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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 and a number of others make them. Currently the Victron units are the most simple to install and also the least expensive making them a good value. A Victron BMV-600S single bank monitor can be purchased for just $184.25. I chose to do this article with the Victron BMV-602S. I personally use a Xantrex Link Pro but they all do basically the same thing.


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 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.

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 units.

About the time Xantrex signed on to re-label the TBS monitors Victron found a new manufacturer to build their units. The Victron BMV-602S is pictured on the right and bears little resemblance to the TBS built monitors.


The Victron shunt is quite unique because they have added a printed circuit board to it so that wiring is easier. Shunts are not really directional 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 the only cable that needs to be run the monitor display and is literally "plug & play". The UTP cable is very similar to phone cable, only slightly more robust. The power supply wire simply connects to the positive battery post and the B1 terminal of the Shunt.

This shunt has two power supply inputs for two banks as it can monitor the voltage of a second reserve bank.


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 dificult to illustrate on a boat. I actually photographed this a while ago, on a boat, and decided not to use 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.


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 have connected your DC negative wires.

A shunt reads the loads on the system as measured 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, it will NEVER be seen or measured by the monitor. All DC loads on-board should be read by the battery monitor. inverters, battery chargers, solar, wind, alternator, 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 most boats just do not have them. 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 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.


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. Note 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.


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. Because it is on the wrong side of the shunt and it can not being seen or measured 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 made by Blue Seas is called an MRBF or Marine Rated Battery 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.


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.


Once you have chosen you 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!


This is a close up of the crimped pin for the power supply cable. I would leave well enough alone and not cut the wire shorter unless it is absolutely necessary. This pin fits nicely in the shunt socket.


Use a small flat bladed screw driver and simply slide the orange tab towards the shunt to open the clamping mechanism. In this photo I have not yet slid the orange tab towards the shunt.


With the tab slid backwards simply push the pin into place. It will slide all the way into the socket just about up to the plastic.


Here's a prime example of why I like the Victron simplicity. This is an older Link 10 and it requires five wires to be installed and then screwed down at the monitor end. This is certainly not difficult but requires some level of precision, access and can be a tad tedious.

The current Xantrex monitors, Link-Lite & Link-Pro, still connect exactly like the old Link 10 and on top of that they cost more money.


Rather than a shunt mounted PCB, like Victron has chosen, which offers true "plug and play" simplicity the Link series shunts still require wire stripping, crimping, and the physical need to manually wire the shunt. The blue & red wires from the previous photo, and not seen here on the shunt, go to the positive battery post with in-line fuses.

Again not difficult to wire but more tedious. I still have a Link-Pro on my own vessel and I am of the opinion that the Xantrex units are slightly better built but you certainly pay dearly for that quality, which may not even be necessary.

That being said if you don't need to monitor the voltage of a second bank, really not all that necessary if it is just a starting or reserve bank, then Victron also offers the BMV-600S for just $184.25.

Ideally unless you are taking a "resting voltage" reading of a secondary bank it really won't tell you much of anything close to accurate.


Battery monitors can display many different values on the screen including voltage, amp hours consumed, amperage, state of charge and more.

The "V" screen, as shown here, measures voltage for the house bank. This voltage reading is showing the battery being float charged.

This particular model, the Victron BMV-602S, can monitor the voltage of two banks as can the Xantrex Link-Pro.


The "VS" screen tells you the voltage of a second bank. Seeing as I used one battery for this illustration the meter is showing the same voltage as the the "V" screen.

I should mention that there has been one person on the net complain that the V & VS screens, even when fed from the same source voltage are not in sync. This meter happens to be properly calibrated but an experienced sailor and electrical engineer on SailboatOwners.com has had two units with voltage readings from .01 - .03 volts off when sensed from the identical source.

Is a variance of .01 to .03 volts a big deal? No, not at all, but I just wanted to make you aware so that you don't panic if your V & VS screens do not completely agree. Victron might need to do some better QC with the V & VS screen readings!


The "I" screen shows current in/out. This shot is showing no loads or charge current.


This "I" screen shot shows the monitor measuring a negative load. A negative load is denoted by the - symbol.


This screen shows a positive charge current as denoted by the lack of the - symbol..


This is the CE or Consumed Energy screen. It shows the amount of amp hours consumed from the battery. After the battery receives a full charge this readout resets to 0.0 Ah denoting a fully synchronized monitor.

If you draw a current of 10 amps for a period of 4 hours you will show -40 Ah on the CE screen.


