# Preview of updated K2: testing of "new" K2 sample



## evan9162 (Aug 5, 2007)

PhotonFanatic was kind enough to send me a sample of a 'new' version of the K2. The part number is LXK2-PWC4-0160. Using the K2 part number decoder ring tells me that this should be a 160 lumen at 1A part. Notice the lack of an alphabetical bin marker - it looks like Lumileds is moving to the Rebel part numbering system for K2s. It's likely they will also move to the rebel binning structure for Vf and Luminous flux as well.

These parts don't seem to be available anywhere yet, nor are they listed anywhere either. Given the recent release of higher brightness Rebel parts, using the thin film die and new phosphor, it's reasonable to assume that this new version of the K2 is also using the same construction for the die/phosphor.

First up, a visual comparison between the existing K2 (PW12-S00) on the left, and the 'new' K2 on the right:

Head on (apply directly to the forehead!):






You can see that the new K2 has a different phosphor, since you can see the dot pattern of the die through the phosphor now, much like the difference between the 100 lumen rebel and the older rebel. In addition, the silicon submount is a gold color - however, I think I've seen K2s with gold colored silicon submounts before, so I'm not certian that it's an entirely new feature.

And from the side:





The die/phosphor combo is shorter, again like the difference between the new and old rebel. This should make the beam project relatively more forward (less side emitted light) compared to the old K2. So it looks like indeed, the new K2 is using the thin film technology, which eliminates the sapphire substrate part of the die.

Let's check out the beam profile:





The new K2's beam profile is a little different, projecting less out the side as predicted. This might affect the beam slightly when used with reflectors.


Here is the raw performance data for the new K2:


```
Current (mA)		0.1	30	130	310	670	980	1260	1570	1930
---------------------------------------------------------------------------------------------
Vf			2.53	2.75	3.05	3.25	3.47	3.60	3.68	3.78	3.89

Watts					0.40	1.01	2.32	3.53	4.64	5.93	7.51

Lumens					33	75	141	187	221	257	292

Lumens/W				84	74	61	53	48	43	39
```

This part is supposed to be 160-180? lumens at 1A. It looks like this part is performing at the high end of the bin range.



Compared to other power LEDs in the same class:

First, Vf:





The Vf of this sample is higher than most of the others. This will cause it to take a hit in the efficiency department. 


Next, output:





This sample is performing about equal to the Cree XR-E P4 bin. Hopefully better performing versions of the new K2 will be available when the update to this part is announced. It would seem rather silly that the Rebel would out-perform the K2 - Lumileds can produce very high performing LEDs in the rebel line - there doesn't seem like much reason to keep those improvements from getting into other products immediately.

Efficiency:





Even though this sample about equals the XR-E in output, it lags in efficiency, due to the higher Vf. 



Finally, "droopyness"





If the rebel didn't have "anti-droop" technology, then the new version of the K2 also doesn't. The new K2 scales pretty much the same as all the other parts.

While this was just a sample part, it's nice to see Lumileds finally get their buts in gear and get the K2 performing in the range of the Cree and Seoul parts. This sample definitely wasn't a performance leader - hopefully the final release parts perform better. Lumileds is going to have to stay on the ball with this if they are going to keep up with the pace that Cree has set in the last year for performance increases. 

Of course, we'll have to see how long it is before Lumileds decides to make these new K2 parts available for everyone.

The time frame, performance, and pricing of these new K2 parts will all effect how willing people are to use them. If we have to wait to long to get the improved parts, people will begin to fear "another K2", where parts were promised but never delivered. The new K2s will have to perform much better than this sample for people to decide to use them vs. the higher performing Cree parts (Q4, Q5, and better).


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## Opto-King (Aug 6, 2007)

Hi,
Where have you bought the "new" K2 LEDs?


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## Nereus (Aug 6, 2007)

Thanks for the info! :thumbsup:

-N


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## vic2367 (Aug 6, 2007)

yeah ,,,thanks for that info,,,will the led wars be heating up again ?


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## Manzerick (Aug 6, 2007)

Wow.. Looks promising!!



I hope I get the job in the LED division of Phillips!!!


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## evan9162 (Aug 6, 2007)

Opto-King said:


> Hi,
> Where have you bought the "new" K2 LEDs?



