Before the age of lithium batteries, any project needing to carry its own power had to rely on batteries that were much less energy-dense and affordable. In many ways, we take modern lithium technology for granted, and can easily put massive batteries in our projects by the standards of just a few decades ago. While the affordability of lithium batteries has certainly decreased the amount of energy we need to put in to our projects to properly size batteries, there’s still a lot of work to be done if you’re working on a bigger project or just want to get the maximize the efficiency and effectiveness of your DIY battery pack.
The main problem with choosing a battery, as [ionworks] explains, is that batteries can’t be built for both high energy and high power, at least not without making major concessions for weight or cost. After diving in to all of the possible ways of customizing a battery, the battery guide jumps in to using PyBaMM to perform computational modeling of potential battery designs to hopefully avoid the cumbersome task of testing all of the possible ways of building a battery. With this tool virtually all of a battery’s characteristics can be simulated and potential problems with your setup can be uncovered before you chose (or start production of) a specific battery system.
While customizing a battery pack to this extent might not be a consideration for most of us unless the project is going to be big enough to run something like an electric car or a whole-house generator, it’s a worthwhile tool to know about as even smaller projects like ebikes can benefit from choosing the right cell for the application. Some of the nuances of battery pack design can be found in this guide to building packs from the standard 18650 cells.
Header: Lead holder, CC BY-SA 3.0 .
It’s the old “Pick 2 out of 3” game.
Spoiler alert: it’s everywhere.
It’s like sleeping under short blanket – you either have your feet cold, your arm cold or you sleep in convoluted position.
Cute, single, sane
I can live without that much energy density as long as the battery doesn’t burn down my house.
Lithium batteries have a sefety problem and there is zero interest in fixing them.
That’s a blanket statement that’s partially true. Modern lithium cylindrical cells have pressure discs that disconnect if there’s a short and pressures get too high, but the problem cells are typically the lowest cost the manufacturer could get and they omit the pressure release to save a few cents and get more capacity.
Also, since everybody wants to charge as fast as possible, chargers in low cost products are typically not those that comply to best charging practices. Most cells that have problems have them during charging due to this fact. It’s rare that a cell pack ignites during discharge usless it’s being abused either electrically or mechanically.
They don’t all have a safety issue and there’s plenty of interest (and results) in improving the ones that do.
Lithium batteries aren’t all the same just because they all contain a few percent of lithium followed by a lot of very different other parts. While plain NMC is not as insensitive as we’d like, the way that chemistry is turned into batteries and how they are used can make a big difference. If a cell is shorted by something or is zapped with too much power by a bad charger but then safely disconnects itself due to overheat or overpressure, well there you go. But even as for innate risk, other chemistries using lithium can be more stable – LFP, LTO, or SSB’s are an option depending on how far you want to push it.
Anyway, many fuels can fill an enclosed area with a flammable mixture that can be set off by a small spark, while you can’t light an open bucket of diesel if you toss a lit match in, so we obviously can tolerate some nonzero flammability risks. And if the worst should happen, even a minimally supplied firefighter can still continuously soak up the heat with regular water, as long as they have enough and are prompt with it. It’s sort of like an electrical transformer fire – if you keep it cool until there’s no more electrical heat input to relight the flammable liquid that’s inside, that’ll work. At least it’s not like a runaway engine, where the metal parts can go flying in all directions if you don’t get it smothered in time. Reasons to operate energetic machinery at a safe distance from your house…