Charge Time & Consumption Rate - Fleetwood Discovery Owner's Manual

Charge Time & Consumption Rate
Calculating Run Times:
Calculating run time figures
when operating 120 Volt AC
electrical items with an inverter
can be exponential due to
battery characteristics. Flow
characteristics of electrons vary
with different battery types and
chemical compositions. Deep
cycle batteries are generally
designed to slowly release
a majority of their charge
capacity. Deep cycle batteries
are rated in amp hours (Ahrs)
with the discharge occurring
over an extended period of time
before the battery is charged.
Engine starting batteries are
designed to quickly release large
amounts of current for a short
duration, 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 that 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 figures 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 that 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 eleven
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 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 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% efficiency loss figure, this
calculates to a total of 17.6 amps
DC. If the battery bank capacity is
Discovery, Discovery LXE, Pace Arrow, and Pace Arrow LXE
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
maintain the batteries in their
proper operating range.
165