Another light goes BANG!

[Vic303]

Thread from CPF. OP was using Energizer brand primary CR123's in a BH Falcata.

http://www.candlepowerforums.com/vb/showthread.php?t=267165

IIRC, Energizer also makes the batteries labeled for SF.

[dookie1481]

oh snap

[dookie1481]

I hate lithium batteries. A necessary evil, I know, but damn I wish something else with a relatively high power density was available. I remember throwing PRC-119 batteries into the Atlantic and hearing them pop.

Jay

[UVvis]

Ouch.

I'm kinda surprised that the poster seems to be focused on the flashlight manufacturer rather than the battery.

I've had two lights pop on me. Both times, it was the result of bad cells, as best as I can tell. Nothing that bad though.

[decodeddiesel]

Reading the back story it sounds like he had received a replacement bulb assembly from BH right before this happened. He installed it, still didn't work, and left the flashlight on the couch. Two hours later he hears a "pop" followed by the catastrophic failure. While this sucks, physics can explain it.

When the bulb "popped" some sort of mechanical failure occurred. If the "bulb" was really an LED unit this failure could have left a circuit with extremely low resistance.

V=IR -> I=V/R

If you have a 6 volt system (2 CR123A batteries in series), let say you divide by the effective resistance of copper which is 1.69x10^-8. This give a theoretical current of 3.55x10^8 Amps, or 355 MILLION amps. If we then plug this into the equation for power in a circuit, P=IV we see 2.1x10^9 watts or 2.1 giggawatts lol, which as we all know is more than enough power to send Marty McFly back in time and apparently blow a nice sized hole in a couch. :D

Obviously there is a lot more to it than that mathematically, but basically the over-current situation created a very rapid thermal run away in the batteries. This thermal degradation created a chemical reaction which in turn converted the stored chemical energy into mechanical energy.

Physics is a bitch.

[Vic303]

The Falcata is an incan, not an LED.

I think some folks at CPF have a couple good ideas as to why it KB'd--either a short allowing current flow to bypass the bulb , or he left it on, and got into a reverse-charging situation.

Still that is a primary reason I went to single cell lights and to the LiFePO4 RCR123's for my Novatac.

[decodeddiesel]

The Falcata is an incan, not an LED.

I wouldn't know, I don't **** with anything that has "Blackhawk" written anywhere on it. Still though it doesn't change the basic physics of the situation.


I think some folks at CPF have a couple good ideas as to why it KB'd--either a short allowing current flow to bypass the bulb...

This is exactly the situation I just described.


...or he left it on, and got into a reverse-charging situation.

I would really love to hear a rational and analytical explanation of this phenomenon.

[dookie1481]

I wouldn't know, I don't **** with anything that has "Blackhawk" written anywhere on it. Still though it doesn't change the basic physics of the situation.



This is exactly the situation I just described.



I would really love to hear a rational and analytical explanation of this phenomenon.

http://en.wikipedia.org/wiki/Reverse_charging#Reverse_charging

I assume this is why you are supposed to change both batteries at the same time.

Jay

[dookie1481]

Reading the back story it sounds like he had received a replacement bulb assembly from BH right before this happened. He installed it, still didn't work, and left the flashlight on the couch. Two hours later he hears a "pop" followed by the catastrophic failure. While this sucks, physics can explain it.

When the bulb "popped" some sort of mechanical failure occurred. If the "bulb" was really an LED unit this failure could have left a circuit with extremely low resistance.

V=IR -> I=V/R

If you have a 6 volt system (2 CR123A batteries in series), let say you divide by the effective resistance of copper which is 1.69x10^-8. This give a theoretical current of 3.55x10^8 Amps, or 355 MILLION amps. If we then plug this into the equation for power in a circuit, P=IV we see 2.1x10^9 watts or 2.1 giggawatts lol, which as we all know is more than enough power to send Marty McFly back in time and apparently blow a nice sized hole in a couch. :D

Obviously there is a lot more to it than that mathematically, but basically the over-current situation created a very rapid thermal run away in the batteries. This thermal degradation created a chemical reaction which in turn converted the stored chemical energy into mechanical energy.

Physics is a bitch.

You didn't include the resistance of the bulb, I think (it's been a while since E&M).

Jay

[UVvis]

My thoughts where that he got a bulb that has failed in a way that it was more than just a runaway resistor.

Lithium Primaries have the PTC that increase resistance as they warm up and should essentially cut off battery flow. The batteries are most likely at fault.

Most 123A cell batteries only have a peak sustained current of 3.5Amps or a bit more.

decodeddiesel, dude, step away from the physics. :) It's all chemistry anyway... :)

[decodeddiesel]

You didn't include the resistance of the bulb, I think (it's been a while since E&M).

Jay

Actually I left out the effective series resistance (ESR) of the batteries themselves, but the bulb was assumed to fail into a "closed" situation which would leave it with virtually the effective resistance of copper which was annotated in my argument. Not unheard of given the addition of additional electronics onto bulb packages by flashlight manufacturers.

Thanks for the wiki link. I am familiar with the terminology, and have experienced it with catastrophic effects at my work (multi-cell Li-Po batteries becoming unbalanced). I guess the reason why I did not figure this into my argument is two fold.

First the OP (or victim) mentioned that he had 2 fresh new CR123s in the circuit. Obivously you can get flawed batteries which could lead to this happening, but it didn't seem the case given the bulb swap.

Secondly in order for this to occur the flashlight must be on and the circuit must be completed. From the victim's testimonial this didn't sound like the case, though it is plausible. I have heard of Surefire X200 failing catastrophically in this manor when the user uses a fresh battery with a depleted battery.

What blows my mind is that this whole thing could have been prevented with a $0.05 fuse. Imagine if a child had been using that flashlight when it KB'd. :eek:

Another vindication as to why BH is on my NFW list (No ****ing Way).

[decodeddiesel]

decodeddiesel, dude, step away from the physics. :) It's all chemistry anyway... :)

Oh no he didn't! ;)

ETA: Yeah we're working with CR123As at my work too. They should be limited, but often times they are not and you can drive them into an over current situation very easily. They get hot fast.

[UVvis]

Oh no he didn't! ;)

NERD FIGHT! :D


ETA: Yeah we're working with CR123As at my work too. They should be limited, but often times they are not and you can drive them into an over current situation very easily. They get hot fast.

Did you check out the PSDS's (product safety data sheet) for most lithium based cells? Usually they state that in the event of a fire, you will not be able to extinguish the cell, but you can cool surrounding cells to keep the fire from spreading.

[dookie1481]

decodeddiesel, dude, step away from the physics. :) It's all chemistry anyway... :)

http://imgs.xkcd.com/comics/purity.png

[MarshallDodge]

IIRC, Energizer also makes the batteries labeled for SF.

Interesting. I am with decoded on the short circuit but I have had a flaky Surefire (Engergizer)battery.

I have a Surefire G2 that my wife purchased for me as a Christmas present a few years back along with a box of their batteries.

Recently the G2 suddenly quit. At first I thought it was the bulb but I did a continuity check and it passed. It was one of the batteries that just up and died. The other one was fine, with the batteries placed in series it makes me wonder....

[decodeddiesel]

Did you check out the PSDS's (product safety data sheet) for most lithium based cells? Usually they state that in the event of a fire, you will not be able to extinguish the cell, but you can cool surrounding cells to keep the fire from spreading.

While it may be possible Li-Po cells that are "envelope packaged" are typically an "if one goes you better run" type of situation. We shorted a 3 pack of 2000 mAh cells once to see what it did...it was a bad idea. :eek:

[MookNW]

Ka-Ching! Early retirement.