LifePo4 Charge Performance

[otrfun]

Thinking seriously about replacing our two GC2's with a pair of 100ah LifePo4's. Hearing a lot of chatter about how lithiums accept a charge much quicker than lead cells.

Very familiar with how our GC2's charge after being discharged to 50%. It typically takes our 45a converter 2.5 - 3.0 hours to charge them from 50% to ~90% (at 14.4v).

Assuming a pair of 100ah LifePo4's were discharged to say, 10-20%, roughly how long would it take a 45a converter to charge two 100ah LifePo4 batteries to 90-95% assuming the converter remained at 14.4v the entire time?

Thanks!

[Itinerant1]

LilasCook wrote:
Hi...I'm attempting to choose the importance of the issues I am having with my new 12V 4 cell 80ah LIFEPO4 battery that I bought of Aliexpress and how to best continue while Im still ready to question the buy. It accompanied a 80a BMS with bluetooth capacity and Ive been utilizing a bluetooth application on my telephone to screen execution. I have completed 4 cycles on it up until this point and at present the best I have seen out of it is about 55ah. While charging, the voltage distinction between cells is inside 0.004V. As the voltage at cell 1 draws near to 3.4V, that phone begins to charge a lot quicker than the others and the overvoltage trips as cell 1 surpasses 3.6V while the other 3 cells are still scarcely enlisting 3.4V. During release, the voltage distinction is strong to inside 0.003V and as cell 4 methodologies 3.2V, it depletes a lot quicker than the rest and undervoltage trip is initiated as cell 4 arrives at 2.67 voltages while the other 3 cells are still around 3.1V.

You should start your own thread. Maybe brand of cells, did you top balance plenty of other questions.
You would get more useful help at diysolarforum.com it's orientated towards lfp build and more of the issues your quetioning about. Scoll down to Lifepo4 section. Here you might get speculation from folks that read about lfp but no hands experience.

[LilasCook]

Hi...I'm attempting to choose the importance of the issues I am having with my new 12V 4 cell 80ah LIFEPO4 battery that I bought of Aliexpress and how to best continue while Im still ready to question the buy. It accompanied a 80a BMS with bluetooth capacity and Ive been utilizing a bluetooth application on my telephone to screen execution. I have completed 4 cycles on it up until this point and at present the best I have seen out of it is about 55ah. While charging, the voltage distinction between cells is inside 0.004V. As the voltage at cell 1 draws near to 3.4V, that phone begins to charge a lot quicker than the others and the overvoltage trips as cell 1 surpasses 3.6V while the other 3 cells are still scarcely enlisting 3.4V. During release, the voltage distinction is strong to inside 0.003V and as cell 4 methodologies 3.2V, it depletes a lot quicker than the rest and undervoltage trip is initiated as cell 4 arrives at 2.67 voltages while the other 3 cells are still around 3.1V.

prototype pcb assembly services

[BFL13]

OP, good explanation of the situation.

Have same problem with our TC for battery space and MW operation, but not the weight issue. You want LFPs for the weight, high discharge rate without alarming off the inverter, and more AH, while any gen time reduction is a bonus. Got it!

Fixed ours with a pair of SiO2s (act a lot like LFPs) for half what LFPs cost around here, but you could save weight with the LFPs. No temperature issue with SiO2. LFPs are coming down in price in the States maybe so that could help.

Had trouble with our battery compartment being able to hold two 6s but not two G27s. With AGMs/SiO2/LFP you can stack them on their sides if that works. Not with ours. Moved the batts to inside the camper under the closet floor since these batts don't need to be vented as much as FLAs. Your camper might have an opportunity somewhere inside to move the batts to if you need to. That would help solve the temp issue with LFP and keep the weight saving value.

So you are right to be looking at LFP for the reasons given. You might be able to get the same benefit from SiO2 if you can stand the weight being like the 6s and not have a temperature issue. LFPs have a longer "life" in terms of cycles you can do, so if you are young that could even up the Money part. (Any new battery could outlast you if you are getting on like some of us 😞 ) We are too old for LFP.

On that, there is the question of how long with that RV and what happens with the LFPs when you sell it. Have to yank them out to put in your new rig and get a FLA to put in the old rig. So leave some wiring in the old battery box if you move the batts to inside.

Some solar might help too. It does not weigh very much and can bring in lots of AH.

