Forum Discussion
203 Replies
- FreepExplorer
time2roll wrote:
BFL13 wrote:
The rate is a curve. There are no straight lines.
How do they get four times with .40C vs .25C?
Can anybody please explain? What am I missing?
Your posted graph is a good representation.
The charging curve for LiFePo4 is pretty flat though.
I have a 12v 271 ah pack that I built for my truck camper and it's usually fully charged by the time lunch is finished, when there is full sun. It takes all day on a cloudy day. This is with 600 watts of solar panels.
I went from FLA to AGM to LFP. I'll never go back.
I've been away from this site for a while and came back to let everyone here know about some new Winston cells that are going for cheap. I'm not sure where to post about it or what the forum rules are so it would be nice if a mod gave me a little direction on that. - 3_tonsExplorer IIIThe fact that LiFePo4’s charge faster than Lead Acid can been substantiated per numerous industry papers (readily googled, ad nauseam...), and many credible personal accounts (RV.net)...Along with a near lack of voltage sag, long life and no maintenance, it’s this rapid charge characteristic that makes Lithium (and variants) the practical ‘elemental chemistry’ of choice for solar charged UPS power walls and regenerative braking in autos, and a worthy attribute at higher latitudes where peak harvest periods are often greatly limited...
3 tons, in the high Nevada Desert :) - BFL13Explorer IIThere are two straight lines--the constant current in Bulk at .25C in the one graph and the constant current in Bulk at .4C in the second graph. One takes four hours and the other takes one hour. How can that be?
If C is 100,
25a x 4h = 100AH and they haven't even started the Absorption stage yet.
40a x 1h = 40AH and then the 15 minute? Absorption stage gets the batt full to 100AH? BFL13 wrote:
The rate is a curve. There are no straight lines.
How do they get four times with .40C vs .25C?
Can anybody please explain? What am I missing?
Your posted graph is a good representation.- FWCExplorerI thought you already explained the math - you can charge their LiFePO4 at 1C, whereas you can only charge their SLA at 0.25C, thus the LiFePO4 can be charged 4 times faster in bulk.
Now you don't have to charge the LiFePO4 at 1C, so 0.4C is also a perfectly acceptable rate of charge. - BFL13Explorer II
FWC wrote:
Is your concern the wording of this specific document, or the actual time taken to charge the battery?
I do not have an "agenda". Getting tired of being accused of that :(
Math is math. I just want to understand why I can't make sense of this math. Or is it "Sales" math ? - FWCExplorerIs your concern the wording of this specific document, or the actual time taken to charge the battery?
- BFL13Explorer II" Stage 1 of the SLA chart above takes four hours to complete. The Stage 1 of a lithium battery can take as little as one hour to complete,
making a lithium battery available for use four times faster than SLA"
FWC, it is just the Bulk Stage they are talking about here. Your explanation is as I mentioned under the "usually " part.
In the quote above, they say it "Can Take" (by using 1C vs .25C ?), but the graphs use .4C vs .25C and the graphs show one hour vs four hours.
How can that be? - FWCExplorerThe difference is the LiFePO4 stays in bulk charge at the full charge rate (be it 0.4C or 2C) up until it is almost fully charged. LiFePO4 only takes 15 min to an hour in 'absorb' to reach 100%. Lead acid requires several hours in the absorb phase to get the last 10 - 20% of charge into the battery.
It is also important to get lead acid back to 100% as often as possible, so waiting those hours for the absorb to finish is important. LiFePO4 doesn't care about being charged back to 100%, so if you are OK with just going back to say 95% SOC, then you don't need the absorb phase at all.
On a related note - folks often claim that the care and feeding of lithium is more complicated than lead acid. This illustrates that this is not the case, lead acid requires a 3 (or 4 stage) charge profile, whereas lithium is fine with 1 stage, and ideal with 2 stage. - BFL13Explorer IIIn this paper they claim the LFP charges four times faster than the SLA and show how that is done.
https://www.power-sonic.com/wp-content/uploads/2019/04/How-to-charge-LiFePO4-batteries.pdf
In the SLA graph it shows 25% charging rate and in the LFP graph they use a 40% charging rate. They then say the Bulk Stage using those rates takes four hours with the SLA and one hour with the LFP.
Beats me how 40% is four times 25%.
Usually the story is the Bulk Stage is shorter, ending at a lower SOC with SLA., so the LFP is faster for the time it stays at full constant amps while the SLA is tapering amps in the Absorption Stage. Or they say you can use 1C vs .25C to get the four times for the Bulk Stage. How do they get four times with .40C vs .25C?
Can anybody please explain? What am I missing?
About Technical Issues
Having RV issues? Connect with others who have been in your shoes.24,303 PostsLatest Activity: Aug 19, 2025