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In hopes of saving someone from a similar very disappointing outcome, I am posting my experience. I purchased 64 LFP cells from Simon Lin of Dongguan Huanhuan Energy Ltd.n AliBaba.
I purchased 64 200Ah CALB cells in November 2019, arrived January 6th, 2020. They were connected in parallel and balanced overnight (not charged) and put into service in a 4P16S, 800Ah configuration January 7th.
Cells have been cycled lightly, typical usage cycle is between 85% to 96% SOC. Twice they were cycled down to between 50 and 60% SOC. Charge rate never exceeded 50A and was usually between 35A and 40A (<0.05C). Absorb is 3.45 or less for less than a half hour. The only time they have been above that until the capacity tests was for a one-time, full-bank, parallel top-end balance at 3.65V.
During a recent snowstorm and 3-4 days with limited recharge, they reached their low-end cutoff (3.065V, 49.0V bank). The cells were all within 10mV balance at this time thanks to a 10A active balancer.
At cutoff they had produced 644Ah. There is perhaps 6-7% capacity below 3.065V and the cells began this cycle at 97-98% charged. Therefore, 644Ah should represent roughly 92% of the capacity which indicated conservatively a full capacity around 700Ah, well below 800Ah.
I purchased two ZKETech EBC-A10H testers to evaluate the capacity of my cells. My tests are done at 20 degrees Celsius as follows:
Charge cell to 3.65V, cutoff charging when charge current falls to 1A, immediately begin capacity test.
Capacity test – 10A discharge (0.05 x 200Ah), 2.6V cutoff
Recharge – charge at 0.001C (1.6A) to 3.1V, then 20A charge to normal.
I have now tested 19 of the 64 cells and the mean is 164.72 Ah standard deviation of 4.13. Assuming less than 1% capacity below 2.6V and an initial charge to 100% that means these cells are about 166 Ah cells, 83% of stated capacity. Even adjusting a couple percent for testing below standard temperature (20 vs 25), that’s still significantly below spec.
In hindsight, I should not have purchased these cells until I had the ability to capacity test them. Since the cells are usually cycled so lightly, I was not aware there was an issue until the deep discharge and shutdown. If there is something I am missing or have done incorrectly, please let me know. These cells were advertised as new, 1.5-year old batteries which shouldn’t be a problem for LiFePO4 cells. They were 3.29V when I received them and reasonably consistent across the set. The only explanation I have been able to come up with is that these cells had been used heavily before I received them. If so, not only is their capacity reduced from the heavy use but their lifespan will be much shorter than promised. I have exchanged quite a few messages with Simon Lin since discovering this and have provided him test data and details but he has offered no explanation or resolution.
Please let me know if there could be something else that is causing them to perform so far below specification.
I purchased 64 200Ah CALB cells in November 2019, arrived January 6th, 2020. They were connected in parallel and balanced overnight (not charged) and put into service in a 4P16S, 800Ah configuration January 7th.
Cells have been cycled lightly, typical usage cycle is between 85% to 96% SOC. Twice they were cycled down to between 50 and 60% SOC. Charge rate never exceeded 50A and was usually between 35A and 40A (<0.05C). Absorb is 3.45 or less for less than a half hour. The only time they have been above that until the capacity tests was for a one-time, full-bank, parallel top-end balance at 3.65V.
During a recent snowstorm and 3-4 days with limited recharge, they reached their low-end cutoff (3.065V, 49.0V bank). The cells were all within 10mV balance at this time thanks to a 10A active balancer.
At cutoff they had produced 644Ah. There is perhaps 6-7% capacity below 3.065V and the cells began this cycle at 97-98% charged. Therefore, 644Ah should represent roughly 92% of the capacity which indicated conservatively a full capacity around 700Ah, well below 800Ah.
I purchased two ZKETech EBC-A10H testers to evaluate the capacity of my cells. My tests are done at 20 degrees Celsius as follows:
Charge cell to 3.65V, cutoff charging when charge current falls to 1A, immediately begin capacity test.
Capacity test – 10A discharge (0.05 x 200Ah), 2.6V cutoff
Recharge – charge at 0.001C (1.6A) to 3.1V, then 20A charge to normal.
I have now tested 19 of the 64 cells and the mean is 164.72 Ah standard deviation of 4.13. Assuming less than 1% capacity below 2.6V and an initial charge to 100% that means these cells are about 166 Ah cells, 83% of stated capacity. Even adjusting a couple percent for testing below standard temperature (20 vs 25), that’s still significantly below spec.
In hindsight, I should not have purchased these cells until I had the ability to capacity test them. Since the cells are usually cycled so lightly, I was not aware there was an issue until the deep discharge and shutdown. If there is something I am missing or have done incorrectly, please let me know. These cells were advertised as new, 1.5-year old batteries which shouldn’t be a problem for LiFePO4 cells. They were 3.29V when I received them and reasonably consistent across the set. The only explanation I have been able to come up with is that these cells had been used heavily before I received them. If so, not only is their capacity reduced from the heavy use but their lifespan will be much shorter than promised. I have exchanged quite a few messages with Simon Lin since discovering this and have provided him test data and details but he has offered no explanation or resolution.
Please let me know if there could be something else that is causing them to perform so far below specification.
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