hipringles
Solar Enthusiast
- Joined
- Jan 31, 2021
- Messages
- 214
This is the f’ng problem….
I have been careful to not put metals or conductors “on” the pack. There is always a piece of plywood above the hole (build is not yet completed) and nothing touching the metal. The night before I was doing some work on the Shoilet and I needed to move the plywood out of the way.
What we figure happened - I f’ed up the top balance packs. Essentially, the supplier top balanced in packs of four, I got in packs of four, I kept all packs together for the most part….. until I put the final assembly together and mixed up two cells…..
from what we can tell - preliminary results - indicating that cell 1 that went up was supposed to be be in jar 2 and not 1…. And the supplier is going to let me know which others I mixed.
Point for me is to put a permanent S/N and group number on the cells. The imbalance was enough
View attachment 82540
So are you saying you took cells which were at different SOC and paralleled them? Ie, in the first "parallel" group you had 2 at a higher SOC than others?
OR are you saying you took 4 cells at a higher SOC, and series connected them to the lower SOC group?
The first should not cause issues, minus a few minutes of very high amperage between cells when you parallel them. The cells will balance to each other as they charge (basically a top balance), and will not cause a short or any issues.
The second would result in crap capacity in the pack. The only way it results in letting out the magic smoke is by the BMS not cutting off charging when the first cell group hits ~3.65.
If your BMS is not monitoring per cell, but rather for the whole pack voltage, then #2 could also be a problem.
Part of it is the BMS and part of it is me. I am going to assume I did something incorrectly (caused a short somehow)
"Caused a short somehow" when building the battery is immediately obvious. It is not something that will sneak up on you later.
Causing a short over time is likely due to either: connections getting loose, or something changing in the "environment" (aka container) that the batteries are in, such as someone dropping a metalic object on the studs, the batteries wiggling against a metal surface and drawing a short, etc