Li-Ion 4S2P Welded Pack Build
© Mark Qvale - 1 July 2018
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Introduction
Now that I am past the joy of building a spot welder, it's time to put some packs together! This then is my first spot welded 4S2P pack and it will be interesting to see how it compares to my soldered packs of the same size. You can see my write up on my DIY Battery Pack Spot Welder here -
DIY - Battery Pack Spot Welder
As Built Specifications:
- Assembly time - ~1.5 hours or less
- Weight- 409 grams
- Rated Capacity - 6900mAh
- Nominal Voltage - 14.8v
- Continuous Discharge Current - 20A
- Charge Current - 3.5A
- Cuttoff Voltage @ 5A - 3.1v/cell
- Pack dimensions - 78mm x 74mm x 40mm (3" x 2.9" x 1.6")
NOTE: If you don't have a spot welder, you can solder the tabs instead. Use soldering flux with a hot, blunt tip iron and be careful that you don't get the cells too hot.
Parts for this 4S2P pack
For this quick build I chose Sanyo NCR18650GA 3500mAh cells. Below are most of the other parts I used.
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- 8x Sanyo NCR18650GA Li-ion cells
- 1x 4S Balance connector extension
- 10X Kastar nickel battery tabs
- 1x 14ga red silicone wire
- 1x 14ga black silicone wire
- 2x 4S2P Cell Separators
- Card Stock (insulator)
- 2x 1.5" x 3" Pro Gaf tape
- 2x 1.5" x 3" x 3/16" packing foam
- 1x 100mm shrink tube, 100mm long
Cell Separators
Using the two cell separators is really nice because they firmly hold the cells in place while you work on the pack. Additionally they hold the cells apart so air can circulate around and through the whole pack. The gap between is larger down the center to accommodate the 14ga and balance lead wiring.
Link to the STL print file - 52178 Cell Separator
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| 3mm gap for cooling and wires |
Assembly
- 1. Start by sliding the cells into the pack separators and put a couple dabs of hot glue to hold them in place
- 2. Trim the nickel straps to fit and spot weld the strips in place
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- 3. Secure the balance cable between the cells with hot glue
- 4. Route each balance wire and solder to the middle of one of the tabs for each cell pair
- 5. On the opposite side, solder the two 14ga wires, add a piece of shrink tube and hot glue in place between the cells
- 6. Add some pieces of heavy card stock under the tabs which are welded to positive terminals
- 7. Add your choice of battery connector (Anderson Power Pole shown)
- 8. IMPORTANT - Test that the balance connector and battery plug have the correct voltages and polarity
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- 9. Completely cover each end with a layer of thick cloth tape (Pro Gaf tape shown)
- 10. Add a layer of 3/16 thick packing foam to each end. Secure with cellophane tape
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- 11. Shrink the 100mm shrink tube around the pack, charge and go fly!
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See Also
Comments? Questions?
