MurphyGuy
It just needs a bigger hammer
- Joined
- May 20, 2020
- Messages
- 4,129
I'm trying to figure out if I have an "actual" bad cell, or just one cell with a higher self-discharge rate than the others.
These are brand new LG Chem N2.1 cells that have never been cycled.. were destined for the Chevy Bolt.
I have a 25 kWh (480aH) pack that is 4/8P 14s. (LG Chem modules are stacked two 60ah cells to each module)
The first two runs with this battery went perfectly, albeit short as the grid power came back on fast. But this last outage, I ran the battery for a longer time and when I activated the off-grid system, I noticed one cell was 64 millivolts below the rest. Most were at 3.620 to 3.630 (storage voltage), but this one cell (#12) was at 3.570.
Running the battery down to 25% capacity and then charging it back up to 90%, and that cell was still 0.050 below the rest.. I could tell the BMS was working to bleed off the other 13 cells.
The grid came back up so I shut the system down.. decided to charge that specific cell with an 18650 charger (LOL). 480aH of cell and I had a 1400mW charger hooked up to it with alligator clips. (BMS Disconnected) It took quite a few hours of charging to bring it up with the other cells, which I let rest at 3.915 to 3.921.
I brought that #12 cell up to 3.916 and then disconnected the charger and monitored its resting voltage over the next 10 days using a Fluke every 8 hours or so. It dropped 0.001 volt right away, and now it has settled to dropping about 0.001 every 24 to 36 hours or so. In 10 days, we've gone from 3.916 to 3.909.
The rest of the cells in the pack haven't dropped a single millivolt after the first day of rest.. they were disconnected during a charge cycle but only about 10 amps were going into the pack at the time.
Does this sound like I have 13 really good cells and 1 normal? Or 13 normal cells and one trouble maker?
Anyone ever heard of these kinds of issues fixing themselves as a new battery sort of "breaks in" ? This entire pack has only been cycled 4 times, and most of that was bouncing between 3.6 and 3.9.. This was the first time it was ever discharged below 3.6 volts.. I'm wondering if it just needs to stretch its legs..
These are brand new LG Chem N2.1 cells that have never been cycled.. were destined for the Chevy Bolt.
I have a 25 kWh (480aH) pack that is 4/8P 14s. (LG Chem modules are stacked two 60ah cells to each module)
The first two runs with this battery went perfectly, albeit short as the grid power came back on fast. But this last outage, I ran the battery for a longer time and when I activated the off-grid system, I noticed one cell was 64 millivolts below the rest. Most were at 3.620 to 3.630 (storage voltage), but this one cell (#12) was at 3.570.
Running the battery down to 25% capacity and then charging it back up to 90%, and that cell was still 0.050 below the rest.. I could tell the BMS was working to bleed off the other 13 cells.
The grid came back up so I shut the system down.. decided to charge that specific cell with an 18650 charger (LOL). 480aH of cell and I had a 1400mW charger hooked up to it with alligator clips. (BMS Disconnected) It took quite a few hours of charging to bring it up with the other cells, which I let rest at 3.915 to 3.921.
I brought that #12 cell up to 3.916 and then disconnected the charger and monitored its resting voltage over the next 10 days using a Fluke every 8 hours or so. It dropped 0.001 volt right away, and now it has settled to dropping about 0.001 every 24 to 36 hours or so. In 10 days, we've gone from 3.916 to 3.909.
The rest of the cells in the pack haven't dropped a single millivolt after the first day of rest.. they were disconnected during a charge cycle but only about 10 amps were going into the pack at the time.
Does this sound like I have 13 really good cells and 1 normal? Or 13 normal cells and one trouble maker?
Anyone ever heard of these kinds of issues fixing themselves as a new battery sort of "breaks in" ? This entire pack has only been cycled 4 times, and most of that was bouncing between 3.6 and 3.9.. This was the first time it was ever discharged below 3.6 volts.. I'm wondering if it just needs to stretch its legs..