Where to place SmartShunt?

[Peregrine1983]

Hi all,

I just purchased a Victron SmartShunt so that I can monitor amp hours in/out/remaining in batts, etc. instead of just voltage at the panel.

I have a rather complex FLA battery system with 2 banks - 1 house and 1 start, but the house bank is made of 4 separate battery boxes in different locations around the boat.

I always use these house batteries together and in parallel. All batts are 12v 100ah marine deep cycles.

I'm debating where on the negative side to place the shunt to monitor this house bank.

If I just pick a battery and attach the shunt at the negative terminal of one of the house bank batts in the most "central" location, will I get fairly accurate reading if the 3 house batteries are always in parallel?

Thanks so much for any help.

[Pandor]

No. By the sound of it, you are going to have a difficult time achieving your goal of one monitor across four disparate batteries. You must place the shunt upstream of only the batteries (and all of them). There can be no other ground wires connected to any batteries downstream of the shunt.

[Statistical]

No. Shunts can only record current that flows across them. Having it one 1 of 4 battery neg terminal means you would be recording only roughly 25% of the current flows. That means any SoC calculations are going to just be random garbage.

The only way I can see this being accurate is having a battery busbar which has batteries only connected to it, then the shunt then a negative load bus bar

[All batteries connect here] ---------- [ Shunt ] ----- [All load negatives connect here]

[Peregrine1983]

That’s what I was afraid of. Thank you. I’ll have to figure something else out.

[CSYChip]

If you are running the batteries in parallel, there must be some point where the negatives are tied together. That would be the location for the shunt. In my system the house batteries come to a bus inside the circuit breaker panel. By putting a shunt there, I get a read on my usage while avoiding the engine which I don't want anyway.

[Peregrine1983]

Originally Posted by CSYChip

If you are running the batteries in parallel, there must be some point where the negatives are tied together. That would be the location for the shunt. In my system the house batteries come to a bus inside the circuit breaker panel. By putting a shunt there, I get a read on my usage while avoiding the engine which I don't want anyway.

Thank you. Yes, I wanted to avoid the engine as well. I'm thinking there's a big negative house bus hiding somewhere.

[Peregrine1983]

Hi all, just following up to my original question - can I place this shunt between my negative bus and the ground terminal on my motor?

[Statistical]

Originally Posted by Peregrine1983

Hi all, just following up to my original question - can I place this shunt between my negative bus and the ground terminal on my motor?

No. Shunts can only measure current flowing across them. Not current anywhere else on any other circuits.

Unless every electrical device is wired to the ground terminal on your motor a shunt placed between it and the negative bus would record only some (or possibly zero) current.

It really has to be this for a multi house battery system:

[Battery neg terminals] <-------> [Some common connection point/busbar] <------> [Shunt] <-----> [Busbar for load & charger negative terminals]

Most people intentionally leave the starter battery out of the shunt "loop" because they don't really care about a combined house/starter soC number as it would largely be useless but it has to be on the negative of ALL house batteries and the only way to do that is for all the house batteries to be combined at some point and then the shunt placed there and then ALL loads on the other side.

If you want to use a shunt and have multiple house batteries and you don't have some common point where all the battery negatives are connected but no loads are connected then to have any useful data you are going to need to some rewiring.

It can be as simple as two busbars. Run all the battery negative terminals to the first bus bar. Relocate all load & charger negative terminals to a second nearby busbar. Now run a wire from the first busbar to the shunt to the second busbar. At this point 100% of the current flow to and from all the house batteries will flow across that single point where the shunt is located.

[Statistical]

Originally Posted by Peregrine1983

Hi all, just following up to my original question - can I place this shunt between my negative bus and the ground terminal on my motor?

No. Shunts can only measure current flowing across them. Not current anywhere else on any other circuits.

Unless every electrical device is wired to the ground terminal on your motor a shunt placed between it and the negative bus would record only some (or possibly zero) current.

It really has to be this for a multi house battery system:

[Battery neg terminals] <-------> [Some common connection point/busbar] <------> [Shunt] <-----> [Busbar for load & charger negative terminals]

Most people intentionally leave the starter battery out of the shunt "loop" because they don't really care about a combined house/starter soC number as it would largely be useless but it has to be on the negative of ALL house batteries and the only way to do that is for all the house batteries to be combined at some point and then the shunt placed there and then ALL loads on the other side.

If you want to use a shunt and have multiple house batteries and you don't have some common point where all the battery negatives are connected but no loads are connected then to have any useful data you are going to need to some rewiring.

One of the challenges with multiple house batteries and shunts is often there is either no busbar (everything just haphazardly wired directly to various battery negative terminals) or there is only one negative busbar which has connections to both the batteries and the loads. Neither allow a place to put the shunt such that all house load current flows across the shunt.

It can be as simple as getting one or two new busbars. Run all the battery negative terminals to the first bus bar. Nothing but but connections to batteries on that busbar. Relocate all load & charger negative terminals to a second nearby busbar. Now run a wire from the first busbar to the shunt to the second busbar. At this point 100% of the current flow to and from all the house batteries will flow across that single point where the shunt is located.

