Battery Monitor Diagram
The battery monitor is a very useful tool for a boat-owner who has to survive on battery power. When properly installed, calibrated and monitored they can extend the life of a battery bank especially when used smartly.
With new battery technologies costing three to ten times what wet cell technology does and many boaters moving to newer technologies such as Gel, AGM, TPPL and LiIon accurate monitoring of an expensive bank is almost a prerequisite.
People often ask me questions about how to install a battery monitor so I took some time and tried to make it simple. They are actually easy to install but there are a couple of "gotcha" traps that you may find your self falling victim to.
There are a fair number of monitors on the market. Blue Seas, Xantrex, BEP, Victron, NASA and a few others make them. Currently the Victron units are the easiest to install and also the least expensive making them a good value. A Victron BMV-600S single bank monitor can be purchased right here for $184.25. Buy A Battery Monitor (LINK)
I chose to do this article with the Victron BMV-602S.
I currently use a Xantrex Link-Pro on my own boat but they all do basically the same thing. The Victron however is a significantly better deal than the Xantrex..
From left to right I have three generations of battery monitor represented. The original Link 10 was manufactured by Cruising Equipment Company and they really started a good thing. Despite many of the "LINK" products tending to be a little buggy they were generally well regarded and loved by boaters.
Somewhere along the way Cruising Equipment became Heart Interface and then Xantrex bought Heart Interface.
Xantrex then found TBS Electronics in the Netherlands and began importing and re-branding the TBS made monitor as the Xantrex XBM (pictured in the middle). The XBM was the identical monitor to the Victron 501 and was a very, very reliable device. It also offered a computer interface option something new to battery monitors at the time.
Eventually Xantrex made the switch to all TBS built battery monitors such as the current Link-Lite and Link-Pro. They have proven to be solid though very expensive units.
About the time Xantrex signed on to re-label the TBS monitors Victron found a new manufacturer to build their units, though I don't know who it is. The Victron BMV-602S is pictured on the right and bears little resemblance to the TBS built monitors.
Victron BMV-602S Shunt
The Victron shunt is quite unique because they have added a printed circuit board to it so that wiring is much easier. Shunts are not really directional devices but because Victron added the printed circuit board / UTP cable connector it does make it directional.
The shunt is labeled -LOAD and -BATTERY. DO NOT wire this backwards or it will not work properly. The side labeled -BATTERY must be connected to the battery neg post and the side marked -LOAD must see the system negative loads.
This monitor is VERY easy to install. It has just two wires, a UTP cable & a power cable. The UTP cable is 10 meters or roughly 33 feet long, allowing plenty of display mounting options. The UTP cable is the only wire that needs to be run the monitor display. It's literally "plug & play". The UTP cable is very similar to a phone cable, only slightly more robust. The red power supply wire simply connects to the positive battery post and the +B1 terminal of the Shunt.
This shunt has two power supply inputs, +B1 & +B2 for two banks, as it can monitor the voltage of a second start/reserve bank.
If you click the image it will make it larger and easier to read. I tried to wire this up on the bench to replicate what one might see on-board a boat. This is explanation is just far to difficult to illustrate on a boat. I actually photographed this quite a while ago, on a boat, and decided not to use any of the photos.
Obviously the house bank would be multiple batteries but the point is the same and a single battery was used for illustrative purposes only. If your boat is not wired with a positive or negative distribution buss it can help organize the wiring tremendously.
I have also shown a Blue Seas double MRBF (marine rated battery fuse) block on the battery post. I use one for the house bank and one fuse for the alternator which I generally always wire direct to the house bank.
Loads Yes & No!
OK here's the gotcha we talked about. Nearly every instance of trouble shooting battery monitors I've come across can be lead directly to where you've connected your DC negative wires.
A shunt reads the loads on the system as measured as voltage drop, in mV levels, across the shunt. This shunt is a 500 amp 50 millivolt shunt. This means that at 500 amps there will be a 50 mV drop across the shunt. Knowing this the monitor manufacturer can make the display correspond to any load from 0 to 500 amps or 0 to 50 mV.
If any load, such as a bilge pump ground, is wired ahead of the shunt or on the -BATTERY side of it, the load will NEVER be seen, recorded or measured by the monitor. All DC loads on-board should be read by the battery monitor. Inverters, battery chargers, alternators, solar, wind, DC distribution panel, LPG detectors etc., etc., on and on.
Keep in mind that many marine alternators are case grounded and thus the system ground, which on most boats is the engine block, is the ground path for the alternator. While I much prefer an isolated ground for alternators many boats just do not have alternators with this feature and they use the case as the ground. Due to this, the ships main ground connection should be connected to the -LOAD side of the shunt and NOT ahead of it or on the -BATTERY side.
Anywhere you see a green arrow is safe to connect DC negative load wires. The ONLY wire that should connect to the battery is a single negative jumper wire from the -BATTERY side of the shunt. No other wires should be connected on either the neg battery post or the -BATTERY side of the shunt.
Reading Charging Current
In this photo I have a Guest battery charger connected to the system. The battery monitor is reading a positive +5.68 amp charging current, as it should. Take note of the location of the black alligator clip in the next picture for a good example of why it really DOES matter where your negative system wires are connected.
Measuring Nothing !!
The only thing different in this photo is the location of the chargers negative lead. The charger is still putting out about 5.68 amps, however, because the negative lead is on the wrong side of the shunt it can not be seen or measured by the shunt. If it can't be seen by the shunt it can not be logged or read by the battery monitor. Don't jump the shunt.
Whether you are drawing a load or feeding the system a charge current the negative load wires must be on the load side of the shunt not the -BATTERY side.
I am a strong believer in over current protection or fusing of battery banks, even start banks on smaller axillary engines, despite this not being a requirement to meet in ABYC E-11.
This product is called a battery terminal fuse.. These fuses are meant to protect the wiring from dead shorts and are easy to install. I use the double version for the bank and the alternator wire. As always choose your fuses based on the wire gauge you are protecting.
Every positive wire connected to a batter should be fused within 7" of the battery or as close as you can get. This includes inverters, alternators, battery chargers, bilge pumps or stereo memory wires.
Interestingly enough the black fuse holder for this Victron battery monitor is 7" from the ring terminal for the battery post.
Making The Connections
This is the back of the BMV-602S. There is a port for the computer connection kit, which can be purchased at additional cost, an alarm and the UTP cable connection port.
Plug & Play
Once you have chosen your location, drilled the hole for the monitor and run the UTP cable, simply plug it in to the socket. If you can plug in a fax machine you already know how to connect the monitor to the shunt. This could not be any easier. Kudos to Victron for making this so easy!
Now plug the UTP cable into the shunt.
Click, that's it!
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