By Mike Gridley
Electricity on a boat typically comes from battery power (when not connected to a power source or a generator). Using electronics like televisions or microwaves while away from shore requires battery inverters to convert the current from the battery and change it from DC to AC. Monitoring that flow of energy manages the electrical load running through the boat and can guard against completely discharging your boat’s batteries – preventing damage or a shorter life cycle.
For this My Boat project, we wanted to monitor a large inverter bank. We sought the advice of our electronics expert Brian Kelly of Bayland Enterprises. He recommended a Victron Energy Precision Battery monitor model BMV-602.
Basically a “fuel gauge” for your batteries, the monitor is capable of measuring charge and discharge currents as well as calculating the state-of-charge and time-to-go for a battery bank. Critical functions include programmable alarms for excessive discharge rates and when the state-of-charge reaches a pre-set low reading indicating it’s time to recharge the battery bank.
Getting started with the install, we chose the electrical panel as the logical location for the monitor. The panel was opened up and existing wires were tied back for clear access.
With the position selected, a pilot hole was drilled then a hole saw was used to cut out the required-size space.
Reopening the panel, the monitor gauge was inserted and the locking ring secured.
Brian is professional working with panels all the time, so he is comfortable with a hot panel. We strongly recommend that the power be turned of before working on any electrical projects.
Next, the UTP cable, essentially a network data cable, was plugged into the back monitor and fed down through panel housing to the bilge. After the cable was secured with zip ties, the panel was buttoned up and the work was now in the bilge. Brian drew the short straw so he crawled in to fish the cable from below the panel to where the bank of inverter batteries was below deck. He secured the cable with zip ties along the way.
While Brian moved forward by the batteries I was able to utilize the slack in an existing wire as a fish line. After taping the cable to it, Brian pulled the cable through to the batteries – much quicker fishing the cable ourselves.
The next task was to install the system’s key component, the shunt. This device measures the amperage flowing in and out of the battery bank during charge and discharge cycles. Victron Energy has a wide range of shunts for different loads and the shunt included in the BMV-602 kit was rated for 500 amps.
Since the shunt is installed on the negative side, Brian removed the main negative cable from the battery bank. He then measured for the length of negative cable to be made up to run from the shunt’s mounting location to the battery bank. He selected the correct gauge of marine-grade battery cable and cut the required length. Then marine-grade terminals were crimped on and the connection protected with heat shrink tubing.
Back below, Brian made quick work of connecting the negative cable to the battery bank. Next, the shunt was held in position and mounting holes were marked, then drilled. The holes were filled with silicone and the shunt was mounted with stainless steel screws. With the shunt in place, the main negative cable was hooked up to the shunt, followed by the negative cable from the battery bank.
With the negative side completed, Brian next connected the positive power supply wire with an inline fuse to the battery bank and the B1 terminal on the shunt. After cleaning up the cable and wire with zip ties, the monitor cable was plugged into the shunt.
Back at the electrical panel, the Victron battery monitor displayed the bank’s voltage indicating that everything was connected correctly and working properly. After calculating the capacity of the battery bank, the monitor was programmed and it was ready to go.
Beyond voltage – that can range from 70 to 90 volts DC – you can also monitor current in amps, amp hours, state-of-charge as a percentage, time-to-go and the temperature of the batteries.
The Victron monitor proved to be quite easy to install and the information it provides will bring you peace of mind and the capabilities to stay on top of your battery banks.
This project is featured in the Summer 2015 issue of Boats&Places.