[Johan Leopard51]

If your panel does not presently have Volt & Amp meter in the panel (this would be on an as-built shunt), then likely the simplest / most certain would be to cut your Neg busbar, then install shunt as the “bridge” over that gap you created with the cut. Secure the shunt & torque properly as this would be 200A to 400A on big cables crimped professionally.

I don’t think it will matter where along the bus bar, as the way I understand it all current in the DC circuit will pass through that gap. So whether some batteries connect at one end of Neg busbar and some at other end and inverter sits somewhere in the middle and alternator(s) somewhere else along busbar, the current charge and discharge passes through all of the busbar part 1, the shunt and the busbar part 2.

The busbar is not like a switch in a circuit or a load in the circuit (with Neg and Pos side), see it is a long leg in the circuit that you must entirely bridge with the shunt.

But I am a chartered accountant, I’m sure an electrician will shout if my advice is wrong.

[Statistical]

Originally Posted by Johan Leopard51

If your panel does not presently have Volt & Amp meter in the panel (this would be on an as-built shunt), then likely the simplest / most certain would be to cut your Neg busbar, then install shunt as the “bridge” over that gap you created with the cut. Secure the shunt & torque properly as this would be 200A to 400A on big cables crimped professionally.

This would only work if 100% of loads & chargers are wire to the DC panel. In many cases always on loads and chargers are not wired to the DC panel and as such their current to & from the battery would be missed.

I don’t think it will matter where along the bus bar, as the way I understand it all current in the DC circuit will pass through that gap. So whether some batteries connect at one end of Neg busbar and some at other end and inverter sits somewhere in the middle and alternator(s) somewhere else along busbar, the current charge and discharge passes through all of the busbar part 1, the shunt and the busbar part 2.

This is not correct the current for loads & batteries on "part1" would not be seen by a shut wired between part 1 & part 2. If nothing on part 2 had current and everything on part 1 was on the shut would show 0 amps despite the batteries discharging.

It really does need to be:

[batteries] <-----> [shunt] <----> [all loads & chargers]

Anything that bypassed the shunt (meaning wired to the left of the shunt on the diagram above) will NEVER be recorded by the shunt. Getting a shunt to record something is trivial pretty much anywhere you put it it will sometimes show some amount of current but a shunt used for SoC monitoring needs to see all current all the time.

[Peregrine1983]

Thanks so much for the input, Statistical and Johan. Here are some photos of my panel and what’s behind it. Our boat was professionally re-wired in 2022, so things are pretty organized.

All my loads are run through this panel, with the exception of an auto bilge pump, which is direct wired.

I imagine that I could place the smart shunt on the main - DC feed and have things pretty covered, see first photo at left.

[Statistical]

Originally Posted by Peregrine1983

Thanks so much for the input, Statistical and Johan. Here are some photos of my panel and what’s behind it. Our boat was professionally re-wired in 2022, so things are pretty organized.

All my loads are run through this panel, with the exception of an auto bilge pump, which is direct wired.

I imagine that I could place the smart shunt on the main - DC feed and have things pretty covered, see first photo at left.

Yes just prior to the main DC feed could work however keep in mind the shunt also needs any charging current too otherwise it will not correctly reflect rising SoC. If those are wired to the main DC panel then great you are all set but that isn't common.

[Johan Leopard51]

Originally Posted by Statistical

This would only work if 100% of loads & chargers are wire to the DC panel. In many cases always on loads and chargers are not wired to the DC panel and as such their current to & from the battery would be missed.



This is not correct the current for loads & batteries on "part1" would not be seen by a shut wired between part 1 & part 2. If nothing on part 2 had current and everything on part 1 was on the shut would show 0 amps despite the batteries discharging.

It really does need to be:

[batteries] <-----> [shunt] <----> [all loads & chargers]

Anything that bypassed the shunt (meaning wired to the left of the shunt on the diagram above) will NEVER be recorded by the shunt. Getting a shunt to record something is trivial pretty much anywhere you put it it will sometimes show some amount of current but a shunt used for SoC monitoring needs to see all current all the time.

That’s interesting, thanks for correction. On our boat the Neg busbar is (as shipped by R&C) in two parts with the shunt as the “bridge”, but seems to me there are supplies and loads on both sides of the bridge. Or at minimum, one of the sides definitely has both loads and sources. The other side may only supply the other smaller Neg busbar at the DC fuse panel so only loads.

I’ll try figure from SLD the different DC “routes” but what had me on my train is that in our case several negative cables could be both ‘source’ and ‘load’ as for example (1) the Victron charges and discharges and (2) because of ACR that mostly charge house but if house happy the house also charges starter batteries.

With one house battery, would the “best” place for the shunt then be in-line next to the 400A fuse on the house battery bank big cable that runs to Neg busbar?

Sorry for confusing opening post - he has multiple house batteries - he should maybe bring one Neg cable from each and all house batteries to one new Neg busbar, then a fat fuse and shunt between this busbar and the distribution Neg busbar?

All of this confusing me for when we plan to put in a big new 52V house bank in addition to keeping the 12V house bank!

[Peregrine1983]

Here’s the finished install. I really appreciate the help. I just cut the main negative and placed the shunt in between. Seems to work like a charm.