charging lifepo4 with 4808srf

[maxwell652000]

ok so now i have a soneil 4808 ,,,,before i was charging a 48v/20ah lifepo4 pack(16 cells,, charge volts per cell 3.65) with a 12v smart charger isolating 4 cells at a time,,,charging the 4 cells at a time kept them very well balanced,,,now that im using the 4808 im charging all 16 cells at once (less headaches)whats weird is the whole pack is charged to capacity but the first 4 cells in the string (starting at the negative post)all have voltages between 3.6v to 3.8v where as all other cells are at 3.34v,,,could it be that when the 4808 goes into the final stage of charging and the amperage is substantially lower that it has a problem sending that current all the way through thus accounting for the higher voltages on the first 4 cells? hmmm keep in mind all cells are filled to capacity cause when i use my 12v charger and isolate 4 cells at a time it shuts off in less than a minute indicating a full charge. im looking forward to the 16cell bms that gary and fechter (i hope im not leaving out other contributers) are coming out with

 

[slayer]

quote

all have voltages between 3.6v to 3.8v where as all other cells are at 3.34v,,,could it be that when the 4808 goes into the final stage of charging and the amperage is substantially lower that it has a problem sending that current all the way through thus accounting for the higher voltages on the first 4 cells?

hmmm keep in mind all cells are filled to capacity cause when i use my 12v charger and isolate 4 cells at a time it shuts off in less than a minute indicating a full charge. end quote




It may be possible that because it is being bulk charge they will habe a difference at the end of the charge ...but that is why each cell that are being rated at 3.3 volts working .they are being charged over 3.3 v (say up to 4.2 volts but ideally 3.65 volts) cause when resting they go back down when no load on them ..anything over 3.40 volts resting about 15 minutes after charged i think is just a top charge that does not hold any ah ...as soon as you put a load it will loose that little more ah you have so as a whole pack you will get most of the rated ah your pack is supposed to give you

 

[fechter]

When the charging current gets below about 100ma, the voltage of the charger drops to the float voltage, which is a few volts lower. Not sure why the last 4 cells would be any different than the rest.

Yes, I hope we have the BMS board ready soon.

 

[GGoodrum]

I agree, anything over about 3.40V is simply a surface charge on the electrodes. Some LiFePO4 cells will hold this surface charge in definitely, and others will bleed this off on their own. I know, for instance, the LiFeBatt cells will bleed off the surface charge in about 10-15 minutes, but healthy a123 cells will hold the surface charge for months. This really doesn't have anything to do with the quality of the cell, just more to do with the cell structures.

I think we are pretty much done with the BMS. I just finished the final PCB layout, which I will turn in tomorrow morning.

-- Gary

 

[slayer]

I can t wait for a final and perhaps a brand new thread with the pics and specs and a user friendly description of how to install on our existing packs Gary.

 

[maxwell652000]

thanks guys for the informative response ,,learning new stuff all the time

 

[Tom_D]

Here is a repost of Soneil 4808srf instructions for tweeking the voltage and amperage settings. The voltage can be upped from the factory 57.6 to 58.4v, which would for a 16cell a123 series would be 3.65v per cell. I have fould that it works best where cells (or groups of parallel cells) are matched pretty well, for this series bulk charge with the Soneil. These instructions appear to be straight from the manufacturer.