3 batteries in boat

Question

question

alfonso asked Jul 23, '21

3 batteries in boat

My Currently my installation is this and I wanted to add a victron battery monitor.

2 X Volvo Penta 4.3 GXI 225 hp engines with 75 A alternator each.

1 X Victron Phoenix Smart IP43 Battery Charger, 12/50 (3)

2 X Victron Energy ARG080201000R Argodiode 80-2AC 80 A

3 X Independent batteries from 12v to 150 ah each.

I want to add a monitor for the 3 batteries so I bought a victron BMV 702 (motor batteries) and a BMV700 (Auxiliary battery).

Attached is the installation diagram that I think is correct. Can you tell me if it is correct? Thanks.

BMV Battery Monitor

ac-sl1200-bmv.jpg (479.2 KiB)

2 |3000

Attachments: Up to 8 attachments (including images) can be used with a maximum of 190.8 MiB each and 286.6 MiB total.

Modifications Space

Node Red Space

Answer 1 · 2021-07-24T06:21:18Z

JohnC answered · Jul 24, 2021 at 06:21 AM

Hi @Alfonso

The BMV on "bat aux" is correct.

The other will only monitor "bat1". To monitor both 1/2 together, take the -ve from "bat2" directly to the BATTERY terminal, not the LOAD terminal. Essentially, join the 2 bat -ves together before the shunt.

2 |3000

Attachments: Up to 8 attachments (including images) can be used with a maximum of 190.8 MiB each and 286.6 MiB total.

Answer 2 · 2021-07-24T10:50:33Z

alfonso answered · Jul 24, 2021 at 10:50 AM

hi John,

but the bmv 702 instructions for main / aux batteries state this:

install3.jpg (36.2 KiB)

1

2 |3000

Attachments: Up to 8 attachments (including images) can be used with a maximum of 190.8 MiB each and 286.6 MiB total.

JohnC ♦ commented · Jul 24, 2021 at 11:30 AM

@Alfonso

Yes, but there the BMV will give the full current treatment to #1 batt and only measure the Voltage on #2 as one of the 3 auxiliary functions.

You've followed this in your own diagram, but all you'll see is the V of bat2. If that's all you want then fine.

0 ·

Answer 3 · 2021-07-24T11:56:14Z

alfonso answered · Jul 24, 2021 at 11:56 AM

The problem with measuring bat1 and bat 2 together is that you could have measurement errors. For example, if bat1 has a voltage of 13.7v (full) and bat2 has 11.9v (discharged) the shunt would show 12.8v, apparently everything is correct but it is not. Ultimately bat1 and bat2 are only used to start the engines and should not have consumption (if the ignition is not on). Now I wonder if the bmv702 shunt is really useful or just a direct voltage monitor to each battery (bat1 and bat2) would be enough.

3

2 |3000

Attachments: Up to 8 attachments (including images) can be used with a maximum of 190.8 MiB each and 286.6 MiB total.

JohnC ♦ commented · Jul 24, 2021 at 12:20 PM

The V's won't 'average' as they're on the +ve side of each batt. B1 cable will give the V on bat1 and B2 the V on bat2. No matter which way you wire the shunt.

But yeh, for most a V reading on starter batts would suffice.

0 ·

alfonso JohnC ♦ commented · Jul 24, 2021 at 02:19 PM

So what information do I get by connecting the - of bat2 to the shunt battery? If I understand it correctly, I get joint consumption information from bat1 and bat2 if I connect them both - to the battery of the shunt.

I appreciate all the information. I am learning a lot from your advice.

0 ·

JohnC ♦ alfonso commented · Jul 24, 2021 at 02:58 PM

You'd get the (joint) consumption info, but you may find the charge info of more use. Be interesting where the Tail current finishes up if you were charging both or just one.

I haven't done this though, but might be fun.. :)

0 ·

question