LiFePo4 lithium battery charging questions

[ewarnerusa]

TL DR – I have some questions related to charging 12V LiFePo4 lithium batteries:
*How to best use my solar to charge batteries?
*Assuming I usually keep the lithium batteries at a partial SOC, what if I want occasional 100% SOC?
*What about charging from my tow vehicle?
*What about charging with OEM converter?

Full version:
Hello all. It has been a long time since I've posted here! Current project, my 10-year-old quick and dirty wiring job for inverter install on my TT is due for an overhaul. My exposed-to-the-elements inverter wiring needs replacing along with the 2 x 6V GC batteries.
Here is what I have now:
*2 x 6V GC batteries in series (~200 Ah total)
*2 x 140 12V solar panels mounted fixed and flat
*Morningstar Tristar PWM controller
*1500 watt PSW inverter
*OEM WFCO converter (55 amp)

I’m thinking that since I want to replace the batteries and some wiring, I want to relocate the batteries from on the tongue to the pass through storage alongside the other electrical components. So I am considering a switch to a single lithium (LiFePo4) 12V battery 100Ah. Current top candidates are Renogy, Battleborn, and Dakota. I am contemplating my charging options if I do this swap.

How to best use my solar to charge batteries? The Morningstar controller is fully programmable and I downloaded a suggested lithium battery charging profile from their website. It relies on the concept of never bringing the lithium battery to 100% SOC as this can be stressful to the lithium battery. From what I’ve learned, lithium works great at partial charge levels vs FLA which should be kept at 100% SOC as much as possible for best health. So the Morningstar config actually does away with the voltage regulating features and changes it to an on-off switching controller via high voltage disconnect (HVD) and reconnect (HVDR) in order to avoid any absorption or float charging. The HVD is 13.8V and HVDR is 13.3V. So controller is in bulk charging mode until the HVD setpoint of 13.8V is reached, then charging is stopped (disconnected) until the voltage drops below 13.3V at which time the charging turns on again and this cycle repeats indefinitely. They say this should get a lithium battery to ~90% SOC and no further, allowing for many cycles without stressing the battery by bringing it to 100% SOC.

But what if I want occasional 100% SOC? My thought is if we’re heading out camping for the long weekend, then I do want to recharge to 100% just prior to and if possible during each camp day. It seems like a few of the lithium battery manuals say that FLA charging profiles that can reach 14.4V and an absorption phase will work fine to fully charge. I think I can put together a “while camping” charging profile based around 14.4V absorption setpoint to accomplish this. 13.3V float?

What about charging from my tow vehicle? My tow vehicle delivers 12V via the trailer plug. No upgrades in wiring or anything there, just whatever the OEM setup is for the 7-pin trailer connector. But I confirm that it brings the trailer battery voltage up to the alternator voltage of 14.2-14.4V. Since this is on the upper end of lithium charging voltage, and considering that I probably don’t want the alternator trying to push 14.4V indefinitely while driving, should I be disconnecting this charging source? Or maybe consider it sort of a topping off charge for the typical 1-2 hr drive to the camp spot?

What about charging with OEM converter? My OEM converter is a WFCO 55 amp model. I have one time ever seen it charge at 14.4V, every other time I have ever used it I see 13.6V. I usually have it switched off via the breaker panel and let solar do the work. I expect I would continue this practice. But it seems like I could use it if I wanted and assuming it continues to only charge at 13.6V, it should be fine for partial charging?

Thanks for any feedback!!
Ed

[3_tons]

“what was your state of charge the previouse day when the sun went down?”

I honestly don’t recall, but if it’s of any help we’ve been using about 30 a/h per day…I have two independent parallel systems, one of 300w MPPT and one (add on) of 140w PMW, and can discontinue charging from either (or both) when strategizing the days net harvest so as to purposefully avoid arriving at 100% SOC (which is typically unnecessary)…

It’s by this means (of anticipating the days harvest vs deficit…) that I might (say, in the AM) shut down one system in preference to the other, to steer-clear of the upper charge limit of 100% SOC (100% is unnecessary due to LFP’s deeper DOD), and in actual daily practice of say ‘to-and-fro’ harvest and discharge occurrence (assuming daily harvest and discharge patterns remain fairly consistent), it’s mostly a ‘set once and forget affair’ that requires little if any intervention…If either of these two aforementioned patterns begin to change, then either of the two solar PV systems can be either taken off line or put back on line (per one’s own informed estimation…) in anticipation of the new conditions..

