Victron shunt drift ?

[Kcdaniels]

My system consists of...

600 ah lithium 12 v
Victron 2000 inverter
3 - Victron 100/50 charge controllers
Victron shunt 500
1430 watts panels on RV roof......

My question is after two or three days the shunt shows about 96% charge showing around 13.8 ?
I have changed the settings on the shunt without much affect..
Here is a screenshot of what I'm talking about. Is there something I'm missing ?

 

[Samsonite801]

What is the Charged voltage set to on the Shunt vs the absorption and float voltages set to on the chargers? I assume of course you have the Ah set right on the Shunt as well?

 

[fat_old_sun]

My question is after two or three days the shunt shows about 96% charge showing around 13.8 ?
I have changed the settings on the shunt without much affect..
Here is a screenshot of what I'm talking about. Is there something I'm missing ?

The resting voltage of a fully charged (100%) 12V LFP battery is 13.8. Your Victron appears to be accurate, showing a net draw of 25Ah from a 600 Ah bank or 96% SoC.

 

[MisterSandals]

the shunt shows about 96% charge showing around 13.8 ?

Guessing the SoC of a battery using voltage, under load (7A), is not very accurate (i do it all the time so i know!)

Counting coulombs is the most accurate method of measuring SoC. There will be drift, mostly when the load or charge is below the threshold of the monitor/shunt. I had a lot of tiny loads and during cloudy days and low light where charging was low. This created a drift became noticeable after a few days. I had to do a sanity check all the time with voltage. After a while i only looked at voltage (you will learn your system if you do this long enough) so i removed the Victron BMV.

But this:

We're gonna need some pics of this Loveshack!

 

[Kcdaniels]

What is the Charged voltage set to on the Shunt vs the apsorbtion and float voltages set to on the chargers? I assume of course you have the Ah set right on the Shunt as well?

 

[Kcdaniels]

Guessing the SoC of a battery using voltage, under load (7A), is not very accurate (i do it all the time so i know!)

Counting coulombs is the most accurate method of measuring SoC. There will be drift, mostly when the load or charge is below the threshold of the monitor/shunt. I had a lot of tiny loads and during cloudy days and low light where charging was low. This created a drift became noticeable after a few days. I had to do a sanity check all the time with voltage. After a while i only looked at voltage (you will learn your system if you do this long enough) so i removed the Victron BMV.

But this:
View attachment 170043
We're gonna need some pics of this Loveshack!

? its not what you think lol.....back in 2013 my wife and I bought and remodel a small cottage and put a Lot of Love into it . we came up with "LoveShack. So when we bought the RV we decided to call it " loves Shack 2.0 ?

 

[Kcdaniels]

What is the Charged voltage set to on the Shunt vs the apsorbtion and float voltages set to on the chargers? I assume of course you have the Ah set right on the Shunt as well?

 

[RCinFLA]

Victron monitor have charge and discharge 'fudge' factor settings that need to be setup to match your particular battery.

They are usually defaulted for lead-acid batteries. LFP charge and discharge is much more efficient than lead-acid batteries. Use 1.01 for discharge Peukert value and 0.99 for charge efficiency. Lead-acid would be like 1.25 and 0.85, respectively.

The Peukert exponent pertains to derating of battery discharge capacity based on level of discharge current relative to their AH size. The heavier the load current, the more it fudges up the actual discharge current measured, eating up more of battery capacity remaining in battery.

There is also a charge efficiency factor. It sucks for lead-acid, particularly for upper 15% of capacity recharging. This is where you hear the bubbling in lead-acid battery which is the result of breaking up water in electrolyte to hydrogen and oxygen gas. This eats up charging power to power the electrolysis of water that does not contribute to actual battery recharging,.

For Columb counter, it multiplies the respective charge and discharge fudge factor before summing the cumulative amp-seconds for charge and discharge currents.

There will always be come errors in the current measurements, particularly for low currents. You need to do a full charge periodically to reset the battery monitor's Columb counter to 100% SoC to clear out cumulated errors over time. Victron has conditions of voltage and charge current taper off for declaring a full battery, that trips the reset of Columb counter to 100% SoC.

Victron monitor only works on total battery stack array voltage, so for LFP batteries you have to keep up with cell balancing or 'full state' may be falsely declared by battery monitor, or never declared due to not meeting the Victron full battery criterion.

A good couple hour absorb level charging performs two functions. Since BMS balancing only typically occurs when a cell gets above 3.4v you need an absorb level for some time to accomplish balancing. Second, this also resets the Victron monitor to 100% state of charge.

