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!

[3_tons]

As per my previous thread stated observation (updated):

“I might definitely lean more in the direction of SiO2 where (in the approx following order):

1) If weather conditions might include ‘extended excursions’ at or below 32F while having no provisions for keeping battery above 32F (e.g. heated compartment or batt. blanket - note, Li safely discharges to about -4’ish F). For some users this criteria could be paramount..

2) Initial cost...However, this issue is often mitigated by the long cycle life of LiFePo4, while LiFePo4 entry-fees seem to be slowly dropping...

3) Ultra high amperage discharge rating of SiO2’s well exceeds all other competing Battery types - might highly depend on one’s amperage requirements (??).

4) Where Recharge ‘C rate’ is not a critical parameter - this more in terms of off-grid solar peak-period harvesting window...

5) Where ‘required-usable’ DOD (depth of discharge) and voltage-sag (vs LiFePo4 alternative) can be offset by having more battery capacity - assumes no space or weight restrictions - Not always of primary consideration or limitation.

6) Where unattended self-discharge rate can be mitigated by an active charging device - something to well consider when off grid...

7) Where battery venting is not a concern.

😎 Were a SOC meter capable of accurately measuring SiO2 SOC is available (TBD)...”

I would again submit that much of this depends on region and is application dependent -JMO

3 tons

[3_tons]

I will add to my previous that while Li’s need to be periodically re-balanced (per Trojan’s advisory), they do not need to be fully charged upon every usage cycle...this is a most advantageous aspect...

I have no idea what Trojan means by their proprietary “contactor” device (thus, comments better reserved for Trojan...), but from my own perspective, those who opt for Li batteries would be best advised to get themselves a capable, full function ‘Lithium compatible’ SOC Meter (such as Victron’s bluetooth BMV 12)... Beyond the customary SOC display, this is the best way (in my view the ONLY* practical way) to stay informed regarding active charging status and to observe the BMS’s real-time functioning...Having said that, know that ‘post charge’ (i.e. having attained trigger voltage and brief hold duration) it normally takes an additional say 10-15 min for the BMS cell-balancing to complete it’s regime...

It’s my opinion that battery built-in type displays are rudimentary at best and inferior to a full function SOC meter.... JMO

*having previous attempted a Xantrex LinkLite meter

3 tons

[BFL13]

Does anyone or himself have that link itinerant1 posted last year, that showed the charging profile graphs for different Li batts, including LFP?

ISTR it showed charging at 100 amps to 100AH batt with amps starting to taper around the 85% SOC mark, and you could see how it would go at 50 amps rate, kind of like with my ugly graphs. Thanks.

It was something like this one. Here it gets confusing by saying amps start to taper at 60% SOC, but if you "overcharge" it can go to 95% before tapering.

https://www.powerstream.com/LLLF.htm#:~:text=During%20the%20conventional%20lithium%20ion,per%20cell%...

[3_tons]

Trojan is Trojan, but my interpretation of this wording is that, beyond the initial first use set-up, balancing should occur at least once weekly (excluding a long term storage scenario)...This is to ensure that the cells receive a periodic maintenance re-balancing...

Proper cell balancing requires the proper charge voltage* which generally ranges from about 14.2v to as high as 14.6v (depending on manufacture’s spec’s), though with most Li brands, BMS voltage cut-off occurs at 14.6v... For certain chargers (like PowerMax @ 14.6v), voltage loss via battery wiring will most likely negate this sole issue.

*Conventional (non-Li specific) PD 92xx bulk operating voltage

3 tons

[BFL13]

Trillium says:

"Note: Once a set of batteries have achieved a balanced condition, they should remain balanced through normal use
and charging. In order to keep batteries in balance and avoid over-discharge, ensure that batteries not in storage
receive a full charge weekly."

So that would apply to all LFPs I suppose? I am guessing they are worried about that business where the battery is "top balanced" so is vulnerable to going too low?

On the chargers not getting the bank to spec voltages, Trillium says that can lead to endless "cycling" and bad things wrt balancing. So might be a good idea to get the voltages set right, depending.

" Under many commonly-used lead-acid
profiles, the normal charge termination criteria will never be met, and the current will cycle indefinitely until the charger
is unplugged. Even after the charger is unplugged, the battery may not be ready for use until it is allowed to balance for
approximately 10 minutes. In the case of the 12.8V batteries, if there is a desire to use the batteries immediately after
unplugging the charger, the contactor can be manually closed using the status button on each battery"

[3_tons]

“ This could be from wiring inverter to bank, but more likely low 120v voltage input to the charger. I see that at home where my converter will still operate with the long extension cord from the house, but it does lower amps than usual and the input voltage is below the required 105v specified.”

