Victron Shunt not reading correctly

[Sean Murry]

Hi MVA. You have probably forgotten more about this stuff than I will ever know, but i find it hard to think the shunt is faulty. The monitor itself I could see might have a glitch, but the shunt itself is a pretty simple thing. Piece of brass with battery connections and a port a cable connects to that goes to the monitor. The monitor is receiving information from the shunt as it should, power in, power out and current voltage. With that information I can calculate the SOC, which is what the monitor is failing to do. I am fine with the way things are as I have enough information to monitor by battery status, just can't take a quick look and read the SOC. I instead look at the voltage, and then can quickly calculate SOC

[Perry Butler]

Originally Posted by Sean Murry

Hi MVA. You have probably forgotten more about this stuff than I will ever know, but i find it hard to think the shunt is faulty. The monitor itself I could see might have a glitch, but the shunt itself is a pretty simple thing. Piece of brass with battery connections and a port a cable connects to that goes to the monitor. The monitor is receiving information from the shunt as it should, power in, power out and current voltage. With that information I can calculate the SOC, which is what the monitor is failing to do. I am fine with the way things are as I have enough information to monitor by battery status, just can't take a quick look and read the SOC. I instead look at the voltage, and then can quickly calculate SOC

If you have entered the parameters correctly and it still reads 100% how can you say "i find it hard to think the shunt is faulty" ? If you've entered the correct parameters, the shunt IS faulty.

I wouldn't trust using voltage to determine SOC with lithium batteries. Lithium batteries have a essentially flat voltage until they get low. That's why a shunt is important. It measures amps in and amps out.

With our 200 ah's of SOK lithium batteries I just look at the amps depleted to see if I'm OK. The lowest we went last winter was -105 ah's, or 47% SOC. Two days of sun and we were at 100%.

How often do you resync your batteries when you are positive they're 100%?

Food for thought,

Perry

[BobG]

Originally Posted by Sean Murry

I instead look at the voltage, and then can quickly calculate SOC

Sean, did you buy your 2019 trailer new from Escape with 4 Battleborn batteries or did you you have to replace a lead acid battery with the lithium batteries? Where are the lithium batteries mounted? Did they fit on the tongue or did you install them inside the trailer?

[Sean Murry]

I bought the 4x100 lithium batteries after I bought the trailer. I have them installed in the storage box at the front of the trailer

[Sean Murry]

I admit I may not be understanding how all this stuff works, but when I look at my monitor on my phone I can see the amps that have been put back into the battery by solar or plug in, and I can see the amps that have been used. So with that information I am assuming the shunt is doing its job sending that information to the monitor. I know that the voltage of lithium is a fairly flat curve, but it is still a curve. I use the attached chart to determine SOC from the voltage readings. (The monitor does give me voltage to two decimal points so seems pretty accurate)

[Sean Murry]

Forgot the attachment

[Sean Murry]

Sorry Perry, forgot to answer your question as to how often I sync. Before heading out on a trip I bring the trailer home from where I store it. I plug it in and leave it overnight until fully charged (14.4V). I used to sync every time I did that, but it made no difference to the SOC readings so now I don't bother to sync

[Sean Murry]

Is not the shunt a simple brass device that transmits a limited amount of information such as amps in/out and voltage to the battery monitor. I don't think the shunt has any computing power. The monitor itself would do the computing based on the various parameters that are set up within the monitor. So if a SOC is constantly reading 100%, would that not be a monitor fault and not a shunt fault?

[Perry Butler]

Originally Posted by Sean Murry

I admit I may not be understanding how all this stuff works, but when I look at my monitor on my phone I can see the amps that have been put back into the battery by solar or plug in, and I can see the amps that have been used. So with that information I am assuming the shunt is doing its job sending that information to the monitor. I know that the voltage of lithium is a fairly flat curve, but it is still a curve. I use the attached chart to determine SOC from the voltage readings. (The monitor does give me voltage to two decimal points so seems pretty accurate)

Either your app is incorrect, the data you input is incorrect, it's wired incorrect, or the shut is incorrect. I'm guessing one of your data inputs is incorrect, but I don't have your phone in front of me. Pick one.

