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]

I believe Trojan is adding the cover your rearend with deny deny deny warranty claim options.

With the price of lfp cells now and some homework a nice size battery bank can bebuilt at a very reasonable price equal to or less than lead batteries. Even this concern of cold temps is something that can easily be figured into the build/ placement of batteries and if that can't be overcome than lfp isn't a good fit for your wants and stay with tried and true batteries already on the market.

I thought I had colder temp readings but I don't. Last Nov I had outside temps of 7f with compartment temps of low 40s and my cells dropped to 32f which stopped charging but had no problem still using them. I took my small heater I have and throw it in the compartment within 20 minutes all cells above 35f. I think having the ability to monitor cell temps is important because going off ambient temps is just that ambient temp.

Here was just mild temps of 29f in the morning.

[BFL13]

time2roll wrote:
I assume the Trojan BMS is of superior capability to throttle the current based on temperature.
The others are just connected or not.

Don't see it saying the BMS does that. The guide says that current must not exceed the max currents for the temp ranges, but it does not say the BMS will do that.

Seems like it is your job to have your charger's current limit match the situation. You can't adjust the current from a 55 amp converter! So if it is 35F, what are you going to charge it with? Who has a 15 amp charger handy?

My question is what happens if you hit the battery with a 55 amp converter at 35F? The Auto Shut Off safety the BMS (I guess) does, says only that it protects against "over-current", namely 120 amps.

What protects it from 55 amps at 35F? Over-voltage will make it shut down at any point, but would voltage spike immediately to 15.X if you start with 55 amps at 40% SOC, eg?

It says if you do cause a shut down, you have no power at all, so if you need 12v for the RV you need a way to have that until the LFPs can be restarted. Itinerant1 told us about his episode with that. Similar to the classic low battery at 3am and now no furnace fun time that can happen.

If you hit a FLA with a high current above its "natural acceptance rate" it just accepts what it can and nothing bad happens. I always made sure I didn't go over the max amps for my AGMs and now the SiO2 mod-AGMs, but I don't know what would happen if you go over their max amps.

I am really surprised this current limitation with LFPs has not come up with all the talk of "faster charging". Trilliums say you can only do the 110 amps if the battery is above 73F, under that and it is 56 amps.

it seems the LFP guys here have at least 200AH worth, so that would allow 100amps charging most times and they likely have 60 amp chargers so it just doesn't get noticed I guess. Still wonder what they do at 35F. 30 amp max with 200AH. Turn on the 60 amper and stick your fingers in your ears in case they explode? 🙂 That can't be right.

[time2roll]

Buyer beware

[3_tons]

time2roll wrote:
I assume the Trojan BMS is of superior capability to throttle the current based on temperature.
The others are just connected or not.

AFAIK, that assumed Trojan capability is not apparent to me.

3 tons

[time2roll]

I assume the Trojan BMS is of superior capability to throttle the current based on temperature.
The others are just connected or not.

[3_tons]

BFL13 wrote:
https://www.trojanbattery.com/pdf/Trillium_UsersGuide.pdf

Some interesting things here. Chap 6. Note need to wait after balancing before using. Note weekly need to charge to true full. Note danger from not recharging soon after a low voltage shut off.

Seems LFPs do have a need to be properly taken care of, but in their own way. The BMS will not save you from in-attention, it just helps.

There’s no Boogyman here that I can see here, or have ever experienced in ACTUAL LiFePo4 usage...

From my perspective Trojan is merely saying that:

1) Make sure battery is fully charged (then a brief period of rest to balance) before first use.
2) When not in storage, make sure to fully charge at least weekly to provide for occasional BMS cell balancing.
3) It’s not a best practice to routinely fully discharge any battery, but if you do, it’s important to promptly recharge the battery...

3 tons

[3_tons]

BFL13 wrote:
So what is the Trillium spec all about? Why them and not yours?

In my view there’s nothing all that unusual here, as it seems only appropriate that different manufactures may have different in-house recommendations - some more conservative than others (a matter of ‘Best Practices’ I would suspect) likely intended to extend service life...

I would also point out that of all the LiFePo4’s I shopped and studied, Trillium is the only one that I’ve seen that recommended a reduced current below 41f to 32f, but is also one
of only two that I saw (BB the other) which states charging below 32f IS allowable, though at a much reduced rate... Having read at least one or two white papers (of which source I can’t no longer recall), nor have I seen a reduced charging rate advisory above 32f, so I believe that in this regard Trojan is the outlier.

None of this really matters much to me because my 200a/hr Li is housed within the camper’s heated interior (and seldom habitat in freezing weather anyway), but where the battery resides unheated, I suspect that in the interest of longevity it might simply be a ‘Best practice’ to follow Trojan’s recommendation...

3 tons

[BFL13]

https://www.trojanbattery.com/pdf/Trillium_UsersGuide.pdf

Some interesting things here. Chap 6. Note need to wait after balancing before using. Note weekly need to charge to true full. Note danger from not recharging soon after a low voltage shut off.

