Overheating LF3XT

[rlichter]

The other week I had a potentially dangerous experience: I was using my new LiteFlux LF3XT with a six or seven year old CR123A, set at maximum brightness, standing on its tail. I just happened to reach over and touch the light after it had been on for a matter of maybe two minutes and it was very hot. There was no obvious problem with beam brightness. It was almost too hot to handle, so I turned it off, took it apart, and removed the battery. The Sanyo CR123A was extremely hot. Fortunately, the LF3XT survived. It seems to be working perfectly with a Battery Station CR123A (just purchased) and on maximum brightness just gets a bit warm after several minutes. This seems normal.

Either there was an intermittent problem with the flash light itself, or a problem internally in the CR123A. I have been unsuccessful in finding information on what might go wrong with a lithium primary, especially one that's near the end of its shelf life, that could cause overheating (and potential explosion). I continue using the flash light on the assumption that the problem was the battery, but I'd like to know about the physics involved. For example, an older primary might have lower voltage and/or increased internal resistance; things like that, to confirm my assumption is safe. I'd appreciate any information and speculation on what might have gone wrong. Thanks.

 

[soli]

You might want to try over in the LED Flashlights section, this area is more to do with the general operation of the forum and potential issues it may have.

 

[DM51]

Moving it...

 

[Beacon of Light]

Seems like this would be better answered in the battery section.

 

[DM51]

Seems like this would be better answered in the battery section.

I moved it to LED Flashlights as I think it is more likely to be something that can be noticed with any small high-performance light when it is left tail-standing. I doubt there is a problem with the battery.

The demand (on CPF and elsewhere) for smaller and smaller lights that emit more and more light has led to manufacturers pushing nearer and nearer to the boundaries of what can safely be achieved.

Most of these small lights are designed to be held in the hand, which (although the user may not realise it) is an efficient method of conducting heat away from the body of the light. The direct contact from the hand is many times more efficient as a heat conductor than air. What this means is that if you leave a light tail-standing, it is going to get hotter than it will if you hold it in your hand.

That is what I think happened here. I don't think the OP actually has anything to worry about in this case; the light got hot - surprisingly hot, in a short time (2 minutes). That is what I would expect from a small high-performance light.

Note that he said "almost too hot to handle". It was obviously not so hot that he had to drop it. The human hand is actually a good gauge to use as a sensible limit of temperature for lights and the batteries inside them. If you can hold it, it's OK. If it's uncomfortably hot, it should probably be turned off and allowed to cool. If you yell "YEEOW!" and have to drop it, that's when you need to start worrying.

In this case, it did not have a human hand to augment the heat-sinking. It just became rather hotter than usual, because it was in tail-stand mode. I don't thinik there is anything unusual in this, nor anything to worry about.

 

[Flying Turtle]

Curious problem. I can only think of one very old report of someone having a wiring problem with this light. Doesn't seem likely that a battery would act like this, but what do I know.

Geoff

 

[rlichter]

"Most of these small lights are designed to be held in the hand, which (although the user may not realise it) is an efficient method of conducting heat away from the body of the light. The direct contact from the hand is many times more efficient as a heat conductor than air. What this means is that if you leave a light tail-standing, it is going to get hotter than it will if you hold it in your hand."

Sure it will get hotter but I have been unable to even approach recreating the thermal problem with the new battery. Most of the time I use the LF3XT on a Fenix head band (modified for the larger diameter), there is no body contact; in fact as I sit here typing the light has been sitting on its tail on my desk on full brightness for five minutes...and it is barely warm. I'll contact LiteFlux directly and see what they think of the situation.

 

[DM51]

I see what you mean now (I was a very slow getting the point). Either that first battery was a weird one (like FT, I've not heard of anything like that happening before) or there was some kind of short in the light that was due to that battery. Was its shrink-wrapping OK?

But it's a strange one. If there was a short, you wouldn't really expect the light to come full on - you might see a very dim light with a short, but it would be very bright with most of the energy going via the short into heat.

 

[rlichter]

Re: Overheating LF3XT, followup

I queried LiteFlux about this event and their reply made the following points.

1. The resistance of a lithium battery will increase if it is stored for a long time.
2. The increased resistance may be the source of the overheating problem.
3. Do not leave the flashlight at maximum brightness for a long time.

Implied by omission is that the LF3XT is not the cause of the problem.

 

[Flying Turtle]

Not a very satisfying answer. Never heard that deal about increased battery resistance. Hopefully the overheating never occurs again.

Geoff

 

[bansuri]

I've had an LF3XT apart down to the circuit board and the only component I could see that would be able to short circuit would be the leads that exit the end and attach to the emitter board. In that case it would be a short circuit to ground if the (+) lead were to scrape through the anodizing, in doing so it would dim or kill the output completely, an unlikely scenario.

The electronics are all pcb mounted, there's nothing bouncing around in there and for it to short out somewhere that created excessive heat and continued to output the light on 100% would require something special, perhaps a stray solder blob from manufacturing had been bouncing around and landed just right. It can happen.
Does anything rattle around in the head when you shake it? If you can hear it at all it will be faint.

I don't know enough about batteries to comment on that possibility.