I didn't. I was sent a sample that someone else received. These are not available for sale yet. There are no announcments, nor timelines for any new release known. The only thing we do know is that there is supposed to be a Q3 (July->September) release from Lumileds. The updated Rebel released in july. It's possible that that's the Q3 release that was mentioned, and if so, it could be a while before we get these.


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## Nereus (Aug 7, 2007)

Evan, which luminous bin is the Seoul P4 you are using as a benchmark?

-N


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## Opto-King (Aug 7, 2007)

Thanks for the info, will be interessting to see when it "comes out" and how it will look when released.


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## Anglepoise (Aug 7, 2007)

Thanks for testing and posting the info.
I suspect that there are more than a few of us that did not want to re work perfectly good reflectors and are patiently waiting for a 'higher performing '
Lux III ( Gen X ) with its excellent heat sinking , overall build quality and oh so nice and smooth beam.

Lets hope this re launch of the K2 goes better than the first.


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## evan9162 (Aug 7, 2007)

Nereus said:


> Evan, which luminous bin is the Seoul P4 you are using as a benchmark?
> 
> -N



U-bin.


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## evan9162 (Aug 8, 2007)

Lumileds just released a press release today announcing "Lumiramic" phosphor technology, that's supposed to give better performance and much tighter/more control over color bins.

http://www.luxeon.com/newsandevents/releases/PR77.PDF

Here are the more interesting parts that are relevant to this thread:



> Lumiramic phosphor technology utilizes a ceramic phosphor plate and the company’s new Thin Film Flip Ceramic substrateCeramic substrate. TFFC technology, recently introduced in Luxeon Rebel, is the only thin film process that removes the anode and cathode from the light output path and provides an unobstructed plane to which the Lumiramic plate can be applied.



So we know the rebel isn't using Lumiramic



> Lumiramic and TFFC were two of the key technologies used to achieve the 115 lm/W performance announced earlier this year





> Philips Lumileds will introduce Luxeon products with Lumiramic phosphor technology in early 2008 and will begin sampling programs with customers in the lighting community in the fourth quarter of 2007.



So it looks like we won't be getting the 115lm/W parts until 2008, at least not by means of this new phosphor. If we do get 115lm/W from lumileds, it'll be using what the rebel/new K2 are currently using. 

Who knows what this means for when the "new" K2s get released either.


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## ViReN (Aug 8, 2007)

evan9162 Comparatively if we see the currently available *Q5* Crees, they are around 115 Lumens / Watt already aren't they?


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## evan9162 (Aug 8, 2007)

The 115lm/W LED that Lumileds mentioned produced 135 lumens at 350mA.

The Cree Q5 bin is 107-114 lumens at 350mA. They specify a typical Vf of 3.3V at 350mA, which makes the efficacy of the Q5 bin range from 93 to 98 lm/W. Of course, individual samples may have a lower Vf than the typical value, so of course, the efficacy will be higher. But the most you could expect from a Q5 cree would still "only" be 105lm/W.


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## L3D (Aug 11, 2007)

...great job, evan, thank ya for your testdrive and the macropics!


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## beyonder (Sep 21, 2007)

i was begining to lose hope that lumileds would put a rebel die into a k2!

oh well just 30 bucks on those 0100 rebels

went down that k2 road

no drivers

no batts to supply 1500 ma for a reasonable time

what was the k2 for anyway?


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## evan9162 (Sep 21, 2007)

- The K2 is reflow solderable, wheras none of the other luxeons were
- The K2 package is designed to deliver better thermal performance than previous luxeon packages (9C/W case-> junction vs. 13 C/W)
The package and die were designed to allow 1500mA of current safely
The package and die were designed to allow for high junction temperatures (185C in green and blue vs 135C before). This allows reduced heat sinking and for the device to be run in a much harsher (hotter) environment than previous luxeons.
The package and die were redesigned to deliver high lifespan at high temperatures and currents. A luxeon III driven at 1A will degrade to 50% output after 20,000 hours. A K2 driven at 1.5A will degrade to 70% after 60,000 hours. For this lifespan, the Luxeon III junction temperature had to be maintained at 90C or below. The K2 junction temp only needs to be maintained at 120C or below.

So the K2 introduced a high current package and die, with better thermal performance, that's reflow solderable, that allows the device to be run at hotter temperatures with less heat sinking, and maintain output longer than previous devices.

