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