3 tons

[StirCrazy]

3 tons wrote:
Had another good off-grid solar day today, with no meter monitoring, or intervention (100% passive)…

Stats:
200 a/hr LFP (actual load-tested at 215 a/hrs), 440w solar
Starting SOC @ 0700, 41% SOC
End of Day SOC @ 1900, 85% SOC

In approximate terms: A harvest recovery of about 44% of SOC (or 88 a/hrs) to arrive at 85% SOC…

3 tons

what was your state of charge the previouse day when the sun went down?


Im so used to oversizing my setups that if I don't see a 100% soc whent he sun goes down somthing is wrong like its overcast or the solar is broken. 99% of the time I am back up to 100% by early afternooon, in both the 5th wheel and the camper. the fith wheel I had to do this as I need that power as I only have GC batteries in there so I want to go to bed at 100% every night to make sure I have enough power as I only have 230Ah of usable power and I want to be able to survive a few cloudy days. the camper it has half that but has a 24V 235 watt split cell panel, that believe it or not out preforms the 480 watts of 12V panels I have on the 5th wheel..... the camper has no inverter so its just the furnace I am worried about when camping early spring/lait fall/eairly winter. I know I can go 3 days easy with out sun running the furnace 24/7 at 28 degree night temps and mid 30's day time.

[StirCrazy]

jaycocreek wrote:


Interesting and always nice to see individual reports..I have been reluctant to mount solar on my roof,one because of water intrusion and the other,less solar output than aiming at the sun but also there is less fuss mounted..

Yesterday I did the same with one 100 watt portable solar panel and one 100ah LFP..Started at 51% and ended at 83% moving it two times..Plus 30AH roughly...

I was worried about it at first, so I decided to do it myself. I just predrilled the holes, filled them with sealant put some more sealant on the roof where the foot is going to contact it, drove the screws in then sealed everything from the top with self leveling compound. there is no way anything is getting in there.

Steve

[jaycocreek]

A lame excuse it maybe, but mounting on the roof now is almost like starting over ,I need everything except solar controllers but I should update them also...So water intrusion is my story for now...:B

[3_tons]

13 years, six panels, 48 total roof #10 pan head screw penetrations, plus two combiner boxes (all flat mounted) and no leaks…

BTW, I don’t fret going or not going to a full charge which means charging for the most part is a passive activity…

3 tons

[Itinerant1]

jaycocreek wrote:

3 tons wrote:
Had another good off-grid solar day today, with no meter monitoring, or intervention (100% passive)…

Stats:
200 a/hr LFP (actual load-tested at 215 a/hrs), 440w solar
Starting SOC @ 0700, 41% SOC
End of Day SOC @ 1900, 85% SOC

In approximate terms: A harvest recovery of about 44% of SOC (or 88 a/hrs) to arrive at 85% SOC…

3 tons

Interesting and always nice to see individual reports..I have been reluctant to mount solar on my roof,one because of water intrusion and the other,less solar output than aiming at the sun but also there is less fuss mounted..

Yesterday I did the same with one 100 watt portable solar panel and one 100ah LFP..Started at 51% and ended at 83% moving it two times..Plus 30AH roughly...

Not mounting solar on roof because of water intrusion is a lame excuse. Now saying I don't want them mounted on top and rather dance with them through out the day is different story and understandable.
If properly sealed with self leveling lap sealant there should never be a problem. I check my mounts occasionally to see if the lap sealant is starting to show weathering and 6 years now and still looking good in the western sunshine. That's 8 panels with 4 mounts each (32 mounting angled connections) with 5 screws each (160) going into the roof and 3 into the sides of panels. That's alot of possibilities of intrusion and never gave it a second thought.

Add an extra panel or 2 for flat mounting and now your equal to the daily dance without the hassle of wind blowing them over or having them grow legs and wonder off. 😉

But then I'm thinking as of fulltime user and enjoy the set it and forget approach.

