I'm thinking of replacing my 12V lead acid car battery with a DIY lightweight battery based on LiFePO4 cells, but before I dive in I'd like to get some advice...
My plan is to use 4 sets of 2 x ANR26650M1B cells in parallel, to give 13.2V output, and high output current, and about 20Ah capacity.
(These cells seem to be used in commercial lightweight car batteries, so seem like a good choice.)
Now, question 1: Can I just use these 8 cells as a drop-in replacement? With, presumably, occasional balancing out of the car.
I think the answer is no: while my initial research suggests that some people are using off-the-shelf LiFePO4 cells in this way, a whole lot more people write about the protection and balance electronics they're using, and I don't suppose they're all wasting their time.
Question 2: If Q1 = "No", would adding an off-the-shelf balancing and protection module enable the cells to work safely in the car? There are 100A and 200A 4s modules available (eg. https://www.aliexpress.com/item/4S-...r-4-Packs-18650-Battery-Cell/32819634220.html), so they should be OK with starting current (c. 120A in my case). I guess it's a question of whether it's OK to have such a protected battery pack constantly hooked up to c. +14.4V from the alternator, or whether I need to limit the time that the battery is charged from the alternator.
Question 3: is it smarter to use super capacitors plus lifepo4 cells, to enable higher starting current while keeping battery discharging current low? (I started out thinking of combining an RC LiFePO4 battery pack with 6x400F super capacitors, but realised that I could get enough current with the ANR26650M1B cells, and fewer components should mean less to go wrong... if I used the caps I'd include a low-value high power resistor to limit the current that the capacitor bank could draw from the battery, and probably also a 200A circuit breaker on the battery as a short-circuit safety)
My plan is to use 4 sets of 2 x ANR26650M1B cells in parallel, to give 13.2V output, and high output current, and about 20Ah capacity.
(These cells seem to be used in commercial lightweight car batteries, so seem like a good choice.)
Now, question 1: Can I just use these 8 cells as a drop-in replacement? With, presumably, occasional balancing out of the car.
I think the answer is no: while my initial research suggests that some people are using off-the-shelf LiFePO4 cells in this way, a whole lot more people write about the protection and balance electronics they're using, and I don't suppose they're all wasting their time.
Question 2: If Q1 = "No", would adding an off-the-shelf balancing and protection module enable the cells to work safely in the car? There are 100A and 200A 4s modules available (eg. https://www.aliexpress.com/item/4S-...r-4-Packs-18650-Battery-Cell/32819634220.html), so they should be OK with starting current (c. 120A in my case). I guess it's a question of whether it's OK to have such a protected battery pack constantly hooked up to c. +14.4V from the alternator, or whether I need to limit the time that the battery is charged from the alternator.
Question 3: is it smarter to use super capacitors plus lifepo4 cells, to enable higher starting current while keeping battery discharging current low? (I started out thinking of combining an RC LiFePO4 battery pack with 6x400F super capacitors, but realised that I could get enough current with the ANR26650M1B cells, and fewer components should mean less to go wrong... if I used the caps I'd include a low-value high power resistor to limit the current that the capacitor bank could draw from the battery, and probably also a 200A circuit breaker on the battery as a short-circuit safety)
