Hi all
I have a question I can't seem to figure out.
My system is MP2 48/5000 with 6.2kwp solar and 20kwh of storage, 18650 14s200p.
So problem has always been imbalanced cells duing grid feed-in, never understood why. There is no problem whenever it's charging at 4-5kw+, cells stays within 0.01-0.03v, but as soon as its feeding to grid, cells starts to become unbalanced, and will get back to be perfectly balanced once sun goes down.
Here is a day earlier this summer as an example, showing how cells go out of balance when reaching top SoC and starts to grid feed-in, in the middle of the day.
It makes top balancing hard. But I've learned to live with it, and turned off top balancing since it's not really needed, they stay within 0.01-0.02v of each other all the time, well except under heavy load and grid feed.
So today I figured I would try a scheduled charge from grid since price a kwh was low and my batteries were empty.
Weird thing is, cells starts to go out of balance again when charging from grid. It was set to charge from 11.00 to 13.00. At 11.01 already 0.1v diff from lowest to highest.
This picture here however shows later duing today charging at 4kw+ without cells going out of balance?
I find this odd :-) Is it because of using laptop cells, they are all testet multiple times and only using cell that has less than 15% degradation. System has been running for over a year now without any problems except this imbalance.
Or is it because of the 0.4v offset to be able to grid feed, but what would cause same behavior when charging from grid?
Thanks, I hope someone more knowledged than me can chime in :-)
From Rasmus
