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Have you ever hooked up two batteries in parallel with a different capacity, thinking they’d share the load equally, only to find out that one battery is doing all the heavy lifting? It’s a common mistake, and in this video, I’m going to show you why that happens and how to fix it!
I started with a simple setup: a 100Ah battery and a 200Ah battery wired in parallel. I expected them to split the current according to their capacities—one-third for the 100Ah and two-thirds for the 200Ah. But when I checked the current draw with a clamp meter, the results were far from what I expected. This led me down a rabbit hole of research, where I discovered the crucial role of internal resistance in how current is shared between batteries in a parallel setup.
In this video, I’ll take you through the entire process step by step. First, we’ll measure the internal resistance of each battery using a straightforward test, and I’ll explain why internal resistance is so important. Then, we’ll dive into some calculations using Ohm’s Law to determine the conductance of each battery. This will allow us to predict how much current each battery will actually carry in the circuit, which is often very different from what simple capacity-based calculations would suggest.
I’ll also give you practical recommendations on wire and fuse sizes to make sure your batteries are working together as efficiently as possible. I’ll show you how to size your wires correctly based on the load, and how to choose the right fuse to protect your system. Whether you’re using batteries of the same capacity or different ones, these tips will help you avoid common pitfalls and ensure your setup is both safe and efficient.
We’ll even do some live measurements to see how close our calculations come to real-world performance. By the end of this video, you’ll have a deep understanding of how to wire batteries in parallel, taking into account not just their capacities, but also the internal resistances, wire lengths, and fuse sizes.
This video is packed with useful information for anyone working with batteries, whether you’re setting up an off-grid solar system, building an RV power system, or just curious about how to get the most out of your batteries. So if you’ve ever been frustrated by uneven current sharing in your parallel battery setup, or just want to optimize your system, this is the video for you.