Lifepo4 - CV charging or lead acid program adjustment

[pedro322]

Hi!

I looking into buying MPPT controller and I saw that some are offering lead acid mode and LI mode (liion and lifepo4) - looks like voltronic boards. For lead acid I can set usual stuff as float, absorbtion etc. For LI mode I can only set contant chaging voltage and resume charging voltage. I saw bazilion discissions about how to properly adjust lead acid mode in SCC for lifepo4.

I have no idea how this cv is implemented and if its better for battery compared to adjusted lead acid mode as discussed in others threads.

My main concern is battery life. Does anyone use or have SCC with LI mode which is offering CV modes? What are your settings? (Eg resume on 13.4 and CV 13.8)

Ps.: there is no setting for time, just voltage settings for resume voltage charging and contant voltage charging voltage.

 

[sunshine_eggo]

Float mode is needed to set the "floor" that the MPPT will maintain. The idea is to charge it to full and then hold it there until there is insufficient PV to float/power loads.

A good place to start is:

bulk/absorption/boost to 14.4V
float at 13.5V

 

[hwy17]

I use one charging voltage. 55v / 3.4375v per cell. It works well for me, just wouldn't want to float forever on it.

 

[sunshine_eggo]

I use one charging voltage. 55v / 3.4375v per cell. It works well for me, just wouldn't want to float forever on it.

+1

On a 12.8V LFP, I demonstrated attaining 99.7% SoC attained @ 3.40V/cell with a CRAZY long absorption period - 5 hours following a start current of 0.2C.

 

[hwy17]

+1

On a 12.8V LFP, I demonstrated attaining 99.7% SoC attained @ 3.40V/cell with a CRAZY long absorption period - 5 hours following a start current of 0.2C.

I'm considering going down to 3.425. For the winter at least. Maybe even get down to 3.4 winter and 3.425 summer.

 

[sunshine_eggo]

I'm considering going down to 3.425. For the winter at least. Maybe even get down to 3.4 winter and 3.425 summer.

3.4V used to be the more commonly recommended float voltage until low current overcharge became the concern. I'm pretty confident that one could get to 100% SoC @ 3.4V with a long enough absorption period.



The charge was cut off at 0.02C. I suspect that if I ran it down to 0A, it would be so close to 100%, it would be noise.

Note that the charge was done without separate voltage sensing. The bulk would have lasted a little longer, and the absorption would have been shorter, but probably not by a lot.

 

[hwy17]

I'm pretty confident that one could get to 100% SoC @ 3.4V with a long enough absorption period.

With my C rates generally under .1 I feel like the absorption wouldn't even be that long. But I looked at this previous day and I did spend an hour between 54.4 and 55. There's not a whole lot to read into in these charts because it didn't hit the float that day that's just the solar input tapering. My only point here is that I think I still underappreciate how big the difference is between 3.40 and 3.437 in behavior.