SOC matters if you are running an ESS, which is what this topic is about, choosing to use the worst method to calculate SOC will ruin an ESS.
If you don’t have an ESS and don’t care about SOC, then go wild, but for most domestic use cases it is a critical variable for efficient operation and with external chargers and multiple inverters, not using a shunt remains a terrible idea, stated numerous times on many topics, and as per Victron’s guidance.
For small 12V and such systems, that is a different application, but on larger systems with more moving parts, do not rely on the internal metering.
Trust me it’s not a problem. If you have a specific DC load or charger that is not able to be measured with victron use a shunt. I have grid-tied solar and MPPT just not enough to show how well it works on a big system. This is a 450/100 not at 100% with grid-tied inverter charging these curves beat anything I could get with a shunt. My batteries do have their own shunts that I can check but they a within 10-30% of what the system estimates. I take this 48V system 36kwh to 0% with amazing precision and most batteries at 2.6V min just about to disable discharge. Mind-blowing never saw that with a shunt.
Edit, this day last was the first full charge. Just understand, it’s monsoon season and lots of clouds and rain. 8500kw of solar on a 450/100. East and west fasing.
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I found one, which is a 0% to full charge curve. The 70% to 100% is a little steep but with 2hr of absorption, the appropriate current is absorbed. I never had SOC curves this good with a shunt it would be 100% way too early.
I found another deep discharge and charge from 8%. After 15 days of not hitting 100% with charge and discharge based on ESS and MPPT and critical loads.
Hi Jeroen,
I finished my system recently and i’m having this same issue. Discharging the batteries (very short) when there is access PV exported to the grid. I have an SE PV inverter connected to the AC-out.
In my opinion this shouldn’t occur not matter what the SOC is. when there is access PV exported tot the grid the battery should not be discharged.
Did you ever manage to solve this, or narrow it down?
I am also experiencing this strange behavior.
The battery is discharged even though there would be way enough pv power available. Then it recharges the battery from solar.
There is something seriously wrong in the control algorithm. It takes the wrong voltage level. The cut off voltage of the battery should be below the maximum voltage on the DC bus to ensure power flow from the MPPT directly to the inverter. It seems it is switched … It can’t go higher than the battery voltage and then it discharges it again.
I think the problem is not happening as pronounced with the grid feed in limit set to below 200W. Because this minimal power does not generate as big of a voltage drop on the bus, so the controller does not freak out.
Upon further testing I also found that it can do way higher grid feed ins than 200W without issues if the value is slowly ramped up. Like 100W more every 1 minute. This way, the controller has enough time to settle and does not get into this oscillating behavior.
So anyway, Victron needs to fix this as it is clearly a control algorithm issue.
What I see here is only a very small load of -16W and -38W and that appears to correspond to DC Loads (from the Multiplus II).
I had to switch on the setting: “Has DC system” under Settings → System setup in order to get to see it (GUI V2).
Might require a voltage sense cable setup. Anyone here using that already?
Update: this is no longer an issue for me.
My batteries are fully charged by solar. As usual. In a Node-RED flow I check the SOC and consumed amp hours, and when the latter is zero (0) then I set the max charge current setting for DVCC to zero (0). Just to be sure that it won’t be hammering the charged up batteries.
It may keep charging for a little while. With ampel wattage. Until it hits the set pack voltage. Which is 55.2V or 3.45V per cell in my case. Why? That’s because the SmartShunt and JK-BMS are not showing 100% identical values. But after a while, it starts to idle and it does so for hours already. You get it into the Idle state by disabling the maximum inverter power. I set that setting also to zero (0).
Next. I check the power draw , in the same flow, and when that becomes a positive value, meaning that the solar isn’t producing anything anymore. Or not enough. Then I re-enable the maximum inverter power again by writing a -1 to the max inverter power setting. Basically disabling it and the setting will be grayed out again.
Hope this helps anyone here.