©
2017 Sensata Technologies
Page 53
Appendix B – Battery Information
4. Determine how deeply you want to discharge your batteries.
• Divide 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
considered 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 effi 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.
B-5
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
b) List the watt-hours for each load (see Table C-1 for common loads/wattage)
c) Multiply by how many hours per day (or a fraction of an hour) each load will be used
d) Multiply by how many days per week you will use the listed loads
e) Divide by seven =
Average Daily Watt-Hours Per Load
(Total Power).
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 all Average Daily Watt-Hours Per Load
values =
Total Daily
Watt-Hours
.
3. Determine the battery Amp-Hour capacity needed to
run all the loads before recharging.
• Divide Total Daily Watt-Hours by the nominal battery
voltage of the inverter (i.e., 12, 24, or 48v); and then
• Multiply this by how many days the loads will need to run
without having power to recharge the batteries (typically 3
to 5 days of storage) =
Storage Amp-Hours
.
x
___
=
Total Daily Watt-Hours
(days of storage)
÷
___
=
(inverter battery voltage)
