©
2009 Magnum Energy Inc
Page 44
4. Determine how deeply you want to discharge your batteries.
•
Divide the
Storage Amp-Hours
by 0.2 or 0.5 to get the
Total Amp-
Hours
:
a)
0.2 = Discharges the batteries by 20% (80% remaining), this is considered
the optimal level for long battery life; or
b)
0.5 = Discharges the batteries by 50% (50% remaining), this is con-
sidered a realistic trade-off between battery cost and battery life.
Total Amp-Hours
Temperature
80F/27C
70F/21C
60F/15C
50F/10C
40F/4C
30F/-1C
20F/-7C
Multiplier
1.00
1.04 1.11
1.19
1.30
1.40 1.59
Additional compensation:
Low battery temperature: If the batteries are installed in a location that will be exposed to low temperatures, the
output current will be less. In these instances, you will need to determine the lowest temperature the battery
bank will experience and multiply the
Total Amp-Hours
by the Multiplier below.
Inverter ef
fi
ciency: When the inverter is used in a back-up power application the inverter ef
fi
ciency will not be
a large concern; however if the inverter is the primary AC source for the calculated load, the
Total Amp-Hours
should be multiplied by 1.2 to factor in an average 80% inverter ef
fi
ciency.
C.2 Battery Bank Sizing Worksheet
Complete the steps below to determine the battery bank size required to power your AC loads:
1. Determine the daily power needed for each load
a) List all AC loads required to run; and
b) List the Watt-Hours for each load (see table B-1 for common loads/wattage); and
c) multiply by how many hours per day (or a fraction of an hour) each load will be used; and
d) multiply by how many days per week you will use the listed loads; and
e) divide by seven =
Average Daily Watt-Hours Per Load
.
Average Daily Watt-Hours Per Load
AC load
watt-hours
(x) hours per day
(x) days per week (
÷
7) = total power
2. Determine the total power needed each day for all the loads.
•
Add the
Average Daily Watt-Hours Per Load
together =
Total Daily Watt-
Hours
.
3. Determine the battery Amp-Hour capacity needed
to run all the loads before recharging.
•
Divide the
Total Daily Watt-Hours
by the nominal battery volt-
age of the inverter (i.e. 12, 24 or 48 volts); and
•
Multiply this by how many days the loads will need to
run without having power to recharge the batteries (typi-
cally 3 to 5 days of storage) =
Storage Amp-Hours
.
x
___
=
Total Daily Watt-Hours
(days of storage)
÷
___
=
(inverter battery voltage)
Appendix C - Battery Information
