Why are my cells still charging??

[RyanNicholas]

I have had my 4 280ah EVE lifepo4 cells hooked up to a 10 amp bench power supply for over a week now, and the amperage still has not dropped. They've been connected for about 10 days. On two (or possibly three) different nights, the power supply was turned off- but it has been on day and night the rest of the time. I've been trying to fully charge and top balance the cells; they are connected in parallel and to the charger as shown in the picture. I've been using these cells (assembled in series, of course, as a 12 volt battery) for about 6 months - but I never performed an active top balance on them ( I was told the "passive" method of simply connecting them in parallel overnight without a power supply would work, but have recently come across mixed messages about that), so I took the opportunity while having access to a shop to connect them to this power supply but I thought it would only take four days at the most for them to completely top off. The cells had recently reached a very low SOC, after little to no solar juice in a cloudy and rainy climate for several days. But even at a 0% SoC, it should not have taken more than 4.5 days to reach full charge. So, I'm at a loss here and I'm sincerely hoping this is not indicative of any sort of damage or problems with my pretty much brand new battery cells. Help?

I just disassembled everything and tested the voltage on each cell. They are all reading from 3.35 to 3.37 - a slight variation, which seems to suggest the intended balancing was not effective. Any thoughts or advice on all this are welcome. Thank you.

 

[Bubba1]

Your cells were low when you put them in parallel. Would have been faster to get them charged in series with BMS connected. When near full parallel and top Ballance. At 3.6v and 10w you are charging at 36w. Divide by 4 cells and that's 9w a cell. Going to take time. In series At 14v and 10w you would be charging at 140w. Also you don't have to dissemble the bank to check individual cell voltage.

 

[RyanNicholas]

Your cells were low when you put them in parallel. Would have been faster to get them charged in series with BMS connected. When near full parallel and top Ballance. At 3.6v and 10w you are charging at 36w. Divide by 4 cells and that's 9w a cell. Going to take time. In series At 14v and 10w you would be charging at 140w. Also you don't have to dissemble the bank to check individual cell voltage.

I think you're meaning to say 10a, not 10w. But how is the calculation of wattage necessary to figure out what I'm doing here? Charging at the voltage of the cells - and at 10 amps, when they have a 280 amp-hour capacity - should charge completely discharged cells all the way to full in 28 hours. Multiply by 4 and that's four days and 16 hours. They've been plugged in for 10 days.

 

[Bubba1]

Perhaps it's the alligator clips that is causing a loss.

 

[John Frum]

Even if those cells were dead empty...
280ah * 4 cells = 1120 ah
1120ah / 10 amps = 112 hours
112 hours / 24 hours = 4.666666667 days

Have you verified with a dc clamp meter that 10 amps is actually flowing through the circuit?

 

[Bob B]

I agree with @smoothJoey that you need to actually verify the current flow .... and I somewhat suspect that you may be getting lower than 10A sometimes because of the alligator clip connections.
I would replace them and connect with ring terminals and verify the current flow.

We have seen MANY top balancing posts where people thought they had bad cells because it was taking so long to top balance. I have never seen that actually be the case.

 

[lupo]

did you use the power supply for other use cases, so that you know that it works? You might have a loss on the connections but I doubt that it can be that high. If you do not have a clamp meter, usually cheap multi meters can also measure current when putting them in series (but check in the manual first )