24V 18650 LiIon Battery System

     

24V Modular 18650 LiIon Battery System Release status: beta [box doku]
Description	Modular 24V litium ion battery system based on 18650 cells
Author(s)	Uli (Uli)
Last Version	0.2.1 (28.02.2020)

Introduction

This battery system consists of one or several battery cell holder modules, a battery management system module to charge the cells with surplus energy and protect the cells from over- and under- voltage. Optionally a state of charge display module shows the voltage of each parallel cell string.

Battery Cell Holder Module

Designed as a 24V battery, 7 cells are wired in series (7s) and each of these consists of 2 cells in parallel (2p) which makes 14 cells per module (7s2p). As the nominal voltage of a typical 18650 lithium ion cell is around 3.6V, 7 of them in parallel results in a nominal voltage of 25,2V. A typical end-of-discharge voltage is 2.8-3.0V making 19.6-21.0V in a 7s system. A fully charged cell usually has no more than 4.2V, resulting in a maximum voltage of 29.4V for the whole 7s battery system.

Bill of materials (BOM) for one 7s2p battery module holding 14 18650 cells (total price ~11.05$ excluding shipping):

- 2 x single 18650 battery holder 0.44$ (0.88$)
- 6 x dual 18650 battery holder 0.66$ (3.96$)
- 1 x XT60PW Plug 1.50$ (0.75$)
- 2 x 10PCS Gold 1808 125V 250V AC 0451 SMD Fast blow Fuse 15A 2410 ultra-rapid fuses 1.69$ (0.34$)
- 1 x 10PCS DC3 20P 2.54mm Socket Header Connector ISP Male Double-spaced Straight needle Curved needle 1.17$ (0.12$)
- 1 x PCB ~ 5$

Battery Management System Module

yet to come...

State of Charge Display Module

yet to come...

Parts

A complete bill of materials will be listed here shortly.

Housing

There is no design for a mobile housing or case yet, but it will be updated here, when there is one.

Assembly

1. Order PCBs, electronics parts, 18650 cells, cables, and screws
2. Assemble 7s battery cell holder module
3. Assemble battery management system module
4. Assemble current state of charge display module
5. Assemble and connect cables and wires
6. Test basic setup
7. Test battery under load

First batch of the Panasonic NCR18650B cells arrived.

Desk full of tools, electronics and cells while putting together all the parts for the 18650 battery system.

First working version of the 18650 battery system ready for testing.

Debugging

yet to come

Open Issues

t.b.d.