13.6 or 14.6 where we can say that our LIfepo4 battery is full??

[Dhruvil]

Hello,

need to know that the 12.8 v battery will be full when its voltage is 13.6 or 14.6,

what is charging voltage/resting voltage

same 3.4v or 3.65v

if I charged it to 3.65, will it give a 100% charge?
3.4 it will give 95%??


if 3.4 is 100% then why there is extra range given 3.65 same 13.6 to 14.6

 

[sunshine_eggo]

First, chuck the chart. It has no value for charging.

If you've walked up to a battery that has been sitting for about 30 minutes with no charge or discharge, it's pretty accurate.

Per cell manufacturers, a battery is fully charged at 3.65V/cell and 0.05C tail current, so a 100Ah 12.8V battery would be charged after holding 14.6V until the current tapers to 5A. At that point it's full.

Tail current is the "charge end, I'm full" current.

At 3.55 (14.4V), the tail current is about the same.

At 3.45 (13.8V), the tail current drops to about .02C, and you may only get to 98% charge in a typical timeframe.

At 3.40 (13.6V), the tail current drops to a very very low number meaning you have to hold 3.40V for a very long time., and you may only get to 95% charge in a typical timeframe.

Below 3.40, you can't confidently get a battery fully charged in a reasonable time frame.

3.375V is an optimal float voltage to ensure the battery is not over-charged, and it is held at a very high state of charge.

 

[Dhruvil]

okay,

then accordingly if I charge using a 13.6v charger 13.6/4 = 3.4 v it will take around 8 hours and it will be called fully charged means no current flow through the charger.

same way

if I charge at 14.6v then it will take near by 2 hours and it will call fully charged.

both will give me the same discharge rate like 10a at 10 hours.

it means both have the same charge,

 

[sunshine_eggo]

okay,

then accordingly if I charge using a 13.6v charger 13.6/4 = 3.4 v it will take around 8 hours and it will be called fully charged means no current flow through the charger.

Probably about right depending on start current.

same way

Same as what?

if I charge at 14.6v then it will take near by 2 hours and it will call fully charged.

Assuming you are charging with 0.5C, you'll take 2.25-2.5 hours as some absorption time is required.

both will give me the same discharge rate like 10a at 10 hours.

it means both have the same charge,

If one charges at 0.5C to 3.4V and then immediately turns off the charger, they won't be anywhere near 95% charged. The key is the tail curernt when talking about charge voltages.

Again, the chart has no meaning for charging. It's a chart for resting voltages.

 

[Dhruvil]

ignore chart.

so ideally.. if 3.45v with less current will full the battery

..if we charge till 3.65 with less current then we can get higher capacity.


or can you say what the ideal voltage where we can say that it will be full.

 

[scubadoo]

We are travelling fulltime.
All charging sources are set to 14.1V maximum. 230VAC 30A Victron battery charger, 50A Victron solar controller and c75A alternator.
9 year old 4 cell 300Ah Sinopoly and 1 month old paralleled 4 cell 280Ah EVE LiFePO4 batteries.
According to my two shunt based battery monitors (500A Victron SmartShunt and 400A Junctek) both batteries are at 100% SOC when the battery terminals reach 14.1V whether charging at 5A or 130A.

 

[ArtificerD]

SOC calcs are so complicated and almost always wrong, so a final word based on SOC is not as final as one might be led to believe. My LFP manufacturer says to charge to 14.6 AND until 0.02C charge current is reached, then stop.

It is really important to note that both:

1. Charging at excessive rates (i.e. charging source set to 14.6V with initial resting voltage of the pack at say 11.6V will likely exceed 0.5C)
2. Holding the pack at a top balancing voltage for an excessive period of time

will likely lead to Lithium plating out on your terminal. (can't remember if it's the cathode or anode), which will reduce the amount of free Lithium ions floating around in the electrolyte, reducing the capacity of your pack/cells.

I've also heard you should remove the "surface charge" right after achieving the prescribed tail current by performing a short discharge.