Battery Monitor installation question

[SVRocinante]

Good day folks

Ok, so I have all my tools set out, I made up my cable for the shunt and was getting ready to install my new battery monitor (Victron BMV-702) when I noticed that it was supposed to be wired into the negative side & not the positive.

Yes, I’m an absolute newbee, but as you’ll see in a minute, it seemed logical to wire it into the positive side since the positives are all isolated and the negatives all go to the bus.

Anyway, I’ve attached a simplified diagram of my current setup.



Any thoughts on how to effectively monitor my house bank without having to rewire? Is there another brand/type of battery monitor where my current setup would work? Am I simply missing the boat altogether?

Thanks again for the help!

[a64pilot]

You have two choices as I see it.
Check to see if you can put your shunt on the positive side, if so, do so.
Otherwise separate the negatives.
I believe they should both go direct to the engine block.
However as I think that through, electrically it’s no different than what you have, so installing the shunt to the house battery ought to work?

[Maine Sail]

[SVRocinante]

Originally Posted by Maine Sail

Yep, Thanks... that’s,how it’s supposed to be, but it’s not.
Probably no choice, but I’m trying to avoid having to rewire.

I kept the diagram simple, but the reality is that I also have a battery for the windlass that’s wired in and a second housebank as well.

No longer a simple task to put in the monitor...

Thanks again,

[SVRocinante]

Originally Posted by a64pilot

You have two choices as I see it.
Check to see if you can put your shunt on the positive side, if so, do so.
Otherwise separate the negatives.
I believe they should both go direct to the engine block.
However as I think that through, electrically it’s no different than what you have, so installing the shunt to the house battery ought to work?

My assumption, probably incorrect, was that if I did put the shunt on the positive side the values would reverse; current in would be regustered as negative and current out would be registered as positive - so SOC would be “wrong”

Thanks again,

[a64pilot]

Some systems allow the shunt on the pos side, that is why I said to check to see if yours does.
However obviously wire as Maine Sail indicates.

[Stu Jackson]

Originally Posted by SVRocinante

My assumption, probably incorrect, was that if I did put the shunt on the positive side the values would reverse; current in would be regustered as negative and current out would be registered as positive - so SOC would be “wrong”

Thanks again,

In 1998 I bought a new Freedom 15 Inverter Charger and a few years later installed my Link 2000 battery monitor.


I carefully followed the directions.


Because that's why they write directions.



Other than your own mistake and/or assumptions, related to the positive vs. negative wiring, what "logic" could anybody possibly come up with to justify NOT following the directions written by the people who made the expensive machine you're installing?



I'll take this one as a "teaching moment" if you want to explain...


And while you're at it:


For everyone installing a battery monitor: The "Gotcha Algorithm" thread, a "MUST READ"

Link-series Charging Algorithms -- The "Gotcha" Factor!

DEFAULTS are factory settings that are made to be modified to suit your setup.

Also read this one:

Programming a Battery Monitor (by Maine Sail)

Keeping Your Battery Monitor More Accurate Photo Gallery by Compass Marine How To at pbase.com

and his newer 'site

https://marinehowto.com/programming-a-battery-monitor/

[alley]

Originally Posted by SVRocinante

Good day folks

Ok, so I have all my tools set out, I made up my cable for the shunt and was getting ready to install my new battery monitor (Victron BMV-702) when I noticed that it was supposed to be wired into the negative side & not the positive.

Yes, I’m an absolute newbee, but as you’ll see in a minute, it seemed logical to wire it into the positive side since the positives are all isolated and the negatives all go to the bus.

Anyway, I’ve attached a simplified diagram of my current setup.



Any thoughts on how to effectively monitor my house bank without having to rewire? Is there another brand/type of battery monitor where my current setup would work? Am I simply missing the boat altogether?

Thanks again for the help!

My opinion is that the shut should be on the negative side unless installation instructions specifically state it can be installed on the positive leg.

That said, your goal should be to put the shunt between (i.e., in series with) the negative side of the house batteries and the house loads while the engine starter current can take a parallel path.

The danger of using a simplified drawing is that it is not clear where the negative side of the batteries are tied to the engine block, and that's a significant detail in this case.

Hope this helps.

[SV Sailfish]

Originally Posted by Maine Sail

+1

[SVRocinante]

Thanks folks; I’m good.
Appreciate all the good thoughts!

regards,

[mitiempo]

Originally Posted by Maine Sail

Yes you are good if this is followed exactly.

[Boatwright]

After sailing on other boats with battery monitors, reading reviews of same I have some observations:

Given the inattention of many, the readings these expensive gizmos give are an often poor approximation of the actual state of charge of a battery bank. In practice they don't seem to offer any advantage over simple voltage monitoring, and will not substitute for understanding your system's voltage indications.

I've got a low tech solution that has never failed:

An accurate permanently installed digital voltmeter, paper and pencil, and the "computer" between one's ears.

Monitoring battery voltage under a variety of conditions - day, night, different combinations of lighting, refrigeration, nav electronics, etc. - will after a short time give one an excellent feel for the relationship between indicated voltages and voltage after a period of battery rest.

I know, for example, if after a warm day's sail with an evening at anchorage and a bunch of switches turned on we might see an indicated voltage of 12.2. Turn off most of the loads, except for the anchor light and minimal standby electronics, and by morning we will have 12.5v on the meter. As a test, turning off the master switch for an hour, the voltage will drift up a few tenths - therefore we are at about 75% SOC resting.

We have a 200 watt solar array (rated wattage that produces about 1kwh / day) and a Sterling charge controller on our 125 Amp alternator. We rarely use the engine for charging.

This system may not apply if you have a power-hungry setup, but for our simple needs it works fine. Of more importance for our KISS system, is checking water levels, keeping belts tight, equalizing, etc..

[john61ct]

Only if your usage patterns are **consistent** and current flows are low.

SmartGauge is more accurate than the coulomb counters, and requires no calibration or ongoing resetting.

But yes, all such bells and whistles are optional, your boat your call.

[Boatwright]

As I understand it the SmartGauge system monitors voltage patterns over time and uses a computer algorithm to "deduce" SOC. It does not directly measure amp/hours (Coulumbs).

That's why I mentioned paper and pencil, and the computer between one's ears. Personally I'd rather apply the $400 to our budget for a new jib.

[a64pilot]

I’m convinced that someone with a little knowledge, can accurately enough deduce their batteries SOC with an accurate voltmeter and amp meter.
It’s not rocket science, and if you err, err or conservative and you will always be OK.
Some manufacturers or at least one anyway give you a voltage chart under load to determine SOC.
Paradoxically, my voltages are always considerably higher than this chart though, for the indicated SOC.
Lifelines chart.