I'm working through a redesign of my electrical system and would like confirmation of my understanding of voltage drop. The batteries are 4x Trojan T-125's. The boat was not designed for the weight of these batteries and she has a noticeable list. They're over 5 years old and I'm planning to swap them out for a pair of Firefly G31's. There is a separate Group 24 start battery, so no starting load on the house bank circuit except in emergency. The battery compartment (BC) is 25.92' round trip to/from the main bus (MB).
From MB, it's another 11.2 ft round trip to the DC panel (DCP) on 2 AWG cable. It's 10.0 ft round trip from MB to the 80 amp charger/inverter (CI) on 2/0 cable. The cables were sized according to the expected current load and to minimize voltage drop without sinking the boat or the bank account. I'd like to bring the batteries closer, but I'd have to switch to LiFePO due to space limitations.
Using the published Ancor standards for resistance I calculated voltage drop (VD = I × (2 × L × R / 1000)) below. I also added 0.00025Ω per termination per Maine Sail's article:
BC to MB @ 150 A = 2.61%
MB to DCP @ 135 A = .94%
MB to CI @ 100 A = .67%
If all that is correct that would make the total voltage drop from BC to CI=3.28% and BC to DCP=3.55%. Does the voltage drop and cable sizing look right, or do I need to go up a size?
Thanks,
Mike
From MB, it's another 11.2 ft round trip to the DC panel (DCP) on 2 AWG cable. It's 10.0 ft round trip from MB to the 80 amp charger/inverter (CI) on 2/0 cable. The cables were sized according to the expected current load and to minimize voltage drop without sinking the boat or the bank account. I'd like to bring the batteries closer, but I'd have to switch to LiFePO due to space limitations.
Using the published Ancor standards for resistance I calculated voltage drop (VD = I × (2 × L × R / 1000)) below. I also added 0.00025Ω per termination per Maine Sail's article:
BC to MB @ 150 A = 2.61%
MB to DCP @ 135 A = .94%
MB to CI @ 100 A = .67%
If all that is correct that would make the total voltage drop from BC to CI=3.28% and BC to DCP=3.55%. Does the voltage drop and cable sizing look right, or do I need to go up a size?
Thanks,
Mike
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