Electrical, Battery Switch, Part I: Analysis and Installation

The battery switch, dry-fitted in Oystercatcher
The battery bank, which supplies power to the lights and other important equipment on a cruising sailboat, must have a battery switch. Most cruising sailboats, regardless of whether they are big or small, have two battery banks. The primary one is usually called the house bank, while the secondary one is often called the starting bank or the reserve bank. Both of these banks are normally controlled by a single battery switch. This switch is typically located in an easily accessible location, yet one that is as close as possible to both of the banks. In the refitting of Oystercatcher, my Ericson 25, I decided to install two separate battery banks, and in keeping with the norm, I decided to use a single switch to control the flow of energy from either of these banks, depending on the circumstances. This two-part article is focused on the battery switch itself. In it, I will explain my rationale for the switch I selected, the location for it that I selected, and I will explain the approach I took to the wiring of this switch.
Blue Sea Systems brand Battery Switch, PN 6007
There were a number of different battery switches that I could have selected, but ultimately, after some amount of research, I settled on one of the Blue Sea Systems brand m-Series switches. The letter "m" in the name of this series stands for "mini," and rightly so, because the m-Series switches are smaller than all other battery switches I have seen, not only those by Blue Sea Systems, but also those by other manufacturers. These switches are specifically designed by Blue Sea Systems for small to medium-sized boats, where issues concerning space and the placement of new items are always paramount. These switches are also specifically designed for those who use an outboard motor, as opposed to an inboard gas or diesel engine, for their auxiliary source of propulsion. This does not mean, however, that these switches cannot handle significant loads. In fact, if you compare the amp, i.e., amperage, ratings for the m-series switches with the amp ratings for the regular-sized, e-series switches designed for inboard gas or diesel engines, you'll see that the differences between the two are not that great. The m-Series switches, for example, have a continuous rating of 300 amps, whereas the continuous rating of the e-Series switches is 350 amps. I had meticulously planned my DC electrical system, and I knew that I could never exceed 350 amps, much less 300 amps, with everything in the electrical system turned on and in full operation at once. Given that I had an outboard motor, I did not need the extra cranking amps of the e-Series switches. Therefore, given the space considerations that everyone with a small cruising sailboat faces, my choice of a smaller, m-Series switch was a logical one.
Having settled on an m-Series switch, I next needed to decide exactly what type of m-Series switch would best suit my purposes. As I said, I planned to have two different battery banks, so I needed to have a switch that I could, at least, turn from Bank 1 to OFF to Bank 2. The Blue Sea Systems PN 6007 model, that was available locally, and that I ended up purchasing, not only had these capabilities but also the capability to combine the two banks, if necessary. I had every intention of keeping the two battery banks isolated from one another. The 1+2 setting thus would only be used in the event of some emergency. I should note, however, that I planned on using Bank 2 as the emergency bank (and not the starting bank, the house bank, i.e., Bank 1 being used both for house loads and for starting purposes).
So why did I not just use the existing battery switch that came with the boat when I purchased it in 2009? Well, that switch, just like the rest of the electrical system was about 35 years old. There were problems throughout the system. If you'd like to read more, see my article, "Electrical, Original."
The original battery switch on my boat, just like the originals on all other Ericson 25s that I've seen, was located on the bulkhead adjacent to the stove.
The cover for the battery switch was missing. There was plenty of bare copper, just waiting there ready to reach out and touch any careless fingers that might get too close.
The area behind the original DC distribution panel and battery switch was a disaster - a rat's nest of wires, with corrosion everywhere. The previous owner kept loose tools and all sorts of junk in this locker. Does it look like he took any precautions in terms of protecting any of this electrical equipment from the metal tools and other objects that might come into contact with it?
If you've read my article on the installation of the AC distribution panel (Electrical, AC Distribution Panel, Part 1: Analysis and Installation), then you'll know my reasons for using the area around the stove as the home for the panels and other important components of the AC and DC electrical system. For those who might find fault with me placing these items so close to the cooking area, I will say that I took that into consideration, and, when all was said and done, I took steps to protect this equipment with two pieces of high-tech fire-resistant cloth that would be snapped into place when the time came for using the stove.
If you've read the above mentioned article, you'll also know that I had to create some cardboard mock-ups to make sure that I could fit everything I needed to fit into this small space. I also had to deal with the existing holes that were left by the original DC panel and the battery switch after I had removed them.
If you've read that article, you'll also know that I wanted to trim all of these new electrical components with mahogany, so that they would tie-in with the rest of the boat, trimmed as it was with mahogany.
For the battery switch, the battery monitor, and the DC main breaker, I cut three, equally-sized pieces of mahogany.
After I had cut these three pieces, and also the trim pieces for the AC distribution panel and the two bilge pump switches, I dry-fitted them into the space.
The beautiful ribbon-stripes of this sapele mahogany are clearly visible in the picture below. Note that I have rounded the corners to give each trim piece a more curvaceous feel, in keeping with the curvaceous feel of the boat itself. For those who may be curious about what I mean by sapele mahogany, see my article, "Companionway Hatch Construction."
In terms of the installation of the components, I began with the AC distribution panel and the two bilge switches. I then focused on the battery switch. Below you see the switch sitting in front of the trim piece closest to the edge of the countertop. It was necessary for me to install the switch in this place. The Origo brand alcohol stove has two large alcohol-filled canisters that sit beneath the top of the stove. To remove these canisters and refill them, you must lift the top of the stove. This stove top pivots on a hinge that runs along its backside. Therefore, the stove top swings upward from front to back. If I had installed the battery switch in one of the other two locations, I would not have been able to lift the stovetop upwards.
In terms of the installation of the battery switch, I began by taking the trim piece out of the boat and cutting the appropriately-sized hole through it with a hole saw. I then took the trim piece back into the boat and scribed a circle onto the bulkhead, using the trim piece hole as a guide.
I used the cut-out piece as a guide for marking the center of the hole, and then I drilled a pilot hole in the bulkhead for the hole saw bit.
Instead of tearing into it, I took my time with the cutting of this hole. I began by setting the drill to Reverse. Drilling in reverse with a hole saw reduces the chances of chipping the gelcoat.
Voila. Nice and clean. Do you see those three round things that look like screws in the hole? Those are actually holes in the transom of the boat (for the bilge pump through-hulls). You are looking through the dark cockpit locker and then through the three holes to a dark colored fence behind the boat.
The battery switch slipped right into place without any problems. This part of the project was now finished, but I still needed to deal with the wiring of the switch and the protection of these wires in the cockpit locker. That is the subject of the second part of this two-part article.
This ends this posting on how I selected and installed the battery switch on Oystercatcher, my Ericson 25.

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