Most of these improvments are not targeted at the modder that will use one or two. A lot of these improvements have to do with making the K2 more compatible with industry standard manufacturing processes, and making the K2 more compatible with existing form factors by requiring less heatsinking for the same power dissipation.

I would hold onto your rebel-100s. We still have no idea when the improved K2s will release. Lumileds is notorious for dragging their buts on releases relative to smaller LED companies. Though that may be purely for business reasons. Only they really know for sure.


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## chesterqw (Sep 21, 2007)

wow 3.6V near 1A current.. now, that is good news


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## chris_m (Sep 21, 2007)

So the K2 which is due to be released soon performs about as well as the Cree which was released a year ago?


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## jeffosborne (Sep 21, 2007)

evan9162 - wow and thanks for the superb report! I know a lot of time and effort went into it, and I for one owe you my gratitude for the technical details. Great summary post this morning, too. I am guessing you are a technical writer by trade... or could be.

I have used some K2 LEDs in the portable lamps I have built to use with my digital camera. The tint and smooth dispersion pattern of the luxeon line has impressed me - especially compared with Cree and others. 

chris_m, you need to stare harder at the Lumious Flux chart above!

Happy Equinox (almost) ya'll!


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## evan9162 (Sep 21, 2007)

chris_m said:


> So the K2 which is due to be released soon performs about as well as the Cree which was released a year ago?



There are -160, -180, -200, and -240 parts in the PWC4 part number. The 200 should perform around the same as a Q3 Cree or Rebel 90. The -240 Will perform about what a Rebel-100 or Q4 will. There's also a PWC2-110 part that will deliver 110 lumens at 350mA. 

The different output levels will fit into different pricing segments. As a product line, it seems that it will be reasonable competitive.

I seems that you're bound and determined to lay on the hatorade on these products. If you're going to do that, please don't clutter up this thread with meaningless sniping comments.


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## chris_m (Sep 23, 2007)

I just think there needs a little perspective to the "love-in" which seems to happen on here with every Luxeon pre-release announcement. I sometimes wonder whether if Luxeon released a part which was miles behind the current state of the art efficiency but still a little better than what they had released before there would still be people on here swooning over it because it was a drop in replacement for lights they bought back when Luxeon USED to be the performance leader.

I'll give you that certainly the Rebel is a good performing part, but there is as yet no evidence that we will see K2s released in the near future which even do as well as that. Meanwhile some of my irritation is that your graphs seem to show that this K2 you have performs as well as a Cree and the Rebel better, and it does NEED to be pointed out that the Cree part in your graphs is a really old bin, so it's not really a very current comparison. Is all very well you commenting on the bins listed in Luxeon's bin structure - actually seeing such parts in the real world is another matter (noting that Cree has R4 bins in it's bin structure, which is 130lm at 350, so ~290 at 1A).

jeff - I've looked again at that graph, and it still doesn't show the K2 on test performing any better than the Cree P4.


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## Kiessling (Sep 23, 2007)

The difference between a P4 and a Q4 Cree isn't all that exciting IMHO. However, being able to use all the stuff (reflectors, optics, heads, bezels, drivers, ...) we were using back then with the Luxeons again with the K2 is worth a lot. There is experience, the wheel does not need to be re-invented as it had to be withthe Cree and Rebel.

bernie


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## evan9162 (Sep 23, 2007)

chris_m said:


> I just think there needs a little perspective to the "love-in" which seems to happen on here with every Luxeon pre-release announcement.



There's the same amount of "love-in" over Cree announcements and new XR-E bins that are released. CPF is an *enthusiast site*. People get excited over new releases, increased competition, and more choices. Sheesh. Why do you even visit this place if you don't understand that?



> I sometimes wonder whether if Luxeon released a part which was miles behind the current state of the art efficiency but still a little better than what they had released before there would still be people on here swooning over it because it was a drop in replacement for lights they bought back when Luxeon USED to be the performance leader.



Luxeon is a part name. Lumileds is a LED manufacturer.

Anyways, I very seriously doubt it. The V-bin K2s have been available in quantity for about 6 months now, and no one gives a crap because how far they are behind the curve in terms of efficiency. No one is swooning in this thread. The only thing that people are getting interested in is the fact that Lumileds just might get back into competition in terms of efficiency, where Cree and Seoul have been leading for a long time. I thought more choices were a good thing? 



> I'll give you that certainly the Rebel is a good performing part, but there is as yet no evidence that we will see K2s released in the near future which even do as well as that.



