Questions about my flashlight and battery voltage

Hey guys, I got a few questions about my led flashlight.

I just bought a led flashlight off ebay and it's advertised to be able to adjust flood and throw as well as 2 modes of use, full power and strobe. So I got the flashlight and it came with 2 1.5v alkaline batteries. The flashlight worked fine with them, not as bright as I'd like, or as bright as the other lights that I have that are advertised to have lower lumens. This light is supposed to have a CREE R2 bulb and about 120 lumens. The other lights that I have are about 100 lumens, but I'm using CR123a batteries on them, which I'm sure you guys know are lithium batteries and about 3.7v. So I was wondering, if I put my TR14500 (AA lithium) batteries in, the flashlight should still work right? Well, this is where I ran into problems. The flashlight worked and was much brighter, but after about 25 secs it starts flickering, and as the secs tick on the flickering speeds up. Worried the bulb might "pop" I turned it off. I also observed that with the lithium batteries, the flashlight would not enter strobe mode. So onto the questions:

1) Can anyone explain what's going on with the flashlight, and why it behaves the way as described above when powered by lithium batteries?

2) CREE R2 bulbs should be able to handle 3.7v lithium batteries right?

and
3) I'm looking for a bright (100+ lumens) "zoomable" flashlight with multiple modes including strobe mode and able to take CR123a batteries and/or TR14500s, preferable about 25mm in diameter. Any suggestions?

jsze1 said:

I just bought a led flashlight off ebay and it's advertised to be able to adjust flood and throw as well as 2 modes of use, full power and strobe.

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Can you give any brand/model info on it, or provide the eBay auction number?

The other lights that I have are about 100 lumens, but I'm using CR123a batteries on them, which I'm sure you guys know are lithium batteries and about 3.7v. So I was wondering, if I put my TR14500 (AA lithium) batteries in, the flashlight should still work right?

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Terminology issues, we need to be clear on these. CR123A are primary (non-rechargeable) batteries that are nominally 3.0V. The rechargeable Li-ion versions are usually referred to as RCR123 or 16340, and for LiCo chemistry are 3.7V nominal. I assume the TR14500s you're referring to are TrustFire's 3.7V Li-ion rechargeables?

And this light takes 2x AA-sized batteries?

Well, this is where I ran into problems. The flashlight worked and was much brighter, but after about 25 secs it starts flickering, and as the secs tick on the flickering speeds up. Worried the bulb might "pop" I turned it off. I also observed that with the lithium batteries, the flashlight would not enter strobe mode. So onto the questions:

1) Can anyone explain what's going on with the flashlight, and why it behaves the way as described above when powered by lithium batteries?

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The circuitry is probably being run way beyond spec.

2) CREE R2 bulbs should be able to handle 3.7v lithium batteries right?

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The specific LED it's using has nothing to do with anything. Acceptable input power is determined entirely by the driver circuitry.

If the flashlight is designed for 2x AA batteries, that means it's designed for an input voltage that is nominally 3.0V (2x 1.5V batteries in series), and probably has boost circuitry to drive the LED appropriately. Putting 2x Li-ions in there results in anywhere from 7V to 8.4V depending on state of charge, and obviously a light that is not designed for that will not handle it well.

I'll let others recommend flashlight models for your third question.

*EDIT* Sorry Quension, it looks like you beat me to this reply ; darn multitasking got the best of me

jsze1 said:

1) Can anyone explain what's going on with the flashlight, and why it behaves the way as described above when powered by lithium batteries?

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What are TR14500 batteries? Is TR the brand? Are they a primary Lithium battery or a secondary Lithium battery (Li-ion)? If they're Li-ion batteries, then am I understanding you correctly that you installed two (2) 14500 Li-ion batteries in the light that came with 2- Alkaline batteries installed in it? If so, the circuit may not be designed to work with 2- Li-ion batteries; a single Li-ion battery has a nominal voltage of 3.7v so 3.7 x 2 = 7.4v total if the batteries are in series (they probably are). Alkaline batteries are 1.5v each so 1.5 x 2 = 3v total. It's pretty common for a circuit to not function correctly when the user supplies too much voltage.

Most of the time the emitter ends up getting all of the juice from the battery (direct drive), and the emitter will fail if the voltage and current are too high, but usually 7.4v being supplied to an emitter with a vf of 3.7v would fry the emitter in about 5 seconds or less (don't ask me how I know .....), and you said you ran it for 25 seconds, so I'm not sure. It sounds like the higher voltage may be your problem either way. BTW, a primary Lithium CR123 cell has a nominal voltage of less than 3v, not 3.7v.

jsze1 said:

2) CREE R2 bulbs should be able to handle 3.7v lithium batteries right?

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Yes, but you're supplying twice that.

ti-force said:

*EDIT* Sorry Quension, it looks like you beat me to this reply ; darn multitasking got the best of me

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We must never let a thread suffer from lack of replies! :laughing:

Quension said:

We must never let a thread suffer from lack of replies! :laughing:

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I know, I know LOL.... I just didn't want you to think that I came in behind you and basically typed what you said, but in different a way, and completely ignoring what you said. I guess I'm just strange . Truth is: when I clicked the reply button, there were no replies, but by the time I hit the submit reply button you had already posted info that was similar to what I posted .... Thanks for understanding :candle:....