Well just like the CC-CV transition, it's the bank chemistry causing the amps dropping, not the charger, right?
Let's remember that a all a voltage regulator does, once in constant voltage mode, is limit voltage. I say this over and over, but try to think not in terms of a voltage regulator but rather a voltage limiter.
Once you attain the pre-set "voltage limit", let's call that 13.8V, the battery will only accept X current for so long without over-shooting the voltage limit. The VR simply begins PWMing the chargers power supply or field of an alt etc. to match supplied current to the battery voltage limit to avoid over-shooting the voltage limit. As SOC rises, with all batteries, in CV mode, the current has to go down or the limit will be over-shot.
The battery is essentially telling the VR "Whoa, if you send me 30A, at this SOC, I am going above the 13.8V limit." The VR simply holds voltage constant by PWMing the source, to decrease current, in order to not over-shoot the voltage limit.
The taper is very rapid with LFP, especially when compared with LA when holding voltage steady to avoid voltage over-shoot. The current taper to what I consider full on my 400Ah bank at an approx .34C charge rate is about 30 minutes or so. If I boosted the charge voltage to 14.4V the taper is essentially non-existent at a .34C charge rate so any absorption duration is technically now over-charging the cells..
With our solar array at 13.8V the taper is zero because the array is only capable of 10A +/- so when it gets to 13.8V my bank is, for all intents and purposes, "full". Holding 13.8V beyond this point with my solar array is over-charging... Charge rate, voltage limit and CV duration all play a role.
Yes, with lead, you need to ensure the charger doesn't **end** Absorb too early, while with LFP that's not a problem, you want to ensure it doesn't go on **too long**.
Bingo! One of the biggest problems we face with LA is "premature floatulation" or ending absorption too soon. It is a MAJOR chronic issue and millions upon millions of $$$$ in LA batteries are destroyed each year due to sulfation from chronic under charging/under absorbing..
Conversely, one of the biggest problems we face with LFP is over absorbing or holding CV too long......
If a charge source doesn't give good options there perhaps could work around with a good shunt Battery Monitor with a relay, set to disconnect/divert the charge source at X SoC, say 95%?
When you find an Ah counting battery monitor that can remain accurate for SOC, even with LFP, please let me know. For now Ah counting LPF or LA SOC, with any level of accuracy, is simply a pipe dream. I have many, many hundreds of hours of testing SOC devices for LFP and suffice it to say there are currently NONE that work beyond a few cycles.
You could not pay me enough to trust my LFP bank to an Ah counting shunt based device set to 95% because eventually it is going to get itself out of whack. I use one, a Link-Pro, but it is an at a glance guide only and I DO NOT trust it for SOC at all. I can say this because I have tested it, and numerous others, against lab grade equipment.
Keep it simple with LFP and purchase charge sources that can be programmed correctly for the shortest CV duration with the right voltage parameters. Attempting to shortcut LFP & charging/using with an LA mentality destroys cells.
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