Two days ago I made a light out of a luxeon directly driven from 3 NiMh AAs. I measured it, and it was drawing about 600ma. Today I moved it to a new aluminum HS (you may have read about the steel one /ubbthreads/images/graemlins/wink.gif ) and I measured it again...drawing 310ma from the same batteries. Ummm...what the hell? /ubbthreads/images/graemlins/confused.gif It seems to be just as bright as well... /ubbthreads/images/graemlins/confused.gif /ubbthreads/images/graemlins/confused.gif
Luxeon - 600ma one day...300ma the next?
- Thread starter zmoz
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trailstoride
Newly Enlightened
Were the NiMH cells freshly charged when you made the first measurement? NiMH cells can have as much as 1.4 volts when charged. After they "sit" for a day the voltage drops to about 1.2 to 1.25 volts. That alone could account for the differance on the different days. Direct driven LS current varies substantially with small changes in voltage.
Could you have added some extra resistance to it (different threads, too heavy solder contact, smaller wires), or maybe a short happened? Or maybe there wasn't a good ground contact made, either by the leads or by the tailcap/threads?...
Ok...I think my luxeon has been possesed by aliens. /ubbthreads/images/graemlins/jpshakehead.gif I went back out into the dark to play with it...right after I turned it on it seemed dim. Then about 5 seconds later...it got bright again. Went and measured it again...now it's using 430ma. /ubbthreads/images/graemlins/confused.gif /ubbthreads/images/graemlins/rolleyes.gif /ubbthreads/images/graemlins/jpshakehead.gif /ubbthreads/images/graemlins/confused.gif
...Shouldn't affect it in any way... If heatsinkin's adequate, it shouldn't matter if you port it over... If it was something like a flex problem, you'll probably experience another jump in current drain the next time you measure again... It couldn't be that the LS is suffering from terminal heat, because I'd figure if it goes out, it'll steadily decrease in its current draw, not increase...
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zmoz said:
Nope...same wires and everything, if anything they make better contact now at 310ma. The part I find the strangest is that I don't see any difference at all in the light output.
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If everything (seems) the same with the flashlight, check the conditions of the battery(s) in your DVOM. Last time I got "spectacular" results, it turned out to be nothing more than a dying battery in the meter.. /ubbthreads/images/graemlins/icon15.gif
zmoz said:
Nope...same wires and everything, if anything they make better contact now at 310ma. The part I find the strangest is that I don't see any difference at all in the light output.
[/ QUOTE ]
If everything (seems) the same with the flashlight, check the conditions of the battery(s) in your DVOM. Last time I got "spectacular" results, it turned out to be nothing more than a dying battery in the meter.. /ubbthreads/images/graemlins/icon15.gif
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Slick said:
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zmoz said:
Nope...same wires and everything, if anything they make better contact now at 310ma. The part I find the strangest is that I don't see any difference at all in the light output.
[/ QUOTE ]
If everything (seems) the same with the flashlight, check the conditions of the battery(s) in your DVOM. Last time I got "spectacular" results, it turned out to be nothing more than a dying battery in the meter.. /ubbthreads/images/graemlins/icon15.gif
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Actually...I checked it with two different, new meters. /ubbthreads/images/graemlins/smile.gif I swear...it's possesed by aliens... /ubbthreads/images/graemlins/wink.gif
Slick said:
[ QUOTE ]
zmoz said:
Nope...same wires and everything, if anything they make better contact now at 310ma. The part I find the strangest is that I don't see any difference at all in the light output.
[/ QUOTE ]
If everything (seems) the same with the flashlight, check the conditions of the battery(s) in your DVOM. Last time I got "spectacular" results, it turned out to be nothing more than a dying battery in the meter.. /ubbthreads/images/graemlins/icon15.gif
[/ QUOTE ]
Actually...I checked it with two different, new meters. /ubbthreads/images/graemlins/smile.gif I swear...it's possesed by aliens... /ubbthreads/images/graemlins/wink.gif
Doug S
Flashlight Enthusiast
While I would not expect as large a difference as reported, 600 down to 300 mA, with constant voltage direct drive a hotter LED [poor heatsinking] will draw more current than a cooler LED [better heatsinking]. This is due to the negative tempco of Vf. You didn't change ranges on you meter did you? Different meter mA ranges use different values of shunt resistance and can radically change the actual current flowing in this type of scenario.
georges80
Flashlight Enthusiast
At reasonable current levels I'd suspect the battery holder contacts - especially on those cheapy plastic ones with the spring or +ve contact plate attached via a rivet. A careful application of a solder connection at those points will help things considerably - just don't melt the plastic.
Also I would measure with 2 meters, one set to measure current and the other set to measure voltage. Then you can use the voltmeter to probe various points to see where voltage drops are occurring. Certainly the currentmeter will introduce a voltage drop, especially on the low current ranges.
A good powersupply with current limit and voltage/current display is also a nice thing to have ($$) to map the Vf of a Luxeon - especially as it warms up on your target heatsink.
george.
Also I would measure with 2 meters, one set to measure current and the other set to measure voltage. Then you can use the voltmeter to probe various points to see where voltage drops are occurring. Certainly the currentmeter will introduce a voltage drop, especially on the low current ranges.
A good powersupply with current limit and voltage/current display is also a nice thing to have ($$) to map the Vf of a Luxeon - especially as it warms up on your target heatsink.
george.
