10 April 2009

Update: Flashlights and Batteries

First item: My UltraFire C3 flickering problem was in fact persistent. The problem (fairly common on these models, it turns out) is with the way the head mates with the battery tube. The tube must ground on the emitter but, when screwed down, it rests on just two blobs of solder on the emitter back that, on some lights, do not provide good enough contact. The solution is to take a piece of bare copper wire, shape it to fit just inside the head beneath the battery tube, and screw it all together. That fixed it for me. But I'm still steamed I had to correct a design flaw. For $11 it is still an amazing light, but even at that price point there are actually a lot of options.

I was perhaps too bold, or at least naive, with my recommendations in my previous flashlight post. I don't know that I recommended any lemons, but even now with just a bit more research, I'd make some different recommendations. Though not here and now. This is Knife Month, after all. But look for more discussion and reviews to come.

Flashlight and battery tech naturally go hand in hand. Most high-performance lights work best or even exclusively with exotic lithium-ion* batteries (go lithium!) that you basically have to mailorder from Asia. They run at higher voltages, which hi-po lights like. Again, more on this to come.

But I did want to mention one interesting fact, relative to AA batteries and flashlights, as yet another supplement to my original battery post. First, alkaline (disposable) and NiMH (rechargeable) AA batteries produce different voltages, 1.5v and 1.2v respectively. That means that they are not strictly interchangeable. The device they are used in must be regulated to use both voltages. There is also an exotic AA-sized rechargeable lithium-ion battery called a 14500 that runs at 3.6v or 3.7v. But before you drop one of those guys in your light, again, you need to be sure of the voltage range that it will accept. Or you could literally blow up your light.

My UltraFire C3 is regulated for 0.8v ~ 4.2v. That means it will run on any AA you care to put in it, even a 14500. You can even buy an extension tube that turns it into a double-AA light (but not two 14500s, do the math!). The fact that it will run on as little as 0.8v also means it will suck your batteries pretty dry. That's a very good thing.

But different battery chemistries (see my first supplement) can change the way your light performs. More expensive lights are digitally regulated to produce a consistent amount of light as the battery draws down. When drawn down close to dry, some switch into "moon mode," a low-power draw that produces little light but sucks that last bit of juice from the cell. However, cheaper lights are usually direct drive. Basically, the power goes straight from the battery to the bulb or LED emitter. In these lights, the kind of battery you use can really change performance.

For example, in my UltraFire C3 (per this review), a 2500mAh NiMH lithium battery* will produce a consistent 40 or so lumens for about 90min, and then output drops steeply until completely dead at about 130min. A good alkaline AA will produce about 36 lumens when fresh, but steadily declines to about 4 lumens at 100min, then running at that level out past 220min. Two different batteries give you two quite different lights.

The reason for this difference (per Wikipedia) is that even though "the nominal NiMH voltage is lower, it sustains for the length of the discharge cycle, because the low internal resistance allows NiMH cells to deliver a near-constant voltage until they are almost completely discharged. Alkaline discharge voltage drops more towards the end of the discharge cycle."

High drain on alkalines also decreases their effective capacity. "Alkaline batteries, which might have approximately 3000 mA·h capacity at low current demand (200 mA), will have about 700 mA·h capacity with a 1000 mA load. Digital cameras with LCDs and flashlights can draw over 1000 mA, quickly depleting alkaline batteries. NiMH can handle these current levels and maintain their full capacity."

Bottom line: For direct drive lights, NiMH = more light for less time, while alkaline = less light for more time. (Whew.)

This is just geeky tech abstraction if you only need a light to occasionally find your car keys, but in more critical applications, knowing precisely what to expect from your light may be more important. For such uses, one should really own a quality light with digital regulation and accurate manufacturer-supplied performance specifications (like this Fenix LD01). And always have on hand a spare battery and backup light.

*Further tech point: Disposible lithium (NiMH) batteries and rechargeable lithium-ion batteries are not the same thing. Both are lithium based, but two different chemistries, voltages, etc. Lithium, the psychotropic drug, is related to these batteries chemically, but the Lithium Press just topically.

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