24V 18650 LiIon Battery System
| 24V Modular 18650 LiIon Battery System Release status: beta [box doku] | |
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| 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
description yet to come...
BOM (total ~21.07$):
- 3 x Battery Protection Board Module 24V 20A 7S Lithium Li-ion LiFePO4 Battery Battery BMS Protection Board with Balancing 5.27$ (15.81$) - 2 x 20pcs Car Fuse Holder PCB Board Medium Mini For PCB Board Safety clip Insertion Type 2.55$ (0.26$) - 1 x 10pcs DC3 20P 2.54mm Socket Header Connector ISP Male Double-spaced Straight needle Curved needle 1.17$ (0.12$) - 1 x PCB ~5.00$ - some thick wire
State of Charge Display Module
yet to come...
Addidtional Parts and Materials
- 10pcs Brass standoffs M4 hex 40mm 3.51$ (1.40$ per module) (additional shrink insulation recommended) - 20pcs nylon spacer M4 6mm 1.48$ (0.30$) (for additional insulation of brass standoffs at very top and bottom) - ribbon cable 16 WAY Flat Color Rainbow - insulation tape (e.g. for DC3 cable) - solder wire
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
Debugging
yet to come
Open Issues
t.b.d.
