1. Introduction
1.1 What is a BMS
A battery management system, or BMS, is an electronic device that protects and manages rechargeable
battery cells.
2. How to Build a Battery Pack
2.1 Safety Precautions
● Keep metal tools away from exposed terminals
● Wear safety glasses
● Battery cells and electronics can overheat and cause fires or release toxic smoke, if they are
misconfigured or used incorrectly. Always keep a Class C fire extinguisher near the battery system,
and ensure that those around it are properly trained to use it.
● Ensure that the all electrical connections are screwed down tight and are not loose
● Battery systems are not a toy. Never let unsupervised children or pets near the battery system.
● Do not connect anything but the BMS’s B- cable to the cell negative BC0 terminal (the one exception
being the BC0 balance wire). The load negative must be wired to the BMS’s C- lead.
● Do not purposely short-circuit the battery pack
● Do not accidentally short-circuit the battery pack
● Do not submerge the battery pack
● Do not purposely connect the battery pack to a load that dissipates more than the BMS is rated to
handle.
2.2 Planning
2.2.1 Gather Components
● Battery cells (we recommend the Overkill Solar 100Ah LiFePO4 cells, which are the perfect size for our
BMS modules). We also give very detailed diagrams, mechanical drawings, bill-of-materials, and BMS
configuration parameters to ensure a smoother DIY experience.
● Bus bars (used to link the battery cells together. While it’s possible to use stranded insulated wire and
ring terminals, this is considered bad practice, and is arguably more expensive). The easiest approach is
to purchase properly-sized bus bars with your battery cells (Overkill Solar’s 100 Ah LiFePO4 cells
include bus bars). If you purchased other batteries that did not come with bus bars, they may be made
from copper bar or pipe; see Appendix F.2.
● The Overkill Solar BMS, which ships with the following items:
○ Balancing lead
○ Temperature sensors
○ 2-pin cable for external switch
○ Quick-start guide
○ Bluetooth module and cable (optional)
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