To keep up with cell balancing you should do this at least about every couple of months, but actual time period depends on condition of batteries and how hard you run them from a percent AH C rate of peak discharge current and spread of min to max SoC cycling.

 

[chrisski]

Try adjusting the charge efficiency factor.

For my Victron BMV712, I was getting a drift where it started at 100%, then next day would read 99%, next day 98%, etc., drifting downwards about 1% per day.

I’d reset it to 100% SOC by “synchronize to 100%” when the battery was charged, but the drift would continue.

Adjusting the “charge efficiency factor” fixed it.

EDIT:
Last thing you can do is set the “charged voltage” to .1 volt less than your charger absorption voltage.

 

[Kcdaniels]

Victron monitor have charge and discharge 'fudge' factor settings that need to be setup to match your particular battery.

They are usually defaulted for lead-acid batteries. LFP charge and discharge is much more efficient than lead-acid batteries. Use 1.01 for discharge Peukert value and 0.99 for charge efficiency. Lead-acid would be like 1.25 and 0.85, respectively.

The Peukert exponent pertains to derating of battery discharge capacity based on level of discharge current relative to their AH size. The heavier the load current, the more it fudges up the actual discharge current measured, eating up more of battery capacity remaining in battery.

There is also a charge efficiency factor. It sucks for lead-acid, particularly for upper 15% of capacity recharging.

For Columb counter, it multiplies the respective charge and discharge fudge factor before summing the cumulative amp-seconds for charge and discharge currents.

There will always be come errors in the current measurements, particularly for low currents. You need to do a full charge periodically to reset the battery monitor's Columb counter to 100% SoC to clear out cumulated errors over time. Victron has conditions of voltage and charge current taper off for declaring a full battery, that trips the reset of Columb counter to 100% SoC.

 

[Kcdaniels]

"

They are usually defaulted for lead-acid batteries. LFP charge and discharge is much more efficient than lead-acid batteries. Use 1.01 for discharge Peukert value and 0.99 for charge efficiency.

Thank you.....those are the settings I'm using?

 

[chrisski]

Here is my BMV 712 settings that work for me:

I don’t have the SCC settings handy.

 

[Kcdaniels]

Here is my BMV 712 settings that work for me:
View attachment 170160
I don’t have the SCC settings handy.

Thank you....ill try some of your settings and see if it helps

 

[chrisski]

Thank you....ill try some of your settings and see if it helps

I had the shunt for both lead acid batteries and then upgraded to lithium.

I can’t remember specifically what settings fixed my issues, but both sets of batteries took a bit of work to tweak.

 

[Kcdaniels]

I had the shunt for both lead acid batteries and then upgraded to lithium.

I can’t remember specifically what settings fixed my issues, but both sets of batteries took a bit of work to tweak.

Yeah I've tweaked the settings but so far didn't do much...ill report back with the new settings and see if it get closer

 

[cinergi]

if your SCC/charger configuration isn't set to charge the battery above 14.2 volts (the 'charged' voltage in your shunt config) and hold that sufficiently long for the shunt to consider the battery charged, it won't automatically re-sync to 100%. That's why the charged voltage and the 'tail current' settings are so important.

 

[Kcdaniels]

if your SCC/charger configuration isn't set to charge the battery above 14.2 volts (the 'charged' voltage in your shunt config) and hold that sufficiently long for the shunt to consider the battery charged, it won't automatically re-sync to 100%. That's why the charged voltage and the 'tail current' settings are so important.

So if I up my scc to say 14.4 would that help ?

 

[cinergi]

So if I up my scc to say 14.4 would that help ?

I don't think I've seen your SCC config here, so I don't know what their bulk/absorb voltage settings are. Like chrisski mentioned, the shunt needs to be set just below (0.1v) the absorb voltage of the SCC so that the shunt sees that the battery has reached that voltage with less than 4% of your Ah current (600 * .04 = 24 amps) flowing for at least 3 minutes... at that point, it will recalibrate itself to 100% SoC.

 

[Kcdaniels]

I don't think I've seen your SCC config here, so I don't know what their bulk/absorb voltage settings are. Like chrisski mentioned, the shunt needs to be set just below (0.1v) the absorb voltage of the SCC so that the shunt sees that the battery has reached that voltage with less than 4% of your Ah current (600 * .04 = 24 amps) flowing for at least 3 minutes... at that point, it will recalibrate itself to 100% SoC.

Here is a shot on one of my scc. The other two are same settings.

 

[cinergi]

yep -- that's why. SCC Absorb is 14.02 .. less than the shunt's 14.2 ... so I'd set the shunt to 13.9