Help with battery design - 18650 - 14S16P

Redbeardbeer

New Member
Joined
Nov 7, 2021
Messages
25
Hi all.

I'm now back to square 1 trying to design my powerwall/battery.

First rendition was to make 16P 'bricks' and connect these in series to make a 14S16P.
If I want to add more capacity, I have to add another 14 packs of 16 cells and parallel them together.
BMS balance leads (using small 7.5amp wire) would be attached to each paralleled set of 'bricks'.

Second rendition was to have bricks of 14 cells in a 14S1P configuration with a common main positive and main negative busbar.
This was much easier to expand capacity as I can just add 14S1P bricks in parallel to the main busbar.
I had planned on putting a 14 pin connector onto each of the 14S1P packs, and creating a 14 pin busbar that would connect these to the BMS would balance each 'cell' across the battery - i.e. cell 1 would be cell 1 on brick 1 and cell 1 on brick 2 etc etc.

BUT - I didn't think about the fact that I would be essentially joining all the cell 1's, 2's, 3's etc across the bricks together by small 7.5amp balance wire....which would be bad as I assume this could cause a lot of current to flow from one cell to another via the balance lead?

Can anyone suggest a design solution that allows me to have a BMS monitor/balance the pack, while allowing modular expansion (and the ability to take a brick out if needed for maintenance without killing the battery)?

Thanks :)

Hunt
 

NVS

Solar Enthusiast
Joined
Sep 14, 2021
Messages
97
Just remember it is important that your pack capacity should be equal. So if 1 pack is 10ah they all should be 10ah. You also want each individual battery to be close in capacity. So adding on to an existing battery pack may not be a good idea.

I would try to calculate your needs and build a battery of that capacity. You didn't say what the mah of the 18650 batteries you are using but 16p of 3500mah cells is only 56ah.

Also may want to make them 20p packs since battery holders are 4x5 cells for 20 batteries. Here is a picture of my 120p pack. I also used fused nickel fused.

 

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NVS

Solar Enthusiast
Joined
Sep 14, 2021
Messages
97
Here is a calculator to make your battery packs easier. Especially if you use recycled batteries.

 

Redbeardbeer

New Member
Joined
Nov 7, 2021
Messages
25
Thanks for that. Cells are used 3200mAh LG lggbmh11865 and range from 3039-3244 across all packs. The capacities of the 14 packs range from 50033mAh to 50125mAh.
The purpose of this pack is more of a 'test the waters' and see what works. Only small scale to run a small inverter if only for 'fun'. Not looking to power a house with a 30kWh pack.
I may have some more cells coming soon - so I could do a 14S32P setup. This might be a bit cleaner actually.

Unfortunately that fused nickel stripping is not really feasible for me here in New Zealand - I've looked at batteryhookup before for bits and pieces and the cost to ship those nickel strips is more than the strips themselves!
We don't have anything like that locally.
 
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