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!

[SV_K]

It can come out better for the LFPs by some amount. The next question is whether that amount is worth the Money for your own situation.

The OP knows now he can get 135 - 115 = 20 more AH in his 3 hours of gen time if he swaps over to LFP. He might think that is worth whatever 200AH of LFP costs or not . ($1,500 ? Yipes!) Only he knows that.

And now I understand BFL It is about the money. Certainly a very valid argument.

Well I'll let you know that when I needed new batteries and knew nothing about nothing I was happy and ready to buy Leads. Because of the placement of my inverter/chargers the off gassing from Leads ruled them out. So then I was left with either Lifelines at roughly $3000 for 600 usable amps, yes I know they can go deeper, but that is what the Lifeline salesman suggested. A friend suggested looking at Lithiums.

I asked around and all I ever heard on these forums was "eek" they catch fire and "oh my what a waste of money". Of course this wasn't from anyone who had them, except for one guy. I called him we spoke he explained his experiences and I took a chance and found some with 1000amps usable for $329 more than the Lifelines including BMS. You do the math.

Well I later sold the bus to a friend and it is still charging up and down despite 7 years of full time use, close to 80,000 miles and 4 years of off-grid use. And they take those Batts up and down everyday they are off-grid. They sew, iron, insta-pot and even ran a hot-tub off those batts and they are still doing well.

The best real world experience I encountered was at a rally with 10-12 very similar busses. Same marque, charge systems, generators and either Leads or AGM's. The year before I'd be right next to them charging a couple hours in the morning and a couple hours every night. Two years later with the lithiums and the same charge settings I only needed to charge 2 1/2hrs a day.

You guys continue to debate why they don't charge faster and I'll just enjoy the magic reality that they do charge faster.

[BFL13]

3 tons wrote:

BFL13 wrote:
Yes solar is hard to pin down for making comparisons. You can also have times when the FLAs and the LFPs could both accept more than what the solar can supply at the time.

The OP was asking about gen times so that makes it easy to do the numbers for whatever the scenario is.

I am used to the idea that solar is slow, low amps and gen time is fast, high amps. Slow solar and fast LFPs? Brings out the Missouri ("Show Me") in you!

Sorry for my confoundedness, but are you contesting that in terms of battery internal resistance there’s no real advantage with Lithium vs FWC ??

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?

All I am trying to say is that you have to specify and "quantify" the comparison for the factors that matter to you (weight? cost?, high discharge rate? whatever) so you don't go in blind spending so much Money

I am not "against" LFPs. They are an option that could be the best choice for some. I do think there is something of a "craze" happening as with tailfins on cars in 1957 with some folks who have not done the calculations for their scenarios.

Good on those who did their calculations and it came out for LFPs at a cost they could afford. That's how it is supposed to work.
------------------

Itinerant1, you have that huge collection of monitoring gear and all sorts of numbers you watch so you know what's going on. I don't sweat it either when camping. Just have a set-up that is right for your scenario and go RVing.

[3_tons]

BFL13 wrote:
Yes solar is hard to pin down for making comparisons. You can also have times when the FLAs and the LFPs could both accept more than what the solar can supply at the time.

The OP was asking about gen times so that makes it easy to do the numbers for whatever the scenario is.

I am used to the idea that solar is slow, low amps and gen time is fast, high amps. Slow solar and fast LFPs? Brings out the Missouri ("Show Me") in you!

Sorry for my confoundedness, but are you contesting that in terms of battery internal resistance there’s no real advantage with Lithium vs FWC ??

3 tons

[Itinerant1]

I'm glad I don't have to worry or think to hard about blfs 20-50, 40-90, or other misc charge range #s.

The scenario I use is this. By the dinner time are the batteries at 60-65% SOC, if they are...great I'm watching tv, charging computer, phone, tablet and maybe pop some popcorn in the microwave and still leaving the inverter on, then by early morning when I wake up at 5am there will be aleast 30% SOC (70% DOD)to make my 12 cup coffee pot and use my microwave for 5 minutes. If not I hook up the generator up for an hour sometime during the day to drop a quick 100ah (20%) into the batteries. Just live life in a psoc at times till solar can finally fill the batteries.

