I've puffed, exploded, deadened, shorted, crashed, smeared, and punctured many a lipo pack, but I've seen actual flames very few times. I'm extremely black-and-white about all aspects of lipos. There are the accepted practices when charging, discharging and storage - and then there are any other ways to perform the same -period. The accepted practices will yield a full and happy pack life (over 600 cycles from some brands), and any deviation will result in reduced life at best, and a 2,000 degree unstoppable torch in your living room or vehicle at worst.

I generally don't like broad generalizations, especially when educating hobbyists, but this is one area that I use them. When we compare NiMH/NiCad packs and Lipo packs, I lump them under the same umbrella: When abused enough, both can explosively vent. Now with the thousands upon thousands of hobby enthusiasts I've interacted with since the beginnings of electric flight, those that have experienced that explosive venting with "round cells" are extremely few, while those that have experienced it to one degree or another with lipos are a far greater number. So are Lipos more dangerous? I don't consider them to be, no. But they do have more than one "rule" to keep them happy. With round cells, they will only explosively vent if they are charged at a fairly high rate well beyond their capacity. This may happen either through charger error or negligence. But simply put, adherence to this one and only one rule will guarantee it will never happen to you. Adherence to all three of my lipo rules will similarly guarantee that explosive venting/flames/puffing or anything at all dangerous or pack life degrading will not happen.
So what are the "3 rules of Lipos"?

Rule #1: Never, under any circumstances, allow the voltage to fall below 3.0v per cell.
Under any circumstances means exactly that - any circumstances at all. Including: while under a heavy discharge load, resting (no load at all), or a very tiny discharge load. Never below 3.0v per cell under any circumstances.
A good ESC with the proper and accurate cutoff voltage configurable to 3.0v/cell under any/all discharge conditions is imperative to have. Several Lipo brands (the smart ones) have started to not warranty packs if they were used with an ESC with either no LVC (low voltage cutoff) or an LVC setting anywhere below 3.0v/ cell.

Rule #2: Never allow the pack to get over 140 deg F.
Just as above, each and every foray above this temperature has a cumulative effect of degrading both output performance and cycle life. The longer it stays hotter, and the more times you get it hotter, the worse it will get, with the results the same as above.

Rule #3: Always store the pack at 1/2 charge when it won't be used for an extended amount of time,
This is a fairly new one. Lipos simply haven't been around long enough to fall into inactive hands for extended periods of time! I don't know the "whys" or "hows" involved, but a pack stored (more than a month or two) at full charge, over time will lose capacity and discharge capability and eventually it will "puff" and be useless. So if you think it may be a month or two before you fly a pack again, discharge half the capacity of a full pack or charge up a spent pack and then discharge down to half capacity for storage.

So there you have it - 3 simple rules for a long and happy cycle life with your Lipos. If you follow them, I feel Lipos are no more dangerous than any other electron storage device (ie. battery).
But what happens when the rules are broken, or more importantly: When exactly is the user at risk of an explosion and fire from a Lipo pack?


There are three instances a lipo will explosively vent and potentially involve flames:
1. A serious impact or similar physical damage to the pack when it is fairly charged (bad crash, puncture, damage to the silver envelope and etc.)
A damaged pack should be destroyed (soaked in saltwater) as soon as possible, and if necessary, stored outside in a safe place should it catch fire until it can be destroyed.

2. Direct short.
A sustained direct short can cause explosive venting and flames almost immediately. Even a very tiny amount of time (1/100th of a second) spent in a shorted condition can reduce lifespan and output capability significantly, if not outright destroy the pack. Keep this in mind when you solder connectors on new Lipo packs! Even a tiny short from one wire brushing another can have large effects.

3. Charger error, charger user error, or most commonly: charging a damaged pack.
Contrary to the above, where you pretty much know you're in immediate danger from a damaged/shorted pack - this is where most of the lipo paranoia and fires come from. "I had just put it on to charge 10 minutes before, and all of a sudden it's puffing up and starting to shoot flames for no reason". I've heard that quite a few times. They want to blame the pack and, they want to blame the charger, want to blame the power supply, to blame everything and except who actually is to blame - themselves.

Charger errors are still very possible in this day of almost everything being automatic. Lipos are even more volatile to being at over 4.2v/cell as they are being under 3.0v/cell. It doesn't take but 10 minutes when charged at the next cell up rate to cause a catastrophic pack failure. I recommend folks to not charge lipos unattended (as in in the garage when you are inside the house doing something else). I charge here at my desk at work with the charger and pack in my view as I work on my computer, or at home beside my desk/workbenches when I'm sitting at them only. Mostly because due to testing, we have a lot of packs very near the end of their lives due to over-discharging, or simply cycle life, and I know the only time they are subject to bad things happening is while on the charger.

With my own personal packs, I have no problem leaving the room or even not monitoring them at all, because I know they have not been abused in any way and are absolutely safe.
Charging a damaged pack is where a vast majority of lipo paranoia comes from, because it seems to be completely at random and may strike at any time. In fact, continuing to discharge below 3.0v/cell can damage a pack so severely, and in so few cycles, it very well may fail catastrophically on the charger when "everything seemed normal, and just like yesterday". So where's the average hobbyists defense against the "random lipo killer inside their charger?" Obviously it all comes down to the 3 rules of lipos. When they're followed, nothing bad happens. Period.

My support staff and I are presented daily with folks that persist in breaking rule #1 "because I know what I'm doing". I recommend to my staff to make sure and teach them about logging cycles, and write down how many man the pack takes in each time. Or at the very least, jot it down once a month. This shows the consumer that the mah in is dropping steadily (depending on the level of damage being done), and when it gets to close to 75% of the original new pack mah, it'll start to fall rapidly each cycle, and it's time to retire that pack. Then we offer them a simple experiment - on a second pack, run the cutoff at 3v/cell, and keep track the same way as well. Invariably, the customer calls back in a few months praising us for our wisdom and cursing the pack brander who told them it was OK to slowly and steadily kill their packs (and put them in danger as well, to put a personal point on it).

When you don't follow the 3 rules above, it's just a matter of time before it happens.

Taken from the Castle Creations Website

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