Seplos BMS

You should configure the SOC discharge on the inverter before it hits undervoltage or capacity protection on BMS. Once inverter reaches discharge SOC it stops pulling power from battery. You can see on BMS current goes to 0 and sits there till it starts charging again.

Some users had issues where FOC would not kick in. Instead of FOC I use backup mode with grid charge, this has not failed on me yet. Basically you set SOC(20%) above your backup(15%). The invert would stop discharge at 20% if power cut to occur it would use discharge from 20% to 15% before cutting. If the battery is not charged for long period of time(days) it will naturaly slowly discharge but since backup mode is configured once the battery reached 17-18% inverter charges it back to 20%.

If BMS is saying 0 current than it means 0. I have seen on some inverters where inveeter would say 0amps but Seplos would still be showing -0.6-1 amps but these were not Solis. In my case once the discharge SOC was reached I have not lost a single % overnight.

you could try to do top balancing again but it could be that you have a bad cell

I'm currently in talks with Solis about updating my firmware, apparently it can't be done OTA.

I'm going to push to get it done anyway, does someone know of a battery that only works with the latest Solis Firmware? I've mentioned Seplos but they have come back saying they don't support that at any firmware.

Does using backup mode with grid charge allow you to set charge and discharge times?

Yuo can still use scheduled charging with Backup mode.

Have some time tomorrow so going to move the cell, and check all the connections. Was reading on diysolar about graphing cell voltage vs current to see if any cells stand out. Will try that. What voltage difference is acceptable when discharging. BMS sit's at about 18mv when idle but as per image hits 60mv @ 14amp but I have seen it climb over 100mv at higher currents. with C8 always the lowest

Hi,

Looking at Reklamos very pretty graphs I went and plotted a few today. I seem to have a 2 batches of 8 cells that are responding together: The top group of 8 cells consists of Cells, 14, 15, 3, 9, 12, 04, 10 and 11, all within 5mv at the start of the graph. The lower group of 8 cells react much more sharply to higher current ( charge & discharge ) are 10mv away from the other cell group and have a range of 22mv from top to bottom, Cells 7, 6, 16, 5, 13, 8, 1, & 2.

Second chart is the cells and the discharge current (dotted line right hand axis) just as the SOC drops from 40% to 10%, which causes the inverter to charge back up to 15%

I think looking at this that I need to redo the top balance of the cells, especially the lower 8. If that doesnt fix then it looks like 8 of the cells have a different impedance and I need to talk to OYE. Does that make sense ?

Hi,

Yup all busbars under the sensors, and nice and tight. the 8 behaving cells 3, 4, 9, 10, 11, 12, 14 & 15, with the misbehaving cells are 1, 2, 5, 6, 7, 8, 13 & 16. For the graphs I just click realtime in the BMS monitoring software and then save that data out to excel every morning manually. I will automate it when I have time, try get the csv data into influxdb then to grafana.

The graphs really do highlight that some of the cells are OK and some are not which was hard to see just looking at numbers.

Modbus over RS485? oh do share when you pretty it up 😀

Just an update, redid the top balancing, wired all 16 cells together rather than 8 & 8. Ran until current was down to 0.04a, disconnected and let sit for 16hours. Then ran a discharge at 50a (.25c) and immediately 8 of the cells started to diverge. The same 8 cells as above, although now in different locations. Discharged about 110ah before tripping the low voltage alarm. The 8 good cells were still reading 3.1x, looking at the labels on the batteries the 8 good batteries are labelled 124-### while the bad ones are labelled 79-### so looks like all the bad ones came from the same batch and have a capacity approx 120ah.

I've contacted OYE so will see how that goes.

Yes, there are a small few complaints on aliexpress store with similar issues, no resolutions. BTW, in the meantime I guess I should drop the battery capacity in the SEPLOS to 130ah, it was reading 84ah when it cut out due to low voltage and dropped to 20ah

It didnt manage to learn previously, would jump from 140 to 200ah on charging then from 80 to 20ah on discharge. I know @reklamos mentioned you needed to be within 20ah for the BMS to learn. I think I'm well outside that, hence the issue. Have asked seplos.