why i call Li fussy
Hi all, This doesn't cover all the concerns for me, but it does show at least some of them: https://youtu.be/_PgthByAYz4
Forum Discussion
Not sure what is up with PT here. Here is the specific heat capacity of LiFePO4 batteries:
... The specific heat of the cell was determined to be 1067 J kg-1 K-1....
Unless someone wants to point out where my math is wrong, the 'back of the envelope' energy needed to warm a 100Ah LiFePO4 from -30C to 0C is 125Wh and from -35C to 5C is 166Wh. It is most certainly not 1540Wh.
This clearly jives with what BFL13 found for Relion batteries (which it turns out have a 10A heater) that they take about 1 hour to warm from -20 to 5C (with a 10A heater that would be ~130W, so pretty close to my 125W calculation).
This whole discussion has descended into the absurd, as they often do, with moving goal posts and made up numbers.
... The specific heat of the cell was determined to be 1067 J kg-1 K-1....
Unless someone wants to point out where my math is wrong, the 'back of the envelope' energy needed to warm a 100Ah LiFePO4 from -30C to 0C is 125Wh and from -35C to 5C is 166Wh. It is most certainly not 1540Wh.
This clearly jives with what BFL13 found for Relion batteries (which it turns out have a 10A heater) that they take about 1 hour to warm from -20 to 5C (with a 10A heater that would be ~130W, so pretty close to my 125W calculation).
This whole discussion has descended into the absurd, as they often do, with moving goal posts and made up numbers.
pianotuna wrote:
BFL13,
Don't get me wrong. Li can be made to work well--so long as the RV is occupied.
I don't "see" posts from FWC. But his calculations appear to be not based in fact. Unfortunately, he won't see my posts either.
See my post about how long it would take using a 1.8 amp heater (~23 watts), assuming ZERO losses, to warm up from -30 F.
About 62 hours (back of the envelope calculation) from -30f to -4f.
My calculation was not to get to 24 f--so it becomes insane to attempt to warm them up to where they can be charged using their internal heater.
To get from -4 f to 24 f is going to take another huge bite of energy.
55 wh x 28 = 1540 watt/hours and 66 hours assuming zero heat loss from the case.
If you use a higher wattage heater it shortens the time--but it doesn't change the number of watt hours needed. It is a zero sum game.
It would require a generator to be run--and a battery management system that would run the heater--but not allow charging.