Enjoy,

Perry

[BobG]

Originally Posted by Sean Murry

I use the attached chart to determine SOC from the voltage readings. (The monitor does give me voltage to two decimal points so seems pretty accurate)

Hi Sean, I looked at the chart and it can be used somewhat but remember it is for open circuit voltage and that is not what you are measuring. It is inconvenient to shut everything down and measure Voc. Also, using voltage, especially when the batteries are under load, to determine SOC for lithium batteries is quite inaccurate. The voltage that you are reading isn't the open circuit voltage. It is while the batteries are under some small or large load.

I am impressed that you were able to fit all 4 100Ah batteries in the storage box? When you installed the batteries did you also install a shunt or are you using the battery monitor that came with the trailer?

I don't know how the the standard battery monitor that Escape uses is wired but I suspect that it is a voltage meter that has a little circuit that converts voltage to SOC based on lead acid battery voltage curve. It is not a shunt that computes SOC from current in and out of the batteries. If so, as you start to use your batteries, the voltage starts to drop and it indicates the SOC is dropping as the voltage initially drops. At some point fairly quickly, the solar charge controller will start delivering energy to the batteries at some higher voltage depending on how it is configured. When the voltage jumps back to 14.4 or whatever the bulk charge voltage is set at, your battery monitor will be reading that higher voltage and indicate 100% SOC.

On the other hand, if you added a shunt when you added the batteries, then something is probably wired in a way the shunt doesn't like. Now days it is fairly easy to find people who understand these systems. I am sure just about anyone who has installed a similar system would be happy to look at yours if you want. I suspect that you are happy with what you have and it works for you but something is causing the problem and is probably pretty easy to sort out for someone who has been there and done it.

Different topic, do you use the WFCO that came with the trailer to charge your batteries? I am wondering if you changed the charging portion to be Lithium compatible? It makes a difference but isn't necessary.

Another note: Again not necessary to change but if your solar charge controller (SCC) is an MPPT and is rated for 20 amps output, then it will throttle back the 3 solar panels when they are near maximum output. If your solar charge controller is a 20 amp PWM unit, then I don't know what will happen. You are using around 350 watts of panel and dividing that by 13 volts gives about 27 amps. If your SCC is rated at 30 amps then no problem. A 20 amp rating is not good.

[Perry Butler]

Originally Posted by BobG

Hi Sean, I looked at the chart and it can be used somewhat but remember it is for open circuit voltage and that is not what you are measuring. It is inconvenient to shut everything down and measure Voc. Also, using voltage, especially when the batteries are under load, to determine SOC for lithium batteries is quite inaccurate. The voltage that you are reading isn't the open circuit voltage. It is while the batteries are under some small or large load.

That's why most use amps out and then check SOC against known values, such as stated ah's of battery purchased. In my case, with two 100 ah batteries, if I'm down -50 amps my SOC is 75%. We're on our second Victron BMV-712 in five years and it's never 100% accurate, but easily within 95%, good enough for me.

Enjoy,

Perry

[Sean Murry]

I do realize the voltage readings are not 100% accurate when either under load or getting charged. I can see the voltage readings drop more than expected when something is running, but when it stops the voltage reading comes back up to where one might expect.

I have the Victron smart monitor. It came with a monitor and a shunt. I installed the shunt and the cable that leads from the shunt to the monitor (like a telephone cable, but the wiring is different, the cable came with the. monitor and shunt)

I changed out the WFCO that came with the trailer. At the time we bought the trailer the WFCO board did not have a lithium setting, so I bought the replacement board with the lithium setting, and set the board to the Lithium setting
We only have the one solar panel 190W

As for the batteries, we got the golf cart sized batteries from Battle Born. They had two shapes available (both 100A). With the golf cart sized batteries I had no problem at all fitting 4 in the storage box. With the other shaped battery I could only fit in 3 batteries. I still have room on either side to store other stuff. I also constructed a wood platform to go over the batteries giving me a bit of storage above the batteries.

[BobG]

Originally Posted by Sean Murry

Is not the shunt a simple brass device that transmits a limited amount of information such as amps in/out and voltage to the battery monitor. I don't think the shunt has any computing power.

The shunt that I have transmits all information via Bluetooth to my phone. Maybe you have a shunt that is different and does require the display to do the computing and send info to your phone.

