Run-Time Plot - NexNeedle 5W

[Roy]

This runtime plot is for the NexNeedle, a Brinkmann Nexstar modified by Mr Bulk to use a 5W LS led. Three Sure Fire Li 123 batteries were used in this plot.

Equipment used is a photocell and a Radio Shack 22-805 multimeter with a PC interface that is using ScopeView software (1.08).

The vertical axis is in ma and the horizontal axis is 15 minutes per division.

Be aware that your actual battery milage may vary from that indicated indicated by this runtime plot.

 

[MR Bulk]

Roy,

Thanks for posting this. You see how that line seems to rise in linear fashion the first 15 minutes? I noticed a similar phenomenon while testing the bare emitters.

With 1W batwings the light meter display normally races upward and hits a plateau, then slowly descends in 1-lux increments, presumably reflecting reduced light output in direct correlation to increasing heat.

The 5W's also hit a plateau, but then slowly creep upward a few lux at a time...

Whyzzat? It's almost like the Luxeon is "breaking in", sort of "acclimating" itself to its new voltage surroundings...mebbe they get even brighter over time?

 

[Roy]

It would be interesting to see what it would do on a bench power supply! With a regulated ps I wonder how long the lux value would keep going up?

 

[evan9162]

Originally posted by MR Bulk:
Roy,

Thanks for posting this. You see how that line seems to rise in linear fashion the first 15 minutes? I noticed a similar phenomenon while testing the bare emitters.

With 1W batwings the light meter display normally races upward and hits a plateau, then slowly descends in 1-lux increments, presumably reflecting reduced light output in direct correlation to increasing heat.

The 5W's also hit a plateau, but then slowly creep upward a few lux at a time...

Whyzzat? It's almost like the Luxeon is "breaking in", sort of "acclimating" itself to its new voltage surroundings...mebbe they get even brighter over time?

<font size="2" face="Verdana, Arial">Mr Bulk-
The above graph may be a result of the Lithium batteries warming up, thus increasing the rate of chemical reactions, allowing for a slightly higher current.

As for the effects you were seeing, that may be due to the luxeon heating up - causing the vF of the emitter to drop slightly. The lowering vF during increased temperature is a known characteristic of LEDs. When this happens in the extreme, it's called "thermal runaway" - the temperature rises, causing vF to drop, causing more current to flow, increasing heat, lowering vF....it's a vicious cycle that makes the LED go *poof*.

-Darin

 

[MR Bulk]

Darin,

Yes, I get what you are saying, and the phenomenon occurs while testing the LS's with a bench constant power supply, as well as with the Luxeon clamped squarely on a mirror smooth aluminum slug for thermal dissipation. Also I am testing them at just 6V -- Hmmm...

 

[hotbeam]

Very nice Roy. Do you happen to have a Space Needle II to conpare this plot against? Would be very interesting given the similiarities between the two lights.

Good job.

 

[paulr]

It's a well known characteristic of lithium batteries that their voltage increases slightly during the middle part of their discharge curve, before falling back down.

 

[Doug S]

[ QUOTE ]
paulr said:
It's a well known characteristic of lithium batteries that their voltage increases slightly during the middle part of their discharge curve, before falling back down.

[/ QUOTE ]
Paul, I believe that you are thinking of LiSO2 lithium batteries. CR123 cells are LiMnO2 batteries which do not exhibit the characteristic you describe except under the conditions of high discharge rate at *very* low temperatures [e.g., -40F or C].