LiFePo4 vs Lead Acid...Some points of interest.

The Battery U link has a charge time graph (scroll down) that has what I need to make a time comparison to do a "0-90". Obviously the "90-100" times are of great interest, but I don't have that for FLA. Their graph does go to 100 on the capacity curve.

I will use my ugly graph figures without inflicting the graph on folks again, unless you all insist. I have it for a 55 amper on 220AH doing a 50-90 which is a 25% charging rate, so that makes it convenient. I just need to do it in proportion for a 100AH batt, easy! Same times at the 25% rate doing 25 amps on 100AH as 55 amps on 220AH.

The FLA Bulk ends at 72% SOC and tapers to 90%. the Batt U graph shows the time for when the capacity reaches 90% on their 100AH batt. It shows Bulk ending at 60% SOC then amps taper.

(Howls of outrage from the usual suspects!--so take that up with Batt U , not me)

So FLA first:

0-72AH at 25 amps = 2.88 hr = 173 min
72-90AH tapering = 86 min
Total time 0-90 = 259 min = 4.32 hr

Now the LFP:

0-60 at 100 amps = .6 hr = 36 min
60-90 tapering amps = 39 min
Total time 0-90 = 75 min = 1.25 hr and 4.32/1.25 = 3.46 times faster
It would look worse for the FLA if we added the 90-100 part.

What about a 40-90 though, perhaps more typical of camping?

FLA : 40-72 at 25 amps = 1.28 hr = 77 min
72-90 still 86 min
Total = 163 min = 2.72 hr

LFP: 40-60 at 100 amps = 12 min
60-90 still 39 min
Total = 51 min = .85 hr and 2.72/.85 = 3.2 times faster

So if you added the 90-100 times it would be more like the 4 times faster claim for a 0-100 looks like. (if anybody would ever do that with an FLA!)

EDIT--in real life an RVer might have a 100a charger and be used to doing 50-90s with his 460AH bank of FLAs. He might wonder how much gen time he could save getting the same AH restored (that matched his AH usage) if he switched to LFP.

Now he can't use the 4 times faster as with 1C vs .25C. He has to do a whole set of calculating to see how much gen time he would save with how many AH of LFP instead of his 460AH of LFP, assuming he will still use his 100a charger.

The fact that Lithium chemistry has a higher charge acceptance rate than Volta’s battery contraption :) (a consequence of less internal resistance and 97% efficiency) might seem entirely self-evident..Cobbled together premises, misdirects and other ‘ad hoc’ bells or whistles will not refute what is hard-baked into LiFePo4 physics...It’s time to engage with reality...

3 tons - Happy as a clam in ‘Harvest 101’

You can determine the bulk/absorb transition point from these curves - if you set your charger CV point at 3.6V per cell, you will transition to absorb at ~ 98% SOC at 0.5C or ~97% SOC at 1.0C. If you set it higher it will go further in bulk.

I charge dozens of lithium-cobalt batteries on a bench top charger every month, and it is 80 - 90 minutes from 3.5V (~empty) to full (ie 4.2V and current less than 0.05C) at 1C. At 2C it is under an hour to full.

I don't charge my LiFePO4 bank nearly that fast as it charges of solar (~0.1C), but once it gets back to 13.9V then the BMS and BMV are showing 98% SOC. I have my absorb time set 30 min, which then gets it back to 100%.

As you well know, the finish line matters for lead acid as if you don't cross the line you increase the rate of sulfation, and shorten the life of the battery. LiFePO4 doesn't care about the finish line, so 98% is fine, but you can take to 100% if you want or have the time.

BFL13 wrote:
FWC that graph does not show the current and Bulk vs Absorption. The battery voltage rises all the way through both stages in LFP and FLA.

Looking for more examples like in previous post showing when Bulk ends with 1C. One is 70% and the other says 60%. I saw one where they said at 0.5C, Bulk ends at around 90% or so. 97% would have to be at a lower rate than 0.5C.

To run a race against time :) we need a start line and a finish line. since the FLA looks bad for the last lap, FLA wants to make the finish line at 90% SOC, but the LFP guy insists on timing to the last electron into the FLA.

Also the LFP guy says he is full when amps taper to 5% of C. The AGM wants 0.5a/100AH so that is going to take a while. BTDT-watching paint dry.

Starting line is another issue. the graphs seem to be using "depleted" to "full" as the course. The FLA guy says to start at a higher SOC so the LFP 4x has less time to run before Bulk ends, and the LFP guy wants to start with zero%.

for this exercise we could pick some sort of finish line that is not extreme--after all Absorption goes to infinity, so you have to declare it is over somewhere. and use zero% for the start.

Then we could do another one with more real life examples such as 20%-90% or whatever. If we are doing this to compare gen times (seems to me that would be the reason to get faster charging) then you always stop the gen at 80 or 90% with FLA. Silly to waste time and gas on the 90-100. OTOH you don't usually run the FLA down so low as 20%. But if you don't use a low SOC, the LFP guy says no fair, because he does better the longer the Bulk stage goes.

time2roll wrote:
OK and still in all practical use the LFP is so much better than the dinosaur FLA.
FLA has no advantage except on initial price for small capacity applications.

Initial price is made up for with higher energy density, more usable energy storage due to true deep discharging capability and long battery life. Also prices are dropping fast and DIY packs are pretty easy and fun to make.

One downside to LFP is cold weather charging, but this can be mitigated with an insulated box and a small heater.

Some people may get a little religious about battery chemistries but the main selling points for me are lower weight, higher energy density, longer life and high charge and discharge rates. When something comes along that outperforms LFP on any of those attributes, I'll be preparing to move to the new chemistry.

