What determines long run time on low?

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MrGearaholic

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Nov 27, 2012
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Hi All,

Not long ago I got an EagleTac D25C xm-l in neutral white. I thought it would be a good vampire light to drain the last juice out of my cr123a's with its low setting of 0.5 lumens. However, I noticed that even with this moonlight mode the light quickly died using a cell that still gave me 2.89 volts (without load). This same cell still gives me a higher output of around 2 lumens (I guess) in my NiteCore Extreme R2, for quite some time now already...

So I don't get it: what is it exactly, that determines how long a light keeps running on low? I naively thought that lights with lower lumen lows should run longer than lights with relatively higher lumen lows.

Is it the xm-l that needs a higher power than the r2, therefore asking a higher current (even on moonlight)? I can imagine that such a higher current makes the voltage under load drop faster. Or is it the operating voltage, the electronics, the efficiency of the emitter, or...??

I'm pretty new to this matter, so maybe some of you experts here can explain what the key factor is?

Thanks!

Sent from my iPad using Tapatalk HD
 
AnAppleSnail

AnAppleSnail

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Location
South Hill, VA
It's all about the driver (Flashlight model) and the LED forward voltage (Individual flashlight). Some driver architectures are good down to 0.8v -- A very dead lithium primary, or a dangerously dead Li-Ion.
 
R

reppans

Flashlight Enthusiast
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Mar 25, 2007
Messages
4,873
I'm really surprised at that - the D25C clicky specs indicate a 0.8-3.2v operating range so I would have thought you could run that sucker down for quite a while. I have to ask the obvious question if you are sure you had the light programmed to group 1 (moon mode on)?

I have that D25A clicky in XML, and although I didn't a do moonlight runtime test with it, I did a low mode (~ 3 lms) test against various Quarks (R5, S2 and XML) and it was on par with the QXML. Also, I found XML lower mode efficiency to be pretty spot on with what 4/7s quotes for its lights... ie, the XML has about 50% the runtime of the XPG on moonlight, 60% runtime on low, etc.
 
M

MrGearaholic

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Joined
Nov 27, 2012
Messages
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Location
Tucson, Arizona
I'm really surprised at that - the D25C clicky specs indicate a 0.8-3.2v operating range so I would have thought you could run that sucker down for quite a while. I have to ask the obvious question if you are sure you had the light programmed to group 1 (moon mode on)?

Yes, I was sure I first programmed it to the 0.5 lumen low. I could comfortably look into the LED. Just tested it again: within a minute it goes black. When I switch the same battery to the NiteCore Extreme it is uncomfortable to look into the LED on low for 10 minutes now already and still going strong.

I guess I would have to measure the voltages under load and compare those: the D25C should have a lower voltage.

If it's the driver architecture and forward voltage, there's probably not a simple rule of thumb one can follow to decide which light is a better vampire based on the manufacturer's specs?
 
E

eh4

Flashlight Enthusiast
Joined
Oct 18, 2011
Messages
2,002
Captain Obvious to the rescue! Your Nightcore Extreme is a much better battery vampire for some reason or another. I must go now, I hear the cry of an innocent who cannot believe that it's not butter.
 
R

reppans

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Mar 25, 2007
Messages
4,873
You had me worried, so I dug up a dead LR61 batt (AAAA from a 9V) that I was using for some earlier runtime tests. Vampire tested them in a Quark AAX and D25A Clicky XML. Starting rest voltage 1.06V. Powered both on ML, back and forth for a while. D25 quit first, but it was close enough and this was one dead batt, already depleted from previous runtime test (100 hrs from an XPG and 50 hrs from XML, btw).

End voltage was 0.96 resting, 0.76 under 50ma load. D25A operating range 0.8-1.5V.

See how much you runtime you get from the NC.... could be something wrong with the light needing warranty repair. It would suck to be throwing away half used 123s.
 

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