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AJW22's 7.5~75kWh PowerShelf
#1
edit 1: added pictures
edit 2: attached 3d models of my battery pack (OpenSCAD source and STL) 

Instead of a PowerWall, I've decided to build a PowerShelf to make better use of the space I have available.  

One shelf will eventually have 10 rows.  One row hosts 1 bank of 14S70P battery, with a dedicated cheap (ie not Batrium) but programmable BMS.  Each 70P pack uses 3d printed brackets of my own design with several (hopefully) improvements over the ubiquitous 4x5 brackets:
* staggered cell placing for higher cell density, more spacing between cells (better air flow/cooling), and easier routing of fuses
* build in LCD voltage display for quick status check
* 70P for physically easier handling, and easier troubleshooting
* tiny, semi-flexible tabs to hold the cells in place during construction.  Cells can easily be pushed out when replacing, and the tabs can be bent back into place.
* dedicated 7mm wide space for 1 bus bar, with many slots to loop cable ties through.  Does not interfere when replacing cells.
* 12.5 x 26 x 6.5cm, Black bracket for the negative side, yellow (was on sale) for the positive side to reduce chance for mistakes and the coolness factor

Still in the planning stage, but a central DC breaker box will combine all the battery banks and the PV/grid smart hybrid inverter(s).  (Dis-)charge to 3.50V ~ 4.00V at rates of no greater than 0.17C (ca 250mA) per cell.  Ie use very conservatively and maximize life; add more banks for more power.
All wiring as well as the bus bars will likely be just AWG12 wire, with XT60 connectors (both pins combined), both connectors at the front for simplicity.  Each cell will be soldered one 1A axial glass fuse on the positive side.  And 3 cells will have their negative sides connected with a single 5A-ish wire.

Some concerns/compromises:
* BMS can be configured to constantly balance cells (ie. not just when cells have reached near full state), but at only 50mA.  I'm hoping that 50mA will suffice to counteract voltage drifts due to IR.
* Cells closer to the front will be utilized veeeery slightly more than the ones at the back.

I hope to have the first bank operational by the end of January 2019.

Questions and Comments Welcome!
- Albert

 
 
 
 
 
Wolf, emerca, MissSolar And 2 others like this post


Attached Files
.zip   AJW22-BatteryPack.zip (Size: 370.54 KB / Downloads: 20)
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#2
Great innovation and planning.  I will be watching this very closely.
hbpowerwall and ajw22 like this post
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#3
care to share the stl files and are you printing using pla
ajw22 likes this post
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#4
Attached my OpenSCAD source and .STL file to the top post. You can change the pack size by opening the source file in OpenSCAD (freeware) and just editing 1 number (the "cells" variable).
It now creates 70P brackets, but you can create brackets as short as 10P or as large as your printer allows.

I print using PLA, though ABS with its higher melting point may be a safer choice in case of catastrophic cell failure.
choncy12 and hbpowerwall like this post
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#5
thanks
hbpowerwall and ajw22 like this post
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#6
Fully sick!
ajw22 likes this post
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#7
I am impressed. I am in the process of building packs of 14S80P with the single holders (about 5kWh per pack). This give me packs of 400mm by 560mm which can be located easily next to each other. So I do not need to go to much in to the height (as I life in a earth quack prone environment). The first pack is fully packed and the next couple of packs are underway. I am looking to use the smaller BMS to have every pack separate controlled like you probably do. I want to start hooking them up when I have six packs (approx. 30 kWh). My current issue is to fin what kind of inverter to use.
ajw22 likes this post
Menno
7S 80P pack. Building 14S40P packs.
"Tell me, and will I forget. Show me, and I may remember. Involve me, and I will understand." [i]Confucius 450 BC [/i]
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#8
Very impressive bud well done! looks great
Walde, Scottietheyoung, ajw22 like this post
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