[Itinerant1]

pianotuna wrote:
The point is that li don't need to be returned to 100%, or at least not very often. So run the generator until there is enough "cushion" and stop charging.

So generator run times are based on consumption--and not the "get to 100%".

Pianotuna well said and hits the nail on the head perfectly. That's exactly how I've been using my setup. Last year I put 27 hours on the eu2200i with 1 to 2 hour hold over charges. In 5 years the generator has roughly 125 hours on it. 🙂

[steveh27]

otrfun,

I have a Class B and space was the reason for me to get Lifepo4. I fit two 100AH batteries in my small battery box which could only hold one 105 AH lead acid. Unfortunately, shortly after getting them I've had a health problem which has prevented me from using them much. I hope to do so starting this April.

[otrfun]

BFL13 wrote:
OP you keep changing the story, so hard to advise. If you are happy with the 80AH you get now doing 50-90s, then you can get the same shorter time as with LFPs just by doing 40-80s instead, with what you have now. Constant 45 amps and no tapering by avoiding the 80-90 part. Same 1.8 hours for 80 AH (not 88AH?)

If you need more than the 80AH for camping, you can get say 115 by doing 40-90s now as I previously explained. You could get 135AH in three hours with LFP too, but do you really need an extra 20AH when it costs $1,500 doing it that way? Goodness!

You could just take along an extra 80 AH 12v Rv battery and use its 40AH "useable" to make up the difference, for $100? Or can you get any solar where you are camping?

No info on your rig, camping scenarios, etc as to what your options are.

The way you keep warping the math to make LFPs the answer, I suspect you just want LFPs no matter what. So just do it and get it over with, or it will be like a toothache until you finally see a dentist! 🙂

Or else we need a good look at the whole situation with rig and camping scenarios to see what your options are that you are working with.

I opened this thread because I've seen plenty of "on-paper" LifePo4 charging scenarios. Wanted to see if they can be confirmed with reports from actual LifePo4 owners. Nothing more, nothing less.

As for me warping the math (or changing the story), in this last post I merely presented an apples to apples (80ah to 80ah) charging scenarios based on my experience with our two GC2's vs. what I *might* expect to get with two 100ah LifePo4's. If my math or assumption about the charging rate is wrong feel free to correct.

Appreciate your suggestions ref increasing ah's with an additional lead cell. We have a truck camper, so space is very limited. Also, our truck camper is pushing the limit in terms of our truck's payload. Any way we can reduce weight is a plus. Two 100ah LifePo4's easily weigh 60 lbs. less than two GC2's. They also offer much more usable ah's between charges and more stable voltage across a vast majority of the discharge spectrum while under heavy load (in our case we need 110a to power our microwave). The low-voltage alarm rears its ugly head way too soon when we load down our GC2's with 110a (only have .15v battery/inverter cable loss at 110a). Every LifePo4 load chart I've seen shows very stable voltage (much higher than 11.0v) from 100% to less than 10% SOC while under heavy load.

In any case, hope this gives you a better feel for our application and why LifePo4's are looking like they *may* be a good fit for us. Outside of cost, and possibly cold-weather performance, we've found very little to not like about LifePo4's.

[pianotuna]

The point is that li don't need to be returned to 100%, or at least not very often. So run the generator until there is enough "cushion" and stop charging.

So generator run times are based on consumption--and not the "get to 100%".

That is why I favor large capacity banks.

[BFL13]

OP you keep changing the story, so hard to advise. If you are happy with the 80AH you get now doing 50-90s, then you can get the same shorter time as with LFPs just by doing 40-80s instead, with what you have now. Constant 45 amps and no tapering by avoiding the 80-90 part. Same 1.8 hours for 80 AH (not 88AH?)

If you need more than the 80AH for camping, you can get say 115 by doing 40-90s now as I previously explained. You could get 135AH in three hours with LFP too, but do you really need an extra 20AH when it costs $1,500 doing it that way? Goodness!

You could just take along an extra 80 AH 12v Rv battery and use its 40AH "useable" to make up the difference, for $100? Or can you get any solar where you are camping?

No info on your rig, camping scenarios, etc as to what your options are.

The way you keep warping the math to make LFPs the answer, I suspect you just want LFPs no matter what. So just do it and get it over with, or it will be like a toothache until you finally see a dentist! 🙂

Or else we need a good look at the whole situation with rig and camping scenarios to see what your options are that you are working with.

