I’m new here and have a specific question / problem that I haven’t been able to resolve.
My batteries are charged to 46%, the voltage at the batteries is 52.8 V, and yet the system switches to float charging even though there is plenty of sunshine and I’m getting almost 1 kW of output. The SoC is set to 15% in ESS, but it never gets anywhere near that low. DVCC is enabled, but there is no active limitation. In the Multis, I have set 50 V as the float voltage under the Charger tab.
Why doesn’t the system discharge down to an SoC of 15%, instead of switching to float charging?
I hope you have a lovely Sunday.
Best regards, Sascha
My system consists of:
3 x VE MultiPlus-II 48/5000/70, one for each phase
Cerbo GX MK2 as the control unit
SmartSolar MPPT 250/70-MC4 VE.CAN
VE.Bus BMS V2
2 x VE LiFePO4 batteries 25.6 V/200 Ah
SmartShunt 500 A/50 mV
8 solar panels rated at 460 Wp, in 2 strings of 4 panels each — one string connected to the MPPT via MC4
Hello Sascha … have a lovely Sunday, and welcome to the forum
Have a look at your setting in the ESS … “Systain voltage” … this voltage is effectively the very last voltage limit for the Multi … below this voltage, the Multi starts charging the battery.
You could also check whether your battery monitor is set to the shunt … and then compare the voltage readings you have in the system. There may be a discrepancy due to faulty screw or terminal connections.
Many thanks. The sustain voltage in the ESS is set to 54 V by the Victron batteries — but temporarily changing it to 50 V didn’t help either. The shunt is configured as the battery monitor, and all the screws, terminals, etc. are rock-solid.
I completely powered down the system, rebooted it and manually set the shunt to the 50% state of charge that the batteries had at the time. That seems to have helped — at least for the moment. The Multis are drawing power from the batteries again and are no longer charging them.
I’m curious to see whether this happens more often now. The phenomenon has only started occurring recently — actually, only since updating the Cerbo to v3.79 … hmm, we’ll see whether it comes back.
… is your ESS mode set to “Optimised without Battery Life”?
Since you aren’t getting any data from a BMS, but from the shunt, you definitely need to “teach” it … a “zero current” calibration should be carried out, and then you’ll have to experiment a bit with the Peukert factor and charge efficiency until it is reasonably accurate. The SOC is calculated by the shunt based on these parameters and should eventually be accurate as well.
Do the LiFePO₄ batteries have their own BMS?
By the way … are you going to add more PV to the roof for the 3 x 5000 Multis?
OGPS
(Ed @ Off-Grid Power Systems - offgridps.com)
5
Please share your SmartShunt settings, ESS settings on the Cerbo, and ESS settings in the assistant (on the primary inverter).
I only have the VE.Bus BMS V2, which the two batteries are connected to—but you can also communicate with the batteries via Bluetooth, and they then report the cell voltage, etc.
No, unfortunately there’s no room—the panels are on the garage. I know, one MP2 would have been more than enough; the other two are for complete backup power on all three phases, in case the power cut lasts longer again.
Sooo … now I know more too. When the battery voltage dropped below 50 V, it went into sustain mode at a battery charge level of 29%.
I then told the ESS Assistant in the MultiPlus units to lower the sustain value to 48 V and resume discharging once the voltage was 1.2 V above that value—but so far, without success.
Here are some screenshots and the configuration of the MultiPlus units.
As I said … a bold setup with three 5,000 Multi units and only 200 Ah and relatively little PV … well, well below Victron’s recommendation … I can certainly understand your basic idea of providing three-phase backup in the event of a power cut … but not with so little battery capacity and PV … a single-phase system with a changeover switch from one to three phases would make more sense here. You can set all the cut-off voltages to 47 V … the old stepped values were from the lead-acid era and were based on different load levels. With LiFePO₄, not that much changes. Have you reduced the output of the Multi units somehow, or can all three draw full power from the small battery?
Yep — 16A on the AC-in side. Unfortunately, I only have a 5x2.5mm2 cable from the house distribution board to the garage (apartment block), and I can’t add any 6mm2 or 10mm2 cables. I’m part of a condominium owners’ association, so I’m “structurally inflexible and restricted”.
Since there are no loads in the flat that could cause problems for the batteries, I only have the usual 200A fuses between the Multis and the batteries.
But I think the new values in the ESS Assistant of the Multis were the deciding factor. I’ll let you know tomorrow how it turned out, once the batteries have either discharged to 15% SoC this evening or haven’t
Sooo — problem found. The battery charge levels were showing significantly too high. In reality, the batteries were virtually empty, but the shunt was still showing over 30%. The reason: the shunt was set by default to 56V as the voltage at which the batteries are considered fully charged — so it reached the 100% mark far too early. This happened several times last Saturday in good weather, with plenty of consumption in the house. In the end, the batteries had almost 25% less charge than the shunt “knew” about, meaning the ESS had no chance of getting down to 15% SoC. The voltage simply wasn’t sufficient, and the Multis charged the batteries from the grid — the aforementioned, and actually unwanted, float charge!
When the batteries are properly topped up, they reach around 56.9V–57.1V. I’ve now entered this in the shunt as well (56.8V), and the batteries’ state of charge now matches the charge-level readings calculated by the shunt.
Steffen, you put me on the right track — thank you