We have no idea when these are coming out. But since people have been getting samples, and the parts have even shown up temporarily on Future's parts listings, so it sounds like it could be soon. Lumileds is notorious for dragging their feet on new releases, a fact that universally annoys everyone.



> Meanwhile some of my irritation is that your graphs seem to show that this K2 you have performs as well as a Cree and the Rebel better, and it does NEED to be pointed out that the Cree part in your graphs is a really old bin, so it's not really a very current comparison.



Well ex-****ing-cuse me for not owning all the latest and greatest LEDs on the planets that meet your standards for comparison. I didn't have anything but a P4 XR-E when I did this test. How am I supposed to include data for a part I don't have? Why not truck on over to my XR-E Q4 review to see it compared there? 

It's people like you and responses like this that discourage people from doing these kinds of investigations and sharing information, when the only thing that happens is that they get sniped at because someone doesn't like some insignificant detail about how things were done. It's definitely goes *against* the spirit of CPF when you behave like this.

This was an opporotunistic test of an unreleased part. It's normally something people look forward to. People don't look forward to someone threadcrapping all over everything just because they feel like making snarky comments that lower the level of discourse.



> Is all very well you commenting on the bins listed in Luxeon's bin structure - actually seeing such parts in the real world is another matter (noting that Cree has R4 bins in it's bin structure, which is 130lm at 350, so ~290 at 1A).



ARC Mania had -200 parts on hand a while ago. The current Rebel-100s hit the mid 230s at 1A. There's no reason that -200 parts shouldn't be in abundant supply whenever they get around to releasing these. Even -240 parts should be reasonable, again, given the current performance of Rebel-100 parts.


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## Anglepoise (Sep 23, 2007)

Keep up the good work Evan. Much appreciated .


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## Calina (Sep 23, 2007)

Anglepoise said:


> Keep up the good work Evan. Much appreciated .


 
+1


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## jtr1962 (Sep 24, 2007)

evan9162 said:


> There's no reason that -200 parts shouldn't be in abundant supply whenever they get around to releasing these. Even -240 parts should be reasonable, again, given the current performance of Rebel-100 parts.


One thing which concerns me isn't that Lumileds can't make a competitive LED. They obviously can with the recent Rebel 100s. Their biggest problem is production. Rebel 100s aren't currently available. They only were for perhaps a month, and even then I couldn't get an answer on buying a specific bin as with the Crees. There may indeed be a -240 K2 soon, but if it's only available for a short time, and not again for weeks or longer, then what good is it? At least when Cree releases a new bin, it'll be out there in large quantity, even if admittedly a little expensive/hard to get in the beginning. I really hope that the K2 -200s and -240s are available in large quantity soon, and at competitive prices. The more players in this ballgame, the better it'll be for everyone.

And thanks for the great review!


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## Doh!Nut (Sep 24, 2007)

I am sure chris m would love to send evan a Q5 to update his tests


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## Grox (Sep 24, 2007)

Anglepoise said:


> Keep up the good work Evan. Much appreciated .



What Anglepoise said :twothumbs

I enjoy all your reviews.

Thank you for the effort.


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## evan9162 (Sep 24, 2007)

jtr1962 said:


> One thing which concerns me isn't that Lumileds can't make a competitive LED. They obviously can with the recent Rebel 100s. Their biggest problem is production. Rebel 100s aren't currently available. They only were for perhaps a month, and even then I couldn't get an answer on buying a specific bin as with the Crees. There may indeed be a -240 K2 soon, but if it's only available for a short time, and not again for weeks or longer, then what good is it? At least when Cree releases a new bin, it'll be out there in large quantity, even if admittedly a little expensive/hard to get in the beginning. I really hope that the K2 -200s and -240s are available in large quantity soon, and at competitive prices. The more players in this ballgame, the better it'll be for everyone.
> 
> And thanks for the great review!



Yes, I've noticed this too, and it's rather puzzling. Huge availability first, then none anywhere. Their production ability / supply chain is very wierd. Perhaps they're diverting their thin film die production to the new K2 ramp. Or perhaps they're just having problems, and can't produce fast enough. Who knows? From what we can see, Lumileds seems to lack production consistency (not in terms of product quality, but in terms of output volumes). Definitely not the kind of behavior you expect from a big player in the LED market.

