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!

[StirCrazy]

.

[StirCrazy]

pianotuna wrote:
Steve,

I was talking about zero volts. Not a "capacity" discharge.

Capacity discharge is a "moveable feast". If you set capacity at 20% of the total then you get a whole bunch more "cycles".

The other factor is "how much remains".

The industry considers batteries "done" when they only produce 80% of their usable amp-hours.

In my case, with telecom jars, "usable" capacity is 278 amp-hours and 80% still allows me 222 amp-hours. That's more than most RV's come from the dealers with.

The reason I want a high capacity bank is to be able to run an O2 concentrator overnight. I refuse to run a generator while sleeping. Assuming I have only 2.67 Kwh--I can't come close to running the concentrator all night.

That turns me into a power pole princess.

BTW the O2 is not for me--but for my partner.

you cant take a sio2 to 0 volts and expect that life cycles that spec is for 100% depth of discharge thats not the same as 0 volt by a long shot.

rated specs are not a movable item, I am not talking about a number of amps but rather a dept of discharge in a % of the batteries rating. this is a direct coralation from voltage to 5 remailing that is for a certian type of battery.

I just looked at them on azmuth solar and no where does it say 0 volts, if you have some lititure that spicificly says recovery from 0 volts I would love to read that as I would find it amazing. 0 volts in an agm or La will filp cells and do all kinda of nasty things. 100% depth of discharge would be 10.8V or 11.1V depending on which format of sio2 you have. which I doubt you would ever get to anyways as your inverter would be shut down long before you reach that voltage. that is the biggest benifit of Li when it comes to inverters they start out at 13.6V for 100% and at 14% they are still 12.5V so you can use more of your capacity for the inverter with out alarms and shutdown.

[pianotuna]

Steve,

I was talking about zero volts. Not a "capacity" discharge.

Capacity discharge is a "moveable feast". If you set capacity at 20% of the total then you get a whole bunch more "cycles".

The other factor is "how much remains".

The industry considers batteries "done" when they only produce 80% of their usable amp-hours.

In my case, with telecom jars, "usable" capacity is 278 amp-hours and 80% still allows me 222 amp-hours. That's more than most RV's come from the dealers with.

The reason I want a high capacity bank is to be able to run an O2 concentrator overnight. I refuse to run a generator while sleeping. Assuming I have only 2.67 Kwh--I can't come close to running the concentrator all night.

That turns me into a power pole princess.

BTW the O2 is not for me--but for my partner.

[StirCrazy]

pianotuna wrote:
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

for the most part you can make any battery last by taking care of it my 6V GC batteries just turned 15 years old this year and are just showing signs of needing to be replaced. I have for the most part boon docked there whole life with a 480 watt solare system and they hardley ever dropped below 70% capacity and only droped below 50% once.

full capacity discharge is 4000 to 7000 on average and depending what format of LifePo4 , the prismatic I see are listed at 4K to 5K cycles at 80% depth of discharge. but I see some that use the 100% dod that it is greater than 2000 cycles, so I guess its depending on the brand and how they choose to rate it. the higher ones in the 7K range are probably the flashlight battery design used by battleborn, tesla and a lot of others.

Steve

[StirCrazy]

3 tons wrote:
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

only if your talking the cheep 15 to 30 buck ones. see below 😉

BFL13 wrote:


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.

.

when you buy a BMS it is rated for a spicific amprage which designates it discharge and charge rates. it is internaly part of the BMS , so part of building a LFP set up is knowing how big of a system you are building and how many amps you want to limit your draw to, and then buying the BMS that meets your needs. they range from 50 amp (well probably smaller but I haven't looked at anything smaller) to 400 amps for the ones I have seen. some have bluetooth so you can customize the different settings and monitor, some don't. some have passive ballancing, some have active ballancing, some have low temp charge cut off some don't. so if you have a charger that puts out 75 amps but your BMS restricts to 50 amp charging then all you will get is 50 amps to your batteries. its all done internaly and that part is not adjustable you have to buy the right one for your application.

here is an example of a good one. it will only allow 120 amps charge or discharge, but that is per battery so if you build two batteries you will be able to putput 240 amps, three batteries 360 amps and so on. there are bigger BMS from other companies this one just focuses on this range.


Steve

[pianotuna]

3 tons,

Unless it is -33 C (-28 f). Then SiO2 is clearly a winner from an economic point of view.

[3_tons]

After reading a few ‘conspicuously evolving’ (but now *tortured...) rationals, I can only conclude that a sufficient and cogent case has thereby been made to recommend LiFePo4’s ...

*(this, possibly the truest form of sincere validation - lol)

3 tons

[pianotuna]

BFL13 wrote:
PT, please explain how the "solar harvest" (Daily AH haul?) would change by swapping out FLAs for LFPs.

Eg, back in the day (2012) I had four 6s and a solar set-up that got the batts full every day restoring the 70AH we used every day.

Capacity was 458AH so 70 down from full each day is a "84-100".

In a special test drawing the batts down for that, I got 156 AH daily haul tracking, 90 AH haul with the solar not tracking but just pointing South and tilted up, and 70AH lying flat all day, at 49N in May.

So what would my "solar harvest" have been in each panel orientation if I had swapped out the four 6s for however many LFPs you want to use to make the comparison?

Please give your calculations, reasoning, and scenario assumptions showing how the daily AH haul would have been greater if only we had LFPs instead?

If PT can't, anybody else can give it a try--I am baffled by that -- so thanks for any help with understanding how that could be.