I have a 6’ round trip run of 0004 aught to the inverter...The ProSine charger is programmable, but since making the swap to Li, I’ve yet to bother with any nagging reprogramming (lol) - as is, the voltage tops out at only 13.7 while the PD (for completion, on boost) is at about 14.3v...

Having said this, understand that with Li, except for an occasional cell balancing, it’s no longer my priority to ensure the battery is fully charged upon trip departure (as would be the case for FWC)...I store the battery at about a 50% SOC (to keep + & - ions in approximate equilibrium), a often begin our trip departure with just the 440w of solar alone... This strategy typically gets us to our favorite OHV spot (trailer in tow...) at about 70-80% SOC (as charging continues...) which is quite sufficient for our several days of outing...It’s in this way that I MIGHT only need shore power for an occasional cell rebalancing, but have yet to use the generator for this task...

Another advantage here is that I haven’t had the need to wrestle the Honda 2200i from it’s uber tight storage compartment...Running the 11kbtu roof-top *air for an hour or two duration via inverter (concurrent with harvest) is quite doable, especially now with so little Li voltage sag...

*w/soft-start

3 tons

[BFL13]

"Yet for even faster charging (say, at home in RV garage) I also have on-board a ProSine inverter (w/100a charger), but the maximum amount of charging amps I’ve ever witnessed going to the Li battery is 67amps and this was while the battery’s beginning SOC was at about 40-45’ish %."

This could be from wiring inverter to bank, but more likely low 120v voltage input to the charger. I see that at home where my converter will still operate with the long extension cord from the house, but it does lower amps than usual and the input voltage is below the required 105v specified.

Not surprised the PD 45 amper does less than 45 after all the threads we had on that a few years ago with Salvo and the gang being hot on that. that one might have a wiring issue common to RVs making matters worse.

The OP never mentioned what amps he actually gets from his when he gave his charging time for a 50-90, but it would have been closer to 45.

[3_tons]

The primary function of the BMS is to avoid catastrophic events and to perform individual cell balancing - the BMS does not govern charging amperage, and for some manufacturers serves as a low temp charge disconnect.

3 tons

[3_tons]

A practical account...In my case I came from two 6v GC’s (at about 105 usable a/hrs) to now a single 200a/hr Li having a much greater DOD, which means that charging frequency has been cut about in half. This also means that it’s often easier to manage a re-charge sometime during the mid-day when temps have warmed a bit (this, a U.S. 40’ish parallel thingy...), or just wait another day or two until inclement weather decides to pass - however I’ve negated this temp issue entirely by simply mounting the battery beneath the dinette seat and repurposing the battery box...

Either way, I mostly camp off-grid, thus re-charging is done almost entirely via 440w of roof-top solar, this divided between two switchable controllers (300w & 140w)...In fact, I can’t even recall the last time I started the genny, but know it was NOT to charge batts!! With this aforementioned set-up I would have little if any concern about managing excess charging amps, and for the most part charging occurs passively without much notice...

Were I to need the on-board 3 stage* PD 9245 45amp charger, charging could be easily managed via the optional Charge Wizard pendant, but even in boost mode I never once witnessed (via Victron BMV-12 meter) this charger outputting it’s rated 45 amps, in fact what’s more typical is roughly about half that amount if even that...

*not Li specific

Yet for even faster charging (say, at home in RV garage) I also have on-board a ProSine inverter (w/100a charger), but the maximum amount of charging amps I’ve ever witnessed going to the Li battery is 67amps and this was while the battery’s beginning SOC was at about 40-45’ish %...

Though I do sense the well stated Li consternations from certain posters, it’s my belief that these concerns are mostly regional and application dependent, but nevertheless are still valid battery type considerations...Thus, with these particular concerns in mind, SiO2 may in fact be the more practical battery choice, and less costly alternative to a temperature sensitive Li...JMO.

In my own (admittedly anecdotal) case example, Li has made charging both less frequent and mostly passive, while ended nagging low voltage alarms (“dang furnace won’t run”!!) while enhancing solar harvest recovery times (to recovery earlier in typical day), this, per various ‘back-to-back’ (FWC to Li) off-grid charging episodes...

3 tons

[BFL13]

Internal Resistance changes with SOC and with Temperature. It changes to different degrees between types of battery chemistry and construction.

I am finding info on how that works with discharge current abilities but nothing yet on how that affects charging currents for different types of battery at different temperatures.

