NEW 2023 Cougar 24rds 5th Wheel - Lithium Batt Question

[snoobler]

Maybe I am mis-stating the function of the BMS (just sharing what WFCO is saying), but the battery does stop accepting a charge more abruptly than a lead acid battery, and that difference is what the auto detect converter circuitry senses.

I tried to describe this in my post. They have different voltage and current behavior than lead acid, but the end points are very similar... 10.5-14.4V total operating range.

Lead acid typically charges at 0.1-0.2C. C = capacity, so a 100Ah battery is optimally charged at 10-20A. At this rate, they are at about 80% when 14.4V is hit and it takes about 4 hours to achieve 100% SoC with about 15% loss (you put about 15% more back in than you take out).

LFP batteries typically can be charged at 0.5C or 50A on a 100Ah battery.

At 50A, the Voltage stays relatively constant until nearly the end where it shoots up rapidly to 14.4V. In order to top it off, it may need to dwell here for 30 minute to hit full charge with very little loss.

If charged at a lower current, like 0.1-0.2C, the ramp up at the end is even faster, and it requires little to no time to top off.

To boil it down to a general comparison, which supports your general statement, Lead acid batteries need about 4h at absorption voltage to fully charge. LFP batteries rarely require more than 30 minutes.

 

[Stircrazy]

Maybe I am mis-stating the function of the BMS (just sharing what WFCO is saying), but the battery does stop accepting a charge more abruptly than a lead acid battery, and that difference is what the auto detect converter circuitry senses.

I defer to your knowledge on these systems, but I see this as similar to the way a battery discharges; a lithium battery generally outputs at an even level until it stops, and a lead acid battery will slowly ramp down until it no longer has “juice”.

What I can say for certain is that having to repeatedly disconnect my solar just to get the converter to auto detect correctly is a non-starter for me. My formerly auto-detect converter that is now lithium-only, solves that issue for me.

And this is from their tech literature: Based on the voltage characteristics at the end of the charge cycle, the converter identifies whether the battery is lead-acid or lithium-ion

ya they both have the drop off its just the chemistry that dictates how and when they drop off. so when a flooded battery charges it has a higher internal resistance than a lithium so it creates more heat so you get a slower charge, where as a LiFePO4 has a very low internal resistance so less heat is created which results in more of the energy going directly to charging. one reason why LiFePO4 batteries charge faster. the other reason is like we said with the flooded batteries the drop off is about 80% and then they need to adsorb along time to get to 100%, with the LifePO4 as mention they go to about 99% then a short adsorption. that is reason two why they charge faster. as for auto detect, (I'll watch the video tonight when I get home from work) the problem with using the BMS cutoff is two major things, 1) you won't know until the end if it is a lithium or flooded, and 2) your using a safety device as a charge limiter and will burn out your BMS eventually.

I was just doing a little light reading and the charger has to go through one complete cycle to determan if you batteries are flooded or LiFePO4 so it is looking for that drop off and coparing it with the voltage and such then it switches to the mode. but that drop off isn't the BMS it is the charge chemistry of the cells.

 

[neeginan]

Have had the trailer for a few months now. After several sunny days in Florida, the Lithium batteries fully charged, hit the ~14.4 volts, and then settled down to ~13.5V. I used them boondocking one Saturday night in central florida and everything worked great. Used about 25% capacity - the furnace was running during the night. They charged up within one full sunny day when I got back. I have since added 2x100ah batteries so I have 400ah now of solar battery capacity. I did another boondocking excursion and used about 12% capacity on that trip. Took a sunny day and a half for the batteries to completely top off again. Bottom line, everything is working well. Thanks for all of the advice here.

By the way, given that the solar system will top off the lithium batteries, even if the WFCO converter fails to recognize that these batteries are Lithium, I decided not to pursue that concern.