Electrical, Battery Monitor, Part I: Analysis and Installation

The battery monitor, installed in Oystercatcher
Battery banks are the foundation of the DC (direct current) electrical system on a cruising sailboat. To maintain these banks, the owner must charge them on a regular basis, usually on a daily basis. To ensure that he is charging them not too much, not too little, but just the right amount, he needs a battery monitor. Of course there are awkward and inconvenient, and not wholly reliable ways to get around this, but who wants to be bothered with this on a regular basis? Why not just check the monitor and know right away the status of the charge? Perhaps it is the cost of the monitor, more than anything else, that turns some people away. I did the research, and I concluded that, to me, it was worth it. I'm not going to go into the details of the Victron brand monitor that I purchased. Instead, I will refer you to the article on this subject by Maine Sail on his Compass Marine website. The purpose of the present article is to describe the steps I took toward the installation and wiring of this particular monitor as part of the larger project of rewiring Oystercatcher, my Ericson 25.
Victron brand, BMV 600 battery monitor
In the rewiring of my boat, I decided to put the new primary battery bank, i.e., the house bank, in the location of the original bank - the center of the lazarette, directly above the bilge. For the secondary bank, i.e., the reserve bank, I installed a plywood shelf on the port side of the lazarette. It's the one to the right in the picture below.
My rewiring plan (that I created after months of research, tedious computer-based labor, and countless trips back and forth to the boat) called for the installation of two, Trojan brand, T-125, 6 volt, golf cart batteries. These deep-cycle, flooded-lead batteries, wired in series, so as to create a 12 volt system, would constitute the house bank. For more on this subject, see my article, "Electrical, House Bank."
For the secondary bank, i.e., the reserve bank, I would use a Trojan SCS225. This deep-cycle, flooded-lead battery, being 12 volts, would stand alone. For more on this, see my article, "Electrical, Reserve Bank."
The Victron brand battery monitor, as I said, indicates the state of charge (among other things).
For the charging of the battery banks, I would rely upon an AC powered battery charger. Specifically, I would use the Iota 45 by Iota Engineering. This 45 amp model that I purchased was the DLS-45 with an IQ4 Smart Charger Controller. I would install this charger just above the ice box. In the picture below, you see me lifting the splash shield that I constructed to protect the charger. For more on this project, see my article, "Electrical, Battery Charger."
The Iota 45 charger would charge both banks simultaneously. To make the Iota 45 do double-duty, charging both banks at the same time, I would use the Blue Sea Systems brand ACR (Automatic Charging Relay).
A 4 AWG (American Wire Gauge) cable would run from the Iota 45 to the House Bank Positive Bus. From this bus, there would run another 4 AWG cable to the stud pictured on the left below. On the stud on the right, there would be another 4 AWG cable. This one would run to the Reserve Bank Positive Bus. Joined in this fashion, the Iota 45 would charge the House Bank, and at the same time charge the Reserve Bank. For more on this subject, see my article, "Electrical, Main DC Circuit."
The DC electrical panels, when I purchased the boat in 2009, were located on the port side of the galley. Although I would remove all of the old electrical system (see, "Electrical, Original"), I would stick with port side of the galley as the home for the panels, switches, and other important items. There were two factors that led me to use this as the home for the above mentioned items. First, there was the issue of water. I preferred the electrical system to be close to the stove rather than close to the sink (on the opposite side of the galley). The stove area, of course, was not ideal, but I would protect the system while cooking by shielding it with high-tech, fireproof cloth that I could snap into place. Secondly, there was the issue of weight. The house bank was located in a good place - low and centered over the bilge in the lazarette. On the starboard side of the transom would be a Yamaha 9.9 high thrust outboard motor. This motor, being a 4 stroke, was significantly heavier than the 2 strokes of old. Given that this motor would be on the starboard side, it made sense to me to locate the reserve bank on the port side of the lazarette. You always want to minimize the distance between the batteries and the major components of the system - the battery switch, the main DC breaker, etc. Therefore, it made sense to put these major components on the port side.
It might not look like it would be possible, but this small bulkhead, where the old battery switch and DC panel were located, would house six of the components of the new system.
Before I could install any of these components, I needed to create cardboard mock-ups.
Much of the interior of the boat was trimmed with mahogany. Therefore, I wanted these components to be trimmed in mahogany. Why not make the boat look classy? For more on how I obtained this mahogany see my article, "Electrical, AC Distribution Panel."
The three trim pieces below would be devoted to the battery switch, the battery monitor, and the DC main circuit breaker.
The dry-fit of the trim pieces.
The trim pieces with their corners now rounded to give them an appearance more suitable for a boat.
I began by installing the AC distribution panel and then the bilge pump switches. After this, I moved on to the battery switch. Having installed this battery switch, I turned my attention to the Victron battery monitor. First, with the mahogany trim piece removed from the boat, I cut a hole through it with a hole saw. Then I reinstalled the mahogany trim piece and used the hole in the mahogany as a template for cutting the hole through the bulkhead.
The hole through the bulkhead, just after I had cut it.
The Victron battery monitor has a square-shaped, white piece of plastic that is used to secure the monitor to a bulkhead or other flat surface.
It also has a threaded, white plastic ring that screws onto its backside. The ring or bezel is helpful for snugging up the monitor against the bulkhead.
Below we see the monitor in place between the battery switch and the DC main circuit breaker.
The monitor comes with a gray, plastic trim piece that snaps into place over the square-shaped plastic mounting piece.
There is more to the installation of the Victron battery monitor than this. For instance, there is an important piece of equipment known as the shunt that must be mounted near the battery bank. Given that the subject of the first part of this two-part article is primarily concerned with the installation of the battery monitor itself, it seemed appropriate to me to address the installation of the shunt in the second part of this article, the part that is concerned primarily with the wiring of the device. 
This ends this posting on my installation of the Victron battery monitor in Oystercatcher, my Ericson 25.

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