A lack of availability of parts definitely hurts them, and makes potential customers switch to another available option, even if it means re-working their design for a new package or beam profile.


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## coolwaters (Sep 24, 2007)

dude a arms race with LEDs...

anyways didnt know that rebels can go up to 1.8 amps...

where and how much did u get them for? i want to try.


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## evan9162 (Sep 24, 2007)

coolwaters said:


> dude a arms race with LEDs...
> 
> anyways didnt know that rebels can go up to 1.8 amps...
> 
> where and how much did u get them for? i want to try.



They really can't. Lumileds only rates the rebels up to 1A of current. 1.8A is severly pushing things.

The Rebel-100s don't seem to be available anymore, which is pretty stupid. At the time I got them (mid-July), they were $6.60 each.


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## Kiessling (Sep 24, 2007)

Not that it seems to be necessary any more right now ... but I still will say it ... Gentlemen ... please be civil and respectful.
Thank you 
bernie


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## evan9162 (Nov 23, 2007)

Well, I got actual shipping parts today. I ordered 3 -160 and 3 -180 parts.

First, the okay part - these things perform pretty much like they should. No surprises here:


```
Current(mA)
		100	350	700	1000	1250	1500	1750	2000
----------------------------------------------------------------------------------------
K2 4-180 #1	26	79	138	179	210	235	256	273
K2 4-180 #2	27	81	141	183	213	237	259	276
K2 4-180 #3	26	79	138	179	210	236	258	276
K2 4-160 #1	24	73	128	168	197	222	244	262
K2 4-160 #2	27	79	137	180	210	234	254	271
K2 4-160 #3	26	79	136	174	201	223	241	256
```

Yep, definitely won't win any brightness contests with these. 

And now the really ugly part:


```
Current (mA)								
		20	100	350	700	1000	1250	1500	1750	2000
-------------------------------------------------------------------------------------------------
K2 4-180 #1	2.66	3.26	3.74	4.12	4.37	4.56	4.70	4.82	4.93
K2 4-180 #2	2.89	3.23	3.69	4.06	4.28	4.44	4.57	4.70	4.80
K2 4-180 #3	2.89	3.23	3.70	4.08	4.31	4.48	4.62	4.75	4.85
K2 4-160 #1	2.96	3.28	3.64	3.92	4.11	4.23	4.35	4.46	4.55
K2 4-160 #2	2.95	3.27	3.61	3.85	4.01	4.13	4.22	4.30	4.38
K2 4-160 #3	2.86	3.18	3.56	3.85	4.03	4.16	4.28	4.40	4.50
```

No, those are not typos. The Vf on these is terrible. The sample I tested had a pretty high Vf already - but these are just through the roof. At 1.5A, there's at least 0.5-0.7V "extra" creeping in somewhere, translating into 0.7-1W of extra heat to be dissipated. That 5.5C/W sure comes in handy to get rid of all that extra heat.

These were so far off, I used two different power supplies and two different DMMs just to verify the results.

It looks like these K2s are starting to live up to the legacy of their earlier ancestors - ho-hum performance and terribly high Vf. 

The relatively low brightness of these is one thing, but having such a high Vf will undoubtely be a deal breaker for using these is any battery powered application.


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## mofiki (Nov 23, 2007)

This is bad news considering the Fedex guy just delivered 6 of these K2 0180 today. Oh well, another $40 spent towards the cause. I've kind of learned not to jump on band wagons over the years or the old saying if everybody is jumping off the bridge, you know? So when people here are pushing Cree or Seoul I didn't pay much attention. Maybe I should have listened. I wanted to use these in a battery application. I wonder if there would be a better use for them like illuminating the inside of my clothes dryer.


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## evan9162 (Nov 23, 2007)

If possible, would you be able to map out the Vf curve like I have done? It would be good to know if all of them are behaving the same way.


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## mofiki (Nov 23, 2007)

My lack of the proper equipment would make my results unreliable. I am a noob to this hobby of light building but I must say I'm getting hooked. 

I only have a BK Precission 1651 power supply which doesn't seem to give more than 600mA regulated current. I've been looking for a good current meter but haven't picked up anything yet. I don't think I would invest in to much more than that except maybe a light meter if they're not to much. Even though I'm enjoying building some lights and messing with leds I can't see that kind of equipment being that useful. I want to get more into machining parts. 

I wish I could help. If there is anything you think I can do I'd be glad to help.


