Luxeon 5-Watt UNDERdriven On 6V...

MR Bulk

MR Bulk

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Forgive me everyone, but all this scientific talk emanating from an eminently qualified few has gotten my head to a-spinnin'. Tell ya what, moment I get my hands on some 5-watters, I'm gonna sacrifice $23.10 worth and just run one as long as I can, until it either

1) gets too hot to hold, and/or

2) fries the emitter

and then I'll get back to ya...

But I sincerely Thank You all for making it grow far beyond what was anticipated when I first posted. And please, do continue the heat transfer theory discussions until I have the opportunity to test...
 
D

Doug S

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Originally posted by MR Bulk:
...in a well-heatsunk big metal flashlight, like say a D-cell Mag -- what would the temps be like? Wayne? Don? Peter? Anybody?
<font size="2" face="Verdana, Arial">Hey Mr Bulk. Does it drive you crazy that you ask a straightforward question and nobody gives a straightforward answer? Perhaps you can take some comfort from the result that it has at least generated some interesting discussion. The problem is that this question doesn't have a straightforward answer. Another significant variable is the large variation in [email protected] on the published Luxeon datasheets. This range is from 5.43V to 8.31V. A sample at the bottom end of this range would draw over 7 watts at 6 volts and one on the top end would draw essentially 0 watts at 6 volts. This latter one we can safety say will not get hot at all.
 
V

vcal

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Mr. Bulk, I don't see how 'ya could get into very much overload trouble at all powerin th 5W [email protected] if yer thinkin' about usin 2 of those 3AA=1"D" batt holders-with alkalines for th 6V. total, -given the higher internal resistance of AAs.

Btw-when do you think we could get a real concrete price on those nifty holder/adaptors-(mentioned above).?

p.s.-as a public safety officer, how would you calculate the fine for going 1100mA in a posted 700mA zone? ;^)
tongue.gif
-$23.??

EDIT:-my math SUCKS today!
please disregard first paragraph above and try NiMH-to get that voltage down to 7.2V.
blush.gif
 
MR Bulk

MR Bulk

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DougS, agree, and vcal, agree too, but I would just run one dummy cell in there with the other 5 AAs and try it at 7.5V...

BTW I have BAD NEWS about the batt holders...see group buy thread where I will bare all...
 
G

Gransee

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Originally posted by Doug S:
You are going to look at the die only and not the slug its mounted on? Dimensions of the die are on the order of 1mm. I would be surprised if your equipment can do this. If your equipment is good enough to see only the die plus slug, you could use the approximation that the measured temperature is the slug temperature [this approximation works since the slug area is large relative to the die area in the view of the instrument] and then use the die to slug thermal resistance to calculate the die temperature [15C/W in the case of the 1W emitters]

If you really must use IR measurement methods, a better way to "calibrate" your technique would be to take a "Star" configuration device and measure the backside under the emitter, calculate the die temp using the Luxeon datasheet thermal resistance, and then compare to your IR measurement of the front of housing. Measurements should be made after thermal steady state has been reached.

For other discussion of thermal measurement methods, see the link below:

http://www.candlepowerforums.com/cgi-bin/ultimatebb.cgi?ubb=get_topic;f=14;t=000376# 000019
<font size="2" face="Verdana, Arial">Thank you Doug. I followed the link and read through the thread you started. Excellent reading all.

I agree a direct thermocouple connection to the die and if that is not possible, to the slug is ideal.

Of course, this may not always be possible at the time it matters most, and that is when the LED is in the flashlight.

So even though the pyrometer is not as accurate, it is more accurate than using a thermocouple against the outside of the flashlight or against one of the heatsink or bulkheads inside the flashlight that can be exposed while the light is in operation.

OK, here we have a luxeon emitter being held tightly against a tempurature probe. Also, the probe is liberally gooped in heatsink compound to facilitate transfer. I believe this is one of the ideas you suggested.

thermal1.jpg


thermal2.jpg


Notice that the thermocouple indicates 10C less than the pyrometer.

You could say this is due to the inaccuracies of the IR method or the heat gradient across the part or both.

Either way, if I keep the pyrometer reading low, the LED is probally doing even better.

Needless to say, the original question was about if a 5W emitter would be ok in a Maglite running at 6v. The answer was, it depends on your heat sink. Well, how do you test your heatsink? Now, if you can get your thermocouple inside the light to measure the slug temp, then excellent. Otherwise, the pyrometer may be a better option. Since our lights are typically quite small, the pyrometer works.

I invite anyone to produce a better method of course since we always want to advance the art.

Peter Gransee
 
MR Bulk

MR Bulk

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Well alrighty then. Lest we forget, Peter is the only one here successfully building durable LS lights for the (semi) mass market. Guess he must know just a little bit about something...
 

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