Top charge issue

[Tulex]

Built my first battery, took forever to top charge, but it got there. Part of the issue other than it just takes a long time with these little power supplies is that it wasn't staying on CC. So, I took advice from here and installed heavy wires and crimped on eyelets before starting my second battery.

This time, the amps is staying constant and the volts climbed. But, it got to 3.53v on the charger and is staying at 10 amps, but it has stalled there. Batteries are at around 3.360 at the ends where the wire is attached, around 3.353 for the inside batteries. Both the Charger and batteries have stalled for over a day at these numbers. Checked the amps on the leads, they show 10 amps. Checked the busbars and wire connections, all are tight.

 

[sunshine_eggo]

Built my first battery, took forever to top charge, but it got there. Part of the issue other than it just takes a long time with these little power supplies is that it wasn't staying on CC. So, I took advice from here and installed heavy wires and crimped on eyelets before starting my second battery.

This time, the amps is staying constant and the volts climbed. But, it got to 3.53v on the charger and is staying at 10 amps, but it has stalled there. Batteries are at around 3.360 at the ends where the wire is attached, around 3.353 for the inside batteries. Both the Charger and batteries have stalled for over a day at these numbers. Checked the amps on the leads, they show 10 amps. Checked the busbars and wire connections, all are tight.

You are charging at a VERY low C rate with cells in parallel. The vast majority of charging occurs below 3.40V, and the voltage curve of LFP is very flat.

Watching LFP voltage increase during a very low C rate charge makes watching paint dry seem like a party in your pants.

Note that you have a metric shit ton of Ah to put in... Cells come at 30-50% SoC. Example:

280Ah * 16 * 50% = 2240Ah

2240Ah/10A = 224 hours

that's why step one of the guide is to install the BMS and charge to full with BMS protection. 10A @ 3.35V = 33.5W. When charging 8S, that's 3.35*8*10A = 268W - 8 times faster.

If you have a 30V/10A supply, you can't charge 16S, BUT, you can charge the 8S adjacent the BMS with the (-) on the protection side of the BMS. Once the BMS triggers protection, you swap the two 8S groups and charge the uncharged 8S group with BMS protection.

Once all cells have been charged to near peak, parallel and top off. Time savings are substantial. Rare that you have to put in more than 10-20% of total capacity once in parallel.

 

[Tulex]

Thanks. I knew it would take a long time, but I had time to kill because I won't be ready to build the next battery for a while. I was just surprised to see it stall out. It climbed from 3.29 to 3.35 at a fairly constantly slow pace, so I didn't expect the stall.

 

[Rednecktek]

Yeah, the stall is always suprising the first time. I started with a fully assembeled 4s pack on a 25a car charger just to get it from the 25%-ish shipping charge to somewhere close to full. That cut a LOT of time out of the too balance phase, but it was still 10+ hours top balancing. I can't imagine how long it would have taken to start from shipoing charge to full on 304ah cells with a little bench supply.

 

[740GLE]

This is where people get frustrated and start cranking the voltage to slam the watts into the cell, avoid the temptation!!

 

[Tulex]

This is where people get frustrated and start cranking the voltage to slam the watts into the cell, avoid the temptation!!

No, not cranking, just trying to understand. I've got plenty of time, just wanted to make sure that if the stall wasn't normal, what should I be looking at.

 

[740GLE]

Stall is normal at such low wattage. Just let it bake.

This is why many people are just assembling full batteries with proper BMS and 2a active balancer and let the balancer sort out the top balance, pretty much zero chance of damaging the cells.

IMO full bench top balance at 3.65v was before adequate active balancers.