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## Curious_character (Nov 24, 2007)

evan9162 said:


> . . .
> 
> It looks like these K2s are starting to live up to the legacy of their earlier ancestors - ho-hum performance and terribly high Vf.
> 
> The relatively low brightness of these is one thing, but having such a high Vf will undoubtely be a deal breaker for using these is any battery powered application.


Having a high Vf is _not_, in itself, a bad thing. In fact, it could make flashlights more efficient. Here's why: The Vf of most present LEDs falls in the middle to top of the range of voltage that a single Li-ion cell has during its discharge. This makes it relatively difficult for a regulator, which has to be able to reduce the voltage (buck) when the cell is fresh, and change to a boost mode somewhere in the middle of the discharge if it's to regulate during the whole discharge period. The resulting buck-boost regulator ends up being more complex and generally less efficient than a straight boost or buck design. If an LED has a voltage that's reliably higher than the cell voltage, a plain boost regulator can be used. This is the case now with lights running from one or two Alkaline or NiMH AA or AAA cells. So a higher Vf could bring us more efficient, less expensive lights which run from a single Li-ion cell such as an RCR-123, 17670, or 18650 and be well regulated during the whole discharge period. (A lot of lights now regulate well only during the first or last part of the discharge because the regulator can only buck or boost but not both. For example, an MRV bucks but doesn't boost, so it regulates only during the very first part of an 18650 discharge. A P1 boosts but doesn't buck, so it regulates only at the very end of the discharge period when using an RCR-123. The Tiablo A8 is unusual in that it has a buck-boost regulator which regulates over the whole discharge period of an 18650 cell. But it's not very efficient.)

What we have to do is look at the LED efficiency in terms of lumens per watt, not lumens for some given current which isn't really a measure of efficiency. If two LEDs supply the same number of lumens per watt, one with Vf a bit greater than 4.2 volts would have a definite advantage for single Li-ion cell lights. But of course, the LED output is often shown for lumens out for a given current. If two LEDs produce the same number of lumens at the same current, the one with a lower Vf has higher efficiency than one with higher Vf because it's consuming less power. But if they produce the same number of lumens out with the same _power_ in, the one with the higher Vf is equally efficient and might be easier to use.

My point is while it's certainly fair to consider an LED to be inferior if its efficiency (lumens per watt) isn't as good as another, having a higher Vf, by itself, isn't necessarily a disadvantage and can actually be an advantage. These LEDs do have poorer efficiency than other modern LEDs. But I'd like to see ones with the same efficiency as other LEDs and with the higher Vf that these devices have.

c_c


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## PhantomPhoton (Nov 24, 2007)

Well there goes my hopes for retrofitting some lights with Lumileds for the next 6 months. 
Guess I can keep anticipating SSC releasing a V bin or something.
Once again thank you for the info Evan9162.


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## mofiki (Nov 24, 2007)

Thanks for that info Curious. Your point of view makes sense and is something I didn't even consider all the while I was complaining about finding a power source, especially when trying to power four leds.


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## Curious_character (Nov 24, 2007)

Sorry, I inadvertently left out the essential word _not_ in the first sentence which I've now corrected by editing. The remainder of the posting was intended to support the statement with the _not_ included. I apologize for the sloppy proofreading.

c_c


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## chris_m (Nov 24, 2007)

I agree c-c, exactly the same thought occurred to me seeing those Vf figures. Of course the problem is that to have a Vf over 4.2V implies 20% worse efficiency to start with even if the lumens/current is the same, so you'd only need to find a 70% efficient buck/boost.

A quick search found me the TPS63000 which would actually seem to give >90% efficiency through the discharge of a LiIon cell driving a 3.5V LED at 200-1000mA, so it's simply the application of such drivers in flashlights that's the issue than the non-availability (I have a feeling I've just generated myself another DIY project!)


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## BentHeadTX (Nov 24, 2007)

Thanks Evan for the update

Sad to hear that the Rebel 100 did not transfer over to the K2. Strange that the Reb100 and K2 are almost opposite to each other with the low Vf/high output Reb smashing the K2 in all measurements.  

With the news of continuing K2 problems, I ordered a Fenix L0D Q4 to replace my keychain mounted FireFlyIII. The FF3 will roar again once I get a K2 240 with lower Vf. 2008?


