More on LFP Charging

[BFL13]

Some "sales" statements here, but also some possibly good info of interest.

One thing is they found longest life (most cycles) was to charge at 14.4v but at lower amps at 0.3C.

Some LFP owners on here ISTR have taken to charging at lower voltages hoping for longer battery life. Perhaps it needs to be established which is correct--lower amps or lower voltage?

They say 14.4 vs 14.6 to reduce stress, and recommend their own charger (of course!) which is single stage 14.4--BUT they say shut charging down-disconnect- once the charger says the batt is full. (light comes on---what makes that light come on? oh well)

They are strongly against floating! see why.

Anyway, it covers some of what has come up on here lately.

https://dakotalithium.com/2021/09/22/how-to-charge-dakota-lithium-and-lifepo4-batteries/

[pianotuna]

Itinerant1,

How do you manage on less than 2304 watt-hours per day? Are the panels actively running the RV during daylight hours? Do you know the total electrical use per day?

[Itinerant1]

Pick your posion for setting and move on with other daily activities, let it do its thing quietly in the back ground. Just have to have confidence in the equipment...if you don't you might need better equipment. 😉

[StirCrazy]

time2roll wrote:
Way too much thought is put into getting 100%. This is another bad hangover from FLA batteries. Skip the headache.

yup. thats why I just let the charger do its thing with a custom two stage configuration. I figured I am getting all the life I need from the absurdly shallow discharges it will normaly be subjected to.

Steve

[3_tons]

time2roll wrote:
Way too much thought is put into getting 100%. This is another bad hangover from FLA batteries. Skip the headache.

Agreed, not much point except for occasional cell balancing…

3 tons

[time2roll]

Way too much thought is put into getting 100%. This is another bad hangover from FLA batteries. Skip the headache.

[3_tons]

“Im not sure I like the way they call charging to 100% overcharging, its not. overcharging is when you exceed the voltage that gives you 100% charge.”

Once the end of charge voltage performs it’s near sudden vertical ramp-up (indicating having achieved max charge holding voltage, but still not yet at 100% SOC), the absorption current then begins over time to taper down until the current eventually cuts out which then indicates cell absorption complete, or 100% SOC - thus, voltage alone just tells part of the story…Higher voltage will help expedite the absorption phase, but if too high can come at the cost of unnecessary cell degradation…3.65v per cell is typically the recommended upper limit, but (if programmable) in my view 3.55’ish is better…Beyond current cutout there’s no need to float a LFP…

As far as 100% SOC goes, the $64k question should be “100% of what??”…An actual load test might reveal more actual amp/hrs that the mfg’s spec, in the case of my drop-ins, 7% more…

3 tons

[StirCrazy]

BFL13 wrote:
Some graphs here of interest. Scroll down. One has the Absorption SOCs for some lower C rates.

These guys seem to have a clue, lots of interesting (IMO) posts on some of the things being discussed here.

https://forum.solar-electric.com/discussion/351996/charging-lfp-lifepo4-batteries-to-90-soc-or-not

Im not sure I like the way they call charging to 100% overcharging, its not. overcharging is when you exceed the voltage that gives you 100% charge.

I just spent the last 10 days on the island and never got below 96% and was back up to 100% before 9am every day. I have no issues going to 100% on my solar charger as I am camping and it is always drawn down that night so in my mind I am not storing it. the last day I turned off my panels and left it at 97% and turned a light on for the entire drive from pender Island to kamloops, was 96% when I got home :R but I'll leave it there till the night before I go camping again and top it off, or if I have a deicent drive I will just leave it and turn the solar on so it charges while I travel. I have my solar charger set to 14.4V charge and 13.6 float and so far I am very impressed with the setup.

[3_tons]

Agreed…However much of this depends on how and by what means one elects using to accomplish a charge.

