I purchased a US3000C and hooked it up to my existing setup - Axpert MKS-4K + US2000 used without solar as a battery backup.
Everything seems to be working fine, I bumped my charging from the 20A set for the US2000 to 40A for US2000 + US3000C. I am now getting an ‘Abnormal’ status on one of the cells in the new battery.
Below is the output of the ‘soh’ command, should this be something to be concerned about or would it rectify itself over time? I would’ve thought the BMS would take care of balancing the internal cells if they are out of sync.
Battery Voltage SOHCount SOHStatus
0 3588 0 Normal
1 3589 0 Normal
2 3588 0 Normal
3 3339 1 Abnormal
4 3589 0 Normal
5 3595 0 Normal
6 3585 0 Normal
7 3592 0 Normal
8 3590 0 Normal
9 3593 0 Normal
10 3592 0 Normal
11 3586 0 Normal
12 3588 0 Normal
13 3590 0 Normal
14 3591 0 Normal
I have drained the battery to 70% 5 times and let it charge back up.
That one cell only ever goes up to 3.334V and the battery only reports 90% SOC.
I think I’m going to attempt to take it back for an exchange. I might be wrong, but IMO, a brand new battery shouldn’t have this issue.
A side note, but don’t you think that 3.6V per cell is a little high? My Pylontech bank reports 100% SoC on a 3.5V or so per cell. My bank never goes above 52.8V (reports 100% SoC at 52.4V).
Technically, the low voltage cell is the best of the bunch, right? A bad cell shoots out first.
What happens when you discharge? Do they get balanced then?
Regarding the charging current: I’m assuming the 20 - 40A is a DC current, and therefore roughly at 52V, and not AC @ 230V?
My existing US2000 is happy with above settings with the DC charge rate set to 20A, this is the only setting I changed, so charge voltage should still be 53.2V, which is within spec for the battery.
I disconnected the US2000 and dropped charge rate to 20A. Attached a 3000w load to drop it to 60% then charge it back up. It gets to the point where it gets into this ‘Abnormal’ state on cell 3, and it stops charging.
My biggest concern is after dropping it to 60% 5 times, I still can’t get the whole pack to report above 92%.
I took the battery back, they’re keeping it there to test, but the technician said it sounds like a faulty cell, so they will probably replace the entire unit due to a manufacturing defect.
They’ll hook it up to their test system and check the stats for the battery and get back to me.
It is normal for a new battery to be a little out of balance. Irritating, but normal.
I know you sent the battery back, but herewith some advice anyway.
With such a battery it is important to lower your charge voltage to accommodate the high cell until the battery has had time to deal with the imbalance. In this case I would suggest lowering the charge voltage to 52.5V.
The trick to balancing the battery a little quicker is to charge at up to the point where the first cell exceeds 3.4V. Then slow the charge current way down, to as low as you can get it, and trickle it the rest of the way, so that the balancer has the maximum amount of time to do some balancing. When the highest cell hits 3.55V, discharge the battery again until all cells are below 3.4V, then repeat. This will have to be repeated a number of times, and the Axpert is not the best rig to do it with (with a Multiplus you can do things like running ESS and setting the grid setpoint to 60W, no loads on the output, so it charges really slowly).
Otherwise, just run the battery through several cycles and watch it daily.
Even for normal operation, I would not run at 53.2V. This battery wants 3.485V per cell, or thereabouts, that is where it is happiest. That’s around 52.4V. That’s what I’d go for.
Good to know, thanks @plonkster, with the heavy load shedding that is upon us, I don’t have the time to mess around with an unbalanced battery as I have critical loads that I need to keep up, so I will let the supplier sort that out for me.
The issue wasn’t a high cell, it was a low cell that wouldn’t go higher than 3.3V, other than that, all the other cells were balanced.
In the meantime, I have purchased an additional US3000C which is currently running fine on 53.2V and it’s BMS is reporting as ‘Normal’. I have dropped my charge voltage to 52.4V as you recommended and monitor the system in the coming days.
My understanding is that the problem isn’t the low cell. That cell is more than happy to still accept charge. The problem is the high cell, the cell that first blocks charge.
I think that is the reason why Izak said you want to accommodate the “high cell” and not charge the bank up too quickly, because then the high cell will just jump out every time and block charge for the low cell. At least, this is my understanding.
Yeah, I tried that a few times and learned there is a teeny T&C on dropping the volts.
Dropping the overall bank volts assumes all the cells are more or less in sync. If they are not, the total bank voltage is still below the setting set, do nothing for the cell/cells shooting out.
Dropping the charge amps on the other hand works every time to give the balancer time to catch up, irrespective of the volts, which you can then drop as an additional setting if one wants.
Titibit: To fix that issue on a DIY bank, as it does happen under frequent heavy loads or on a new bank, I connect a charger to that one cell for a few minutes at low SOC to boost it slightly. At high SOC it then tends to be a wee bit higher, the balancer sorts that over time.
Once the cells are settled over a period of time, the problem goes away UNLESS the cell is faulty.
LFP cells have a very flat charge curve. They get stuck at 3.3V for a really long time before they move up. Even a slightly low cell will appear to be grossly under voltage. Also, at 52.4V, the battery is basically 99% full, regardless of what it’s own estimate says. Simply running it at the lower voltage should not impact load shedding that much.
Forgive my ignorance, I am still learning about all this stuff, but I thought that Victron and Pylontech is a match made in heaven, i.e. the battery communicates with the inverter to set everything automatically such as charge current, voltage etc. Is this not so? Or does one only “fiddle” when there is something wrong?
And are the high battery voltage alarms (new battery) anything to worry about?
I don’t mean to hijack the thread, but it seems related to the OP.
It is a small backup system for a server consisting of a 48/1200/13-16 Multi, Cerbo GX and a Pylontech US3000C. The office park does not have generator power between 18:30-06:00.
I installed the system myself. I did not do much configuration since I understood it to be pretty much plug-n-play. Most of the setup was to update the firmware of the inverter and cerbo and to connect it to the VRM portal.
The battery alarm only happens after a cold start and only once. The system has not been running continuously for long. It has been on and off as I wrestled everything into the server rack. It should stay on now that it is installed at the office.
I suspected something like this. Used as a battery backup, you would need to configure the multi not to overcharge the battery. May I please contact you privately and assist you with configuration?
It makes sense that the Cerbo needs to boot and get comms going with the battery and inverter so having the proper stand-alone inverter settings gives me peace of mind.
It is comforting to know that there are knowledgeable people around who are willing to help!!
