Pre Charging before top balancing

[utkvols]

I have 8 EVE 304ah cells that I am in the process of pre-charging prior to top balance with a bench supply @ 3.6V, hovering around 7A with 14ga wire/ring terminals. I've tried to read all I can about this process. I understand it is going to take a while. I have perused the up in smoke section to rile up a healthy amount of anxiety to hopefully avoid any blue smoke.

Individual cells all arrived at 3.301 V +/- 0.005 V with a cheaper model Fluke multimeter.
I've been charging 4P @ 3.6V. I'm probably close to 35 hours in and voltage is around 3.39 after they have rested overnight.

I've only been doing this during the day when I'm within sight or earshot of the cells. At this rate, it's going to be weeks to get both 4P sets tanked up before I can place in series. My question is, if my bench charger is set to a lower rate, say 3.55V, is there any risk of overcharging? In other words, the cells cannot go beyond the set voltage on the bench supply correct? I have confirmed voltage is accurate with my fluke and cells seem to be of very narrow voltage so I don't think I would see voltage creeping over from the other cells when wired parallel. I want to leave these on the bench supply 24/7 rather than 8 or so hours per day. If I do this, I'd probably move them to the overhang beside the barn as an extra precaution just in case there is a bad cell.

Once the 3.55V is achieved, I should bump the voltage to 3.65V until the current drops to naught?

 

[RCinFLA]

You should use #10 or #8 gauge wire and keep length as short as possible to reduce voltage drop through cables.

When you approach voltage limit on power supply the voltage drop in cables will greatly increase the time to finish off current taper down. Many voltage/current limited power supplies also start to taper their constant current as they approach voltage limit. This also increases top off time.

Never raise power supply voltage limit above 3.65v to speed up process.

 

[utkvols]

I will switch to a larger gauge - so there should not be a risk for cell voltage going any higher than the set bench supply voltage? I'm aware to not exceed 3.65 on input

 

[Dynoman]

I will switch to a larger gauge - so there should not be a risk for cell voltage going any higher than the set bench supply voltage? I'm aware to not exceed 3.65 on input

If the cells are charging when you are not nearby or observing them, set the power supply voltage at 3.50 volts and not more time than overnight without checking. Set the voltage on the power supply (while measuring with the Fluke multimeter) and the leads disconnected from the battery. Then attach leads to the battery.

Once 3.50 volts is reached set power supply for 3.65 volts while observing using the same procedure as above. It will not take long once the cells are at 3.50 volts to reach 3.65 volts.

Note: I have been reading some posts lately that some of the newer cells will not reach 0 amps or near 0 amps when charging to 3.65 volts.
I have some older 280ah CATL cells and once the current reached 0.1 amps on the power supply called it good. In any case probably not a good idea to continue to charge for hours once 3.65 volts is reached. It is a judgement call, but I would not leave the cells at 3.65 volts for more that 1 hour and probably less.

FilterGuy wrote a good document on top balancing cells. See attached document. Also many other documents are available by clicking Resources at the top of the web page of this forum.

 

[utkvols]

Thank you!! I will follow this advice