Not All Batteries are Created Equal

A project log for Wee Bug

Fluffbug but smaller

dehipude Éhipu 12/01/2023 at 18:080 Comments

With the new PCB in version 6.0 I switched to the bigger 16340 battery that I originally used in #Fluffbug, thinking that the extra weight is not so great, and extra capacity will be useful. Also those batteries are much easier to find, since they are commonly used in vapers. And incidentally, with version 6.0 I started to have problems with power. The robot would work on a fully charged battery for maybe half a minute, and then the servos would get all shaky, and soon the protection circuit would kick in and shut the power down.

I initially thought the shaky servos are because those small 2g servos come in two versions: 3.7V and 5V, and maybe I got the 5V ones this time. So I made a PCB version 6.1 where I added a boost converter to give the servos consistent 5V voltage. It didn't make any difference, though, the servos were still shaky. I tried added capacitors everywhere I could, but that didn't solve the issue.

On a hunch, I made a professional adapter out of a paperclip, and inserted the previous 14250 battery. Suddenly all the power problems went away, the servos are no longer shaky (both with the boost converter and without). Interesting. So I went looking for a 16340 battery from a different batch, and lo and behold, the power problems are also gone. It was the battery all along.

Turns out that you really have to be careful where you get your batteries, because they differ not only in capacity (by the way, don't believe in what they print on them, a battery with that capacity would need to be four times bigger with this chemistry), but also in their C-rating, which is basically how much current you can draw from it at once.

You need to somehow find a "reputable" source for your batteries, which is a bit of a problem, because obviously this is a lemon market. Out of curiosity, I also tried a battery removed from a vaper that I found on a sidewalk. Turns out that it performs really well, despite being a no-name thing. I guess the manufacturer of those devices found a trusted source.

So if you really want to save on the battery, check your sidewalk for a free one. You will also save the environment from being poisoned with toxic lithium.