why i call Li fussy

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.

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.

2oldman wrote:

Itinerant1 wrote:
I couldn't imagine the condensation from extreme cold to warming temps inside the trailer.

I'd be buying propane every 3 days.

Sorry I missed replying to this post.

You are exactly correct 2oldman. That's why I go to a campground with 50 amp service. My power needs are 4700 watts continuous, with spikes to 7300 watts.

Hi time2roll,

I'd love to accommodate you. There is a little thing called covid. Travel is still not recommended.

I just got back to Regina after spending 50 days in Toronto looking after a friend with a broken pelvis. They are finally "on the mend".

I've tried extremely hard to NOT mention SiO2 in this thread.

How about just get those SiO2 batteries installed and get us a trip report. Those that want to fuss with LFP can do the same.

BFL13,

Don't get me wrong. Li can be made to work well--so long as the RV is occupied.

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.

I agree that a 1.8A heater is not going to heat a battery very quickly. I also don't think Battleborn are a very good option in general and there heated batteries are poorly implemented, both Renogy, LiFeBlue and Relion all have a better heated battery if you don't want to roll your own.

However the rest of your assumptions are off by an order of magnitude. As I pointed out earlier, the heat capacity of a LiFePO4 battery (it is not Lithium metal) is around 1000 J/kg/c which is about 1/4 that of water. To go from -35 to +5C would require 166Wh (1000J/kg/c*40c*15kg/3600s). At 23W with good insulation that would be 6 hours.

For Relion, the heating time for -20 to 5C is 1 hour which would imply they are using a ~10A heater. Therefor the heating time for -35C to 5C would be about 1.5 hours, which seems pretty reasonable to me.

pianotuna wrote:
1.8 x ~13 =~23 watts. A 100 amp-hour battleborn is 31 lbs. It is going to take one heck of a lot of time to raise the temperature to that level where charging is safe.

The Li is a little more than 53% as dense as water. So it would take about 1.8 watts per pound to raise the temperature 1 degree F.

31 x 1.8 =~ 55 watt-hours.

If we started from -30 F and need to get to -4 F then it would consume 26 x 55 = 1430 watt-hours. That, unfortunately, is more than 100 amp-hours. It would also take 62 hours.

In my case, where I might be starting from -35, it is more or less impossible. Even if there are zero losses outside the case of the battery.

This, without detailed information from the particular maker, is just a guess--but I believe it may be in the ball park for "best case".

2oldman wrote:

PerryB67 wrote:
Does Battborn, Renogy, etc. have a LFP battery with a heater that can sit for months without charge, without the built-in heater running, and then two days before leaving can you turn that heater on?

LFPs can sit for a long time without being charged. Since the heater only draws 1.8a, and is very smartly controlled, yes.

What is that "1.8a" for how long?

FWC calculated 10-15% of battery capacity to heat it up from -20C to +5C with 125W in an hour, so that would be 12.5 DC amps with an inverter. The 120v charger doing the heating first would be at say 55 amps or whatever the heater "accepts" --not clear on that. Anyway 1.8a DC does not seem nearly enough.

Perry can start the furnace and has 12v on arrival at the storage at -20C, since nobody said the LFPs are dead or at BMS shut down. You can draw from them down to minus whatever, but can't charge them.

So you would need say 20AH left in (usually stored at 50%?) to run the furnace and lights etc before getting some charging going somehow (scenario?-- take the rig home to load it up and while there plug into the stick house? Generator? Solar? )

That 20AH would be a higher percentage of the capacity at -20C than at +5C so storing at 50% would leave enough?

It is true you can organize things to operate in those temps down to the -20s but not down to PT's worst case scenarios AFAIK. I think he is right to say they are "fussy", especially in the mystery temp range 0-5C where you should use "reduced charging amps". That does not mean they are bad just fussy. Other batts have their own ways of being fussy--eg charging AGMs to 0.5a/100AH.

IMO Perry made a good choice and does not need to second guess himself for his scenarios. There are conflicting info/opinions on all this low temp stuff, so hard to tell what is Gospel. If you don't have LFPs then no worries! Or if you do, there is always, "What, me worry?" to go by. :)

Reduced charging amps at 3C would be a problem for me where it would then take too long to recharge the bank using the generator. Can't run the gen all day. If it never got above 5C, it would be doom for getting through the next night. Have to be able to charge at full amps from the start.

1.8 x ~13 =~23 watts. A 100 amp-hour battleborn is 31 lbs. It is going to take one heck of a lot of time to raise the temperature to that level where charging is safe.

The Li is a little more than 53% as dense as water. So it would take about 1.8 watts per pound to raise the temperature 1 degree F.

31 x 1.8 =~ 55 watt-hours.

If we started from -30 F and need to get to -4 F then it would consume 26 x 55 = 1430 watt-hours. That, unfortunately, is more than 100 amp-hours. It would also take 62 hours.

In my case, where I might be starting from -35, it is more or less impossible. Even if there are zero losses outside the case of the battery.

This, without detailed information from the particular maker, is just a guess--but I believe it may be in the ball park for "best case".

If there is a serious concern about it being cold enough for ABS to crack, then you have far more to worry about then your camper batteries, your appliances, your vehicle, the electronics all have plenty of ABS components that could also crack.

I have personally used LiFePO4 and LiCo batteries down to about -45C, and they work fine, albeit with a much lower usable capacity and voltage.

I decided to do more research. Turns out that conversation I had with Battleborn last winter was accurate.

From Battleborn's web site: https://battlebornbatteries.com/faq/

"Storing batteries in subzero weather (-15°F or more) has the potential to crack the ABS plastic and more importantly could cause a faster loss of capacity, in some cases drastically more than the typical 2 – 4% per month loss."

"Battle Born Batteries protect themselves from charging in cold temperatures and won’t accept a charge once the internal cell temperature drops to 24°F. At this point they will continue to discharge even down to -4°F. At this temperature we recommend no longer pulling power to avoid damaging the batteries."

Guess I'm not starting that furnace!

We camp to much in all kinds of weather and I'm not getting into moving batteries back and forth from heated storage. That was Battleborn's suggestion last winter.

I'm asking these questions for my Airstream friend with a battery box located outside the camper on the tongue. His Lifelines are starting to lose capacity.

Enjoy,

Perry