Seems LFPs do have a need to be properly taken care of, but in their own way. The BMS will not save you from in-attention, it just helps.

[Itinerant1]

No clue. To me their specs are all over the place when looking at charging and they even say it's ok below freezing, granted really low but still goes against white papers I read. Low cut off at 8v, high cut off at 15.2v which seems lower than normal and high. Trojan must know something others don't.

[BFL13]

So what is the Trillium spec all about? Why them and not yours?

[Itinerant1]

BLF13 I sent an email to Elite Power Solutions LLC where my Lifepo4 batteries come from and ask the specific question of charging at above freezing temps.

Message: Hello, When the GBS cells get below 32f the bms protects the cells by not allowing the charge to happen but once the cells reach a temp above 32f and start to charge again is there a certain amount of current it should be reduced to and wait till above a certain temp. Example, I have 500ah (20 cells), I can charge at 125a with my Magnum inverter/ charger. Will I harm the cells charging at .25c while they are at a lower temp (say below 40f) or should I reduce the current some?

Response: The system disables charging when any cell is below 32F. No amount of charging is safe below this temperature.

0.5C of lower is the recommended charge rate for longest life. At 125A / 500Ah you are at C/4 so you are well below this limit.

Message: Just so I understand correctly in colder temps above freezing there is no harm in charging at the recommended 0.5c charge rate for longest life of the cells.

Response: Correct

Regards,

Elite Power Solutions LLC
_____________________________
So if I had the ability to charge at 250a there should be no harm on my 500ah battery bank and charging at what I can of 125a certainly won't hurt them.

[BFL13]

Steve has a bee in his bonnet about something or other, but I like his posts that make you think, and you have to "work for it" when responding.

I think the main problem is the usual difficulty in being clear to everyone what you mean when typing up a post on the internet. The trouble is that everyone does not pick up exactly what you meant by what you said the first time around, and might even get annoyed.

I remember "Communications" when it was divided between Transmission, Medium, and Reception. It all has to line up to be successful.

[pianotuna]

Steve,

I find some of your statements misleading.

1. not all li can discharge at high rates. When they are BARE without bms it is true--but at least some BMS designs limit discharge rates to 1C

2. SiO2 can be taken to 0 volts--so the capacity is 1C, but you do loose cycles.

3. SiO2 can be charged at 27 amps. There is no bms to protect the battery--that is on the shoulders of the owner.

4. LiFePo4 can only be taken to 20% state of charge. The makers get around that by building a 120 amp-hour battery and using the BMS to limit it to 100 amp-hours. As with most batteries going deeper costs cycle life.

I think pouch cells are a bit riskier than the approach that Tesla and other makers are using. One poor pouch may dramatically reduce the entire capacity.

I believe LiFePo4 are GREAT, but only if there is zero cold weather use. If there is--then the MUCH more expensive lithium titinate chemistry needs to be used.

It is at this moment -22 F where I am located. Last night was -35 f.

[BFL13]

Note that you do not have to own LFPs and have experience with them to observe that 80/40 = 2

Yes, 40-80s means fewer lifetime cycles than 50-90s but not that many fewer. Just another trade -off. How many times a year will you ever do that as a weekend warrior? Or are you a full-timer off grid?

You still have to recover the batts (AGM or FLA) after some successive incomplete recharges, so for that aspect 40-80s or 50-90s same deal.

You don't have to guess the time it takes to do a 50-90 with an 80 amper on 200AH of FLA or AGM, see my ugly graph posted earlier. EG it takes about two hours with a 70 amper.

You can't use the 80 amper on the single 100AH SiO2, AFAIK. It's specs say 27 amps max. You can't throttle back the amps of the charger. A FLA battery will throttle back the amps it takes in by acceptance rate, but I could not find out anywhere if the SiO2 will do that without any harm.

I did not even dare to use my 55 amp converter on the single, but now with two at 200AH I can. With the single I had to use my Vector portable at its 20 amp setting, and not use its 35 amp setting.

On that, nobody has really answered my point about charging LFP at under 41F where Trillium spec says 15 amps max for the 111AH batt. What happens when you apply your 55 amp converter to that batt at 35F? Will it be damaged? If so, how do you accomplish the recharge with your 55 amper? Do you also need a Vector portable that you can set to 10 amps and not dare to use the 20 amps setting?

I think that would be of interest to any LFP owners. Those who have them might say what they do and how that works. (Once the LFP gets over 41F you can really go after it with the high amps)

There are many trade-offs in each scenario for choosing battery types for an RV set-up, so the more info and points of view we can get the better.

The OP started with an exaggerated idea of how LFPs would save him generator time compared with the set-up he has now. But he also has other very good reasons to be looking at LFPs or perhaps SiO2, so on balance, IMO he is a good candidate for changing his type of battery.

The Money factor is hard to evaluate since we don't know what anybody else can afford.

