Charging Deep Cycle Batteries on the Hook
This article describes some of the initial changes I made to our boats electrical system. It also explains how I’m expanding the system for charging deep cycle batteries from a wind turbine and solar panels as part of my solar off grid living plans.
My electrical system is constantly evolving on the Rock ‘n Row. When we first purchased her, the 12 volt system was powered by two 8-D starter batteries in the engine compartment. This is how the original electrical system was designed, and it’s a common setup for most boats. However, the problem with this configuration is that a long weekend can leave you with a dead starter battery and no way to start your engines. This isn’t as big of an issue for a sail boat, but it’s huge risk for a power boat.Because structural repair on the boat (such as replacing the bulkheads holding up the floor) required my immediate attention, I didn’t have much time to devote to the electrical system. Over a weekend, I wired up the 12v marine battery configuration you see here. I placed these deep cell marine batteries on the floor and made a simple wooden box to fit over the top. This was less than ideal because it took up valuable floor space, but it also allowed easy debugging, rewiring, and servicing. Over the last year and a half, this 12v marine battery system has withstood the test of time and performed excellently.
These deep cell marine batteries are electrically isolated from the starter batteries through a trail charger and are additionally protected by a low voltage disconnect, which some people call a 12v battery monitor. This type of configuration is called a ‘hotel’ battery bank since it powers the ‘hotel’ loads (lights, music, water pumps, etc). This means that powering my lights and other electronics will not drain my starter batteries. The 12v battery monitor will disconnect the batteries in the event that I am in danger of draining them to the point of deep discharge damage. An LVD (low voltage disconnect) can extend the life of your batteries by protecting against this single failure mode.
Now that I have finished the lions share the structural repair work on the boat, I’ve begun work on a more permanent 12v marine battery system. From an electrical standpoint, I’m not really changing much. I’ve constructed a series of shelves under the floor to house my hotel batteries. I am adding a 1000 watt Xantrex inverter and upgrading the wiring between the batteries and inverters to 4/0 welding cable.
I got the inverter as a gift from my friend Ken. His parents were upgrading the inverter on their luxury yacht and he didn’t have any use for it himself. The inverter will have one job and one job only: charging deep cycle batteries, specifically the 48 volt ‘drive’ pack that powers the electric outboard.
I’m getting ready to install a wind turbine and solar panels this summer. The idea goes like this: a computer will detect when the deep cell marine battery ‘hotel’ bank is fully charged from the wind turbine and solar panels. It will then turn on the inverter which will begin charging the 48 volt drive bank. Once 20% of the energy has been removed from the hotel bank, the inverter will be turned off until the panels and turbine can fully recharge the hotel battery bank. In this way, I have enough charge in the hotel bank for use during the day and evening, but any extra power can be allowed to ‘trickle over’ into the drive bank.
By moving the deep cell marine batteries below the floor, I better utilize space and save valuable floor real estate. I’ll be using this space to construct a folding table/bar for laying out my navigation maps while underway, and mixing cocktails while on the hook.