Outback FX-R Series Installation Manual
Planning
12 900-0166-01-01 Rev A
Bank Size:
Battery bank capacity is measured in amp-hours. Determine the required bank
specifications as accurately as possible, beginning with the items below. This avoids underperformance
or wasted capacity.
These ten items are obtainable in different places, summarized in Table 3. Some of the information is
specific to the site or application. Some can be obtained from the battery manufacturer. Information on
OutBack products is available from OutBack Power Technologies or its dealers.
A. Size of load:
B. Daily hours of use:
C. Days of autonomy:
D. Application: This often helps define or prioritize the previous three items. Off-grid systems often
require enough capacity to last for an extended period before recharging. Grid-connected systems
frequently need only enough capacity for short-term backup during outages.
E. Conductor efficiency: Wire size and other factors
will waste power due to resistance and voltage drop.
Typical acceptable efficiency is 96 to 99%.
F. Inverter efficiency: FXR specifications list “Typical
Efficiency” to help estimate operating loss.
G. System DC voltage: Each inverter model
requires a specific DC voltage to operate.
H. Battery voltage: Most individual battery
voltages are less than the system DC voltage.
The batteries may need to be placed in series
to deliver the correct voltage.
I. Capacity: Battery capacity, which is measured
in ampere-hours (amp-hours or Ah), is not
usually a fixed number. It is specified based
on the rate of discharge. For example, the
OutBack EnergyCell 200RE is rated at 128.4
Ah when discharged at the 4-hour rate (to
terminal voltage 1.85 Vpc). This is a high rate
of discharge that would hypothetically drain the
battery in 4 hours. The same battery is rated
at 170 Ah when used at the 20-hour rate.
In general, use the 8-hour capacity or less.
The larger the load, the more severe the
discharge. In these cases conservative values
with faster discharge times from the table (for
example, the 2- or 3-hour capacity) are better.
To choose accurately, the best method is to divide each Ah figure by the discharge in hours. (An
example from Table 3 for the OutBack 200RE would be 119.1 ÷ 3 hours = 39.7 Adc.) If the number is
equal or greater than the load size (in DC amperes), that column can be used as the capacity.
NOTES:
~ The battery’s selected rated capacity may have little to do with the actual hours of use; this figure
simply reflects the rate of discharge.
~ Use battery specifications for terminal voltage 1.85 Vpc whenever possible.
~ Capacity ratings are for batteries at 25°C. Capacity is reduced at cooler temperatures.
J. Maximum depth of discharge (DoD): Most batteries cannot be discharged below a certain level
without damage. The bank requires enough total capacity to keep this from happening. DoD is
usually described as a percentage, although it is shown as a decimal in calculations.
Any losses are essentially amp-hour
capacity that the system cannot use.
The battery bank size can be
increased to account for losses.
These are the most basic
and essential factors used
to determine bank size.
Table 3
Battery Bank Elements
Item Source of information
A
. Load Size
Site-specific
B
. Daily Hours
Site-specific
C
. Days of Autonomy
Site-specific
D
. Application
Site-specific
E
. Conductor Efficiency
Site-specific
F
. Inverter Efficiency
Inverter manufacturer
G
. System Vdc
Inverter manufacturer
H
. Battery Vdc
Battery manufacturer
I.
Capacity Ah
Battery manufacturer
Example:
Model
Discharge in Hours
1 2 3 4 8 20
200RE 82.0 120.0 119.1 128.4 148.8 170.0
220GH 127.3 151.4 162.9 169.6 190.8 206.0
J
. Maximum DoD
Battery manufacturer