[jaycocreek]

3 tons wrote:
Had another good off-grid solar day today, with no meter monitoring, or intervention (100% passive)…

Stats:
200 a/hr LFP (actual load-tested at 215 a/hrs), 440w solar
Starting SOC @ 0700, 41% SOC
End of Day SOC @ 1900, 85% SOC

In approximate terms: A harvest recovery of about 44% of SOC (or 88 a/hrs) to arrive at 85% SOC…

3 tons

Interesting and always nice to see individual reports..I have been reluctant to mount solar on my roof,one because of water intrusion and the other,less solar output than aiming at the sun but also there is less fuss mounted..

Yesterday I did the same with one 100 watt portable solar panel and one 100ah LFP..Started at 51% and ended at 83% moving it two times..Plus 30AH roughly...

[3_tons]

Had another good off-grid solar day today, with no meter monitoring, or intervention (100% passive)…

Stats:
200 a/hr LFP (actual load-tested at 215 a/hrs), 440w solar
Starting SOC @ 0700, 41% SOC
End of Day SOC @ 1900, 85% SOC

In approximate terms: A harvest recovery of about 44% of SOC (or 88 a/hrs) to arrive at 85% SOC…

3 tons

[StirCrazy]

otrfun wrote:


You mentioned "equalization" again. Why and how would you "equalize" a lifepo4?

no I am not sayign you should or want to, you don't want to but, some people who have 3 stage chargers with equalization AND they are adjustable outputs. they should set there equalization to the same charge voltage if they cannot turn it right off. this way it will never cause you an issue.

[otrfun]

StirCrazy wrote:
cell ballancing won't happen untill you are full, so by setting equalization and float the same as charge voltage you will allow more time for top ballancing. Im not talking days but maybe an hour or two extra time for the top balancing process depending on your bank size.

I get the impression you may be talking about a passive balancer? I've used both passive and active balancers. Neither have worked quite as you describe.

The several passive balancers we've used start operating when charge voltage reaches a preset voltage threshold (typically 3.4v - 3.5v). Charge current and balancing will terminate when the BMS reaches high-voltage cut-off. Or, balancing will terminate when charge current drops below the passive balancer's min. charge current threshold (~100ma). It doesn't continue to operate after reaching "full" or 100% SOC. What I like about an active balancer, the more imbalance, the more current it moves, with or without charge current. The downside it can undo a top-balance if left operating below ~3.4v for long periods of time.

You mentioned "equalization" again. Why and how would you "equalize" a lifepo4?

StirCrazy wrote:
most people just charge them and as soon as they reach 100% they turn off the charger because so many people are scard of letting them sit at 100% becasue of myths propagatd that are intended for storage and maybe the issue is the definition of "storage" to me if you are camping you are never in a storage situation. and when I got home from a trip I would probably give it a day on the charger to make sure it was top ballanced then unplug it if I was going out again next week, and not worry about it being at 100%. or run somthing to bring it down to 90% then plug it in again the night before I am leaving to make sure its full for the trip. to me storage is realy when we are talking in terms of months. so lets say I am working a ton of OT at work for the next two months and I know I am not going camping. run the batteries down to 70 or 80% and unplug. but then before a trip I am charging them the night before to 100% again.

I agree the whole overcharging thing is somewhat overblown. Until we've each had time to flush this out through personal experience, I guess we'll just to have trust companys like Battleborn. When I spoke to them last year, their only caution was not to float their 100ah lifepo4 at 14.6v for more than week or so. It's one small, but important gotcha. They also alluded to the fact that a single-stage lifepo4 14.6v converter/charger would probably not be their first choice for charging a lifepo4 battery. Without a float or absorption stage you run some risk of overcharging---especially if you're the set-it and forget-it type.

[3_tons]

If one were to do a online search for ‘Assumptions, Cretin Fabrications, and Mythologies’’ they’d likely come across topics like Bigfoot, the Lock-nest Monster and the many ‘cultured folklores’ surrounding LFP batteries - lol!! 🙂

3 tons

[StirCrazy]

otrfun wrote:

StirCrazy wrote:
ya he also mentiond that people thing LFP is more finiky than it actual is with the capacity usage and charging. I learned about the float, and to set it for your normal charge voltage as most people don't let there LFP equalize long enough to actavate the cell balancing. never thought that would be an issue.

What do you define as "normal charge voltage" or "float voltage" for a lifepo4?

