To be honest, I’m a bit overwhelmed by all the settings…my question is, which setting do I have to change so that the voltage doesn’t go down to the 47 V and instead keeps the battery at the sustain voltage (set to 50 V)?
Use VRM to find out how much current is being drawn from the batteries at those points in time. You may have a really large load and it is causing voltage drop.
EDIT: I see 3.35A , that’s insignificant. Please show whole plot from VRM with axis labels.
Also show SoC from the SmartShunt,
I would re-inspect the tightness of the battery cables and lugs on busbars (if any).
You should set the minimum SoC in the ESS menu to something like 20% to allow the multiplus to recharge the battery from grid if it gets too low (assuming you have grid).
Just saw that you edited your message while I wrote my answer:
The SoC minimum value setting in the ESS is already at 20%…am I right that this is the problem? That my SmartShunt was not calibrated so far and at the time when the alarm occured, it reported 44,3% and therefore the MultiPlus didn’t stop discharging?
At 50V, batteries should be way <20% SoC, so the smartshunt is wrong.
Since it is the battery monitor, the Cerbo uses its information to determine when to recharge.
I suggest you do a full recharge of the batteries to synchronize the smartshunt to 100%.
Then it will work correctly. You can do this by changing ESS mode to “Keep Batteries Charged” until you hit full voltage (anything over 55V). Then switch the mode back to Optimized. I’m assuming you have grid.
The system is under external control, you have a bms connected.
The real question now is how is the bms
programmed?
At keep batteries charged the ve bus raises its charge voltage 0.4v above the absorption set. Your reaches (almost) 0.1v lower than that, so you do have voltage drop over your cable even under no charge amps or load.
I just had a look at the manual again where I got the charged voltage of 52,8 V from and noticed that I overlooked that this is only for lead batteries, o dear
I googled and found 56V (= 3,5 V per cell) as a recommendation. Is that correct?
@lxonline Thanks for putting me in this direction. I was always wondering what the “External control” means because I thought that it only has to do something with the ESS mode that’s also named like this.
My BMS is Daly and I use the SerialBattery driver to connect it.
I have DVCC enabled and I think I understand this a bit more now: in the SerialBattery parameters page, I can see the following:
So the maximum voltage is limited to the 55,2 V by SerialBattery. This is 3,47 V per cell, and this is also the setting where SerialBattery considers 100% charge.
Is this a meaningful value for LiFePo? What do you have as 100%?
And both SmartShunt 100% voltage and the SerialBattery should be the same, am I right?
In the data sheet of my Eve LF280K cells there was no absorption time specified. I took the 3.45 V for the start and to be on the safe side.
I set this for the MultiPlus and SerialBattery (MAX_CELL_VOLTAGE parameter) and 3.37 V as float voltage (FLOAT_CELL_VOLTAGE in SerialBattery). For the SmartShunt I set 55V (= 55.2V absorption voltage - 0.2V).
After the full charge yesterday, I didn’t have the low voltage issue today - the discharge stopped at 20% SoC / 52,46 V (=3,27 V per cell). I will observe this in the next few days. Tomorrow will be quite sunny, so I hope that the battery can be fully charged.
For completeness, here is the SoC and voltage graph of the last 24 hours for your reference:
- the discharge stopped at 20% SoC / 52,46 V (=3,27 V per cell). I will observe this in the next few days. Tomorrow will be quite sunny, so I hope that the battery can be fully charged.