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Battery Information
Battery Bank Sizing
Battery capacity
Battery size or capacity is just as important as the
battery type selected for use with the Freedom SW. The batteries are the
most important part of your system, so Xantrex recommends that you
purchase as much battery capacity as possible. A large battery will extend
running time and ensure that your inverter/charger delivers full rated surge.
Xantrex recommends a minimum battery size of 200 amp-hours (Ah)
for moderate loads (<1000W) and greater than 400 Ah for heavy loads.
See “Estimating Battery Requirements” for information on a more detailed
calculation.
About Amp-hours
A number of different standards are used to rate
battery energy storage capacity. Automotive and marine starting batteries
are normally rated in cranking amps. This is not a relevant rating for
continuous loads like an inverter. Deep-cycle batteries use a more suitable
rating system such as amp-hours (Ah).
Amp-hour capacity is the number of amps a battery can continuously
deliver during a specified number of hours. It is represented by the product
of the two —amps multiplied by hours.
A typical marine or RV battery rated for 100 Ah can deliver 5 amps for 20
hours (5 amps × 20 hours = 100 Ah). This same battery can deliver a higher
or lower current for less or more time, limited approximately by the 100 Ah
figure (50 amps for 2 hours or 200 amps for 1/2 hour), but usually the
capacity figure given is only accurate for the specified duration (20 hours).
Estimating Battery Requirements
Calculating Battery Size
Step 1: Compute Amp-hours
For each appliance, compute the number of amp-hours that will be used
between charging cycles, as follows:
1.
Obtain the wattage. If the wattage is marked on the nameplate rating,
use that. Otherwise, multiply the marked voltage and amperage:
WATTS = VOLTS × AMPS
.
2.
Obtain the Watt-hours by multiplying that amount by the hours the
appliance will be used:
WATT-HOURS = WATTS × HOURS
.
3.
Obtain the amp-hours that the appliance requires by dividing that
amount by 10 (the factor for the Freedom SW, which is a 12-volt
system):
BATTERY AMP-HOURS USED = AC WATT-HOURS/10
For example, a 100 W light bulb that is used for 4 hours will use 400 watt-
hours (Wh) and the inverter will consume approximately 40 Ah from a 12
volt battery.
4.
Enter this information on the blank calculation worksheet (page 56).
Step 2: Calculate Battery Size
5.
Complete the rest of the worksheet; see Table 7, “Battery Sizing
Example” on page 54 for an example.
Freedom SW 3K2K InvChg Install Guide.book Page 53 Wednesday, October 12, 2011 4:40 PM
