Diy Solar power box

[Meguinness]

Hi guys, I'm new to this forum and anything related to solar . Im building a power box using 18650 cells , I made 3x 3s15p packs 30A each with bms and connected in parallel to give me 12v output. As I want to be able to recharge the batteries using a power brick and my 120w solar panel kit I purchased and connected a automatic stepup/Stepdown buck converter so when I use the 19v 5a power brick the buck will step down the charging voltage to 12.6v and I assume that when connecting the solar panel kit the buck will automatically stepup or down depending on the panel voltage maintaining the 12.6v output. What current should I use to charge the packs in parallel? The buck as CV and CC that can be regulated. , Would 12.6v at 2A be ok ?
Thanks

 

[snoobler]

Lithium NMC is pretty worthless for 12V applications. With 3S, you have a functional range of 9-12.6V where most 12V systems will cut off at 10.5V further reducing you available capacity. When you push NMC to 4.2V with every charge your cycle life starts to look like lead acid - around 500-600 cycles unless you used very high quality cells with much higher ratings. If you want to increase cycle life, limit charge to 4.05. Now 3S in 12V has a functional range of 10.5-12.15V, which is probably only about 40% of the total capacity of the cells, so your 90Ah battery only has 36Ah.

If by 30A, you mean 30Ah, then each cell has a 2Ah rating?

What did the cells actually test for capacity?

What's the charge current rating for the cells? It should be on the data sheet. It's typically notably lower than the discharge current. Assuming 0.2C, that's 400mA/cell. Since you have 15 cells in parallel, that's 6A/pack or 18A peak. Of course, that assumes your paralleling method and pack interconnects distribute the current evenly.