Lifepo4 Top Balance thread lost so I am reposting

[Skiffmaster]

Greetings,

About a week ago I joined the community and posted my first thread about top balancing Lifepo4. Somehow that post dissappeared (admin tried to help but with no luck) and so I am reposting the topic.

My son is a bowfisher. Here in Ga. (USA) nighttime bowfishing is very popular. Its a benefit to our ecosystem because it targets large invasive fish (like Asian Carp) and its a lot of fast paced fun. Outfitting a boat for nighttime bowfishing however can be challenging. Super bright lights surround the boat while a trolling motor runs non stop quietly searching for the fish. With outings lasting 4 to 6 hours thats a lot of energy needed on a small 16 to 20 ft vessle. Many bowfishermen use generators but the noise is a big negative with those. Lithium power banks are the perfect solution which is what brought me here.

I purchased 16 100ah 3.2v CALB (gradeA) cells that I assembled into 3 batteries. 1 battery is an 8s configuration giving me 100ah of 24v for the trolling motor (with an Overkill Solar 24v 100ah BMS). The other two are 4s 12v 100ah (each with its own Daly nonbluetooth 100ah BMS). They come together to give me 200ah of 12v for the lights.

Ive been careful to research and learn about Lifepo4, but its a relativly new technlogy and there are a LOT of opinions out there (so be careful what you read). I read in several places that top balancing a really nice grade A set of cells is not really necessary in most cases.... NOT TRUE. I bought the best most matched and paired cells you could get. They were all made together with consecutive serial numbers. They came with extensive paperwork showing how matched they were in voltage, capacity etc... So I DIDN'T top balance. Mistake.

So you can imagine my surprise when (on my first full charge) the Overkill BMS gave me the readout pictured below. Hopefully no harm has been done, but I have the cells out now and have bought the right equipment and will be properly top balancing them this week.

Thank you to the guys helping me in my original post. That post somehow got gone and no one knows how or where. Being new I cant recall the names but thanks for your help. Didnt want you to think Id just fallen off the boat.

Regards,

Skiffmaster

[Skiffmaster]

https://imgur.com/VqtQ64K

[T1 Terry]

I couldn't get the link to actually display anything, but when using LFP cells like you have for anything other than very high discharge electric vehicle use, you need to condition charge the cells first.
Charge all the cells you have in series in the battery till all the cells balance evenly @ 3.6v. Let it sit over night and then recharge to 3.6v in each and every cell in the battery pack. Take note of just how much more you need to put into the battery and which cells were lower than the others. If you have a run away voltage cell, a lightbulb across that cell will add a load that the other cells don't so they will continue to fill up, stop each time the high cell reaches 3.6v and wait for it to drop back to 3.4v before starting the recharge. When you are at this stage, keep the charging current low so you aren't putting in much more than the lightbulb is taking out. 12v halogen light bulbs are great for this job and you can add as many as you like in parallel to increase the load. Often you will have a few cells side by side going high voltage, you can connect the bulb load across multiple cells as required.
Once you reach the even 3.6v, 14.4v on a 12v battery and 28.8v on a 24v battery, bring the cell voltages across the battery up to 3.8v, they should all stay together this time with no cell run aways. Once you have achieved this, the battery is ready for service.

Cell capacity can only be measured at 100% charged and 0% charged, any where in between has no voltage to capacity reference, 3.2v can be 40% SOC to 80% SOC or even higher, so the only voltage you need to refer to when charging a battery is the 3.45v to 3.5v mark in all the cells, that means it is fully charged and the 100% SOC can be set on a meter if you use one.
Quality battery meters allow you to set the Puekert factor which is 1 for a quality LFP cell battery and charge efficiency is 100%, neither are actually that perfect, but it is less than 1% off so any other setting will throw the calculations the device makes into nonsense readings ..... just remember, all cells at 3.45v of better after charging and rested for 5 mins is 100% SOC, so reset the meter each time.

T1 Terry