Rechargeable lithium batteries like ours are used in a wide variety of applications, from portable electronics to renewable energy systems. Connecting multiple lithium batteries in parallel is a smart way to increase capacity and achieve a longer-lasting power source. However, if done incorrectly, it can lead to safety hazards and battery damage. In this blog post, we will guide you through the process of properly connecting lithium batteries in parallel while ensuring safety and efficiency.
Disclaimer: Always use caution when working with lithium batteries. Follow the manufacturer's guidelines and safety precautions, and consider seeking professional help if you are unsure about any step in the process.
Why connect batteries in parallel?
Connecting multiple batteries in parallel is the easiest way to increase the capacity of a system without changing the voltage. The total capacity is simply the sum of all the individual capacities. For example, connecting two of our 12 volt 100 amp-hour update batteries in parallel creates a system with a 12 volt 200 amp-hour capacity (100 + 100 = 200).
Materials Needed:
Before you begin, gather the following materials:
Lithium batteries of the same chemistry and voltage rating. Make sure the voltage difference between the cells is within 0.25 volts to minimize the possibility of sparks when connecting! Too much voltage difference can create an unsafe situation where the cell with a higher state of charge (SOC) will try to charge the cell with a lower state of charge. Since lithium cells have very low internal resistance, even a small voltage difference when connecting can turn into a high inrush current that can damage the cell or create a hazardous situation.
Personal protective equipment (PPE) such as gloves, goggles, or a face shield.
Wiring and connectors (make sure they can handle the required current).
Insulation and heat shrink tubing to prevent short circuits.
Step-by-step guide:
Safety First:
Before you begin, make sure you are in a well-ventilated area and wear proper safety gear, including gloves and safety glasses. Keep the terminal protectors installed until you are ready to connect the cells together.
Check battery compatibility:
Make sure the lithium cells you intend to connect in parallel have the same voltage and SOC. Mixing cells of different specifications can result in unbalanced charging and discharging, which is unsafe. Batteries at different SOCs should be charged or discharged to within 0.25 volts to prevent damage from excessive current.
Connect Batteries:
Connect batteries in parallel, which means the positive terminals are connected to each other and the negative terminals are connected to each other. You can use heavy-duty copper wire or bus wire to make these connections. Be sure to size the wire based on the maximum amperage it will see. Here's a handy chart to choose the right size wire.
Use Insulation:
To prevent accidental shorts, insulate all exposed connections with insulation or heat shrink tubing. This will help protect your battery and reduce the risk of electrical fires. If the battery is used in a mobile application (RV, trailer, etc.), clamp the battery with a battery clamp.
Double-check Connections:
Before energizing parallel batteries, double-check all connections to make sure they are secure and in the correct orientation. Loose connections can cause inefficiencies and potentially dangerous situations.
Monitor and Test:
Once the batteries are connected, monitor them closely, especially during the initial charge and discharge cycles. This will help you ensure that the batteries are working together harmoniously and that no problems will occur.
Additional Resources:
For more detailed information, you can refer to the following resources:
Battery University - Parallel and Series Battery Configurations
This resource provides an in-depth explanation of the pros and cons of series and parallel battery connections.
DIY Lithium Battery Builder's Guide
A community-driven guide to building a lithium battery pack, including parallel connections.
How to Build a Lithium Battery
This tutorial covers all aspects of building a lithium battery, including parallel connections.
Conclusion:
Properly connecting lithium batteries in parallel can be a beneficial way to increase capacity and enhance your power source. However, safety is always a top priority when working with lithium batteries. By following the steps outlined in this guide and the recommendations of battery and BMS manufacturers, you can create a safe and efficient parallel battery configuration for your specific needs. Always monitor your batteries and stay informed of best practices to ensure the longevity and reliability of your power source.
