SK48v100 batteries shutting down

[defed]

I have a pair of SK48v100 batteries, in parallel, that I purchased in June. So far, they have been working fine. Today when I realized I didn't have any internet I thought my inverter had shut down. When I checked on the system, everything was powered off, including the batteries. I reset them w/ the reset button and they came back online. I checked the voltage, the BMS screen said 49.9v (3.1v per cell) and I verified it w/ my meter. After a couple of minutes, they shut down again. The BMS screen does not say it shuts down for low voltage...so I can't figure out why they are shutting down. The manual says they auto shut down at 48v...I know they have been getting low due to the winter months, but they are not down to 48v.

Any ideas why they are shutting down?

I did notice that the BMS says they are at 35% charge and the victron smart shunt says 13%...I think one of the 2 has 'drift' due to the erratic (low) charging I have been getting during these poor sun months.

 

[defed]

Now that I have some light and charge coming in, they seem to be staying 'on' now that they are charging...

I still have 2 lights on the indicator, the BMS says 50v...so seems they should not have been shutting off.

One thing I have noticed....1 battery says 36% SOC and 38 ah remaining, the other says 46% SOC and 48 ah remaining....not sure why they seem to not discharge equally together, I always thought it may be due to not always getting a full recharge to reset them, and the values were drifting over time as it may have been losing track of the 'ah in' and the 'ah out' on each. They have never charged equally either....one always has, for example 1 amp going in and the other .7 amp going in....voltages are almost always equal, but never the amps going in and out. One battery does have slightly higher capacity, but it's like 104 ah vs 103 ah, so I don't think that should cause any problems.

 

[Benjamin Yang]

The battery may not be fully charged. This may result in an inaccurate battery charge calculation.

 

[Mark-]

I have a pair of SK48v100 batteries, in series,

In series, really?

 

[Adam De Lay]

I have a pair of SK48v100 batteries, in series, that I purchased in June.

I’m assuming you meant parallel?

I checked the voltage, the BMS screen said 49.9v (3.1v per cell) and I verified it w/ my meter. After a couple of minutes, they shut down again. The BMS screen does not say it shuts down for low voltage...so I can't figure out why they are shutting down. The manual says they auto shut down at 48v...I know they have been getting low due to the winter months, but they are not down to 48v.

Is the 49.9v you read on your meter when there’s no load on the batteries? They spring back to a resting voltage with no load, so you could have hit 48v but now it’s higher with no load.

Constantly sitting at the low end of your pack capacity will mess with your SOC numbers. I know I have to manually charge up a couple times during the winter just to let my cells rebalance and have my SOC reset.

 

[defed]

I’m assuming you meant parallel?

Is the 49.9v you read on your meter when there’s no load on the batteries? They spring back to a resting voltage with no load, so you could have hit 48v but now it’s higher with no load.

Constantly sitting at the low end of your pack capacity will mess with your SOC numbers. I know I have to manually charge up a couple times during the winter just to let my cells rebalance and have my SOC reset.

yes, i meant parallel.

when i powered the batteries back up, the voltage was 49.9v and each cell was 3.0XX to 3.1XX...i never powered the inverter back on, so they were sitting at no load. after a cpl of minutes, while i was trying to see where the problem was, they shut down again (twice). so there was no chance of a load pulling them down at that point. it is possible that the initial shutdown was triggered by an in rush pulling them down below the level - the only load connected to them is a fridge. initially, i was fixated on the bank voltage being good (so there was no possibility of the cells being low in my mind), so as i hurriedly scanned through the 32 cell voltages, it is possible there was a cell at 2.9XX that i overlooked. i presume if 1 cell is under voltage, it will shut off? but after 3 shutdowns, there was no register on the UVP count...now i'm not sure if this only counts at 48v or the 46v level.

after i was able to get a charge going in, they stayed on, so it does make sense that there was 1 cell that was low. i need to get them charged back up, i'm fairly certain they are not that well balanced (probably about 250mv difference still)...i was told by dexter and this group not to worry so much about them balancing - they will work it out, just use them....but i don't know as if they have. and especially in the winter here in the NE, i have been running at a deficit and they were rarely getting full again.

i had not considered that, in an extreme example, if 15 cells were 3.5v and a single cell was 2v, the battery would say it is 54.5v but it would still shut down because the one cell is out of range....so voltage/SOC are not the only things to consider, and i overlooked that aspect while troubleshooting.