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Old 11-01-2019, 15:22   #1
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Victron 712 to batteries in parallel

Two batteries, each 12 volt, feed common bus bar (+) and bus bar (-). Victron is adament that their 712 monitor be the only connection to the negative pole of the battery, of which there are 2. So 712 can't just be hooked to (-) bus bar.

Manual is not much help.

I assume two batteries in parallel are effectively 1 battery. Therefore, I should be able to hook system ground side of 712 to the bus bar, and both leads going to each battery to the battery negative end of the 712. After moving anything directly connected to a negative battery post to the bus bar (monitors, etc.)

I'm worried there's something I've not considered here, such as differences in the two batteries, possble complications of common (+) with separate (-), I don't know.

Do I need to just connect one battery to the 712 and forget the other?
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Old 11-01-2019, 15:32   #2
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Re: Victron 712 to batteries in parallel

The shunt is connected to the negative bus of the battery bank. The number of batteries or cells in the bank doesn't matter, it is treated as one bank.
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Old 11-01-2019, 15:43   #3
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Re: Victron 712 to batteries in parallel

Quote:
Originally Posted by Paul L View Post
The shunt is connected to the negative bus of the battery bank. The number of batteries or cells in the bank doesn't matter, it is treated as one bank.
Thank you, Paul.

There are two ends of the shunt. The negative bus bar is the "system ground" and one end of the shunt is connected there. But what about the other end of the shunt that is to be connected directly to a battery negative post? Or did I misunderstand you?

Or are you saying that both cables from the negative post of each battery become the "bus" to which the 712 is connected and that is what may NOT have anything else connected?


Victron says not to have anything connected to that side of the shunt, my limited understadning is that it causes a misread of voltage.
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Old 11-01-2019, 16:32   #4
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Re: Victron 712 to batteries in parallel

See diagram, it should help.
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Old 11-01-2019, 21:19   #5
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Re: Victron 712 to batteries in parallel

Your bank is one big battery.

Only one negative return and one energized positive post are connected to loads and charge sources. all the other posts are "intra bank" connections.

Think of your buss bar as part of your outside distribution wiring, not part of your bank wiring.

All load and charge current must be routed through your BM's shunt. Which must be sized higher ampacity than ALL currents totalled that may be flowing at once, just like the bank fuse and isolating switch.

So one side of the shunt is the only connection to the negative return post of the bank.

The other side of the shunt goes to the negative buss bar.

All loads and charge sources's currents get routed through the buss, through the shunt and then to the bank.
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Old 11-01-2019, 22:12   #6
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Re: Victron 712 to batteries in parallel



https://drive.google.com/file/d/1LjZ...ew?usp=sharing

Apparenly I don't know how to upload a JPEG.

I apprecieate the difference between a parallel and series battery set up, but mine is not hooked up quite like that. Both batteries are hooked to common bus bars (+) and (-) that also have loads connected to them, including another bus bar in the engine room.
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Old 11-01-2019, 22:53   #7
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Re: Victron 712 to batteries in parallel

Foxy Battery Diagram - Cruisers & Sailing Photo Gallery
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Old 11-01-2019, 23:03   #8
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Re: Victron 712 to batteries in parallel

its simple - your bank of two batteries are connected in parallel - The wire connecting like posts and the posts themselves form a bus, one neg and one pos. the lines that lead to your ground and distribution panels are feeds.

You want to interrupt the negative feed with the shunt. The shunt will read the current flow to/from the bank and report it on the nvm. You don’t want to bypass the shunt by say hooking up a bilge pump, inverter, etc directly on one of the negative battery posts, because any current flowing AROUND the shunt won’t be seen by it. The positive side of those things doesn’t matter- the shunt reads only the negative side.

So connect one batts negative post to the other, connect one of them to the shunt, and put every ground in the boat on the other side of the shunt - you may need a bus bar tho tie all your grounds together

Hope that helps,

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Old 11-01-2019, 23:09   #9
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Re: Victron 712 to batteries in parallel

Quote:
Originally Posted by Erik Dolson View Post
Rewire it so the 12v batts are in parallel but only have a single connection to the bus bars..
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Old 11-01-2019, 23:19   #10
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Re: Victron 712 to batteries in parallel

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Originally Posted by Paul L View Post
Rewire it like the diagram I posted above.
Rewire the house bank batteries? That's not a small job. The boat was built by TPI in Rhode Island in 1994, supposedly a top builder at the time. Each battery has an isolation switch. All has worked well until this question came up.

I'm not sayng you're wrong, but I am wondering why it was done the way it was if that's wrong, pointing out it has seemaingly worked well over decades, wondering if there's a work around to rewiring the house banks — such as the one I suggested of having the negative lead of each battery overlap at the battery side of the shunt, and the shunt connect to the bus bar.
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Old 12-01-2019, 01:50   #11
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Re: Victron 712 to batteries in parallel

Quote:
Originally Posted by Erik Dolson View Post
Rewire the house bank batteries? That's not a small job. The boat was built by TPI in Rhode Island in 1994, supposedly a top builder at the time. Each battery has an isolation switch. All has worked well until this question came up.

I'm not sayng you're wrong, but I am wondering why it was done the way it was if that's wrong, pointing out it has seemaingly worked well over decades, wondering if there's a work around to rewiring the house banks — such as the one I suggested of having the negative lead of each battery overlap at the battery side of the shunt, and the shunt connect to the bus bar.
If each battery has an isolation switch then it sounds more like you one start battery and one house battery. Is this correct. The shunt on the battery monitor can only monitor one bank. That bank can be made up of one or more batteries.
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Old 12-01-2019, 02:02   #12
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Re: Victron 712 to batteries in parallel

Your parallel wiring for sure is not the common way, but is ok and does its job.
Make sure all wires are more or less equal length.

Here is how you should install the shunt. The connections on the shunt are marked -Load and -Battery. Make sure you connect the bus bar wire to the -Load connector and the wire coming from the battery goes to -Battery. Not easy to have both wires from the two batteries connected to the one connector. Depends on thickness of wire terminals. Good luck.

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Old 12-01-2019, 10:01   #13
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Re: Victron 712 to batteries in parallel

Quote:
Originally Posted by Erik Dolson View Post
I am wondering why it was done the way it was if that's wrong
It is not uncommon for boats to have been wired wrong by todays best practice standards.

But before you re-wire post a detailed confirmed-accurate (ideally by a pro using a DMM) diagram, just using words can cause misunderstandings.
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Old 12-01-2019, 10:06   #14
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Re: Victron 712 to batteries in parallel

Erik,

YES - hook up the two neg leads from your batteries to the shunt, and the other side to your negative bus bar. Done
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Old 12-01-2019, 10:34   #15
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Re: Victron 712 to batteries in parallel

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Originally Posted by Paul L View Post
If each battery has an isolation switch then it sounds more like you one start battery and one house battery. Is this correct. The shunt on the battery monitor can only monitor one bank. That bank can be made up of one or more batteries.
No, these batteries are effectively wired in parallel as the house bank. The start battery is in a differenct location and although it can be connected to house bank if needed, is isolated.

My guess is that there is an isolation switch for each battery (572 Ah each) so that one can be taken out of the circuit if that is required for any reason.
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