When you say "most people don't let their LFP equalize long enough to activate cell balancing", what you do mean exactly? As 3tons mentioned, lifep4's do not require equalizing. Are you saying there's a specific voltage necessary to activate cell balancing? And/or a specific amount of time is necessary to accomplish cell balancing?

cell ballancing won't happen untill you are full, so by setting equalization and float the same as charge voltage you will allow more time for top ballancing. Im not talking days but maybe an hour or two extra time for the top balancing process depending on your bank size.

most people just charge them and as soon as they reach 100% they turn off the charger because so many people are scard of letting them sit at 100% becasue of myths propagatd that are intended for storage and maybe the issue is the definition of "storage" to me if you are camping you are never in a storage situation. and when I got home from a trip I would probably give it a day on the charger to make sure it was top ballanced then unplug it if I was going out again next week, and not worry about it being at 100%. or run somthing to bring it down to 90% then plug it in again the night before I am leaving to make sure its full for the trip. to me storage is realy when we are talking in terms of months. so lets say I am working a ton of OT at work for the next two months and I know I am not going camping. run the batteries down to 70 or 80% and unplug. but then before a trip I am charging them the night before to 100% again.

the whole issue is there is a lot of sterio type carry overs from Nickle mettal hydride and other forms of Li batteries that people assume apply to LFP also. some may verry well still apply but not in the same ways. the old 20 to 80% operating range isnt one of them. yes I would say to avoid using the bottom 10% but there is no reason not to go to 100%, just don't leave it there for long term storage. and this 90% range will increase the cycles you'll get out of your pack because thr 3000 to 4000ish is based on 100% cycling. and if you think about it if you fully cycle your batteries twice per week at 3000 cycles thats going to last your 28 years. even if you cycle it 6 days a week that will still last you just hy of 10 years, and remember that 3000 cycles isnt a measure of when the battery will stop working but rather when it has degraded down to only having 80% of its original campground. beyond that it may run for another 20 years at a slower degradation as that first 20 % is the fastest and it slows down as it goes. so realy if you have a 400AH bank and you only use say 200 of it, in 28 years you will only have a 320AH bank and as long as you havent abused it to cause dammage and its still normal cycling it will peobably last you a lot longer than most of us will live at that level. so yes if your going to use them in the winter find a way to keep them warm, if the usage its self dosen't do it, charge them to 100% often to keep them ballanced and when you are "storing" take some of the charge out so its not sitting full. I still have to look into this one more and find out exactly how thats harmfull or if it even is in all conditions, maybe its fine in the summer and only bad in the winter of vise versa.

Steve

[ewarnerusa]

I am not speaking for StirCrazy, but I think I may have an idea what he is referring to based on what Battle Born said in a link I posted earlier in this thread.
https://battlebornbatteries.com/set-tristar-ts-45-ts-60-pwm-charge-controller-used-lifepo4-battle-bo...

...You can use a voltage range between 14.2-14.6 volts for the bulk and absorption charge stage, There is no problem using an absorption voltage of 14.6 volts. We use a set absorption time of at least 20 minutes per battery because our BMS uses a passive balancing at the top of the charge cycle. When the battery voltage exceeds 14.2 volts this balancing will occur and ensures that the cells remain at the same state of charge, which helps for pack longevity and performance. This preset time will allow and ensure that this balancing occurs. The controller should sense the voltage preset has been hit during its charge cycle which will allow it to move to a float voltage. If a 90 minute absorption does not fully restore the battery and achieve a full charge then it may indicate the battery is out of balance and needs an extended absorption charge to reach a balanced charge. If you have any questions, call us at...

[otrfun]

StirCrazy wrote:
ya he also mentiond that people thing LFP is more finiky than it actual is with the capacity usage and charging. I learned about the float, and to set it for your normal charge voltage as most people don't let there LFP equalize long enough to actavate the cell balancing. never thought that would be an issue.

What do you define as "normal charge voltage" or "float voltage" for a lifepo4?

When you say "most people don't let their LFP equalize long enough to activate cell balancing", what you do mean exactly? As 3tons mentioned, lifep4's do not require equalizing. Are you saying there's a specific voltage necessary to activate cell balancing? And/or a specific amount of time is necessary to accomplish cell balancing?