Top Balance voltage drops

[Archetype-IS]

I top balanced the 4 EVE 280ah cells to 3.61vs and let it parallel for 3 days. Day 1 at 3.61, Day 2 at 3.571, Day 3 at 3.541v. Will it continue to drop to 3.5v or 3.4v? I plan to put the BMS on and let it be. All cells measured exactly the same or maybe off by 0.001v or so.

I guess LiFePo4 cell doesn't like to stay on the top for too long.

Thanks.

 

[HRTKD]

Yep, that's normal. The _nominal_ voltage is 3.2v. It will usually settle around 3.4v if given long enough.

 

[mrzed001]

I top balanced the 4 EVE 280ah cells to 3.61vs and let it parallel for 3 days. Day 1 at 3.61, Day 2 at 3.571, Day 3 at 3.541v. Will it continue to drop to 3.5v or 3.4v? I plan to put the BMS on and let it be. All cells measured exactly the same or maybe off by 0.001v or so.

I guess LiFePo4 cell doesn't like to stay on the top for too long.

Thanks.

If you paralleled and charged them to 3,61V then the top balance is finished.
You should disassemble it and put in serial.
Cells do not like if you hold them on high SoC.
So now they need a load to loose at least 10% SoC.
Better for cycle life if you never again charge them to over 3,5-3,55V.

 

[MisterSandals]

Will it continue to drop to 3.5v or 3.4v?

It might be worth separating the cells, making note of their voltages and seeing if any of them self discharge more than the others. With them all in parallel, they're supporting one another and any oddities will be masked.

You should of course label your cells and take notes.

 

[Archetype-IS]

Finally finished hookup the 4S 12V 280AH EVE batteries.

I see the voltage dropped:
1. 3.526
2. 3.509
3. 3.518
4. 3.523

Voltage diff: 0.017v according to the XiaoXiang BMS app. Cell #2 seems to be discharge faster from the first Top balanced of 3.61v.



Thanks.

 

[MisterSandals]

Cell #2 seems to be discharge faster from the first Top balanced of 3.61v.

keep your suspect cells from cell 1 (negative end) and cell 4 (positive end); all the weird chit happens on the ends.

And, this illustrates why labeling your cells with numbers can get confusing because the cell positions are also numbers. Notes get confusing easily.

 

[Archetype-IS]

Hooked up the inverter to test. The started voltage at 14.1v and quickly dropped to 13.3v. It that how it behavior?

Cell
1. 3.337
2. 3.335
3. 3.334
4. 3.336

Different of 0.003v.

I guess they do need to discharge that top voltages fast.

Doing a slow 8amp discharge test.

 

[mrzed001]

Hooked up the inverter to test. The started voltage at 14.1v and quickly dropped to 13.3v. It that how it behavior?

Cell
1. 3.337
2. 3.335
3. 3.334
4. 3.336

Different of 0.003v.

I guess they do need to discharge that top voltages fast.

Doing a slow 8amp discharge test.

Perfect
You will see that if you get bigger Amps out of the battery the V will fall even more. If load stops V goes up.
That is normal behaviour. This is why you need a shunt based battery monitor to know the current SoC of your battery.

 

[HRTKD]

Just from turning the inverter on, it will suck some out of the battery. The capacitors need to get charged. But it should level out and recover a bit. The bigger the inverter, the bigger the effect. My 1000 watt inverter is small enough that I don't even notice.

 

[Archetype-IS]

Just from turning the inverter on, it will suck some out of the battery. The capacitors need to get charged. But it should level out and recover a bit. The bigger the inverter, the bigger the effect. My 1000 watt inverter is small enough that I don't even notice.

I do have a shunt for monitor. Hope to see 280ah on full discharge/disconnect by BMS or inverter. We will find out in a few days.

Thanks.