Prismatic cells on the way, what do I need?

[RossA]

Hey everyone, I have 8 304 AH EVE cells on the way and they should be here within the next few days. (Ordered through Alibaba the end of November). I have a LV2424 Hybrid Inverter Charger and an 8s JK BMS which I believe has active balancing capabilities of somewhere around 5 amps.

Can you kind folk help me understand everything else that I need in order to get this battery bank set up properly? I am going for a 24v bank. The battery will be a house battery for a school bus conversion. I believe the bus bars for the cells comes with the cells. I just don't know what the easiest way to get the batteries all balanced correctly is. Will the BMS balancer do a good enough job if left for a little while? Do I need to get a separate 24v charger? ( I don't have one). What about compression of the 8 cells?

Any and all guidance is greatly appreciated.

Thanks!
-Ross

 

[Bud Martin]

Here is the info about top balancing:

Top Balancing LiFePo4 Cells using a low cost benchtop power supply.

To get the paper, click on the orange at the top of this page. This is a tutorial with detailed steps on how I top-balance my LiFePO4 Cells using a low-cost benchtop power supply. To get the tutorial, click on the orange "Download" button...

diysolarforum.com

May I ask who the seller is that you bought the batteries from?
Are you going to do capacity test to verify that they are what they sold?

 

[RossA]

Here is the info about top balancing:

Top Balancing LiFePo4 Cells using a low cost benchtop power supply.

To get the paper, click on the orange at the top of this page. This is a tutorial with detailed steps on how I top-balance my LiFePO4 Cells using a low-cost benchtop power supply. To get the tutorial, click on the orange "Download" button...

diysolarforum.com

May I ask who the seller is that you bought the batteries from?
Are you going to do capacity test to verify that they are what they sold?

Thank you, I ordered them from Docan Powers company on Alibaba. Everything I've read about the company tells me that I shouldn't have much to worry about. Of course, it would be nice to fully capacity test, but I'm not sure if it would be worth the time/cost unless you know of a cheap way to do it.

Thanks,

 

[Bud Martin]

Thank you, I ordered them from Docan Powers company on Alibaba. Everything I've read about the company tells me that I shouldn't have much to worry about. Of course, it would be nice to fully capacity test, but I'm not sure if it would be worth the time/cost unless you know of a cheap way to do it.

Thanks,

Great! I don't think you will have issue with these cells based on the feedback we see here.
BTW, ordering in the end of last Nov and now you are getting the cells is pretty good, I thought it will be close to 3 months due to what is going on at the port right now.
Is it cheaper than the Texas warehouse? I believe it is about $150 each (free shipping from Texas).

 

[RossA]

Great! I don't think you will have issue with these cells based on the feedback we see here.
BTW, ordering in the end of last Nov and now you are getting the cells is pretty good, I thought it will be close to 3 months due to what is going on at the port right now.
Is it cheaper than the Texas warehouse? I believe it is about $150 each (free shipping from Texas).

Since It was my first time, I'm not sure I got a better deal than what they are doing with the Texas warehouse. I think I paid $158/cell and that covered everything. Last I checked on their website, thats what I'm seeing them listed as at Texas as well. The only positive is that I didn't have to pay sales tax since it was through Alibaba which maybe saved me $80 or so.

 

[triplethreat]

The Houston warehouse price of $158 for those cells includes everything except a Paypal fee of 5%, which amounts to around $30. Shipping from there, if they are in stock will usually be around 1 week in the continuous 48 states.

 

[chrisski]

You mention busbars on the way. I found out after I received mine, that some people will double stack the busbars to cover the amount of current that is being used. In my case, I do not need double busbars since I am pulling 50 - 100 amps tops off the 280 ah cells, but if you are running closer to 200 amps per battery, may need to consider that.

Knowing the types of nuts and studs that come with them is good. I bought nuts for yhe M6 studs while waiting, only to find out better serrated nuts came with the batteries. I now have 50 M6 X 1.0 nuts I will never use.

I did purchase serrated washers with some nice teeth that bite:

https://www.amazon.com/gp/product/B07R59HPCF

As far as a capacity test, an 8S pack would take me between 4 days and a week to top balance, drain one by one at 20 amps, and then top balance again. For that amount of time, I would not think its worth it unless you want to go through the work. If you had actual capacities of the cells, with only one battery, there’s no special way to arrange them. I had two sets of 8 S batteries and did not do the capacity test with the 280 ah cells, which I thought would take me two weeks, but did do it with the two 25 ah batteries, which took me 4 days. I got no really useful data except the cells range from 24 ah to 26 ah, but did not change the way I built the battery.

Ought to Top Balance. I don’t think the BMS will do a good enough job to balance. It will only balance at a certain setting, mine is > 3.4 volts and the amps balancing is a bit of a mystery, but I suspect its only an amp. THat may not be an issue if all cells are delivered at the same state of charge, but if for some reason, one cell was way off, that would cause problems. Disassembling these battery packs is a pain in the but.

 

[HRTKD]

@RossA , since these cells will be deployed into a mobile environment, there should some form of cell compression. You need to keep the cells from moving. This will eliminate any stress that movement could put on the cell terminals. The cell compression also increases the number of life cycles.

If you don't already have them, there are a few tools that are needed:
small gauge crimper
large gauge crimper
heat gun for heat shrink tubing
large gauge cable cutters
multimeter
power supply for top balancing

 

[RossA]

@RossA , since these cells will be deployed into a mobile environment, there should some form of cell compression. You need to keep the cells from moving. This will eliminate any stress that movement could put on the cell terminals. The cell compression also increases the number of life cycles.

If you don't already have them, there are a few tools that are needed:
small gauge crimper
large gauge crimper
heat gun for heat shrink tubing
large gauge cable cutters
multimeter
power supply for top balancing

That kind of list is exactly what I was looking for. Thank you! As far as cell compression, what would you recommend?

 

[HRTKD]

That kind of list is exactly what I was looking for. Thank you! As far as cell compression, what would you recommend?

Compression depends on how OCD you are. There are guys using springs on threaded rod to allow for some expansion, some are skipping the springs while using the threaded rod (me), others are using strapping tape and then there are the folks that may not be aware of the benefits of compression and are doing nothing.

I used a torque wrench on my compression fixture that measures in the inch pounds range. It doesn't take much to get the cells sufficiently "snug". There is a forum thread that provides guidance on how much torque to use.

Here is what my simple solution looks like.

 

[Bvillebob]

I know it's heresy to say this around here but if you're getting cells from Docan there's a good chance you won't need to worry about top balancing. I've made three purchases of 16 cells each time from them, all arrived within a couple of milivolts of each other, and when assembled into batteries have stayed within 5-6 millivolts across the charge/discharge curve.

The first battery I built I was going to just charge them and then individually top up any cells that were low, but none were, the next couple of batteries, 24v x 600 amp hour, I just assembled them and they've tracked perfectly. Top quality cells avoid a lot of issues experienced with lower quality cells.

 

[Browneye]

Steve at Overkill has some good content on diy pack - nav to their site and download the manual in pdf - 80 pages!

I bought a $60 bench cc/cv power supply and did a full top balance on 4 lf230 cells before assembly, and still had to do quite a bit of fine tuning at full charge to get them fully balanced.

Overkill also has tools and materials list.