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

" I think you're missing the point that a LiFePo4 will stay in bulk until it is approximately 97% charged before tapering off then the adsorption phase if you use a 2 stage charger is only minutes

A FLA will go out of bulk at about 80% and take hours for adsorption."

I don't know why you would think I was missing that if you read my post.

There are a number of versions out there of just when tapering starts with an LFP where initial charging rate is 1C. Also saw where the Absorption Stage is longer with a lower charging voltage. Whatever, let's see a credible profile for that and use it.

Yes about the charging efficiency difference. Note that varies with SOC in both cases, but perhaps in different ways. IR changes with SOC.

FLA Bulk Stage lasts to a certain SOC at a particular voltage depending on the charging rate. It will go into the 90s SOC at a low rate and can start tapering at 60% SOC at a high rate. My "ugly graph" shows how that works. We have the info for a 25% charging rate close enough (AGMs almost the same as FLA)

So just because you start off at 4 x the charging rate, does not mean you will get to full in 1/4 the time. Need more info and then we could see what really happens for how much faster the LFP is.

BFL13 wrote:
Thank you, FWC.

I am not sure 1C does get you 4 x faster with LFP than .25 C with SLA, since there are some reports that at 1C with LFP, tapering starts earlier (60% seen, eg), while with .5C, tapering starts later at a high SOC (90-95% in some reports, but some say higher than that)

You would have to know the actual charging profile of the 1C for making the comparison. I don't have that info. It would be interesting to do the time comparison with that info. We know the way the SLA works at .25C

I think your missing the point that a LiFePo4 will stay in bulk untill it is aproximatly 97% charged before tapering off then the adsorption phase if you use a 2 stage charger is only minuits.

A FLA will go out of bulk at about 80% and take hours for adsorption.

also for when you combine the internal resistance difference between the two styles a LFP will adsorb more of the same charge as energy while a FLA has a lower efficency and converts more of the energy it is given into heat than LFP so just pulling numbers out of my A$$, say a FLA battery has a internal resistance that results in a efficency of 80% and thats probably being generous,that means for every 10 amps of charge you put in only 8 is going to the capacity. the LFP as a comparason would have a effency of say 97% so out of that 10 amps 9.7 would goto the capacity and only 0.3 dissapated by heat.

so if we take two batteries that are down 100AH and need to be charge up at say 25amps

so FLA after 4 hours taking efficency into account is at 80% and starts tapering down to adsorption phase 2 to 4 hours.
LFP after 4 hours is at 97% and entering adsorption couple minuits to an hour say. so in this situation the charge could be twice as fast, or even more depending on the adsorption phase of the FLA.

when you start getting into 1C rates then the difference is going to be even more. say you using a 100 amp charger for thoes same two batteries, the FLA will start to build heat and the internal resistance will raise lowering the efficency and the amount of aceptance into the battery where at 1C the LFP will just chug along. charged in an hour where at that charge rate the tempature comenstation will actualy lower the amprage on a FLA (I have watched this with mine several times) so the same charge supply could result in a difference of 8 times the charge speed depending on the internal temp of the FLA battery. this can happen to a LFP also but it takes much more than a 1C charge to cause it. most of the new prismatic cells are rated up to a 5C as long as you are using tempature compensation or battery cooling.

Steve

Not sure. Eg the blurb says the LFP is full when amps taper to 5% of C but you see 2-3% for FLA and 0.5a/100AH for AGMs to be full. So we need an equal stop line. Need that 1C charging profile to see how long they are both tapering and at what amps etc. to get the times right.

Some LFP advice says to charge to say 90% and not bother to charge higher, so if you made 90% the stop line in each case, that would make the SLA look better. However they like to use going to full and make restoring that last 10AH or whatever really stretch out the SLA times.

Whatever, it would be fun to see the numbers using an actual 1C LFP profile.

It is kind of a moot point isn't it? Even if the taper starts at 90% as opposed to 95%, SLA still has another 3-6 hours of absorption, so LiFePO4 at 1C will still charge at least 4x times faster.

Thank you, FWC.

I am not sure 1C does get you 4 x faster with LFP than .25 C with SLA, since there are some reports that at 1C with LFP, tapering starts earlier (60% seen, eg), while with .5C, tapering starts later at a high SOC (90-95% in some reports, but some say higher than that)

You would have to know the actual charging profile of the 1C for making the comparison. I don't have that info. It would be interesting to do the time comparison with that info. We know the way the SLA works at .25C

Itinerant1 wrote:
3 tons your missing nothing. Same, same different thread.

Yep, a seemingly continuous pattern of DDD (deliberate disingenuous disinformation) and yet another dogged excursion down the same old rabbit hole...I suppose continually shifting the ‘goal post’ long enough and often enough kinda makes it come true (??)...

3 tons - in RealVille

BFL13 wrote:

FWC wrote:
Why do you think the graph must be at the maximum charge rate? It is an example charging curve, not necessarily the fastest you can charge at.

As they clearly state, the maximum charge rate for their lithium batteries is 1C. Are you disputing that? Otherwise this is a silly discussion over semantics.

You did not RTFQ, and apparently missed where I said way back you can do LFPs at 1C, so please take the time to RTFQ. More coffee maybe! :)

OK, maybe I am starting to understand. You are not doubting that LiFePO4 can charge 4x faster than SLA, but you think that there is something wrong with their charge rate diagram. On that point I agree, there is something wrong with their diagrams. However I am not sure why this is important? We all know you can charge a lithium in an hour or so (if you want to) and that it takes 6-10 hours to charge an SLA.

3 tons your missing nothing. Same, same different thread.

FWC wrote:
Why do you think the graph must be at the maximum charge rate? It is an example charging curve, not necessarily the fastest you can charge at.

As they clearly state, the maximum charge rate for their lithium batteries is 1C. Are you disputing that? Otherwise this is a silly discussion over semantics.

You did not RTFQ, and apparently missed where I said way back you can do LFPs at 1C, so please take the time to RTFQ. More coffee maybe! :)

To be clear, 1C means the battery can be charged to 100% in 1 hour. 2C would be 100% in 30 minutes. .5 C means 100% in 2 hours, etc...

LiFePo4 cells in general can be charged to 80% capacity in 15 minutes. Whether the manufacturer rates them to that level depends on specific characteristics of that particular product.