This is the SOC or State-of-charge screen. This screen is the best way to monitor the SOC of the battery with this monitor. This screen is only useful provided you have programmed the monitor correctly, it's synchronizing the way it should and is wired properly. This readout calculates the amount of energy available in the battery and is Peukert & CEF / Charge Efficiency corrected. The screen ranges from 0% = dead to 100% = full.

Counting amp hours is good but may not always reflect the true state of charge of the battery. For example if the battery is drawn down heavily & at a high rate of discharge current you will get less usable Ah's than its rating. If drawn slower than the 20 hour rating you can get more Ah's out of it. The SOC screen corrects for the Peukert component and CEF, the Ah screen does not.

Please take the time to read the manual for these monitors as they are generally more difficult to program and master than the actual installation!
 

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Freedom 39
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Excellent write up. My only complaint is that you didn't do this 2 months ago when I installed my Victron!!! Since my install, four other boaters around me have purchased and installed the Victron units and all of us love the simple installation and the useful information provided.
 

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I just did my bmv600 install this weekend, and it's already proving it's worth. Confirmed my long standing suspicion that my boat has a stray current or voltage leak somewhere...now Maine, how about a writeup to identify oem wiring issues :D
 

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Discussion Starter · #4 ·
I just did my bmv600 install this weekend, and it's already proving it's worth. Confirmed my long standing suspicion that my boat has a stray current or voltage leak somewhere...now Maine, how about a writeup to identify oem wiring issues :D
You may not. Check the manual for:

Ith: Current threshold. When the current measured falls below this value it will be considered as zero Amps. With this function it is possible to cancel out very small currents that can negatively affect long term state-of-charge readout in noisy environments. For example if an actual long term current is +0.05 A and due to injected noise or small offsets the battery monitor measures -0.05 A, in the long term the BMV can incorrectly indicate that the battery needs recharging. When in this case Ith is set to 0.1, the BMV calculates with 0.0 A so that errors are eliminated. A value of 0.0 disables this function.

Insert a DVM measuring mA and check to see that you really have phantom load. The easiest way to check Ith is to disconnect all the "loads" and see what the monitor reads when only connected to the battery with NOTHING else in the path other than the battery. If it is not reading zero wwhen only conencted to the battery, with nothing else conencted to the battery then it is an Ith/noise issue whcih can be adjusted out. This is a step you want to perform anyway...
 

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Telstar 28
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Nicely done Maine Sail.
 

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Courtney the Dancer
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Excellent article Maine. I installed a 600 last spring and now I don't know how I would get along without it.
 

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Congrats on a really nice job, Maine! This will certainly be helpful to lots of folks out there.

One note on fuses: the new terminal type fuses you illustrate are one of only three common types of fuses which have an Ampere Interrupt Capacity (AIC) high enough to meet present ABYC standards for positive wires connected directly to the battery. The other two are ANL and Class T. Most breakers in common use DO NOT meet these standards, though the new class of Blue Seas Systems breakers do.

Thanks again for a very nice job.

Bill
 

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Discussion Starter · #8 ·
Congrats on a really nice job, Maine! This will certainly be helpful to lots of folks out there.

One note on fuses: the new terminal type fuses you illustrate are one of only three common types of fuses which have an Ampere Interrupt Capacity (AIC) high enough to meet present ABYC standards for positive wires connected directly to the battery. The other two are ANL and Class T. Most breakers in common use DO NOT meet these standards, though the new class of Blue Seas Systems breakers do.

Thanks again for a very nice job.

Bill
Bill,

As per our previous conversations the AIC issue is an important one. I often see circuit breakers connected to HUGE banks that have sub 3k AIC ratings and owners who know nothing about what the AIC rating even is..

I only use ANL, MRBF's or Class T when connecting to a battery bank. With new battery technologies like TPPL & LiIon we could very well exceed the Class T AIC rating at some point...;)
 

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Maine Sail,

Once again you have made my life easier with one of your tutorials. Based on this latest one I have ordered the Victron 601 for my boat. I just finished a fairly major rewire of the batteries and main panel. Your post took away any aprehension that I had concerning installing a battery monitor.

Thank you!

Bill
 

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Wow!

Maine Sail - great write up and timing. I was just grieving over the task of selecting and installing a battery monitor for the upcoming season.
Your knowledge and effort are greatly appreciated!:D
 

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Maine,

I've had the battery monitor on my list of things to buy soon. However, I now am the proud owner of a Xantrex MS2000 Pure Sine Wave Inverter/Charger and the Xantrex System Control Panel. (Sequitur kindly pointed out that things like a washing machine need a pure sine wave inverter to work.)