LFPs being the best-buy for number of cycles might make sense if you are 40, but not so much sense of you are 80. Scenario is everything!

[StirCrazy]

I am starting to see a lot of bad comparasons and boarderline advice when it comesomparing differnet battery types and such. I dont claim to know everything about every battery but I do know a lot about a few and when someone mentions a new type I read about it.

BFL13 wrote:
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?)

what is being recomended here, cycling a deep cycle between 40-80 , yes you can charge it faster but now you are droping below 50% every cycle which lowers the life cycles of the battery and also this way you wont be able to get it back to 100% very often which is fine for a few cycles but you realy should try to hit 100% every so many cycles or you can impact the life span of the battery.


but one thing that is realy starting to burn my bridges is the comparason of aples to oarnges to apples instead of apples to apples.

LiFePo4 (Ill just refir to as Li from this point forward) is now the cheepest battery per usable AH, has a very high discharge rate and also has the highest charge rates, if you have the equipment to take advantage of it.

this whole thing of saying cycle between 40 to 80% so you get faster charging is skewing the exparament to get the results you want instead of a real comparason. if you take a 100 amp Sio2, a 200 Amp deep cycle and a 100 Amp Li, they all got simular usable capacity well the Sio2 has 80ah, the deep cycle has 100ah and the Li has 100ah.

(and yes you should be able to use the full 100ah out of a reputible li batter maker as they actualy use a little higher of a capacity and use the BMS to set the low and high charging limits to prevent damage while still giving you 100% so no you dont have to cycle between 0 and 90% or 10-90% or what ever the rhumor of the month is at the time. yes on raw cells you do but thats a different creature)

so with a 45A charger (lets change it to 40A charger just to make the numbers work easier haha) we are going to take 80ah from each battery, so the SIo2 as we have seen from BFL13's experiance can only use 25A from the charger would take over 3 hours just to get to 90% and then what ever the adsorbtion phase is give or take depending when it kicks in. the deep cycle would be in a simular situation depending on the type of battery would probably be able to take a larger initial charge but with the adsorption phase and such would be looking well over three hours also. the Li would use the full output and with the tiny tiny adsorbtion phase, like a min or two would take aproximatly 1ht and 45 min to recover to 100% .

now if you want to skew things so you dont have to use the adsorption on the Sio2 or the deep cycle then lets scew things the way of Li also. there is a good chance that when you upgrade to Li batteries you have to upgrade at least the charger section of your converter/power pannel or bypass it with a different charger, so why not take advantage of that and throw a 80 to 120 ah li compatable charger in it.

now with a 100 ah charger lets compare things, and we will get rid of the adsorption phase and not worry about battery life dammage hell lets just say an 80amp charger to keep the math simple again.

sio2 on the 80a charger can still only accept 25amps so to recover 80ah it will take 3.2 hours. deep cycle can do a little better depending on temp and aceptance rate I am going to guess about 2 t0 3 hours (would have to have the battery specs to make a closer guess and even then with out timing it , it would still be a guess but that should be in the ball park) Li, to replace 80 ah with a 80amp charger would take 1 hour.

so if we are skewing things lets skew everything to there major advantage or nothing at all. I have deep cycles in my 5th wheel that are now 15 years old and are just starting to get week but still have another season or two they could do (I am waiting to see if shipping is coming down more on Li cells after covid is over) last year shipping was three times the cost of the cells to canada this year it is roughly the same which is one reason they have become more affordable and if you build them your self hands down the cheepest battery to get especialy if you are buying enough for a larger bank. I can get 16, 280AH cells right now for 1800.00 delivered, plus another couple hundred for BMS and materials to build the boxes, that will let me build a 840 usable ah 12v set up for the 5th wheel which is almost 4 times the capacity I have now, and upgrade the camper with a 12V, 280AH setup which is alomst 3 times the capacity of my two 6V batteries. also for the fith wheel it will be 1/2 the space used and 1/3 to 1/2 the weight up front. the camper it would be 1/3rd the weight and 1/3rd the space roughly.

having said that I dont plan on having to charge my batteries when it is realy below 0, I will have the batteries in the heated space so that when they charge from solar in cold temps they will be warm. a good BMS will have cold temp charge cutoff anyways to protect from that and even though you cant charge them if there cold you can discharge them to -20C so in my case that will be good enough to start the furnace to warm everthing up to the point they can charge.

there are some cases like in Pianotuna where he is using his for work in some pretty extream cases where spending a bunch extra money on something like Sio2 makes sence, especialy since he can write them off for business, or some one who does extream cold weather camping and doesnt want to use a genny to supply power for the initial warming of the rv, but for genneral spring to fall and some mild winter camping which I would guess most of us fall under any battery will work, it just comes down to size, weight, usable capacity, life span and price (per usable AH). right now with some of the new battery that have been popping up or especialy if you can turn a screwdriver and put cells togeather Li has turned into the leader of every class.

Steve