11-24-2018, 04:09 PM
(This post was last modified: 11-26-2018, 02:55 PM by ajw22. Edited 2 times in total.)
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
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





