Usually the hardest part of adding extra amp hours is finding space for the batteries. Despite considerable advancement in battery technology they're still large, heavy objects. Even once you've found the space you still have to consider ventilation and perhaps even the effect on trim. An ideal location must be clean and dry, away from all sources of ignition, offer some protection from damage, and have easy access for inspection and maintenance.
Most people assume the batteries go in the engine room. Considering the above criteria, this might not be the ideal spot. Often batteries are placed under berths or settees but, since they emit hazardous gasses when being charged, this is not ideal either. On Wired, I have a huge lazarette. It has easy access and is the perfect location for our new bank.
Our new ammeter gave us a good idea how large a bank to install. On average, when cruising, we know we consume about 200 amp/hrs @32vdc daily. This is a lot considering how much of our electrical load is AC serviced by the generators.
You can get a good estimate of usage by making a simple list of things you will run, their amperage and how long you are likely to use them. A 5 amp light on for four hours will consume 20 amp/hrs (5×4). A 10 amp fan running four hours will consume 40 amp hrs (10×4), etc. Add together the various electrical consumers and you will get a good estimate of your daily needs. It's not rocket science.
Many experts say that an ideal house bank would hold four or five times your daily amp/hr needs. As our vessels become more loaded with electrical devices this is becoming less practical. On Wired we'll never go more than a day without being plugged in or running a generator so I'm satisfied with anything more than 24hrs reserve. Even deep-cycle batteries shouldn't be discharged below 50%, so your battery bank should be twice as large as your estimated consumption between charge cycles.
Common practice is to construct multiple banks and 'switch' from side to side. Most professionals now advocate one larger capacity bank rather than switching between two smaller capacity banks. I made two banks, but plan on leaving the 1/2/both/off switch in either the 'off' or 'both' positions. This bank is for house loads so we installed deep-cycle batteries not 'starting' batteries.
Old Hatteras' are 32vdc. Most of you will be more familiar with 12 volt systems. The principals are the same but the mechanics differ. I wired four 8 volts in series to produce a 32v battery. Two of these 32v assemblies in parallel doubled the amps while remaining the same voltage. I did the same on the other side, that's 16 batteries total.
Our batteries are rated at 198 amp/hr @ 8 volts. Our combination of series (increased voltage, same amp/hr) and parallel (increased amp/hr, same voltage) wiring yielded a total of 792 amp hours at 32vdc. Since we said we would only discharge 50% of our rated capacity that's 400 amp/hrs at our disposal.
The first job was to construct the boxes. The large size of our banks dictated custom made boxes. I used a full sheet of three-quarter inch plywood, some epoxy and some stainless screws. This is basic stuff but measure carefully, build strong and take the time to make a seaworthy installation. The goal here is to make a secure containment device for large, heavy objects and any fluids that might spill during maintenance or charging. You don't want to drip acid into your bilge, so take your time and do a good job. I included a top to protect the terminals and wiring and ensured the box is well secured and has adequate ventilation.
Wiring is straightforward but if you're not completely sure, engage a professional. Safety first and yes, neatness counts. The short jumpers used to connect batteries in series can be purchased ready made. Make sure they are adequately sized. Like many things in life, bigger is usually better. The primary cables usually will have to be custom made. Good quality 'Marine Battery Cable' is expensive but mandatory, don't skimp. After roughing in our installation I carefully measured our runs. A length of water hose makes similar turns and allowed me to assess the practicality of my proposed route. I attached a fishing line to the hose before removing it and used it to help pull the cable into place. This part of the job can be frustrating and took longer than expected!
The two primary cables did not run the same route. Our positive cable runs from the batteries to the main panel (via switches and fusing). The negative cabling runs from the batteries to a large negative bus nearby. Cable size depends on amperage and distance. I used 00 cables. You need to consult a chart or engage a professional for guidance regarding cable size. I completed the job by installing a high amperage fuse next to the on/off switch to protect the wiring.
Total material costs for this project topped out at just shy of $3000. Total man hours about 25. No small commitment but the joy of spending long evenings without running the generator, now that's priceless.
Peter Patterson is a Canadian Coast Guard certificated Master and an ABYC certified marine technician. He is a former Canadian Yachting Association Instructor/Evaluator and powerboat instructor. Peter is currently cruising the Caribbean while he waits for winter to loosen its grip on his home cruising grounds.