[otrfun]

BFL13 wrote:

otrfun wrote:
OP here. Appreciate everybody's replies!

Really likin' the fact LifePo4's can accept full charge current for most of the charge cycle. I'm thinking our 45a converter will suffice with two 100ah LifePo4's for the time-being. If we can charge two 100ah LifePo4's from 10-20% to 90-95% in approx. 3 hours I think we'll be fine. That's approx. 150ah being placed back in the LifePo4's which is approx. double the ah we'd get into our two GC2's in 3 hours.

Looking forward to this LifePo4 upgrade!

150/45 = 3 hrs 20 minutes
45 x 3 = 135 AH

Best you can do with two GC2s is a 40-90 = 50% of C20, = 115 AH from a pair of 230 GC15s

that would be 40-80 at 45 = 92AH/45 = 2 hours, plus an hour to do the 80-90 with tapering amps =23 AH so :

115 AH takes 3 hours with a pair of GC2s
135 AH takes 3 hours with a pair of LFPs

BUT when you really want LFPs no matter what, you can call 135 twice 115 if you like. 🙂

Ok, might have been a bit optimistic.

We get ~80ah out of two GC2's when discharging from 90 to 50%. Takes us 2.5 - 3.0 hrs. to charge back to 90%. No doubt some get more ah and charge faster, but this is what we've managed with two different sets of GC2's.

Based on what I'm hearing here, two 100ah LifePo4's should easily accept the full 45a output from our converter at 14.4v for the full duration of an 80ah charge (say, 50 to 90%). *If* this is true, it should take approx. 1.8 hrs. to charge back 80ah.

So, not quite twice as fast as I had originally claimed/hoped, but (for us) possibly 28-40% faster. Still a decent improvement.

[BFL13]

time2roll wrote:
And 80% every day for a week or two and the FLA really needs a top 100% charge. Lithium would not care.

Yes, but that would only matter if that were the scenario. Solar helps with that too.

You have to start with the whole story up-front and then design your set-up. If LFP makes it work cost-effectively and other types don't, that's it. Be rare that LFP is the only thing that would make it work at all.

[time2roll]

And 80% every day for a week or two and the FLA really needs a top 100% charge. Lithium would not care.

[BFL13]

My ugly graph gives the charging times for a 220AH FLA bank when doing a 50-90 at 70, 55, and 35 amps. Let's compare those times to do that 88AH with LFP with those same three charging rates.

70 amps initial charging
LFP - 88/70= 1 hr 16 min
FLA- 2 hr 9 min

129/76 = 1.70

55 amps initial charging
LFP - 88/55 = 1 hr 36 min
FLA- 2 hr 19 min

139/96 = 1.45

35 amps initial charging
LFP - 88/35 = 2 hrs 31 min
FLA- 2 hrs 57 min

177/151 = 1.17

In this scenario, you see how the time advantage of the LFP shrinks as the charging rate is reduced. With solar at its low amps, you can see how that would fit in.

Before getting LFP, if "faster charging" is your reason to do that, it would be a good idea to do this sort of calculation and be able to tell how much of an advantage you can get with your existing amp size charger, what size charger you would need to make it "worth it", and see if your rig can handle that increase in charger amp size--especially if it would require a higher wattage gen to run it.

Money is not the only factor--there is the temperature "thing" that you may or may not be able to work around.



PT. the SiO2 spec says they have a slightly higher internal R than a regular AGM.

EDIT--change the scenario for the OP to do a 40-80 instead of a 50-90 and you can see why--constant amps at 45 amps with FLA and almost the same for LFP. Scenario is Everything!

[3_tons]

From all that you’ve provided, for seriously cold WX applications (e.g exterior unheated battery compartments), I doubt anything could perform as well as SiO2...

3 tons

[pianotuna]

Oddly enough the folks who sell SiO2 claim they are low resistance internally. But clearly not nearly as low as LiFePo4

-28 c heading for -37, -18 f heading for -35

[3_tons]

“There can be an advantage. How much of an advantage "depends". Is that much of an advantage worth the Money? What is the scenario?”

Money and other abstracts aside, Li has a very low internal resistance which results in shorter charging times compared to FWC’s put in the same scenario...Agree that cost could be the final determinator ...

3 tons