Most chargers of lead acid design will have a Float stage, though I see no need to Float except as a means to avoid an extended period at 14.x Absorb voltage…Harvest is my primary charging source of choice, and it’s typically more moderate output is often low enough to negate the need for supervised charging…But as far as the PD goes (used for occasional ‘attended’ cell-balancing function), upon the completion of 14.x cell-balancing (as witnessed per Victron BMV 712, current holding at zero…), thereafter, I discontinue use of the PD.

3 tons

[Itinerant1]

Years ago I use to use 14.2v absorb and 13.6v "float". For the past 3 or so years just been using 14.1v absorb and 13.6v "float". 14.1v is the lowest I'll go fo the reason my SOC will reset the capacity to 100% whenever the pack voltage reaches 3.49 to 3.52 V per cell on average.

Packs performing just fine. Depending on batteries/ cells and what bms it has might dictate what voltage is needed for balancing of cells and resetting soc capacity.

If someone wants to use full capacity of the batteries or just partial it won't make a difference as long as the cells stay in some sort of balance with a periodic recharge.

Nothing better than individual choices, one size doesn't fit all.

[Microlite_Mike]

S Davis wrote:
My EVE LF280N cells are rated at 3500 cycles from full charge to 2.5 volt cut off and that is at 1.C in a compression fixture. I am not to worried about charging them up to 100% SOC and using the full capacity. From what I understand if you draw your battery down 20% and then charge it back to 100% that is only 20% of a battery cycle.

At 3500 cycles I think for most users they will age out before cycling out, I think there are many more factors that will affect cell life more than using the manufacturer stated capacity.

The bold part is something to really consider with LifePo4 batteries. I think too many people who have converted to LiFePo4 batteries from Lead/Acid chemistries are still hung up on a lot of the "rules" that applied to them. I'm pretty sure that 10-15 years from now my batteries will me a lot more alive than me.:B

As for discharging to 100%, my deepest discharge in 4 seasons was 81% (2x 100ah Battleborns). To me that says my battery bank is "right sized". If one is regularly seeing 100% DOD then I'd suggest adding more solar, running generator more often, or reduce power use if possible. That can come at an inopportune time. Best to always have some "cushion", not for the sake of the batteries but for my personal comfort.

[Cptnvideo]

My Victron solar controller defaults to auto absorption, but I chose to go with 15 minutes.

[jaycocreek]

Cptnvideo wrote:
I'm happy with what I do but I'm not saying it is the correct thing to do. The charger part of my 3kw inverter/charger is turned off and the converter that came with my 5th wheel is unplugged. So battery charging (whether plugged in or not) is only done by the solar panels.
I bulk charge to 14.2V, then absorb for 15 minutes, then float at 13.6V.

That's pretty much the way I do it for my truck camper and the converter charger..I am curious why Victron LFP default are what they are (14.2-2hrs absorb-13.5 float)..Everything I read on the net had absorb ion way lower...I wonder what there reasoning is for that...

[Cptnvideo]

I'm happy with what I do but I'm not saying it is the correct thing to do. The charger part of my 3kw inverter/charger is turned off and the converter that came with my 5th wheel is unplugged. So battery charging (whether plugged in or not) is only done by the solar panels.
I bulk charge to 14.2V, then absorb for 15 minutes, then float at 13.6V.

[S_Davis]

My EVE LF280N cells are rated at 3500 cycles from full charge to 2.5 volt cut off and that is at 1.C in a compression fixture. I am not to worried about charging them up to 100% SOC and using the full capacity. From what I understand if you draw your battery down 20% and then charge it back to 100% that is only 20% of a battery cycle.

At 3500 cycles I think for most users they will age out before cycling out, I think there are many more factors that will affect cell life more than using the manufacturer stated capacity.

[BFL13]

Some graphs here of interest. Scroll down. One has the Absorption SOCs for some lower C rates.

These guys seem to have a clue, lots of interesting (IMO) posts on some of the things being discussed here.

https://forum.solar-electric.com/discussion/351996/charging-lfp-lifepo4-batteries-to-90-soc-or-not