Large Scale Central

16340 versus 18650 Lithium Batteries

My favorite online store (aliexpress) offered me these 16340 batteries recently, and I found some battery holders and a charger.

They are 16mm x 34mm [the 18650 in the photo is 18mmx65mm, so these are a little thinner and a lot shorter.] They claim to be 5800mah, but I assume that’s a figment of someone’s imagination. Still, as our little trains don’t gobble power like an RC car, they should work fine, and give me some options for smaller locos.

I was thinking of making a small cube, with the BMS (Battery Management System) pcb on top. Here’s a horizontal 18650 pack next to the stack:

Finally, I ordered some more 18650s and they turned up with BMS already built in (confirmed by the vendor.) They will just fit in my pack even though they are a little longer.

The real question is whether I still need a BMS. I wasn’t even sure if it was a good BMS, so I left the single battery with a couple of Aristo light bulbs providing a drain, and after a night or so the lights went out and the battery turned off. It does accept a charge again, so I’m inclined to believe its a BMS.

The big question now is how they work as a 4-pack in series. I think they will produce the usual voltage until one of them decides it has gone too low. Whether they will all charge at the same time, and whether they will charge until one decides it is full remains to be seen.

I still think the BMS is needed to keep the charge levels consistent across the pack.

I’m assuming you are referring to my single 18650 cells.
It’s never been clear to me that the simple chargers and BMS actually do that. A ‘balance charger’ will, but I suspect the BMS used in a typical 4S 14.8V pack will turn off charging when one cell reaches the upper voltage limit, irrespective of the state of the rest?
If I’m right, then these 4 will do exactly the same thing. One will decide it is full and then they all stop charging as they are in series.