You hit on something else I want to touch on. In my case, since the enclosure was not capable of holding in much pressure, the cells heated then fizzled and flamed; no explosion. Now, let’s take those same cells and put them inside an aluminum tube, seal up both ends, and do the same thing… BOOM! It literally would be a pipe bomb. I would never charge a Li-Ion cell inside the flashlight. I know they make many models with charge ports, but I would never use that. I want the cells in open air when they are charging, so i can see if anything is going wrong.
That vent and PTC on the + end of a cell is there to prevent a cell explosion. it does no good when the cell is inside an air-tight chamber.
On a related note, I’ve heard of discharge explosions as well. I suspect they are much more rare, and every example I’ve seen are multi-cell configuration. This leads me to think of possible reverse charging due to unbalanced cells.
Sharing this experience requires a little bit of humility; but if putting this out there saves someone from making the same mistake with potentially worse consequences, then it’s worth it.
This is great discussion, and its always good to learn something new when it comes to safety. The importance of the considerations involving the normal venting process of cells (any cell that will do so) is definitely a concern that most of us dont often ponder. One thing Ive noticed is that most of the cheap cells I used to purchase (trustfires and other cheap Chinese cells) would create a pressure build-up in a sealed host when used in high amperage discharge situations: loosen the tailcap and a great his of gas suddenly escapes. Not good at all! But then Ive experienced this with alkalines in stock maglites when they were still incandescent (and higher discharge rates than the stock LED versions of today). Ive also read about others having a mag rupture on alkalines but I dont remember the details. I purchased a highly modified 3 x XML mag from a reputable high volume builder and the tailcap was drilled and sealed with a burst disk in case a NiMH cell vented.
As a sport wreck penetration diver (SCUBA) we used HID’s powered by a remote battery canister. We were taught to equalize the pressure inside the canister before and after each dive. The reason was to double check the amount of gases the cells vented above atmospheric pressure immediately after the discharge. A great escape of gas upon venting the canister is a tell-tale sign of aging cells that might need to be replaced before they become dangerous, creating a risk to the entire dive team.
All in all, Im surprised that we dont hear about a lot more catastrophic failures when it comes to batteries. But thats one hell of a good thing! Especially in our hobby, where repeated high discharge cycles are the norm and people often skimp and use cells that I wouldnt give to my worst enemy.
Hi NightCrawl, many raw Li-Poly cells are supplied without protections. Usually the cells get protection added when they are assembled into packs. In this case, I didn’t have one on this pack.
Having the PTC in most cases will prevent catastrophic failure. However, I tend to err on the side of caution these days and assume that there are no safety devices. This keeps me from becoming complacent and relying on them.
A final note; the protection devices built into cells are generally there to prevent internal cell failure from escalating into a catastrophic failure. In my opinion, these are not designed to keep the cell safe when introduced to any and every possible external event (i.e. overcharge, short, overheating, puncture, etc.). While they may provide some rudimentary protection from those abuses, the result may only be mitigated damages (ex. leak/vent instead of explosion).