Big Data for a Tiny Trailer: Installing a Victron BMV-700

The new 2016 T@bs that are starting to come off of the line now and make their way to new owners have a battery monitor installed by the factory. Kudos to Little Guy and Pleasant Valley for addressing this and helping owners have a better understanding of their battery health. It appears that they are install the SeaLvel II monitors which will monitor tanks and battery. According to the manual, the SeaLevel II will, “The system also shows the RV battery voltage by measuring the voltage which powers the display. ” This is an OK method to keep track of your battery and will work for many people but it is not really all that different from the inexpensive cigarette style battery monitors many of us have been using. I realized that I needed something more detailed and accurate than what the inexpensive battery monitors provided. Monitors that use the voltageat the meter will never really provide an exact state of charge of voltage because it automatically accounted for either the charge coming into the battery or the draw being pulled from the battery. For example, tonight, it showed around a 12.68v because I had a few lights on inside of the T@b. I knew I was actually getting 13.6v. I would have to unplug from shore power or solar, during the day, and turn off all DC power draws to get a closer to true readying, and even then, I knew that depending on how I inserted the monitor into the outlet, I tend to get different readings. A lot of people are perfectly fine with this. If you only want that level of understanding, than the cigarette monitor or SeaLevel II are great choices for you. I desired something more precise to give me more confidence and actionable information when I boondock.

Choosing the Battery Monitor

I did a little research and found that there were a few good monitors and they were all expensive and required some wiring. Bogart Engineering, Xantrex, and Victron were consistently the most frequently recommended by other RVers and those who do other types of power monitoring. In addition to giving you a more accurate read, these monitors provide you with some additional data to allow you to some analysis of your use.

My research led to the Victron BMV-700. I believe the others were of similar quality, but this seemed to provide the simplest wiring installation, which was very appealing to me. These monitors use a shunt, connected to the negative terminal of the battery. Most of them use an RJ45 cable to connect and send data to the inside display. It is important that there be no other connections to the battery prior to the shunt or else the monitor will not capture the data. For example, prior to installing the shunt, I wired my solar ports directly to the battery. Now they come after the shunt. I will now be able to measure how much solar I gained during the day.

Features

The Victron BMV-700 lets you either choose a very simple set-up or choose from some advanced settings. A few monitoring options include:

• Battery voltage (state of charge in volts)
• Current (current being drawn from battery)
• Power: (watts being drawn from battery)
• Consumed Amp-Hours (How many Ah used)
• State-of-charge: (current % of battery charge remaining)
• Time-to-go (based on current draw, time before battery needs to be recharged)
• Alarm (you can set an alarm to go off when the charge drops to your desired setting.)
• Has a data port that allows you to attach either a USB cable or Bluetooth dongle to help you analyze your data.

There are a number of options that let you really dial in your preferences.

Wiring the Shunt

I unplugged from shore power, turned the battery switch to off, and unplugged the solar cables. I made sure to cover all ends of the cables with electric tape while working with them to avoid any unwanted, shocking, experiences. Here is how I am currently wired:

• The positive of the first battery goes to the second battery. This allows the two 6v batteries to be connected in series and give me 12v. Nothing else connected to battery 1.
• On battery 2, from the positive, I go to the battery switch. I had previously wired the switch to the negative, but with the shunt wired to the negative, I believed it to be better to wire to the positive. The Blue Seas switch I am using is designed to be connected to the positive and I am using a high quality battery cable to connect to the switch, being careful to make sure no metal can be touched between them. Also from the positive side is a wire to go to the shunt.
• On the load side of the switch, I have the positive wire to the trailer and the 2 Zamp positive wires. (I installed a second Zamp port.)
• On the negative side of battery 2, I have the cable going to the shunt and nothing else but the cable coming from battery 1.
• On the shunt, I connected the negative cable from the battery to the battery side of the shunt, and to the load side of the shunt, I wired the negative trailer wire and the 2 negative Zamp cables.

Fishing the Wire

The installation was not complicated. I used a wire fish tool and was glad that I did. Here were the steps I followed for fishing the wire:

1. I fished through the wall, then taped the end of the RJ45, making sure to wrap and protect the connector so that it did not catch on other wiring, and then pulled the wire back through the section that I had just fished. I started with the bottom cabinet below the sink in my S model, fished it through the opening to the left that led up the wall to the area behind the toilet, where the little hatch is located.
2. From there, I located the are on the bottom left, where other wires ran, and into the area in the driver side bench.
3. Next, I drilled hole from the cabinet below the sink to the small storage space below the fridge.
4. Then, I removed the vent in that storage area and cut a tiny hole in the screen, just enough for the RJ45 to fit through. That screen needs to be sealed if you cut it. You can sew that closed or use some type of sealant. I am planning to do both.
5. I then fished the cable through, where it exits via a vent. I fished the cable through a semi-rigid wire loom and secure it below the T@b by utilizing existing wiring. It created a very tight hold on the looming. My battery box has a space for the looming to enter the battery box. Once it is there, the cable just connects to the shunt.

Completing the Installation

To complete the installation:

1. I removed the Alde control panel plate and fished the RJ45 cable through that hole.
2. Used a hole saw and hole saw attachment with my drill to create a hole for the display above the Alde panel hole.
3. Brought the RJ45 cable up through the new hole and connected it to the display.
4. Then I snapped the display into the provided mounting plate and out the display into hole.

I did not use the provided screws for the mounting plate. I may install them, but the mounting seems snug enough without them that I would like to try that first. I may also use some 3M mounting squares instead of the screws.

Concluding Thoughts

The installation was not difficult. It took longer than I wanted it to because the days are growing shorter and I really needed daylight to complete some of the tasks. Ultimately, if you really want to better measure and analyze your power consumption and gauge your battery health, an advanced monitor is the way to go.