Lithium CR123a - flat discharge curve?

[ltiu]

I remember reading that the SureFire 6PL can run for about 11 hours on a single set of Lithium CR123a batteries. I also read that it produces 80 lumens of light.

But I read that it only produces 80 lumens the first few hours then the light output slowly drops until the 11 hour max before it dies.

Question: I thought lithium CR123a batteries have a flat discharge curve. How come the SureFire 6PL's light slowly gets dimmer as the battery gets used up?

I thought the definition of a flat discharge curve is that the 6PL would stay bright. Then when the battery is completely spent, the light shuts down, with no dimming.

Am I missing anything here?

Any insights and words of wisdom appreciated.

 

[DM51]

Moving to 'Batteries Included'...

 

[SilverFox]

Hello Ltiu,

If you direct drive the LED from the battery, you can expect a reasonably level output of light gradually dropping off at then end of the discharge.

However, I believe in the 6PL there is a circuit. Now the battery is providing power to the circuit and the circuit is responsible for the light output. You now are at the mercy of the circuit.

Tom

 

[Lighthouse one]

I have one light that works exactly like this and I like it a lot. Many like a light that is perfectly flat in regulation...but my slowly dimming light runs nearly 12 hours on an 18650. How often do I use it for 12 hours straight...never- but it can do it if needed! It's very strong for 2 hours- then tapers slowly.

 

[effulgentOne]

http://www.candlepowerforums.com/vb/showthread.php?t=176621
(look at the purple curve)

In a 6PL, it runs for about 3 hours bright, then tapers off but still provides light for at least another 8.

The circuit in the LED module provides regulated output for a few hours, then it drops out of regulation because the batteries can't provide enough power anymore. Rather than going completely black, it then leaves you with a little light for many more hours, leading to a somewhat misleading runtime figure.

 

[ltiu]

http://www.candlepowerforums.com/vb/showthread.php?t=176621
(look at the purple curve)

In a 6PL, it runs for about 3 hours bright, then tapers off but still provides light for at least another 8.

The circuit in the LED module provides regulated output for a few hours, then it drops out of regulation because the batteries can't provide enough power anymore. Rather than going completely black, it then leaves you with a little light for many more hours, leading to a somewhat misleading runtime figure.

One thing I do not get.

If the CR123a lithium runs with a flat discharge curve, then drops dead how does the regulator know when to start reducing the output? If the battery starts tapering off, it should taper off quick leaving little time for the dimming process to run it's course.

or

Maybe the CR123A lithium does not actually run with a flat discharge curve all the way and does some tapered output towards the end like alkalines?

 

[SilverFox]

Hello Ltiu,

You may find this thread informative...

Tom

 

[mdocod]

there is no cell, in any chemistry, made by any company, with a perfectly flat discharge curve, it simply does not exist and probably never will. CR123s have a flatER discharge than other chemistries that consumers are familiar with, When compared to Alkaline cells, they are significantly "flatter" but not perfect.

 

[ltiu]

OK, thanks for the information guys. I feel better now with my questions answered.