LiFePo4 vs Lead Acid...Some points of interest.

[3_tons]

When evaluating the two different battery types (i.e. Lead acid vs LiFePo4), I found this ‘to the point’ summary to be both informed and helpful...

https://www.power-sonic.com/blog/lithium-vs-lead-acid-batteries/

3 tons

[FWC]

I 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.

[BFL13]

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 ?

[FWC]

Is your concern the wording of this specific document, or the actual time taken to charge the battery?

[BFL13]

" 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?

[FWC]

The 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.

[BFL13]

In 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?

[larry_cad]

clicky

[FWC]

That appears to be a fairly reasonable comparison, although they don't mention cost. The nice thing is Power Sonic sells both, so maybe there is less baked in marketing BS.

[grizzzman]

I would not agree with some of what they say there but for Each there own.