How Many 12V Batteries for 3000W Inverter

UPDATE: at 14:30 I used the wrong formula. It should be Capacity=Current/C-rate or 250A/0.2C=1,250Ah.
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In this video, I'm tackling a question that some of you have asked: How many 12V batteries do you need to power a 3000W inverter? While I typically recommend using a 48V system for efficiency and simplicity, I understand that some of you already have a 12V inverter and need to make it work. That's why in this video, I'll break down everything you need to know to get your 12V system up and running effectively.
We’ll start with the basics: understanding your inverter's efficiency and how it impacts the power your batteries need to supply. A 3000W inverter can deliver up to 3000 watts of power to your appliances, but it’s important to note that inverters aren’t 100% efficient. In fact, most operate at around 90% efficiency. This means that your batteries need to supply more than 3000W to account for the energy lost during the conversion process. I’ll walk you through the math and explain how this affects your battery requirements.
Next, we'll dive into battery selection. For those using lithium batteries, I'll explain why these are generally the best choice for off-grid systems. I’ll calculate exactly how many 12V lithium batteries you need, depending on their capacity, to reliably power your 3000W inverter. For instance, if you're using 12V 100Ah lithium batteries, you’ll need three of them in parallel to meet your power needs. If you have larger 12V 200Ah lithium batteries, two in parallel will suffice. I’ll break down the calculations step-by-step to make it easy to follow.
After covering the batteries, we'll move on to wiring and fusing. This is a critical part of your setup, especially with a 12V system where high currents are involved. I’ll explain how to size your wires and fuses correctly to prevent overheating and other issues. You’ll learn why it’s sometimes necessary to use thicker cables or even multiple cables in parallel to handle the current safely. I’ll also show you a diagram that outlines the wire and fuse sizes needed for different setups, including how to split the current across multiple wires to make your installation easier and safer.
And for those of you considering a 48V or 24V system, I’ll explain why I typically recommend a 48V system for a 3000W inverter. With a 48V system, you can reduce the current, simplify your wiring, and even save on costs in the long run. I’ll show you the wire and fuse sizes needed for a 48V setup and compare it to what you’d need for a 24V system, so you can see the advantages for yourself.
I’ll provide some tips on how to connect your batteries to a busbar, why fusing each battery individually is a good safety practice, and how to choose the right busbar for your high-current system.
But what if you’re using lead-acid batteries? Lead-acid batteries have different characteristics and limitations compared to lithium. I'll discuss the concept of C-rate, which is crucial for understanding how much current you can safely draw from lead-acid batteries without drastically reducing their lifespan. To power a 3000W inverter with lead-acid batteries, you’d need a whopping 13 batteries in parallel! I'll explain why this setup is much less efficient and more cumbersome compared to a lithium setup, and why you might want to consider upgrading to lithium if you haven’t already.