LFP is notable for how its IR is higher at low SOC. I think this is why they don't want you to go to "zero" with them. It may be that they fudge where "zero" is. Also they might fudge where "full" is with some battery monitors.

EDIT--I see Itinerant1's sig has his bank in its "usable" amount. I don't do wh, but that would relate to his 500AH somehow 🙂

It comes back to the question why they have such high discharge rates and low charging rates, when you would think they would be the same.

Note that I cannot confirm that SiO2 can't take higher charging rates and will just throttle that down to what they can take. A couple of info guides said they can be charged at high amp rates but not for a long time. How long was not defined. So I personally don't do it since I cannot afford to keep buying new ones!.

With LFP they talk about resting the battery after a full recharge so it works best on the next discharge. It is not clear it has to do with balancing or just how LFP cells work.

I don't see where BMS controls the charging current, even the expensive ones. they do have cut-offs for excessive currents and voltages, but I don't see where they "dial" the current to match the acceptance rate at various temps and SOCs. Seems like that is up to you not to use a charger that cranks out too many amps.

https://batteryuniversity.com/learn/archive/how_does_internal_resistance_affect_performance

Scroll down past the talk time part to the good stuff.

[pianotuna]

Steve,

Good to know:

"it goes on to say that under -20 they very quickly go to less than 50% of the original capacity which is probbly why -20 is listed as the min operating tempature."

However, the dendrites are why no charging is recommended at low temperatures.

Further to SiO2, over 600 cycles, when going to zero volts, to 80% of OEM capacity doesn't sound bad to me.

I'd be interested to know the same figure for LiFePo4

[StirCrazy]

pianotuna wrote:

StirCrazy wrote:
for your charging LFP I would assume at 41 they will take a 1C rate, but I will look into it for you some more. My thinking is the actualy charg rate is 4 to 5C and the 1C is an artificial limit put in place by the BMS to prevent us people from overcharging and making to much heat in them which can distort the plates and wreck the battery. there is a drop off in cold but its not as extream as lead acid and such and I am not sure if it would affect them for 99% of the people with a big bank and lower 45-70 amp chargers. at any rate you are not going to dammage the cell as your BMS will control the charge rate as it is monitoring both the voltage of each cell and the tempature of the pack. this is why if you build one dont get a 20 buck BMS, it will work but will not have cold charging cutoff and such. a good BMS will cost 100-150 cdn but will protect your cells properly.

Steve

I believe it may be more about dendrites growing than plate warpage. The dendrites grow, penetrate the cell separators, and short out. The higher the voltage, the faster they grow. That is why the bms limits charging rate. That results in catastrophic failure, which is why I will NEVER have any house bank in my warm living quarters.

In the bad old days of nickel cadmium and nickel metal hydride, sometimes a LARGE voltage could be used to "burn off" the dendrites, allowing for a little more lifespan, but at reduced total capacity.

just found this from a study on cold weather preformance .

Low temperature performance of LiFePO4 cathode is investigated by charge/discharge test and electrochemical impedance spectroscopy (EIS). The results show that the effect of charge temperature on charge and discharge capacity is very slight in range of ?20 to 20 °C

it goes on to say that under -20 they very quickly go to less than 50% of the original capacity which is probbly why -20 is listed as the min operating tempature.

Steve

[StirCrazy]

pianotuna wrote:
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.

1, Most BMS limit to 1C but thats charging rate not discharge, C1 would be discharge 😉 but if you have a 560AH bank which is two 12V batterys build with 280ah cells that gives you a discharge of 560Amps .. i would call that high. even if you have a store bought one that is only 100ah and discharge 100amps out of it for the size of battery that is a pretty high discharge, two of thoes gives you 200 amp potential and so on. do any ove these other batteries we are talking about have over a c1 discharge rate?

2, all my stuff above was taken at the design to not harm the battery in any way, thats why sio2 is concidered 100 to 20, if we are going to start saying we can take it down to 0 with a little bit of dammage then we have to say for GC batteries we can take them from 100 to 20% instead of 50% as it only reduces the life a little , or Li from 100-0 and get 130ah out of the battery instead of 100 as it only affects it a tiny bit. this is the part of comparing oarnges to apples or apples to apples I was talking about. using an even playing field that maximizes the life of each battery. it doesnt mattery how many battery cells they use to build a 100ah battery , what is important is the advertised capacity and if you get that. to me building a safty factor into a battery is just a little bonus.

3, so I have discovered I thought there would be aceptance rate throttling with Si02 like there is with Lead acid, that is a huge down side for Sio2 if thats the case, but still can work for people.