But then the batteries are only 5 years old with daily 35-40% +/- depth of discharges totaling 1,600+ cycles so far.

[BFL13]

Yes solar is hard to pin down for making comparisons. You can also have times when the FLAs and the LFPs could both accept more than what the solar can supply at the time.

The OP was asking about gen times so that makes it easy to do the numbers for whatever the scenario is.

I am used to the idea that solar is slow, low amps and gen time is fast, high amps. Slow solar and fast LFPs? Brings out the Missouri ("Show Me") in you!

[time2roll]

With flooded batteries you have a longish absorption time where the battery may accept less power than the solar can produce.
With lithium they will generally absorb all the power until they are full and all solar after that is unused.

So all this will depend on usage, battery, battery size, solar capability, clouds, season, intermittent shade etc. In the end lithium should be less restrictive and generally utilize the solar same or better than the flooded.

[BFL13]

With FLA and AGM, the SOC reached when Absorb starts depends on the "charging rate", where higher amps will raise the battery voltage sooner at a lower SOC (but you still get it all done faster because the Absorb tapering amps are still higher)

A lower charging rate makes the time it takes to get the battery to the high set point (Vabs) longer and the SOC higher before amps taper.

It is easy to show this on graphs with a charger on 120v supply, but not so easy with solar where the input is changing all day as the sun goes up and then down. A 20 amp controller might be at 20 amps at noon, but 10 amps later in the day with the sun lower.

So you can invent a scenario for when the batts get full enough and what the amps are by then for when to say amps are tapering from being in Absorb or just from the fact the sun is getting lower.

If the situation is two GC2s and 200w of solar, mid-summer, nice day, you can expect the battery bank that was low at sunrise, to reach Vabs in the afternoon when solar amps are lower than back at high-noon, so the SOC will be in the 90s % zone before Absorb starts from the battery having reached Vabs. Could be at 97%, whatever. It could be some of each effect making the amps taper later in the day.

Amps tapering later in the day from the sun getting lower also happens with LFPs!

So----if that is typical (what I see with my solar anyway), then there will not be much difference if you swap out your FLAs and put in the same AH size bank of LFPs and leave your solar the same. Just a little "faster" near the end of the daylight period.

You can make the scenario look better for the LFP side if you get the batts near full before lunch and the sun and solar amps are still rising!

So it is necessary to pin down just what the actual scenario is with the whole story so you can make comparisons with actual numbers. "Arm-wavy answers" are for salesmen ("drummers")

LFPs have their place, such as for weight savings, but this "faster charging" business is too much smoke and mirrors the way it is so often presented. You want to see some numbers and get your calculator working.

It can come out better for the LFPs by some amount. The next question is whether that amount is worth the Money for your own situation.

The OP knows now he can get 135 - 115 = 20 more AH in his 3 hours of gen time if he swaps over to LFP. He might think that is worth whatever 200AH of LFP costs or not . ($1,500 ? Yipes!) Only he knows that.

[SV_K]

Hi BFL,

No fight here either.

I’l do my best to explain what I, as a layman, have seen, learned and experienced after 7 years of Lifepo4 ownership and use. If my terms and spellings are incorrect bear with me.

As mentioned Lithium have extremely little internal resistance. Therefore Peukert’s Effect does not apply. Which results in almost every bit of amps fed to them being used. This is one of the reasons that common alternators can burn up. The average alternator does not sense any resistance and therefore outputs high amperage over a longer time than they are designed for.

As I understand things a depleted Flooded Lead will accept a charge with little resistance, but as the SOC climbs the resistance continues to climb, hence the need for an absorb voltage with diminishing amperage over time to work with the climbing resistance.

With lithium there is really no absorb. For example my solar controllers are currently set at 100amps charge rate, the coach takes about 15 and the remaining 85 go into the battery consistently without wavering in full sun until the target voltage is met. Once the target voltage is met it does technically go into absorb, yet all it really does is quickly drop the amps until the batt. voltage matches my programmed float voltage. This “absorb” lasts no longer than 5 minutes.

