DIY Manual

4 | P a g e 10-543-1 REV A
DIY Manual
For a 50% DOD battery bank, multiply 4500Wh by 2 = 9000Wh.
NOTE: What does this mean? You want to consume 4500Wh a day and
you want to draw down your bank no more than 50%, so you need
a bank that is twice as big.
For a 20% DOD bank, multiply 4500Wh by 5 = 22,500Wh.
NOTE: Reason for multiplication factor of 5: 100% / 20% = 5. 22,500Wh x 20% = 4500Wh. To
consume 4500Wh and only draw down your bank by 20% requires a bank 5 times as large.
Determine Quantity of Batteries
Now we decide on the number and size of the individual batteries for your bank.
1. Determine watt-hour capacity of the selected battery (i.e., the 6V, 225Ah Trojan T-105
battery):
a. 6V x 225Ah = 1350 Wh
b. Each Trojan T-105 stores 1350Wh of energy (100% DOD).
2. Determine quantity of batteries required. How many T-105s are needed for our 9000Wh
bank (50% DOD bank)?
a. 9000Wh / 1350Wh = 6.67 batteries
b. No one makes a 0.67 battery, so round down to 6 (or up to 8).
NOTE: Why not round up to 7 batteries? That would make for uneven strings – Not good!
Six T-105s allow for a 3-string 12V bank [(6V x 2) + (6V x 2) + (6V x 2) = 12V] but only 4 batteries
of the 6 can be used in a 24V bank: (6V x 4 = 24V). What if you want a 48V bank using the 6V T-
105? You will need to buy 8 batteries total (6V x 8 batteries = 48V bank).
Possible combos to achieve 9000Wh of battery capacity:
• For a single string, 24V bank, switch batteries. Go with four 6V batteries rated at
370Ah, such as the Trojan L-16:
o 6V x 4 batteries x 370Ah = 8880Wh
• For a 2-string 24V bank, select four 12V, 190Ah batteries:
o (12V x 2) + (12V x 2) x 190Ah = 9120Wh
Panels (or Batteries) in Series – Voltage adds, Current remains the same.
Panels (or Batteries) in Parallel – Current adds, Voltage remains the same.