Re: ARGH: Accident w/Amondotech 123s and SF M2 + Detonator + G&P Tailcap + Chop KL3 Head!
Hello Chronos,
It is good to hear that there were no injuries from this incident. I would suggest that if you happen to be driving in the car when something like this happens, it would be prudent to immediately open all of the windows to dilute and exhaust any harmful chemical gasses.
Newbie and Toppers efforts have shown that when you take a cell, drain it somewhat and couple it with a new cell, drain it at close to a 1C current draw, leave the circuit connected after the lamp has gone out, and add just the right amount of heat, you can cause a rapid vent with flame incident.
Others have shown that if you pair up a dead cell with a new cell, nothing happens.
As far as I know, no one has been able to produce a rapid vent with flame incident with two new cells that test differently on the ZTS tester. I believe this may be on Newbie's agenda for further testing, but am not sure.
I would like to pause a moment and thank everyone that has been doing testing on the various combinations that cause problems, and especially to Newbie for demonstrating a repeatable condition.
It is my humble opinion (and guess
) that we are dealing with a boundary condition. I have tested cells at a variety of current rates and have noticed that somewhere around 1C they tend to get hotter than at higher or lower current rates.
We need heat to activate the chemical reaction. If we have too much heat, the PTC will shut things down, but if we have enough heat just below the PTC threshold, we may be able to initiate the thermal run away before the PTC can trip.
Cells are tested to a variety of "worst case" conditions. I am not aware of any "boundary condition" testing. Clamp a cell in a vice and direct short it and the protection circuits kick in and shut down the chemical reaction. However, taking a cell that is designed for pulse loads (cameras) and subject it to constant loads (flashlight) and you can possibly end up with different concerns and safety issues.
Let's take a look at the recipe for rapid venting with flame.
More than 1 cell.
Cells at differing capacities.
Enough heat to start the chemical reaction toward thermal run away, but not enough heat to trip the PTC.
Current draw in the 1C range. (This may be optional, but you need some current to initiate the chemical reaction. Simply storing cells connect in series at high temperatures does not seem to cause problems.)
A circuit.
A lack of a low voltage cut off. By keeping the circuit connected after one cell is depleted, we give the other cell the opportunity to try to charge the depleted cell.
Looking at your case, we have heat, the possibility that the cells were not matched, a reasonable possible current draw, and no low voltage cut off. The only thing we are missing is the completed circuit. It could be that there was a malfunction with the switch that left it connected...
Tom