4, I beieve that is exactly what I said..........

no body uses pouch cells they are the worst lol, battle born uses a 26650 battery in there set up, these are probably one of the better cells to use but it turnes DIY into a complicated and more expensive affair. another good one is the prismatic cell, this is what DIY is mostly. traditionaly they were used in high voltage high capacity power storage like solar battery back ups for comunication and such and some companies are using these to build batteries also. less soldering, less conections and so on. in fact this type of cell is becoming so populare due to the ease that Battle born has made a propaganda video trying to make them seam inferior which like a lot of posts on here they take select info and use a mix of names to make people thing that prismatic cells are the same as pouch cells or that all prismatic cells are made of plastic (thoes are the first generation)

as for the other style batteries that tesla and battle borm use. one bad battery in the series knocks out a whole bank so same idea, just a lot harder to find the bad battery when your looking through 100's instead of 4 haha.. thats why people get parts of tesla packs for there rv's in the states a lot as one section goes bad and they just replace the whole battery. then a company buys the old one for cheep, pulls it apart and sells off the good sections.

cold weather use to a point isnt an issue as I have tried to explain also. for your self who uses the rv as a acomadation for a bisness purpose yes it is an issue , but for 99.9% of the people will never go camping when it is -20 or colder. if you do camp in that -20 to 0C range the only thing you have to do is make sure the batteries are in a space that is heated by the furnace. they can discharge to -20C and once there warm if you have solar they will charge like normal.

now in your case as I have said when you show up some where at -30 or -40 then ya Sio2 will be better for you and the best part is you can write off the expensive cost.

so I dont see anything that I have said as misleading. I didnt know it was a user controld low amp aceptance rate into the Sio2, but I just learnd that this morning and I find it funny that info wasnt more accesable on there website.

[pianotuna]

StirCrazy wrote:
for your charging LFP I would assume at 41 they will take a 1C rate, but I will look into it for you some more. My thinking is the actualy charg rate is 4 to 5C and the 1C is an artificial limit put in place by the BMS to prevent us people from overcharging and making to much heat in them which can distort the plates and wreck the battery. there is a drop off in cold but its not as extream as lead acid and such and I am not sure if it would affect them for 99% of the people with a big bank and lower 45-70 amp chargers. at any rate you are not going to dammage the cell as your BMS will control the charge rate as it is monitoring both the voltage of each cell and the tempature of the pack. this is why if you build one dont get a 20 buck BMS, it will work but will not have cold charging cutoff and such. a good BMS will cost 100-150 cdn but will protect your cells properly.

Steve

I believe it may be more about dendrites growing than plate warpage. The dendrites grow, penetrate the cell separators, and short out. The higher the voltage, the faster they grow. That is why the bms limits charging rate. That results in catastrophic failure, which is why I will NEVER have any house bank in my warm living quarters.

In the bad old days of nickel cadmium and nickel metal hydride, sometimes a LARGE voltage could be used to "burn off" the dendrites, allowing for a little more lifespan, but at reduced total capacity.

[StirCrazy]

BFL13 wrote:


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)


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!

see I learned somthing about Sio2, I assumed they would have an aceptance rate that would throttle back to a lower charge intake . that whole be a hard stop on me ever buying them if they won't as I set up everything to take the max it can to charge in the shortest amount of time. if I have to change the charger section to buy a Sio2 anyways, why wouldnt I save some money and get Lfp.


for your charging LFP I would assume at 41 they will take a 1C rate, but I will look into it for you some more. My thinking is the actualy charg rate is 4 to 5C and the 1C is an artificial limit put in place by the BMS to prevent us people from overcharging and making to much heat in them which can distort the plates and wreck the battery. there is a drop off in cold but its not as extream as lead acid and such and I am not sure if it would affect them for 99% of the people with a big bank and lower 45-70 amp chargers. at any rate you are not going to dammage the cell as your BMS will control the charge rate as it is monitoring both the voltage of each cell and the tempature of the pack. this is why if you build one dont get a 20 buck BMS, it will work but will not have cold charging cutoff and such. a good BMS will cost 100-150 cdn but will protect your cells properly.

I think if I was 80 or older then I would be looking at prepackaged li solutions instead of building one. money wise they fall inbetween normal acid batteries and Sio2 for initial cost , but still a better per ah cost. I find the older we get the more power we actualy use 😉 I know my dad is starting to ask about solar and good batteries on his diesel pusher after seeing how good my pannels are working. just not sure if they make enough pannels for his power usage haha.

Steve