21700 Li-ion pack build (6s6p)

Summary

In this video, the creator takes you through the detailed process of building a lithium-ion battery pack for UAVs, using 21700 cells. The guide covers checking cell voltages, aligning and connecting cells, spot welding for safe connections, and precautions to avoid short circuits. The battery is wrapped and heat-shrunk for protection before being charged. Emphasis is placed on safety measures, such as using a Lipo charger and monitoring the battery during charging. The creator shares tips on handling the cells with care, ensuring they are properly balanced and tested for performance, all while highlighting the importance of safety when working with such powerful components.

Takeaways

• 😀 Ensure that the cell voltages of all individual cells are in the same range (around 3.6V for storage charge).
• 😀 Align the cells properly using a hot glue gun and a flat surface, with the configuration being 6S6P (6 cells in series and 6 in parallel).
• 😀 Increasing the number of parallel cells boosts both current capacity and milliamp hours (mAh), enhancing the battery's overall performance.
• 😀 Follow the correct sequence when making cell connections: positive to negative, and ensure that connections do not overlap or create loops that could cause sparks.
• 😀 Use spot welding instead of soldering to avoid excessive heat that could damage the cells.
• 😀 Be cautious about not connecting cells that are already connected underneath, as this can lead to a short circuit and sparks.
• 😀 Apply Kapton tape to cover connections during the spot welding process to prevent accidental shorts.
• 😀 Ensure that the positive and negative terminals are clearly separated and insulated to avoid any accidental short circuits.
• 😀 When connecting battery leads, solder them outside the battery first to prevent adding too much heat to the cells during the process.
• 😀 After completing the build, wrap the battery pack with padding to protect the wires, followed by PVC heat shrink to provide a clean finish.
• 😀 Always monitor the battery during charging, particularly when using a lipo charger, and never leave it unattended to prevent potential dangers like overheating.

Q & A

Why are 21700 cells used instead of 18650 cells in this battery build?

21700 cells are used because they are more suitable for the specific needs of the project, particularly for UAVs. They generally offer better performance in terms of capacity and current output compared to 18650 cells.

What is the purpose of checking the voltage of each individual cell?

Checking the voltage of each cell ensures they are in a similar range, ideally around 3.6V, which is the storage voltage. This is critical to ensure the battery pack functions properly and does not experience issues due to voltage discrepancies.

Why is hot glue used to align the cells during the battery pack assembly?

Hot glue is used to temporarily hold the cells in place while aligning them into rows. It provides a quick and easy solution to keep the cells together in the desired configuration without affecting the cells' performance.

What is the difference between '6S' and '6P' configurations, and why are they important?

In the '6S' configuration, six cells are connected in series, and in the '6P' configuration, six cells are connected in parallel. '6S' determines the voltage of the battery pack, while '6P' increases the current and capacity, allowing the battery to handle more power.

Why is spot welding preferred over soldering for this battery pack build?

Spot welding is preferred because it generates less heat compared to soldering, reducing the risk of damaging the cells. Soldering can cause excessive heat, which may lead to potential damage to the lithium-ion cells.

What precautions are taken to prevent a short circuit or spark during the assembly?

The builder uses Kapton tape to cover exposed areas and prevent accidental short circuits or sparks. The cells and connections are carefully insulated to avoid touching the wrong terminals or creating an unwanted electrical loop.

What is the role of balance leads in the battery pack, and why are they important?

Balance leads monitor the voltage of each individual cell in series to ensure they charge evenly. This helps prevent overcharging or undercharging of any single cell, promoting the longevity and safety of the battery pack.

Why is it essential to use a heat shrink PVC tube in the final steps?

The heat shrink PVC tube provides an insulating layer that protects the cells and wiring from physical damage. It also ensures that no parts short-circuit or get exposed to elements that could cause failure or fire risks.

What safety precautions are emphasized when charging the lithium-ion battery pack?

The builder stresses the importance of never leaving the battery unattended during charging. It's crucial to monitor the pack for heat buildup and ensure that it is charged in a safe environment to avoid potential risks, such as fires or battery failures.

What is the significance of the nominal and full voltage of the battery pack?

The nominal voltage (22.2V for 6S) is the typical voltage during use, while the full voltage (25.2V) represents the fully charged state of the battery pack. It's important to charge the battery up to the full voltage for optimal performance and battery life.