Battery Monitor, which brand, which type

[jbinbi]

My boat's setup is as follows.

1 house bank of 420Ah and 2 start banks, one for each engine.

The instrument panel has a battery monitor that lets me select each one of three to show its corresponding voltage level. It also shows As crudely on the top corner, though but only outflow, not inflow.

There is a shunt for the battery monitor.

Since adding solar, I am very keen on knowing how much is going into (and out of) the battery. The MPPT controllers have a LCD display that cycles between V and A, and AH, but the controllers are under a berth, to see them I need to unmake the bed, take off the mattress(es), slide back a piece of wood, and lean over. Not very convenient.

So I am thinking of adding a monitor. I have looked at the Victron, and Balmar Smart Gauge. The smart gauge would be easy to install, and also let me use my current setup to monitor both start batteries. I can leave all wiring in place, including the shunt, the Balmar just connectors to my house bank's terminals. BUT, it doesn't show Amps.

The Victron requires me to substitute its shunt for the current one, not a big deal, but then I can't monitor both of my starts, as the Victron only has the capability to monitor 1 extra battery. But it will show current in and out!

For those with solar, how important is it to know just SOC vs. current used as well. I have read reviews on both of these, mainesail highly recommends the Balmar for SOC. Sorry for the long post, but interested in hearing what others have used and pros and cons. Thanks.

[ErikFinn]

I would consider getting both. Smartgauge for SOC and a traditional amp counter for amps, Victron or whatever you prefer.

[smac999]

you can just add the victron shunt and leave yours. it doesn't sound like your existing one is in the correct spot anyways to show net battery amps. probably only panel draw amps. you can have more then one shunt

just put the screen somewhere else, and put the shunt in correct spot. all your existing gauges will still work. since you already have voltage of the starts monitored just get the cheaper 700

[smac999]

Originally Posted by jbinbi

!

For those with solar, how important is it to know just SOC vs. current used as well. I have read reviews on both of these, mainesail highly recommends the Balmar for SOC. Sorry for the long post, but interested in hearing what others have used and pros and cons. Thanks.

my understanding is while the solar is on the balmar gauge is useless. it won't be correct untill night time when the solar is off.

[Dockhead]

I've tried all these things.

My advice is NONE of them. in my experience, no battery monitor really does anything very useful.

The amp-counting ones like Victron etc. will give you only a very rough idea of SOC, and even then only after investing a fair amount of labor at adjusting the capacity as the bank capacity changes, and frequently resetting them to 100%.

The SmartGauge is far more accurate, and accurate enough, but doesn't tell you anything you can't figure out by yourself by reading system voltage. Also it only works when you're discharging your batteries; it can't tell how much charge you've put in while you're charging.

You can install simple, inexpensive DC ammeters to monitor current going in and out of the bank and out of any charging device (solar, battery charger, alternator), and use a simple, inexpensive DC voltmeter, properly installed (heavy cabling, right to the battery) to read system voltage.

The SmartGauge will save you the trouble of looking up SOC vs system voltage on a table, and I've left mine in place for this reason, and it has a good voltmeter built into it, but in my opinion these minor functions are not worth the cost and space at your nav table. The voltmeter anyway only works on demand; I installed a separate one which is always on.

The amp-counting battery monitors in my opinion are a menace to our batteries. They have a tendency to OVERSTATE the state of charge, as real capacity gets out of synch with actual capacity of the bank, which means we unwittingly discharge them deeper than they should be, which leads to further loss of capacity, and a vicious cycle starts. In my opinion they are worse than useless.

Reading system volts while no charging device is working has the opposite tendency -- any error will be one which UNDERSTATES the SOC, which is a harmless error -- it might lead you to charge a bit earlier than you intended to.

How much error system volts will have depends on the load as a percentage of bank capacity. You will know of course that system volts give a perfectly accurate picture of SOC only in "open circuit" conditions -- bank completely disconnected and allowed to rest for a period of time. If you have loads connected, the system voltage will be pulled down to something less than what it would be in "open circuit" conditions.

But the key fact here, which I discovered over years of experimenting, is that a reasonable sized battery bank will not sag much with small domestic loads. I did a number of experiments meauring true SOC with a hydrometer, and found that as long as I wasn't running any large load (inverter, bow thruster, etc.) and had not in the last few minutes, the system voltage was telling me with great accuracy (within about 2%) what the real SOC was. YMMV if you have a smaller bank, of course, but even double this error 4% or 5% would be plenty close enough, and still closer than what amp-counting meters are capable of probably even in the best conditions. Furthermore, as I said, the error with reading voltage will always be harmless, unlike the case with amp-counting battery monitors.

Keeping an eye on system volts will also tell you something about how far charging has gotten, when you're charging. I'm disappointed that the SmartGauge doesn't do this. Any given battery bank will have a certain voltage it achieves as the charging process goes on at a certain current level. You could make a table, and then have accurate information even during the charging phase.

But you can "eyeball" that and, after getting a feel for it, know when you can stop charging. What I do on my boat is very simple -- when I'm charging with the generator, I just wait for the Victron Multiplus to flip over to absorption, then give it another hour. That reliably gives me a 90% charge.

You can also "eyeball" what is going on when you have a weak charging source like solar hooked up, and loads at the same time. The system voltage (you don't really even need the ammeters) will tell you which way the current is flowing.


All this works just fine. You don't even actually need very precise information about SOC PROVIDED you are not making an error on the wrong side -- overestimating what your real SOC is and delaying charging. You don't really need precise information about what you've achieved in charging -- after you stop charging, within an hour of running normal loads, the surface charge will be off and you'll know where you are.