EDIT--I thought the advantage for LFPs with solar was just that so often you don't get back to full and that sulphates FLAs but LFPs don't care. With the low amps of solar, can't really get any advantage for so-called "faster charging"--but maybe I missed something.

I figure anyone who can afford 4 battleborn batteries would have 2000 watts of solar.

And apparently LI do need to charge to 100% from time to time--perhaps just like SiO2 where it is every 30 days?

I guess a LOT of folks who are going to Li are going to be quite disppointed.

[BFL13]

PT, please explain how the "solar harvest" (Daily AH haul?) would change by swapping out FLAs for LFPs.

Eg, back in the day (2012) I had four 6s and a solar set-up that got the batts full every day restoring the 70AH we used every day.

Capacity was 458AH so 70 down from full each day is a "84-100".

In a special test drawing the batts down for that, I got 156 AH daily haul tracking, 90 AH haul with the solar not tracking but just pointing South and tilted up, and 70AH lying flat all day, at 49N in May.

So what would my "solar harvest" have been in each panel orientation if I had swapped out the four 6s for however many LFPs you want to use to make the comparison?

Please give your calculations, reasoning, and scenario assumptions showing how the daily AH haul would have been greater if only we had LFPs instead?

If PT can't, anybody else can give it a try--I am baffled by that -- so thanks for any help with understanding how that could be.

EDIT--I thought the advantage for LFPs with solar was just that so often you don't get back to full and that sulphates FLAs but LFPs don't care. With the low amps of solar, can't really get any advantage for so-called "faster charging"--but maybe I missed something.

[3_tons]

pianotuna wrote:
3tons,

I'd say the LiFePo4 lower internal resistance means that solar charging would not taper--but would stay pretty much "full bore" as long as there is sun.

I've always maintained that it is possible to design a GREAT battery bank using pretty much any battery type.

If I had won a lottery, I'd go with Lithium Titinate, which iirc make discharge rates on SiO2 look quite modest LOL.

Well, I don’t know much about Li Titinate (though a keen interest in chemistry), but with a more northernly reset in personal scenarios (lol), I would be wise not to rule out the temperature benefits of SiO2, this even where cost were of no object...Just saying : )

With covid being what it is, I doubt Justin would allow me across the border - lol

3 tons

[3_tons]

BFL13 wrote:
No, you should not assume that from what I have said, since I didn't say that.

The OP got his question answered, and I think I learned more about LFPs so I am happy. There is always more to be learned in the spirit of enquiry, which this forum is good at.

Agreed!

3 tons

[pianotuna]

3tons,

I'd say the LiFePo4 lower internal resistance means that solar charging would not taper--but would stay pretty much "full bore" as long as there is sun.

I've always maintained that it is possible to design a GREAT battery bank using pretty much any battery type.

If I had won a lottery, I'd go with Lithium Titinate, which iirc make discharge rates on SiO2 look quite modest LOL.

[BFL13]

No, you should not assume that from what I have said, since I didn't say that.

The OP got his question answered, and I think I learned more about LFPs so I am happy. There is always more to be learned in the spirit of enquiry, which this forum is good at.

[3_tons]

Am I then to assume that any previous claims (whether implicit of explicit...) about,

1) there’s no actual proof or advantage to Li’s lower internal resistance (vs FWC) since this argument (moved goal post?) has been shelved in favor of arguing about variations in constant charging amps??

2) therefore (because of complexities of other complexities...), no one person (whether having actual experience or not), or Manufacturer is sufficiently able to produce satisfactory evidence (to who??) that Li’s have a nominally higher charge acceptance rate?

Why?? because this is a non-quantifiable ‘fools errand’ due to the inexorable variables surrounding ambient temperature and/or charge currents, which exceeds the analytical ambitions of the average ‘enquiring Joe’ to cogently quantify (huh??...”Warning, Secret LiFePo4 Decoder ring required” - lol...)...

If so, I would submit here that while you are certainly entitled your own opinion (as am I, though FWC & Li real-world experienced), your effort here seems more of a curious mental contortion to obscure an attribute of Li that is in many cases advantageous, particularly with solar harvest...

JMO regarding SiO2 vs LiFePo4 (wars - lol : )), while there is some noteworthy overlap, SiO2 (where unheated) wins the temp and initial cost advantage, charge acceptance rate, DOD (usable depth of discharge) and extremely low voltage sag favors Li...

That’s my actual hands-on FWC vs Li experience and I’m sticking with it!!

3 tons

[BFL13]

Battle Born says:

"To summarize this, a bulk/absorb setting between 14.2 and 14.6 Volt will work great for LiFePO4! Lower is possible too, down to about 14.0 Volt, with the help of some absorb time....."

That would relate to the other info that to get to high SOC at constant amps, you need more voltage (but there is a voltage limit you can go to), otherwise tapering starts earlier.

So when I was annoying folks comparing charging times and they insist the LFP stays at constant amps, that "depends". It is complicated!

BB says charging at 50 amps with a 100AH LFP, at around 14.6v tapering would start at about 90% SOC. So if your charger loses voltage in the wiring on the way to the battery, tapering would start at a lower SOC.

Anyway this is just to "clarify" the claims of "faster charging" and define that exactly. Same as we did with those claims that you got 5 times faster charging with AGMs.

Meanwhile there can be good reasons to get LFPs besides faster charging if those other reasons apply to your situation. If your main reason is to get faster charging, then do the math to find out how much faster it would be compared with the charging times you get now.