I hope someone can help me with a problem I’m facing.
My setup is as follows:
MultiplusII 48/10000/140 running the latest firmware 556
16S LiFePO4 battery, 304Ah, with a Pace 200A BMS
Cerbo GX
SmartShunt 300A
The system is configured for ESS with self-consumption and feed-in. DVCC is not enabled.
The installation worked flawlessly until three weeks ago. Since then, I’ve been receiving “low battery” alarms on the Cerbo and the VRM portal. The battery BMS reports a “total voltage fault” which put the battery in the idle state, causing the “low battery” error, I think. Everything appears to be fine within the BMS; there is no cell imbalance, nor any sudden voltage spikes or drops between the cells. Despite the “total voltage fault” message, there are no alarm or error messages stored in the BMS memory.
I have re-configured the settings and ESS several times, which I also had to do after the MultiPlus firmware update. The ESS is set to self-consumption with priority for battery and loads, and surplus power is fed back to the grid. Battery, Optimized without Batterylife.
The current situation is this:
If I turn the battery off for a while and switch it back on in the evening when there’s low solar production, the system works fine until the next day, but with a blinking “low battery” warning. The problems start in the morning: the batteries charge up to 50%, then enter a one-hour absorption phase followed by float. The battery then goes into an idle state. The SmartShunt also indicates an idle state, but without a “low battery” fault or warning. This situation persists all day until late afternoon, when the system switches to sustain mode (and the battery BMS again shows the “total voltage fault”), and the “low battery” alarms start immediately. This has been happening for several days.
I’ve searched many topics and used AI to look for solutions, but haven’t found an answer yet. I hope someone here can provide a solution; it would be greatly appreciated.
I guess theres communication between the BMS and Cerbo? So i guess the battery voltage that is reported in VRM is coming from the BMS directly, at 52.83V. The smartShunt however reports 53.28V. Since theres no current flowing, that voltage difference to me is way too big. I guess you have a bad/loos connection somewhere, some contact resistance or similar issue. If theres no current flowing, then the voltages should be nearly equal. Also double check them with a multimeter
Hi chrigu,
Thanks for your reply, hope you can help me like the last time!!
I checked all the connections between battery/Shunt/circuit breaker/Multiplus. All bolts are tightened with the correct torque.
I can give you a link to my OneDrive to a file with all sceenshots from the BMS and VRM portal during the whole day. I think that the shots are saying more than words it’s like a picture story . For the moment I stopped the whole system because I’am like a zombie behind the screen. I also wait for an answer from my battery supplier. If you are interested for the link let me know (also the way how to send it.
Hi Mac, Thanks for your suggestion.I know that thread very wel. It was me who posted it. The solution at that time was the shut down for some time. After restarting the MP and battery all worked fine (6 months )until now. And now is that solution not working :-((.
Hi chrigu,
Yes the voltage comes directly from the BMS. Smartshunt is new, the cables are well connected. The screenshot from the VRM is when the battery in the idle state. In that situation the smartshunt shows voltages from 41 volt to 58 or even 60 volt. Why? I don’t know. With the battery completely disconnected from the system (multiplus, cerbo and smartshunt) and I mesure the voltage at the direct +/- of the battery output of the Multiplus it gives continuous different measurements from 41 volt to 60 volts and all voltages in between. That’s what you see on the screenshot. The smartshunt give his own voltages
Because the BMS has disconnected the battery. Its the same situation as you describe just after. The MP is trying to charge the battery, but its not there, so it bounces off of the absorption voltage limit, only to then seeing the voltage fall rapidly, so it goes to charging again
But why is the battery in the first place charged to 50% and then start the absorption.
I configured that the absorption stage begins at 56v ( charged100%) and the float to 54v.
I dont know where those 50% come from, but 56V is 3.5V per cell, so i guess one of them is too high on voltage and the balancing cant correct it fast enough, so the BMS shuts the pack down. Do those 56V get reached while its charging? How do the cell voltages look like? Maybe try charging to 54.4V or 3.4V per cell as e test, see how the balancing holds up
Pack voltage is the sum of all cells. Where the ,“independent voltage” comes from, I have no idea. In the last screenshot, the BMS shows 53.84V and the Smartshunt 53.57V. A difference of 0,27v, doesn’t seem like a huge difference to me.
I show you the moment (SOC 50%) when the bms shows the “total voltage fault” and falls into the idle state, at the same time the Smartshunt shows 55,96v. So the MP says: absorption time. But at the same time the Smartshunt starts to show different voltages, see the video I uploaded. Among the different voltages also the lower voltages
what triggers the start of the “low battery” alarm. The MP is staying in the absorption state for one hour and after the absorption into the float state. After some hours the float is changing into the sustain state. Screenshot_20250815-082227|690x318
