24v Battery

[DESERT DWELLER]

I just put together a 24 volt battery. It consists of 24 7s PCB's loaded with 18650 batteries stacked in 4 Towers of 5 PCB'S and one Tower of 4 PCB'S. It has a 60a BMS. I will mainly be using this as power storage to charge my power stations. My question is at what voltage is the battery fully charged? I seem to get different answers from the Internet lol I was also wondering the best way to charge this? Should I charge this at 2a, 5a,10A, 15a? I capacity tested all of the cells prior to assembly and ran everything through the repacker app. All of the PCB'S are at within 10mah of each other at 21743 mah. The cells are LG MH1 INR 18650 lithium ion batteries. I have a small bench power source for charging them but I just want to make sure that I don't mess anything up and overcharge it and start a fire LOL. Any help you guys could give me would be greatly appreciated, thank you for reading and thank you for your time.

 

[Ampster]

Which Lithium chemistry are the cells? What voltages did you use to capacity test them? Is there any way you can use traditional nomeclature to describe how they are assembled. I presume somewhere there are 7 of something in series to get approximately 24 volts?
18650 is a form factor and those cells can come in several chemistry types.

 

[DESERT DWELLER]

Which Lithium chemistry are the cells? What voltages did you use to capacity test them? Is there any way you can use traditional nomeclature to describe how they are assembled. I presume somewhere there are 7 of something in series to get approximately 24 volts?
18650 is a form factor and those cells can come in several chemistry types.

The cells are LG MH1 INR 18650 lithium ion batteries. The chargers that I used were the zanflare and the xtar VC8 which I believe both Discharge at .5c Took about 13 Hours. I appreciate your reply

 

[Ampster]

Okay, I am assuming they are NMC or LMNC with a nominal voltage of 3.7 volts. t would be a voltage of 4.1 volta per cells to reach about 90 to 95 percent of SOC
What I did not understand was if each of your groups of parallel cells was the same size? If not there will be issues because they will appear as one large cell and if different you will have big problems at the top and bottom of the charge/discharge cycles.

 

[DESERT DWELLER]

Okay, I am assuming they are NMC or LMNC with a nominal voltage of 3.7 volts. t would be a voltage of 4.1 volta per cells to raach abougt 90 to 98 percent of SOC
What I did not understand was if each of your groups of parallel cells was the same size? If not there will be issues because they will appear as one large cell and if different you will have big problems at the top and bottom of the charge/discharge cycles.

All of the stacks are connected to one big PCB Connecting them all in parallel. This is what I have put together.

 

[DESERT DWELLER]

Okay, I am assuming they are NMC or LMNC with a nominal voltage of 3.7 volts. t would be a voltage of 4.1 volta per cells to raach about 90 to 95 percent of SOC
What I did not understand was if each of your groups of parallel cells was the same size? If not there will be issues because they will appear as one large cell and if different you will have big problems at the top and bottom of the charge/discharge cycles.

Hope it's OK to post that

 

[Ampster]

All of the stacks are connected to one big PCB Connecting them all in parallel. This is what I have put together

So your BMS is seeing each of those stacks as one cell each for a total of 7 cell stacks. If they are balanced at the top you should be good to go. If only a few millivolts the BMS should be able to handle it.
FYI 4.1 x 7 equals 28.7 volts for the pack.

 

[DESERT DWELLER]

So your BMS is seeing each of those stacks as one cell each for a total of 7 cell stacks. If they are balanced at the top you should be good to go. If only a few millivolts the BMS should be able to handle it.
FYI 4.1 x 7 equals 28.7 volts for the pack.

Okay thank you for that. When I loaded the pcbs, I pulled the batteries straight out of the charger all of them were at 4.2 volts. When it was all put together and I checked the voltage it was at around 29.4 volts or there about. So with a 60-amp BMS, what would be a safe charge rate? 5a 10a 15a. I really appreciate you going back-and-forth with me on this.

 

[Ampster]

So with a 60-amp BMS, what would be a safe charge rate? 5a 10a 15a.

The charge rate should be based on the cell characteristics. The cells have a specification which is probably stated in terms of C rate. Multiply that times the Amphour capacity of the cells times the number of cells in parallel and that is your number. A safe number is probably 0.5C or half the total Ahr capacity, That means you can safely charge you pack from fully discharged to full in less than two hours. Do you need help with the math?

 

[DESERT DWELLER]

The charge rate should be based on the cell characteristics. The cells have a specification which is probably stated in terms of C rate. Multiply that times the Amphour capacity of the cells times the number of cells in parallel and that is your number. A safe number is probably 0.5C or half the total Ahr capacity, That means you can safely charge you pack from fully discharged to full in less than two hours. Do you need help with the math?

Yes, Total beginner here lol and I was never good with math lol, It looks like they have a Max charge current of 3.1 amps and a standard current of 1.55 so ...1.55x24=37.2a?