Primus Wind Power AIR 40 User Manual

AIR Owner’s Manual 11
Simple Tips for Deep Cycle Battery Bank Sizing
ELECTRICAL USAGE - the amount of energy consumed 1 day
in Watt-hours (Wh)
DAYS OF AUTONOMY - days of battery back-up required if
unable to charge the batteries by any means.
DEPTH OF DISCHARGE - limit of energy withdrawal to which
you will subject the deep cycle battery bank.
*Deeper discharge = Shortened battery life.
• Recommeded: never discharge a deep cycle battery
below 50% of its capacity
• O-grid applications, a 25% DoD will extend battery
life signicantly
TEMPERATURE - Standard for most battery rating is
25 ° C (77 ° F).
Cold temperatures = reduced battery capacity
High temperatures = shortened battery life
CALCULATIONS - calculate battery bank size, use example below:
3.) Identify Depth of Discharge (DoD) and convert to a
decimal value. Divide result of step 2 by this value.
4.) Select the multiplier corresponding to the lowest
average temperature your batteries will be exposed
to. Multiply result from Step 3 by this factor. *Result
is minimum Wh capacity of battery bank:
°C ° F Factor
26.7 80 + 1.00
21.2 70 1.04
15.6 60 1.11
10 50 1.19
4.4 40 1.30
1.1 30 1.40
-6.7 20 1.59
5.) Divide result from Step 4 by system voltage. Result
is the minimum Amp-hour (Ah) capacity of your battery
bank.
EXAMPLE:
40% DoD:
18,000 / 0.4 = 45,000 Wh
15.6 ° C (60 ° F) = 1.11
45,000 x 1.11 = 49,950 Wh
49,950 / 48 = 1,040 Ah
• A system load of 6,000 Watt-hours per day
• 3 Days of Autonomy (back-up) needed
• Planned Depth of Discharge (DoD): 40%
• Battery bank ambient average low 15.6 °C (60 ° F)
• A 48V system
STEPS:
1.) Identify total daily use in Watt-hours (Wh)
2.) Identify Days of Autonomy (back-up days);
multiply Wh/day by this factor.
6,000 Wh/day
3 days of Autonomy:
6,000 x 3 = 18,000 Wh
RECOMMENDATION - Keep the number of parallel strings of bat-
teries to three or fewer. More than three strings of batteries, risks
shortening battery life due to uneven charging.
• Batteries in Series = Voltage is Additive
• Batteries in Parallel = Ah is Additive
*Example: 2 12V 100Ah Battery Bank
Series 24V 100 Ah
Parallel 12V 200 Ah
Temp in degrees
In preparation for battery sizing, know: