AmpHour absorb termination

[dgd]

So after reading all I can find about the WBjr and the Classic firmware that interfaces to it, the main purpose of the WBjr seems to be  to provide a more accurate battery  ending amps reading to terminate Absorb mode  (then moving to Float mode)
From the reporting that the firmware provides via  modbus registers, showing + (in) and - (out) amp hour counts for the battery bank it should not to difficult to evaluate a reasonable SOC for the bank.

I am thinking of a LiFeYPO4 bank that would not use Float mode but just Absorbs until a set + Ah reading is reached then the Classic would stop charging - at least until the Ah reading went into deficicit again when it would start charging again.
So what I am really asking for is a third Absorb termination setting.
Currently there is the Absorb time countdown, now with WBjr there is ending amps, and the new mode would be on a user set +ve Ah count.
Additionally a setting to stop charging instead of going to Float would be needed for Lithium batteries
The Classic would need to continue monitoring the AH so it could resume charging.

Anyway, just a suggestion for Classic charging LiFeYPO4 battery bank - maybe just wishful thinking 
Anyone have thoughts or ideas on this?

dgd

[ClassicCrazy]

I have a LiFePo4 battery on an ebike.  With that it charges up to a certain voltage and shuts off maybe to a smaller current to ensure balancing of the cells.  In a solar application how would would you know when to resume charging for this type of battery ?  How would it handle balancing of the cells - via  a BMS ?

[Westbranch]

What BMS would you use and is it possible to hack it?

[dgd]

The BMS systems that I have looked at all have multiple battery string support as the main issue seems to be imbalance of charging between cells in parallel strings. Many configurations of smaller, 5Ah to 40Ah, cells to give larger capacity, several hundred Ah, banks always seem to include some sort of BMS. These connect to individual cells and often have temp probes on each cell.
The LiFe battery supplier will usually provide this and its necessary for battery warranty purposes.
However, the larger capacity LiFeY cells from about 100Ah to over 500Ah, are ususally configured into one string and these do not require a cell charge balancing BMS. They are sold with full warranty without a BMS.
The warranty does require managed charging that means the use of a reasonably accurate SOC system so that cells are not over charged. This SOC measurement becomes necessary because the cells stay at 3.2V from fully charged to 80% discharged.

If a LiFePo4 bank is supplied with a BMS then AFAIK all that is needed if for the Classic to have an input to turn off charging when the BMS instructs it to. boB mentioned an AUX2 input to do just this but I'm not sure if its implemented yet.

If larger LiFe cells are used in a single string with no BMS then the combination of Classic and WBjr with Ah monitoring looks more than capable of managing the charging of these LiFe batteries.

dgd

[mtdoc]

Additionally a setting to stop charging instead of going to Float would be needed for Lithium batteries
The Classic would need to continue monitoring the AH so it could resume charging.

Couldn't you just set the float voltage very low (below rebulk) and achieve the same thing?

[boB]

The BMS systems that I have looked at all have multiple battery string support as the main issue seems to be imbalance of charging between cells in parallel strings.

......................

If a LiFePo4 bank is supplied with a BMS then AFAIK all that is needed if for the Classic to have an input to turn off charging when the BMS instructs it to. boB mentioned an AUX2 input to do just this but I'm not sure if its implemented yet.

Yes, the cell imbalance issue is important for Lithium type batteries and so that's my understanding of the main BMS function.

And yes, the Classic has an active high and active low Aux 2 input function selection to disable charging when active.
That has been in the software for a while now.

boB