The MS2000 has a battery monitor built into it. Do I still need the Victron?

Here's the screen shot that has me wondering.


Secondly, since I now have both the SW2000 and a Freedom 20 inverter charger, and neither are installed, I could do some serious side-by-side tests. Not sure I have time to test every aspect, and I don't have all your meters. That said, is there any test that you'd like me to run, to compare them side-by-side?

I'll be selling the Freedom 20 soon, since the SM2100 was a good-sized boat-buck. Got a bit of buyer's remorse too. I'm hoping the SM2000 is simply fantastic and a worthwhile base to build upon.

Note to all: I thought I got a great deal until I saw the sailnet shop's price. Next time I'm checking here first.

Regards,
Brad
 

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Maine Sail has, again, done a tremendous job. As you may know, he's posted this on many message boards. In most of those, I've linked to what I call "The Gotcha Factor" about the logic in the battery monitors algorithms. The default values in the monitors are set up for 200 ah house banks and certain charging voltages, which can be adjusted to suit YOUR boat's system. It especially comes into play if you have a fridge.

Please enjoy: Link-series Charging Algorithms -- The "Gotcha" Factor!
 

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Why does the battery charger + connect directly to battery?

In your photo, why does the battery charger connect directly to the battery, instead of onto the far side of the battery switch? I've always seen battery chargers connected this way, but I've always wondered whether this is really the right way to do things. Does this change if it's a charger/inverter?

Actually, I guess that brings up a related question: where would other charger sources come into this configuration? So, solar panels, wind generator, the engine alternator: which should connect in front of the battery switch and which would connect behind the battery switch?

How does the placement of these sources affect the power monitoring?
 

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Discussion Starter · #15 ·
In your photo, why does the battery charger connect directly to the battery, instead of onto the far side of the battery switch? I've always seen battery chargers connected this way, but I've always wondered whether this is really the right way to do things. Does this change if it's a charger/inverter?

Actually, I guess that brings up a related question: where would other charger sources come into this configuration? So, solar panels, wind generator, the engine alternator: which should connect in front of the battery switch and which would connect behind the battery switch?

How does the placement of these sources affect the power monitoring?
If your system is wired appropriately none of the charging sources need to be switched. They should all feed direct to the battery un-switched, wind, solar, alt & charger.
 

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In your photo, why does the battery charger connect directly to the battery, instead of onto the far side of the battery switch? I've always seen battery chargers connected this way, but I've always wondered whether this is really the right way to do things. Does this change if it's a charger/inverter?

Actually, I guess that brings up a related question: where would other charger sources come into this configuration? So, solar panels, wind generator, the engine alternator: which should connect in front of the battery switch and which would connect behind the battery switch? ...
Besides what MaineSail wrote, you can easily break part of your alternator if you disconnect the battery while the engine is running.

...How does the placement of these sources affect the power monitoring?
Power monitoring is done on the negative side of the battery, close to the battery terminal. (Because "it just doesn't matter" which side of the battery you measure from, the same number of electrons are flowing out the minus side and into the plus side.) Since it's the only thing connected to the battery terminal, all current must flow through it. So it's not affected by where the charging source is connected. Just don't connect anything else to the negative terminal.

Regards,
Brad
 

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MS's great tutorial notwithstanding, I have a basic question re battery monitors in general, particularly the "state of charge" function, common to all brands I know of.
I understand (I think) that in order to ascertain how much charge is left in a battery bank...starting from a fully charged battery or bank, one must tell the monitor how big the battery was in the first place...similar to the way the gas gauge works in your car...if you didn't know how much gas the tank could hold, how would you determine when it was half full, for instance.
So suppose you had a house bank of 200 AH. That's the capacity of "the tank" you would program into the monitor and, as energy is consumed, SOC would diminish accordingly and all be well. But what if you decide somewhere along the way you wanted to switch another battery into (or out) of your bank via the 1-2-B switch.
I have a client who does just that. He has a two-battery house bank, a start battery, and an "at large" battery which can be dedicated (by switch) to either house or start function. He likes the sense of redundancy he says this configuration gives him. He makes his decision, where to put the orphan battery, based on the SOC he reads from his monitor.
He brought the boat in complaining that his batteries were unreliable...says his system works all the time that way and there's something wrong with his monitor and would I replace it...and his batteries.
Advice??

Howard Keiper
Berkeley
 
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