Edit: For example, I went from 100ah of FLA(50 ah usable) to 200ah of AGM(100 ah usable) to 271 ah LFP(216 usable). Plus I saved enough space going from AGM to LFP that I was able to add an inverter and can now run the microwave without using the generator.

OK and still in all practical use the LFP is so much better than the dinosaur FLA.
FLA has no advantage except on initial price for small capacity applications.

FWC that graph does not show the current and Bulk vs Absorption. The battery voltage rises all the way through both stages in LFP and FLA.

Looking for more examples like in previous post showing when Bulk ends with 1C. One is 70% and the other says 60%. I saw one where they said at 0.5C, Bulk ends at around 90% or so. 97% would have to be at a lower rate than 0.5C.

To run a race against time :) we need a start line and a finish line. since the FLA looks bad for the last lap, FLA wants to make the finish line at 90% SOC, but the LFP guy insists on timing to the last electron into the FLA.

Also the LFP guy says he is full when amps taper to 5% of C. The AGM wants 0.5a/100AH so that is going to take a while. BTDT-watching paint dry.

Starting line is another issue. the graphs seem to be using "depleted" to "full" as the course. The FLA guy says to start at a higher SOC so the LFP 4x has less time to run before Bulk ends, and the LFP guy wants to start with zero%.

for this exercise we could pick some sort of finish line that is not extreme--after all Absorption goes to infinity, so you have to declare it is over somewhere. and use zero% for the start.

Then we could do another one with more real life examples such as 20%-90% or whatever. If we are doing this to compare gen times (seems to me that would be the reason to get faster charging) then you always stop the gen at 80 or 90% with FLA. Silly to waste time and gas on the 90-100. OTOH you don't usually run the FLA down so low as 20%. But if you don't use a low SOC, the LFP guy says no fair, because he does better the longer the Bulk stage goes.

BFL13 wrote:

So just because you start off at 4 x the charging rate, does not mean you will get to full in 1/4 the time. Need more info and then we could see what really happens for how much faster the LFP is.

You are correct, you will get LiFePO4 to full in much less than 1/4 of the time than lead acid. You are focusing on one relatively insignificant point (whether the LiFePO4 goes to absorb at 95 or 98% SOC) and ignoring the elephant in the room, that once lead acid goes to absorb it will be there for 4 - 6 hours before it is full.

The other point that is being ignored is that unlike lead acid, there is no need to get LiFePO4 batteries to 100% full. I can't think of an application where you would care (or could tell) if you only got the battery to 95 - 98% full, in which case you are done in under 1 hour.

But if you insist on chasing down the minutiae, there is almost no difference in the charge curve for 0.5C/1.0C for LiFePO4:

From a Battery University article:

"Increasing the charge current does not hasten the full-charge state by much. Although the battery reaches the voltage peak quicker, the saturation charge will take longer accordingly. With higher current, Stage 1 is shorter but the saturation during Stage 2 will take longer. A high current charge will, however, quickly fill the battery to about 70 percent"

https://batteryuniversity.com/learn/article/charging_lithium_ion_batteries

Has the sort of graph I want for 1C. Note the Absorption Stage time! Where is that 15 minutes ?

(next I will be scolded that not all Lithium -ions are the same, so that graph doesn't count---so find a link to a real LFP one please)

EDIT the idea that Bulk is shorter with higher charge rate is the same as with FLAs but to a different degree of course.

Here is another quite from someone with LFPs who seems to have a clue base on other posts . They work their LFPs hard cycling 5%-95%

"Charging LiFePO4 is a two step process … FIRST step uses constant current (CC) to reach about 60% State of Charge (SOC); And then STEP 2 kicks in until the charge voltage reaches 3.65V per cell. Turning from constant current (CC) to constant voltage (CV) means that the charge current is limited by what the battery will accept at that voltage, so the charging current tapers down asymptotically.

If you had to time the process – STEP ONE (60% SOC) needs about one hour and the STEP 2 (40% SOC) needs another two hours .. I have seen it that way ever since I started working with LiFePO4"

BFL13 wrote:

I don't know why you would think I was missing that if you read my post.

because you keep asking the same question over and over after several have ansered it already. either there is something your missing, or you just gaming people and stiring the **** intentionaly.

BFL13 wrote:

Yes about the charging efficiency difference. Note that varies with SOC in both cases, but perhaps in different ways. IR changes with SOC.

yes it does vary, but with the FLA it is a huge swing, with LFP it is a tiny swing and can almost be concidered non existant. this accounts for a lot of the difference right there.

BFL13 wrote:

FLA Bulk Stage lasts to a certain SOC at a particular voltage depending on the charging rate. It will go into the 90s SOC at a low rate and can start tapering at 60% SOC at a high rate. My "ugly graph" shows how that works. We have the info for a 25% charging rate close enough (AGMs almost the same as FLA)
.

I have not seen your ugly graph, it isn't in this thread. but I wonder if part of the issue is that they are using C rate charging to compare different battery types.

not once in that article did I see what the 20 hour rate was of each battery (unless I missed that) but looking at that article it shows that FLA took 4 hours to get through the first stage I think because it would only handle up to a .25C rate and wouldn't accept any more, where the LFP would accept the 0.4C rate happily and was charged to 97% in 1 hour. that to me shows that the internal resistance is a huge factor between the two batteries. My interpatation could also be wrong as this example lacks a lot of information, the battery capacitys, the charger amprage, how the chargers were set up etc.

after all it is a sales piece not a scientific study.

FWC wrote:
That appears to be a fairly reasonable comparison, although they don't mention cost. The nice thing is Power Sonic sells both, so maybe there is less baked in marketing BS.

that could be true but not nessasarly, which one do they have the largest margin on. I normaly wont use a sales pitch for info as you dont know that info, are they hyping one or the other just a bit because they make more profit of that type?

Steve