Battery monitor useful here?

[seadrift]

Is a battery monitor (BMV 600S) across P1-N3 going to provide total Ah used from the battery bank (12v AGMs), given the arrangement of charger, alternator, etc?

The first figure is the present setup; the second is the change I presume I need to make to get all negative loads 'beyond' the monitor shunt. The inverter is very rarely used.

(It would be difficult for me right now to feed the alternator directly to the battery bank, or install an echo charger.)

[Dsanduril]

If I understand your setup correctly, the shunt would get installed in your proposed system between N3 and the new "T" in the negative line. That would allow the shunt to measure all current in and out of the batteries. The small positive connection is used to power the electronics and to allow display of the voltage, but has little effect on measuring Ah. It could be connected anywhere convenient on the P1-P3 bus, these should all be at essentially the same potential.

[seadrift]

Thanks, Dsanduril, for confirming what I hoped was right. And yes, I forgot to add to the diagram the shunt between N3 and the 'T'.

[smac999]

yes it goes between n3 and T. took me a while to figure out what you were trying to draw. (though you had 6 batteries for a while)..

I would just use the output bolt of the shunt as the T. just bolt both lugs to it.

if you plan to add more large neg wires later then put a big bus bar there instead.

on 2nd thought, where is your inverter chassis ground currently going? normally it's that same bar as well. and will also be big. either 1/0 or 2/0. so you'd have 3 there and need a bus bar of some sort.

[seadrift]

The nitty-gritty of the present system is, of course, more convoluted. The built-in cables from the charger are only AWG 2; all the rest of the battery cables are 1/0.

The negative from the charger connects to the start battery, which is close to the charger; the positive runs via a 1/0 extension to the house bank. The connection of the 2 to 1/0 is made at a battery fuse(!). I was going to run both charger cables to the house bank, using a PowerPost connector, and of course fuse the positive at the battery. And I would add a busbar for the negatives.

[Maine Sail]

Originally Posted by seadrift

The nitty-gritty of the present system is, of course, more convoluted. The built-in cables from the charger are only AWG 2; all the rest of the battery cables are 1/0.

The negative from the charger connects to the start battery, which is close to the charger; the positive runs via a 1/0 extension to the house bank. The connection of the 2 to 1/0 is made at a battery fuse(!). I was going to run both charger cables to the house bank, using a PowerPost connector, and of course fuse the positive at the battery. And I would add a busbar for the negatives.

Just remember that all neg loads and charge sources need to be on the load side of the shunt for it to work properly. This includes;

Start batt neg
Charger neg
Engine neg
Solar or wind neg
Alternator neg if using an isolated ground alt
All bilge Pump neg leads
Any propane sniffer leads
All DC loads

In other words no wires touch the house bank neg terminal other than the battery side of the shunt...

[seadrift]

Thanks, Maine Sail, for your reminder to me (and others).
I have already read your excellent post "Wiring & Installing A Battery Monitor".