Battery Box
04 March 2013
Mike
I've been working on a box to hold the batteries in the engine room. Material is ½ inch exterior plywood covered with fiberglass. Exterior grade plywood uses the same water-resistant glue that marine ply uses. The difference is that marine ply is made from really good wood, and has no voids or plugs in any of the plys. Exterior plywood will have plugs and voids here and there. Since this will not be subject to direct contact with water, I can live with the flaws, and fill them with epoxy. Oh, and the price difference is staggering! The fiberglass will add strength, and protect the wood from any spilled electrolyte (acid). The box has eight partitions to hold all the batteries we'll need.
The "house" bank (used for lighting, pumps, and appliances) will consist of 6 6 volt golf cart batteries of 230 amp/hour capacity. Two hooked together in series will give the equivalent of a single 12 volt battery. I'm using golf cart batteries because they are made for rough use, heavy discharge all day, and a quick re-charge over night. That would kill a regular battery in a very short time. They are also a most economical source of stored power. Sam's Club has them for about half the price of a "marine" 6 volt unit. Another advantage is that I can move them on and off by myself if I have to swap one out in the future.
The other spots will be for the two 12 volt engine starting batteries. One for the main engines (1000 amp) and one for the generator (750 amp). These will have the capability of being combined for a really cold morning, or the off chance that one goes dead. The boat came with 2 massive starting batteries that weigh about 130 pounds each. I won't have them on board since I can't move them myself. The marina guys had to use a small crane to get them off the boat.
I am currently making a filet on all the edges of the box, using epoxy that has been thickened to the consistency of peanut butter. This binds everything together, and provides a smooth transition between surfaces when I apply the fiberglass cloth later on. I managed to run out of epoxy supplies, so I'm waiting for a shipment from Jamestown Distributors later this week. I'm using WEST System epoxy, which is great stuff. It is mixed in a 5 to 1 ratio between the resin and the hardener. I bought some pumps which screw into the appropriate container, and provide the correct mixture with a single pump of each one. Takes all the guesswork out, and gives a consistent product. The down side is that I have to use relatively small batches at a time, or else the epoxy will "kick" (set up) quickly in the container before I can use it all . The epoxy generates heat as it sets up, and a large batch mixed in a tall, narrow container will set if off in a dramatic fashion (read smoke and flames!) Don't ask me how I know ;>)
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