller. This system
can deliver enough power to offset the normal
day-to-day drain on house batteries caused by
various parasitic electrical loads, such as radio
memories, alarm systems and natural self-
discharge of batteries.
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