My AGM to Lithium conversion
Here is a quick article I wrote on my adventure going from AGM batteries to Lithium. http://rvbprecision.com/rv-projects/rv-lead-acid-agm-to-lithium.html http://rvbprecision.com/rv-projects/rv-l...
Forum Discussion
"Absorption" setting on a solar controller is not to be confused with the Absorption Stage the battery does once it has reached Absorption Voltage (Vabs)
Some chargers even use "Absorption Voltage" to mean what they drop to after reaching a higher voltage, so they really mean "Float"--unless they have an even lower voltage for that too!
An LFP should be controlled not to go over 14.6v ever. (So no temp comp allowed!) By using 14.6 as Vabs the Absorption Stage for an LFP will start at well over 90% SOC often seen in LFP info as around 95% SOC when amps then taper while voltage is held at 14.6v until the battery is full.
Advice then varies how long you should leave it at 14.6 before dropping to Float. Some say 20 minutes and others say a week or so won't hurt. From the LFP info I have seen, it is not clear at what lower voltage the LFP stops rising in SOC, so picking a Float voltage could just delay charging time and you should actually just not have any charge left on longer term--all very vague, but it is early days for LFPs and more advice will come out later as people learn more the hard way I suppose. Now it is every man for himself :)
Some solar controllers have a fixed time they stay at Vabs before dropping to Float, EG two hours. Some are programmable for picking that time. Some just get to Vabs and stay there till it gets dark.
So it depends on what your controller design is what to do for settings, and how you intend to operate considering LFP specs.
LFPs do not need to be fully charged to prevent sulfation. Many users choose to use a lower voltage Vabs and set their controllers (and any other chargers) to say 14.4 or less, even 13.8 as seen in above posts, on the advice that the LFP will do more cycles for longer life that way.
Supposedly, Vabs is reached at a lower SOC with a longer time in the Absorption Stage to reach a full charge. ( if an LFP does reach full at the lower Vabs--I am not clear on that. Also not clear that "absorption" is even a proper word for use with LFPs, but chargers and controllers do have that as a setting from FLA usage, so that stays)
(Not to be confused with FLAs that have lower SOCs when Vabs is reached with higher charging rates. The story on LFP is that happens with them at lower Vabs but presumably with the same charging rates. Another thing that should be clarified. Will a higher Vabs mean the LFP "accepts" more amps like a FLA will?)
It would be interesting to get some data from users who are using lower voltage Vabs on just what SOC as seen from their AH counting monitors their LFPs get to when Vabs is reached. That would confirm or not the story that a lower Vabs does mean a shorter Bulk stage and a longer Absorption Stage with LFPs.
Choosing a lower Vabs would "go with" operating the LFP so you could "tune" your Vabs setting to match what you want for an SOC operating range. That range needs to be wide enough to have the AH you use so another factor would be how big your LFP bank is in AH. You would then need a time at Vabs and a time in Float (assuming it still goes higher in SOC at the Float voltage at all) to reach the intended SOC.
From the above replies it looks like that is what LFPers are doing or experimenting with as they get more experience with them.
Some chargers even use "Absorption Voltage" to mean what they drop to after reaching a higher voltage, so they really mean "Float"--unless they have an even lower voltage for that too!
An LFP should be controlled not to go over 14.6v ever. (So no temp comp allowed!) By using 14.6 as Vabs the Absorption Stage for an LFP will start at well over 90% SOC often seen in LFP info as around 95% SOC when amps then taper while voltage is held at 14.6v until the battery is full.
Advice then varies how long you should leave it at 14.6 before dropping to Float. Some say 20 minutes and others say a week or so won't hurt. From the LFP info I have seen, it is not clear at what lower voltage the LFP stops rising in SOC, so picking a Float voltage could just delay charging time and you should actually just not have any charge left on longer term--all very vague, but it is early days for LFPs and more advice will come out later as people learn more the hard way I suppose. Now it is every man for himself :)
Some solar controllers have a fixed time they stay at Vabs before dropping to Float, EG two hours. Some are programmable for picking that time. Some just get to Vabs and stay there till it gets dark.
So it depends on what your controller design is what to do for settings, and how you intend to operate considering LFP specs.
LFPs do not need to be fully charged to prevent sulfation. Many users choose to use a lower voltage Vabs and set their controllers (and any other chargers) to say 14.4 or less, even 13.8 as seen in above posts, on the advice that the LFP will do more cycles for longer life that way.
Supposedly, Vabs is reached at a lower SOC with a longer time in the Absorption Stage to reach a full charge. ( if an LFP does reach full at the lower Vabs--I am not clear on that. Also not clear that "absorption" is even a proper word for use with LFPs, but chargers and controllers do have that as a setting from FLA usage, so that stays)
(Not to be confused with FLAs that have lower SOCs when Vabs is reached with higher charging rates. The story on LFP is that happens with them at lower Vabs but presumably with the same charging rates. Another thing that should be clarified. Will a higher Vabs mean the LFP "accepts" more amps like a FLA will?)
It would be interesting to get some data from users who are using lower voltage Vabs on just what SOC as seen from their AH counting monitors their LFPs get to when Vabs is reached. That would confirm or not the story that a lower Vabs does mean a shorter Bulk stage and a longer Absorption Stage with LFPs.
Choosing a lower Vabs would "go with" operating the LFP so you could "tune" your Vabs setting to match what you want for an SOC operating range. That range needs to be wide enough to have the AH you use so another factor would be how big your LFP bank is in AH. You would then need a time at Vabs and a time in Float (assuming it still goes higher in SOC at the Float voltage at all) to reach the intended SOC.
From the above replies it looks like that is what LFPers are doing or experimenting with as they get more experience with them.
