Monarch SE 2004-------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------- Section 8 Electrical System | 315
However, increasing the discharge load applied to the battery from 5 Amps to 10
Amps on a 100 Ahr battery does not yield 10 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 five 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 to operate the 120 Volt item. There is also a small efficiency 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. 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% efficiency loss figure, 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 figure 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 figure 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 filling batteries. To achieve the highest quality of battery
performance and longevity keep batteries in their proper operating range.
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