I have an 800 amp hour LiTime 12v battery bank monitored by a SmartShunt 500. I use two SmartSolar MPPT controllers to charge the batteries and a Multiplus II to use the power. All the pieces are plugged into a Cerbo GX with DVCC enabled.
I have the SmartShunt set to charged voltage of 14.2 and tail current of 4% and a charge detection time of 5 minutes. The MPPTs are set to absorption voltage of 14.4.
The problem is the system stops charging and enters float but without indicating 100% State of Charge. It typically stalls out at 97 or 98% and there is still plenty of solar power available.
This graph shows the 14.2 voltage and tail current requirements were exceeded for over 20 minutes and yet the state of charge maxed out at 96.8%.
The SOC is only a monitor and nothing to do with the start of float. The MPPT decides when to go to float based on voltage plus absorption time or tail current. You have mismatched settings between SmartShunt and MPPT, you should always have the settings so the SmartShunt goes to 100% before MPPT goes to float.
Post screenshots of your MPPT settings including advanced and SmartShunt.
As for why it did not go to 100% if your data is correct, however, these history plots can have data averaged in them smoothing out actual values.
Both MPPTs say they’re under “External Control”, so if the MPPTs decide when to switch to Float, External Control isn’t an accurate description.
I’ve kept the SmartShunt “Charged Voltage” set to 14.2 volts.
The jump in voltage is what I expect when the batteries become fully charged. The SmartShunt is the device that is supplying the voltage reading to all the other devices and DVCC does have Shared Voltage Sense enabled.
I’ve tried setting the MPPTs absorption voltage to either 14.2 or 14.4 and it doesn’t seem to make a difference. I always set both MPPTs to the same values:
I read the documentation, and it says if the voltage is above the charge detection level and the tail current is below the percentage specified, and the length of time with both those conditions has passed, the SmartShunt should “synchronize” to 100%…and it isn’t.
The other thing that’s got me concerned is I can’t find how long LiTime batteries need to remain at whatever voltage they need in order to balance their cells. The documentation I’ve found only stipulates charging them between 14.2 and 14.6 volts. Obviously not a Victron issue, but if it turns out I need to keep the batteries at 14.2 for longer, then I do need a better understanding of the “External Control”.
The charged voltage should be 0.2v LOWER then the absorb voltage in the charger.
The tailcurrent should be 1, not 4 %.
In the charger you should go to expert mode and individual settings, set absorbtion time to fixed and at least 4 hours to give the batteries time for equalization
External control is normally where you have a BMS connected to the Cerbo and the BMS is controlling the chargers directly. Your MPPT setting is set to 14.2V not 14.4V as you state, BUT the SmartShunt is showing 14.4V so the batteries must have taken control. I did not know LiTime had batteries that could be connected to the Cerbo so confirm this is the case. If your batteries are connected to the Cerbo and managing the charging them making changes in the MPPT settings as in the previous post will make no difference because they are getting their voltage instructions from elsewhere.
In terms of the SmartShunt, this is not triggering the synchronisation for whatever reason despite showing currents lower than 25% and voltages above 14,2V. This could be the voltage / current fluctuating not shown on your history plot.
As a test, I suggest going in the opposite direction to the previous posters suggestion and make it easier for the SmartShunt to synchronise, it may synchronise a little early but you will at least confirm that the units is capable of this. Try 14.0V charged voltage, 6% tail current (48A) and reduce the charged detection time to 1 minute. These are too easy to synchronise but at least they will check that the units is working because these conditions should be met just as soon as you reach the start of absorption.
As long as the max charge rate of the battery pack is larger then the combined power of the chargers external control is not needed and only makes things complicated and opaque.
I have set the MPPTs to both 14.2 and 14.4 and it makes no difference.
The LiTime batteries do not have a BMS that can control a charging device, they are like Battle Born batteries in that the BMS just serves to protect the battery from damage.
I’m now starting to wonder if the Multiplus is the “External Control”. I just pulled up the VE Config file and confirmed the absorption voltage is 14.4 there as well. But I also just noticed on the General tab of VE Config the “Enable Battery Monitor” box is checked and within that section, the “State of Charge When Bulk Finished” is set to 95%. I also noticed in this section the “Charge Efficiency” is set to 0.95 and I believe for Li-ion it should be 0.99. I just read the description (again) of the Multiplus settings and don’t feel that I should change any of those.
I like the suggestion of exaggerated settings for detecting synchronization and will try that: 14.0 volts charged, 6% tail current, and one minute. Unfortunately, today is forecast to be quite cloudy and I doubt there will be enough sun to reach even these values.
I agree with the settings suggested. But those would make synchronization less likely to happen. My fixed absorption time is currently set to two hours…and the system isn’t yet honoring that smaller number.
I’m working with those figures fo at least 2 years, my system synchronizes everey day, as far as the sun shines…
best seen in a chart showing charging power and used amperes, the power should come down when the absorbtion voltage is reached, and the used amperes slowly go down to 1…when synchronized it will reach 0
Well this is very odd, I have no idea how you have got external control if your BMS is not controlling, I do not know what will be controlling. Are you using ESS or DESS.
What is set as the battery monitor in the Cerbo GX. I ask this because the SmartShunt may be synchronising but you are displaying the inverter SOC which is less accurate.
Turn off the battery monitor in the inverter if you are not using any functions in the inverter based on SOC. In the Cerbo GX, settings -system setup - batteries - battery monitor make sure the SmartShunt is selected. Then in settings -system setup - charge control do you have anything under controlling BMS.
Additionally, are you trying to run a VE Smart Network to synchronise the 2 MPPTs. If so disable this, Smart Network and VE Direct cabling do not always play nicely together.
First, thanks for working with me on this. Answering your questions, the SmartShunt is shown as the source for displaying the SoC. And I am using the ESS Assistant, so I don’t believe I can disable the battery monitor function in the Multiplus’ VE Config. None of the devices are participating in a Smart Network – I had that problem before and disabled all of it.
Today’s forecast has plenty of sunshine so I expect to learn if setting the Synchronize parameters to lower values has worked or not.
Lets see how you go, but if you had said at the start that you had ESS it would have saved some head scratching around the external control. Still does not answer why the SmartShunt is not synchronising though, but explains why the voltages do not follow the MPPTs exactly.
Reducing the Charged Voltage to 14.0, tail current to 6%, and detection time to one minute worked! The SmartShunt correctly jumped from 95.5% straight to 100% SoC this afternoon.
So that removed any ambiguity about the process, leaving only the values. My first preference is to get the voltage back to 14.2 so I’ve now made that one change. I’ll see what that does before moving next to the tail current.
Definitely too early, but you now have something to work from. I just wonder if your 5 minute detection time was too long if the external control caused some cycling outside of the detection limit so you never got a full 5 minutes meeting the voltage and tail current. I would leave time to the last change.
