spinningmagnets
100 TW
I'm just starting this thread as a place to park useful info about 4S LiFePO4 as a 12V battery pack. Depending on the components the pack is powering, the charging system desired, and the LVC needed...using 18650 Li-NCA or Li-NCM can be too low at 3S or too high at 4S, however LiFePO4 has a lower nominal voltage that makes it useful as a lead-acid replacement at 4S for providing 12V. In spite of the recent improvements in 18650-cell Li-Ion systems, some people still would prefer the perceived safety of using the LiFePO4 chemistry.
LiFePO4 is very fire-safe, also It is known to last thousands of cycles if cared for properly.
The downsides are that since they are not used very much, there are fewer selections available. Headway cells are well-regarded, but the smallest 38120 version is large [5.5inches long, 120mm], so most packs are physically large rectangles.
Also...since the nominal voltage is around 3.2V per cell, it takes more cells to make the same pack voltage compared to the 3.7V Li-Ion selections. For instance, 48V in LiFePO4 is generally considered to be 16S, and using common 18650 Li-Ion cells, it is only 13S...
It would appear that E-motorcycles and EV-cars want the most power-dense cells. 18650-cell packs rarely catch fire, builders are adding individual-cell fuses, and more robust housings...both of which help with a wreck when you crash...
The most passionate information about using LiFePO4 instead of lead-acid are from boat, RV, and aircraft forums. They want the compact power of lithium, along with the long-life, but...they all deeply fear any kind of fire.
Although the factory recommended charge is to 3.65 per cell, they can be over-charged up to 4.2V in order to make certain to get them fully charged (I don't like doing that). The point I want to make is that they can be charged to 4.2V without the electrolyte disassociating and creating gasses, leading to less contact between the collectors, leading to heat (same current flowing through a smaller area of collector) which then causes more off-gassing in a downward death-spiral. This is part of the reason for their perceived safety. If your 3.65V charger goes out of whack 10%, the battery will still be under 4.0V
LiFePO4 is very fire-safe, also It is known to last thousands of cycles if cared for properly.
The downsides are that since they are not used very much, there are fewer selections available. Headway cells are well-regarded, but the smallest 38120 version is large [5.5inches long, 120mm], so most packs are physically large rectangles.
Also...since the nominal voltage is around 3.2V per cell, it takes more cells to make the same pack voltage compared to the 3.7V Li-Ion selections. For instance, 48V in LiFePO4 is generally considered to be 16S, and using common 18650 Li-Ion cells, it is only 13S...
It would appear that E-motorcycles and EV-cars want the most power-dense cells. 18650-cell packs rarely catch fire, builders are adding individual-cell fuses, and more robust housings...both of which help with a wreck when you crash...
The most passionate information about using LiFePO4 instead of lead-acid are from boat, RV, and aircraft forums. They want the compact power of lithium, along with the long-life, but...they all deeply fear any kind of fire.
Although the factory recommended charge is to 3.65 per cell, they can be over-charged up to 4.2V in order to make certain to get them fully charged (I don't like doing that). The point I want to make is that they can be charged to 4.2V without the electrolyte disassociating and creating gasses, leading to less contact between the collectors, leading to heat (same current flowing through a smaller area of collector) which then causes more off-gassing in a downward death-spiral. This is part of the reason for their perceived safety. If your 3.65V charger goes out of whack 10%, the battery will still be under 4.0V