DIY Lithium Battery – 2b

This is one of a series of articles, describing my journey of assembling and installing Lithium battery cells, as part of my van conversion. I will likely make mistakes and may not even reach my goal of a cheap, yet large Lithium battery bank.
This is the continuation of Part Two of my journey.

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Top Balancing

I used a small 12V Lab power supply to top balance the battery cells. I connected all the positives with bus bars and separately, all the negative ones. My LiFePo cells accept a max. of 3.65V and that’s how I set the power supply. Then set the amperage to maximum (<1C) and I let them charge until the charging amps showed <0.1A. Actually I disconnected the power supply a bit early, when the cell terminal voltages rose above 3.65V

Battery Boxes

Two simple battery boxes will hold four cells each, making a 12V configuration, each with their own 120A charge/discharge BMS. Together they can handle 240A max (240A * 12.8V = 3072W max. output). Charging will probably be limited to 60-80A.

The sides of the boxes are open for improved ventilation and the wood is treated with a few coats of Poly-Urethane to avoid moisture issues. The bottom is covered by a metal plate, cut out of a kitchen baking plate; this will distribute the heat from a future heating pad.

Battery Cells

The cells are inserted into the battery box in a staggered way: +/-, -/+, +/-, -/+. Always check the polarity as Chinese cells use different color codes for the terminals. I used double bus bars to connect the individual cells and applied heat shrink to them, to minimize the chance of shorting them out. I used serrated flange nuts, to hold everything together.

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Compressing three BMS power leads into single lug

Battery Management System

The BMS is placed on a 3/16″ piece of plywood, that separates it from the battery cells. The three 10AWG blue leads (B-) receive one 6AWG-1/4″ lug that will be connected to the main negative battery terminal. The other three black power leads (C-) receive a 6AWG-5/16″ lug.

Threaded Rods

To avoid excessive bulging of the battery cells during charging, four pieces of threaded rod are cut, to secure the battery. Stainless steel washers and nylon lock nuts are used, to keep it in place.

To be continued.

*Disclaimer: I have no professional experience installing battery banks and related components. Consult an expert first, if you want to do a similar project.

Other articles in this series

DIY Lithium Battery – Part 1
DIY Lithium Battery – Part 2a

TOOLS & MATERIALS*

Lab Power Supply
Overkill BMS
Lithium Battery Cells ➜ See Resources below.
Klein MM400 Multimeter
Bus bars ➜ See Resources below.
Hydraulic Crimper
Battery Terminals
Fuse Holder
150A Fuse
Heatshrink
Lugs
Baking Plate
Heat Gun
5/16″ Threaded Rods
5/16″ SS Nylon Lock Nuts
5/16″ SS Washers
Serrated Flange Nuts
Set Screws
Isopropyl Alcohol
Sandpaper
3/4″ Plywood
3/16″ Plywood

*Some of the links above are affiliate links, meaning at no additional cost to you, I will earn a small commission if you click through and make a purchase.

RESOURCES

Lithium Battery Cells

I bought my cells through Alibaba.com from Shenzhen Xuba Electronic Trading Co., Ltd. Their email contact is Pina Long.

Lithium Battery & Solar Info

Will Prowse – YouTube
DIY Solar Forum

Other Resources

My Experience of Buying from China
How to Buy Batteries from China

Disclaimer: I’m not an expert at this and I’ll probably make some mistakes that I have to correct. Always consult an expert if you ever think of doing this yourself.

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