The real world effect of all this is that the lithiums will charge up in shorter time. For example friends have a very similar coach drawing the same amperage and a similar solar array. My Po4’s are full by noon and theirs take several more hours to reach capacity. They were razzing me about my Lithium’s and how I had wasted money, well that was all good while the sun was shining for a week. Then the clouds moved in for several days and they couldn’t fill their Leads. We all laughed together the next day when they woke up and realized I had moved away. I told them, “I was tired of listening to their generator, so I left.”

To each their own.

[3_tons]

BFL13 wrote:
" and as a former two GC battery user (having made a direct GC to Li swap) the harvest recovery rate is substantial"

Please define "harvest recovery rate" (a new term to me), and how that changes when you go from GC2s to LFPs.

It is not lab work. Just what you observe when RVing using whatever your method of monitoring happens to be.

The OP is asking for numbers so he can make a $1,000 decision.

Thanks for looking out for the OP’s interest, but as there are several pages of feedback provided (here and elsewhere) I think it best to leave such due diligence to the OP...I’ll leave ‘battery wars’ to others - lol

3 tons

[BFL13]

" and as a former two GC battery user (having made a direct GC to Li swap) the harvest recovery rate is substantial"

Please define "harvest recovery rate" (a new term to me), and how that changes when you go from GC2s to LFPs.

It is not lab work. Just what you observe when RVing using whatever your method of monitoring happens to be.

The OP is asking for numbers so he can make a $1,000 decision.

[3_tons]

BFL13 wrote:
I am not trying to pick a fight, but what does this mean?

".Yet, due to Li’s uber low internal charge resistance, even a modest amount of solar harvest is fully optimized."

Please explain in terms of AH and time what that amount of solar harvest would be with a pair of 6s compared with a pair of LFPs and what "fully optimized" means compared with "not fully optimized".

It means (minus any word parsing) that Li recharges faster than FWC whether via charger or solar...I understand that some FWC acolytes may not appreciate this, thus claims to such can be easily dismissed... I make no claims as to possessing any independent third party back-to-back Lab data, so one is quite free to disavow my stated experiences as they choose... Either way, the degree as to how much faster might depend on each individual user (equip, harvest etc), but low internal resistance is an actual characteristic of Li, and as a former two GC battery user (having made a direct GC to Li swap) the harvest recovery rate is substantial - In my view, this aspect is worth communicating to RV nets broader audience...

Others may have other opinions...

3 tons

[BFL13]

I am not trying to pick a fight, but what does this mean?

".Yet, due to Li’s uber low internal charge resistance, even a modest amount of solar harvest is fully optimized."

Please explain in terms of AH and time what that amount of solar harvest would be with a pair of 6s compared with a pair of LFPs and what "fully optimized" means compared with "not fully optimized".

[3_tons]

Itinerant1 wrote:
In the big picture getting them charged isn't that big of a deal and who cares if it takes a little longer to charge them. Lifepo4 doesn't need to get full anyways, throw a little solar up on the roof and might even do away with the generator headache unless there is just extremely poor solar conditions.

Exactly, this is where first hand experience matters...When in actual usage, Li does not need to be fully charged - this, due to Li’s often 100% DOD (depth of discharge) rating...Yet, due to Li’s uber low internal charge resistance, even a modest amount of solar harvest is fully optimized. Here where I sit (at about the 40th parallel), genny required for ‘extended period’ (over 3 hr) air conditioning usage only...

3 tons

200a/hr Li, ProSine 2.0, 440w solar, 11kbtu ac with soft-start.

[Itinerant1]

In the big picture getting them charged isn't that big of a deal and who cares if it takes a little longer to charge them. Lifepo4 doesn't need to get full anyways, throw a little solar up on the roof and might even do away with the generator headache unless there is just extremely poor solar conditions.

[pianotuna]

BFL13,

Tail fins???

Ricklight which charger did you get?