Something is wrong with your system. Either the shunt is bad or it is just a voltage meter or the system has a wiring problem. It would be easy for someone who understands these systems to quickly figure out.

You mentioned that you have the same problem as someone else. I am sure there are lots of people out there who would be more than willing to help that problem go away but it would be easier to do by looking at it.

[Sean Murry]

Interesting you are on your second Victron BMV-712 in 5 years.
Maybe I should just get a new one and see what happens
I appreciate everyone's inputs on this. Great forum for trouble shooting

[Perry Butler]

Originally Posted by BobG

Another note: Again not necessary to change but if your solar charge controller (SCC) is an MPPT and is rated for 20 amps output, then it will throttle back the 3 solar panels when they are near maximum output. If your solar charge controller is a 20 amp PWM unit, then I don't know what will happen. You are using around 350 watts of panel and dividing that by 13 volts gives about 27 amps. If your SCC is rated at 30 amps then no problem. A 20 amp rating is not good.

Another

I had mistakenly purchased a 100/50 for 800 watts at 12v on the roof, but it's only rated for 700 watts. However, by purchasing 24v panels instead it's rated for 1,400 watts, so with 24v panels I'm golden. Too often people overpower their controllers.

For starters I'll only be installing 400 watts for our June trip, but in August I'll be adding a third panel.

Enjoy,

Perry

[Sean Murry]

Maybe my Victron is an older version. The shunt I have is a very basic looking piece of equipment. Simple brass job with two battery connections and a port for a telephone like cable to insert, which goes to the monitor. I have to think the monitor has all the computing power that sends the information via blue tooth to my phone. The shunt itself doesn't look like that it would have that type of power

[Perry Butler]

Originally Posted by Sean Murry

Interesting you are on your second Victron BMV-712 in 5 years.
Maybe I should just get a new one and see what happens
I appreciate everyone's inputs on this. Great forum for trouble shooting

Our 5.0 was sold with 465 watts on the roof, a Victron 100/30 SCC, and the already installed 712. The decision to sell was made in December 2022, a month after I received my pacemaker. I got top dollar for our 5.0 because of all the additions we had made to the camper, and no way was I going to remove the 712 in December with Minnesota's weather. I did remove the board that held the Victron 100/20 SCC and its breakers since the only thing needed to do was remove the SAE port wires and the wires to the battery/712. It was wedged in back so was easy to remove.

Originally Posted by Sean Murry

Maybe my Victron is an older version. The shunt I have is a very basic looking piece of equipment. Simple brass job with two battery connections and a port for a telephone like cable to insert, which goes to the monitor. I have to think the monitor has all the computing power that sends the information via blue tooth to my phone. The shunt itself doesn't look like that it would have that type of power

Is your shunt a Victron BMV-712 with the round screen/controller?

How old is it?

Enjoy,

Perry

[John in Santa Cruz]

Originally Posted by Sean Murry

Is not the shunt a simple brass device that transmits a limited amount of information such as amps in/out and voltage to the battery monitor. I don't think the shunt has any computing power. The monitor itself would do the computing based on the various parameters that are set up within the monitor. So if a SOC is constantly reading 100%, would that not be a monitor fault and not a shunt fault?

the Victron SmartShunt has a small processor, and a bluetooth interface, and both voltage and current monitoring. With current firmware, it stores a week or more of history and the phone app can display that history, for example...
(current[blue] and voltage[orange] over 8 or so hours, when my PD4655 was fully recharging a 412AH Lithium pack that starts at about 40% charge state...)



with 4 batteries in parallel, its important that the negative cable from that combined battery goes to the shunt 'battery negative' terminal and nothing else, and the negative cable from the rest of the trailer INCLUDING SOLAR goes to the shunt's 'system negative'.

[Sean Murry]

Thanks John
I don't have the smart shunt. I have the BMV712 smart monitor with the standard shunt provided by Victron. The smart shunt does the same thing just without a display, where your phone acts as the display. The BMV-712 also has blue tooth so I can see everything on my phone. I do have the negative wiring as you have described

[Sean Murry]

Yes it is the BMV712 with the round monitor. It is about 3.5 years old