Cree Surefire E2L runtime on 14670?

Has someone done a runtime test with a 14670 Li-Ion cell on the new Cree Surefire E2L?

WildChild said:

Has someone done a runtime test with a 14670 Li-Ion cell on the new Cree Surefire E2L?

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Not to my knowledge. However:

The new E2L head isn't designed to run on a single cell. It will work off a single fully charged li-ion but will shut down once the cell discharges to 3.7v. 3.7v is at about the 20% mark on a the discharge curve of the typical li-ion cell. As a result, the E2L head will only get ~220mAh out of a nominally 1100mAh 14670. Runtime is expected to be rather short.

enLIGHTenment said:

Not to my knowledge. However:

The new E2L head isn't designed to run on a single cell. It will work off a single fully charged li-ion but will shut down once the cell discharges to 3.7v. 3.7v is at about the 20% mark on a the discharge curve of the typical li-ion cell. As a result, the E2L head will only get ~220mAh out of a nominally 1100mAh 14670. Runtime is expected to be rather short.

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Are you sure? Some numbers found there:

https://www.candlepowerforums.com/threads/147007

4.2V – 100%
4.1V – 87%
4.0V – 75%
3.9V – 55%
3.8V – 30%
3.6V – 0%

I also saw two other threads where SilverFox gave these numbers. A runtime of 4h using a single li-ion would still be nice! Unprotected could probably be used without any risk of overdischarge (3V don't power-up the light). And I guess the cell would get a better cycles life, not being drained too much.

Those are open circuit (no load) voltages. Discharge under load is going to look like this:

http://www.buchmann.ca/chap2_files/image007.gif

But is the 3.7V measured under load or open voltage for the E2L?

What do you think?

Power to run the head has to come from somewhere.

enLIGHTenment said:

What do you think?

Power to run the head has to come from somewhere.

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You didn't understand my question... The 3.7V shutdown you are talking about, was it with the cell under load or by measuring the open voltage of it with no load? I saw a link somewhere about this number for the E2L but I can't remember where. And that was not clear...

WC,

i believe that i understand your question.

what you're asking is was the supply voltage 3.7VDC when the head shutdown, or was the operating voltage seen by the head actually lower due to the drop across the supply's internal resistance while light was being produced, and the 3.7VDC was measured after "shutdown" when no more current was being drawn.

based upon eL's wording, i would understand eL to mean under load. "SHUTDOWN" [emphasis mine] implies that something was running (and therefore acting as a load drawing current from a source) and then "shutdown".

I thought a little about that! For sure, the new E2L has a bucks only circuit. The circuit can at least handle up to 9V (someone tested it with 3 CR123A). Usually, with a bucks circuit, when the battery voltage fall at the LED Vf, it goes to direct drive mode. And with flat regulation, when it goes to direct drive, output tends to fall quickly! Cree Vf is around 3.1V at 350 mA (if they drives the LED at this current and the LED must be driven at a low current to get a 45 lumens output). At 3.1V under load, a Li-Ion is completely depleted. What I'm not sure is the open voltage the battery will recover to after some time. Can it recover to 3.7V?

Anyway, I asked Chao to do a runtime test with a 1470 cell. He has the E2L and the cells. I finally decided to order a E2L anyway because it has a nice battery life on primaries but if the runtime test is good on Li-Ion, I will get those as well! The light seems promising to me!