Improving the Back Cove 37 - Upgraded Electrical Meters

First a disclosure - I am the founder and former owner of Blue Sea Systems and the meters I recommend in this article were developed on my watch while I still ran the company. I now have no financial interest in the company, so I feel free to recommend one of their products in what should be an unbiased blog.

The battery management system that Back Cove installs on the 37 works wonderfully, but the one critical element missing is a true battery state of charge meter. The standard meters on the 37 show only Volts and Amperes, and Hertz and Watts on the AC side. None of these values will tell you how much energy is remaining in your battery bank.

Blue Sea Systems 8000 Series meters installed standard on the Back Cove 37

To accurately know the energy remaining in your battery ampere-hours consumed and recharged must be tracked. To be fair, there are a few instruments available that are able to calculate true state of charge using only voltage, but these should not be confused with ordinary voltmeters such as the standard equipment on the Back Cove 37. However, most state of charge meters rely on the principle of counting ampere-hours in and out.

On my 37, living aboard at anchor, I can operate for about 24 hours before I have depleted 1/2 of my house battery bank's capacity. This is the generally recommended maximum energy that should be taken from the battery before it is recharged. A stock 37 may go a little longer, but from reading other posts here you'll recall that I have structured the electrical system so that there is no need to run the generator unless I am at anchor for more than 24 hours. During that 24 hours I operate the refrigerator, freezer, as well as the cooktop and microwave through the inverter, and all the other loads on the boat. I make no attempt to conserve power. It's a powerboat! If I wanted to conserve power and forgo the comfort it provides, I'd go back to sailing. But, I'm older now and have delusions of being wiser.

But to live like this it is critical to know battery state of charge. For that you will need an ampere-hour meter. There are a number of these on the market. I chose the new Blue Sea Systems M2 Series, shown below.

You can read more about the M2 here.

There are three things I like about this meter:

1. It is a drop-in replacement for the 8000 Series meters that are in the BC37 electrical panel
2. It has a terrific big, bright OLED display
3. It has alarms and an internal relay that function independently and can be triggered by any of the measured values.

The third feature I mention above dovetails well with the Maretron alarm system I discussed in another post. Both of the M2 relay outputs are wired to the Maretron SIM100. The relay function on both the AC and DC M2 meters can be triggered by any value read by the M2. On the AC meter I set for low voltage (<90) and on the DC meter I set for low SOC (<60%). If either of these values are exceeded I receive a text message from the Maretron SMS100 unit.