Technical Support

Hello Guys, I am getting a bit desperate and decided to write here to make sure I am not going crazy. I tried my installer - Effective Home in the UK but they are not doing anything and trying to convince me there is no problem. Sunsynk Technical Support do not want to talk to me on the phone as I am not an installer and have not responded to any of my emails yet.

Here is my problem.

I have a setup with Sunsynk 3.6kWh inverter and Sunsynk 5.12kWh BYD battery. Ever since the long cold snap in the UK in the second half of December, I noticed that the SOC of my battery started showing these strange steep drops or jumps while discharging or charging. It all seems to have started around 21st/22nd of December when during the night the battery SOC fell all the way down to 0% for a couple of hours. After that when discharging you would see the battery going down slowly from 100% to around 80% and then suddenly in the matter of 5-10min dropping by 60-70% all the way down to around 20%. All that while the load is relatively constant. Similar behavior is observed during charging. It will charge gradually up to 20-30% and then in a matter of 5-10minutes it will jump up all the way to 80% or more, while the PV generation is not more than 1500W during these 5-10 minutes. Here are a couple of examples of discharging and then charging to illustrate the problem. To me, this much charge or discharge with the observed loads or PV generation during a period of 5-10 minutes on a 5kWh battery capacity is simply impossible, even if we ignore the limit in the charging and discharging currents.

Example - Discharging: At 13:15 a constant load of about 1200W started and the SOC was at 98%.

At 13:30, fifteen minutes later the SOC has dropped gradually by only 4% down to 94%.

At 13:35, the drop in SOC starts and in five minutes it dropped by 13% from 94% down to 81%.

At 13:40, the drop in SOC in the next five minutes is by another 61% from 81% all the way to 20%. All of this time the Load is more or less constant as can be seen on the graph, however, it is clearly visible that in the first 15 minutes of the period, the battery discharged only 4%, while in the next 10 minutes, it discharged by 74%.

Example - Charging: At 13:06 the battery is at 21% and the PV generation is at 1101W.

At 13:11, only 5 minutes later, the battery charge has jumped all the way to 100% with a PV generation of 1446W. That is a 79% jump in just 5 minutes while the PV generation is less than 1500W. To me, it is physically impossible for a 5kWh battery to charge 79% in 5 minutes under these conditions.

Please, tell me that I am not going crazy and there does indeed seem to be a problem with the battery.

To me, it seems like either some of the cells got damaged during the freezing temperatures in December and the BMS is bypassing them or the BMS itself has developed some fault. Any and all advice would be nice. I have tried resetting everything. I have requested and had a software upgrade since then, but this problem remains.

Thank you! Kalin