Why are dozens of 18650s the best solution for high watt projects/products? Like, I’m sure the Tesla battery isn’t just a thousand 18650s, so why do so many (diy projects and professional products alike) just scale up by adding more of these relatively tiny lipstick-tube sized cells?
In: 2
[removed]
> Like, I’m sure the Tesla battery isn’t just a thousand 18650s
There were indeed Tesla models that actually did that AFAIK. It is also how more or less every li-ion handheld power tool battery is made and I think most e-bike battery packs – those that aren’t stacked pouch cells that is.
> relatively tiny lipstick-tube sized cells?
Easy to find, easy to use, state of the art energy density for the good quality ones, each of those tiny lipsticks can do 25-30 amps current safely.
For most projects – including most commercial projects – having the perfect component is less important than having a cheap, readily available component.
If you’re designing an iPhone – which is going to sell millions of units and has critical power/weight/form factor considerations – you’ll design a custom battery. But if you’re just making a flashlight? You don’t need the perfect battery and it’s not worth the investment it would take to design/produce the perfect battery so you just use ‘off the shelf’ parts.
The Tesla Roadster was made with 6800 18650s. All of their vehicles since have used a slightly larger 2170 cell (4,416 of them in the Model 3/Y long range pack), and the first Model Ys with their new 4680 cells (816 or 828 of them) are rolling off the line in Austin for employees and specialty customers. The primary reason for smaller cells is that as energy travels through the battery, it encounters resistance, which results in energy loss via heat. The shorter distance electrons need to travel within the battery, the more energy you will able to get out of it, and the cooler it will operate. Tesla is moving to larger cells by changing the internal structure of the battery so that it’s built like several batteries wrapped together in a single package, reducing the overall distance the electrons need to travel within it.
[https://www.torquenews.com/sites/default/files/images/tesla_18650_vs_2170_vs_4680_battery_cells.jpeg](https://www.torquenews.com/sites/default/files/images/tesla_18650_vs_2170_vs_4680_battery_cells.jpeg)
Availability.
18650 had been accepted as something of a sweet spot between size and power for a lot of gadgets like torches, vapes and similar.
This means that while there are a range of alternative size options available, 18650 had become the most common, and because of that also the most readily available, and the most cost efficient.
This means that when it comes to choosing a power source for a new gadget, basing it around a common cell means you will be able to build it for cheaper, and have less chance of supply issues than you would with a more esoteric option.
For the same reason we use bricks to build a wall instead of looking for wall-sized rocks. It’s easier to move smaller things around in a factory to put stuff together. Also, just like bricks are easy to make in that cornered shape, batteries are easier to make round like they are. And if you keep them small, it’s less expensive to you when you make a mistake with one and have to throw it out. So in the long run, it is less expensive to use many smaller batteries, which makes them better for things like cars that makers need to make money on.
As others have said, Tesla do that exact thing.
Everyody so far is right, and there’s another reason: batteries fail. If one of your hundred or so cells fails, you change it for 5 bucks. If your single huge battery fails…
Latest Answers