The Great Battery Refit

The completed deck with hatch covers in place

The battery compartment after the original box was removed

The new battery compartment ready to install batteries

The original battery compartment under the aft cabin cushions.

Over the course of the Spring, we noticed that our batteries were holding less and less of a charge.  On a few nights, the refrigerator’s repeated attempts to start would wake Gray up.  Firing up the engine for a few minutes or briefly paralleling in the start battery would provide enough power to start the compressor and then it would run under the house battery alone.  The volt meter would read very low voltage while the compressor ran, but but go back up above 12 volts when the compressor stopped.  By 10AM, the solar panels would have the house back up to 14 volts (suspiciously quickly considering they were reading below 12 volts before sunup).  Of course, when we had wind all night this was never an issue.

Once we got to Luperón, the winds died at night and batteries really became a problem.  In the 10 days between our arrival in the Dominican Republic and our summer trip back to the US, we had to rely on the start battery to keep the refrigerator running through the night.  We decided to rent an apartment for a couple of months to work on some boat projects including the battery bank.  After some looking around, we discovered that the batteries installed by Hanse were not only an odd size (a couple of inches shorter than a Group 31 standard battery) but that they had been discontinued.  We would need to replace the batteries with something else.  It turns out the only batteries readily available in the Dominican Republic are wet cell golf cart batteries.  They are used in many homes as the basis for a backup power system.  These batteries are a very different shape from the batteries provided by Hanse.  We would have to remove the battery box and build a new one.

Once we returned from the US and got settled into the apartment, Gray got to work on the battery system.  First, he pulled out the old batteries and attempted to unravel the the wire spaghetti in the battery box.  Even though we bought the boat new, the wiring was still kind of a mess.  The wires installed by the boatyard during commissioning were labelled, but the Hanse installed wires were not.  Wires were connected directly to one battery or the other.  There were no central buses to organize the wires.  Some of the Hanse battery connections were made with screwed on terminals instead of being properly crimped.

After clipping many wire ties and feeding the wires out of the battery box, Gray got to work on removing the battery box.  The box was very nice, made of fiberglass and shaped specifically for the space and the batteries.  Luckily, it was held in place by caulking so it was easy to remove.  The old box ended up in the flea market where a Dominican family bought it to use as a sink.  We sold the old batteries to the guy who sold us the new batteries.  Even though they won’t hold enough of a charge for our needs, they would power a lamp or other small electrical load while the power was out in town.

Gray built the new box out of pieces of marine plywood we had on board.  The sides of the box were glued and screwed together and then the seams were covered with fiberglass.  A battery box is a great first fiberglass project since nobody can see it.  That is fortunate since Gray’s work came out a little messy.  He’ll practice with more fiberglass projects later.  Before the box could be installed on the boat, Gray had to trace the curve of the hull and cut some plywood to build supports for the box.  He glued down these supports with epoxy putty, then filleted the edges of the joint with thickened epoxy.  Finally, he used strips of fiberglass cloth wetted with epoxy resin to “tab” the supports to the inside of the hull.  Once the supports had cured for a couple of days they felt very solid.

It was a while before the box went on to the supports.  Gray had to unravel and label all the wires running to the batteries, design the layout of the bus bars, fuses, shunts and other pieces of electrical equipment that he was going to add.  Of course, he also had to track down DR versions of all the parts he was missing.  Since the new battery box would stand 3 inches above the sole (floor) of the aft cabin berth, Gray also had to design a framework to raise the sole enough to cover the new box.  Finally, the new batteries vent potentially explosive hydrogen when they charge, so Gray had to install a vent system.

Gray added a 300 amp fuse on the positive wire coming from the battery box.  He used Power Post Pluses as bus bars.  A Power Post Plus is a 3/8″ stud with a round bus around the base.  The round bus has #10 screws for terminal connections.  Big wires like from the batteries and the engine go on the stud and smaller wires go on the bus ring.  On the negative side of the batteries, Gray added a large shunt for the eventual connection of the Trimetric battery monitor we bought years ago.  One day soon it will be connected!  All of this hardware was mounted on the side of the battery box with large wires running into the box.  Gray also added an engine room vent fan connected to the batteries with a voltage sensing relay.  When the voltage reaches 14 volts, the fan will run to vent any hydrogen emitted by the batteries.  The vent runs to a grille in the transom of the boat.  A new MPPT solar controller (a magic box that makes solar panels more efficient by modifying the voltage based on the state of the batteries) rounded out the new installation.

Since the new cabin sole under the berth was 4 inches higher, we decided to discard the cushion.  We sold the foam in the flea market and put the cover away.  We figured it would be easy to cut new foam to insert in the cover if we decided to replace the cushion later.  Initially, we tried splitting the cushion in two to make access to the batteries easier, but that was still too cumbersome.  Since we never sleep back there, we decided to do away with the cushion.

During the course of the wiring investigation, we discovered that our alternator had failed.  A local mechanic took it apart and reported that the stator was melted from overuse.  He told us (in Spanish) that a 60 amp alternator was not enough for the size of our old battery bank (our new battery bank is about twice as large).  Whenever the engine was running, the alternator was spinning at full load.  The small alternator that came with the engine is designed to keep a starting battery topped off, not run continuously at full load for hours (sometimes days) at a time.  We installed our spare 60 amp alternator and hope it will carry us to Puerto Rico.  Our final plan is to connect the small alternator only to the start battery (which we don’t have yet, we start off the house bank for now).  We will rely on the sun and wind to charge our house bank (with occasional help from a marina or worst case a small generator).  We will need to get a new battery charger with an “equalize” function to help maintain our new wet cell batteries.

Gray and Cindy

Tags: battery, fiberglass