Battery monitors -- I'm convinced -- give "false precision" -- a false feeling that you know more than you do, and don't tell you anything really useful.

My recommendation is to use the following equipment:

1. 3x panel ammeters with shunts at (a) battery bank; (b) alternator output; (c) charger output.

2. Voltmeter wired with heavy cabling directly to the bank.

3. Your brain, aided by a table showing SOC vs. system voltage.

The equipment (other than your brain) is cheap.






P.S. don't forget to correct for temperature. System voltage vs SOC is different, at different temperatures.

[ErikFinn]

Great post Dockhead.
I recall we have discussed this before but I find repetition useful for learning.

[Dockhead]

Originally Posted by ErikFinn

Great post Dockhead.
I recall we have discussed this before but I find repetition useful for learning.

Yes, we've discussed this before, but I was trying to give a direct response to the OP.

Besides that, my thinking has evolved. Previously I sort of liked the SmartGauge, but now I've become convinced that it is basically useless. It is at least not harmful, as the amp-counting battery monitors are.

[Cotemar]

My vote would be for adding the Victron BMV-700 with the shunt they provide in the box.

Its well worth the $150

Try and keep your battery bank at or above 12.4 (80%) and your batteries will last forever (7+years)

[shufti]

I'm happy with my Nasa battery momnitor. But almost twice the price of the Victron metioned above.

[Matt Johnson]

We really liked our BlueSeas VSM422. It monitored both banks, the AC system, holding tank and bilge pump cycles. All with programmable alarms and other data too.

On the new boat we are trying a SmartGauge and an old link 10.... because it was there and free. The tanks have no easy way to install sensors, so the BlueSeas wasn't of as great a value this time.

Matt

[a64pilot]

I sort of echo the smart gauge comment, although mine seems fairly accurate when charging.

Only way to know your bank is full when charging is to watch charge current when in absorption, so what good is a monitor here?
Best way to determine state of discharge is bank voltage for me (I have an AGM bank and specific gravity measurement isn't an option)
By having a small load on your bank it will drop voltage slightly, making your SOC determination a little on the safe side, so I have to begun to watch voltage more than the Smart Gauge.
Best use for the Smart Gauge is I think for those that don't want to educate themselves, and just want a device to tell them the SOC of their bank, and if your not willing to spend time to learn about the thing, then its the best thing out there.

But, I sometime wish I had put that money in another battery or another Solar panel

[Stu Jackson]

Originally Posted by a64pilot

..............................
Best use for the Smart Gauge is I think for those that don't want to educate themselves, and just want a device to tell them the SOC of their bank, and if your not willing to spend time to learn about the thing, then its the best thing out there......................

Those two highlighted parts are the crux of the matter, reflecting, in short, pretty much what Dockhead explained.

In the late 80s and early 90s, before the internet boom, it took me many years to figure this all out, from daysailing, to overnight sails, to anchoring out. Now, there's literally no excuse for NOT being able to figure it all out. Heck, a day or two reading Maine Sail's website would "learn up" even the most diehard dumbbell.

However, for example, most good energy budget treatises explain that those three very different loads on your boat electrical system are essential to know before you can adequately size a battery bank.

Most skippers daysail and many go marina to marina, in which case it simply doesn't matter, they're plugged in all the time.

But for those of us who demand proper service from our electrical systems when NOT plugged in all the time, it is critical to learn about how batteries work, and how our electrical systems are designed and work.

Sadly, most people don't have a clue. Ask most about "battery acceptance" and you'll get a blank stare. At least for them, the monitors have helped a tad, but the false sense of security JUST because they have two decimal places on the readout sometimes makes me wonder!

[S/V Alchemy]

FWIW, I'm putting in a Bogart Pentametric shortly. I have wind, solar, alternator and shore power as charge sources, and this seems to have the capacity to read and collate all in and out current. They are more common on "off grid homesteader" setups. Like W-H autopilots, the guy who builds them answers the phone! Best of all, it's programmable and you can get USB output to a PC should you wish:

https://www.youtube.com/watch?v=rABhk70NCbs

[jbinbi]

Thanks for all the replies.

In re thinking this some more, since my current monitor shows V , as Dockhead says (and great post , thanks!), just a table would show SOC fairly well.

However, I really want to know if the solar is outputting and how well. I have learned that even though my panels each output 20As, I have hit this only once, when the sun was directly overhead at the stern. Other times I have checked the controllers, which I explained getting to them is a major major PITA, it turns out I am getting 1/4 to 1/2 of that because the mainsheet is shading or the sun is not direct, etc. etc. issues of solar.

So I guess I really want to have a remote monitor for my panels. And to know what is going out as well. Possibly an ammeter as dockhead and others have said. @smac, the shunt I have is correct, see pic below. New boat, this is installed from the factory. Or maybe just Victron 700.

How do I wire in the second shunt (thinking practicality). In the pic, the bottom of the shunt is coming from the neg battery switch (we have been through this in another thread, typical of French manufacts, Bene, Lagoon, Juneau to have this switch).

With new shunt in parallel, I would probably bypass the switch, attaching another low guage wire up from bottom of the switch where the batteries are attached. However, to connect the top of the existing shunt to a new shunt, I need to wire across with inflexible low gauge wire. Basically this is a bar with insulation that needs to be a few inches away. Any tips on wiring this gauge wire?

[smac999]

I doubt the shunt is in the right spot... the feeder cable is too small. it should likely be between battery and switch. on the big cable. it's likely only capturing one thing. like panel draw. where does the big cable on the top of shunt go?