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## mofiki (Nov 24, 2007)

I fired up one of the K2's I have and ran it for over an hour. It got pretty warm but I didn't have any problems. I was somewhat impressed with the amout of light. It was driven with a Lux-drive 3021-1000 off 4 RCR123 Lithiums. I had to run out and do some errands so I shut it off. When I got back I turned it on and notice everything was running hot within a minute. I did some tests for shorts and found nothing. I turned it on again and poof. It smoked.


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## saabluster (Nov 25, 2007)

mofiki said:


> I fired up one of the K2's I have and ran it for over an hour. It got pretty warm but I didn't have any problems. I was somewhat impressed with the amout of light. It was driven with a Lux-drive 3021-1000 off 4 RCR123 Lithiums. I had to run out and do some errands so I shut it off. When I got back I turned it on and notice everything was running hot within a minute. I did some tests for shorts and found nothing. I turned it on again and poof. It smoked.


Was it heatsinked in any way?


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## mofiki (Nov 25, 2007)

You must know your stuff because you ask the right question. It was heatsinked to a copper pennie which was JB Welded to a threaded barrel peice that was part of a Brinkmann Legend flashlight which fitted into the head of the light and the reflector was modded to fit perfectly against the led body. It did put out a nice beam with even spread of the hot spot. 

BUT; when I noticed it getting very hot on the second run I thought something was wrong so I took it apart and started doing meter checks for a short. The ohms checks found nothing. The checks with the meter set to diode made an audible beep and showed a value on the display via the test leads touching the led solder lead and to the heatsink. When I reversed the test leads no beep. Switch them back and got a beep. I thought something was wrong there so I just pulled the led off the heatsink, which was attached with JB Weld also. I confirmed that I had no shorts and I fired up the led again. That's when it went poof. 

So you think because it wasn't heatsinked is why it smoked?

What about that contact I found in the diode test setting of the meter too. I never fully understood what the beep meant. I know a steady tone means I have continuity. Does that mean there is some capacitance there? I just don't think it was normal for the light and the buckpuck to run so hot that it is difficult to touch. It did not get that hot the first time I ran it.


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## BentHeadTX (Nov 25, 2007)

mofiki said:


> BUT; when I noticed it getting very hot on the second run I thought something was wrong so I took it apart and started doing meter checks for a short. The ohms checks found nothing. The checks with the meter set to diode made an audible beep and showed a value on the display via the test leads touching the led solder lead and to the heatsink. When I reversed the test leads no beep. Switch them back and got a beep. I thought something was wrong there so I just pulled the led off the heatsink, which was attached with JB Weld also. I confirmed that I had no shorts and I fired up the led again. That's when it went poof.
> 
> So you think because it wasn't heatsinked is why it smoked?
> 
> What about that contact I found in the diode test setting of the meter too. I never fully understood what the beep meant. I know a steady tone means I have continuity. Does that mean there is some capacitance there? I just don't think it was normal for the light and the buckpuck to run so hot that it is difficult to touch. It did not get that hot the first time I ran it.



Mof,
You gave up the life of the K2 for science!  Congrats on passing your first mod test of making "magic smoke". Did some pondering on this one. 

This is just a wild guess but it would explain what happened. When you first ran the LED it heated up all the connections and JB Weld. Then you allowed it to cool which caused something to crack (total guess, don't throw anything at me) When you cranked it up again, there was conduction which really heated things up. Once you removed the LED from the heat sink, the amount of heat a high voltage K2 generates smoked itself.  

I once wanted to test an AMD Athlon 850 CPU without a heat sink to see if it worked. Put my thumb on the die and turned the computer on. It reached the surface of the sun temp in about two seconds so I pulled the power cord. My thumb had an AMD tatoo for a few weeks.  LEDs do the same thing to a lesser extent. 

Diode checks and you. A diode allows current flow in one direction but stops it when the polarity is reversed. This explains why you get the beep when the positive and negative is correctly connected (beep) and it reads "open" (no conduction) when wired backwards. If it beeps in both directions, you have a shorted diode and if it don't beep in either direction the diode is open.


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## jtr1962 (Nov 25, 2007)

mofiki said:


> You must know your stuff because you ask the right question. It was heatsinked to a copper pennie which was JB Welded to a threaded barrel peice that was part of a Brinkmann Legend flashlight which fitted into the head of the light and the reflector was modded to fit perfectly against the led body. It did put out a nice beam with even spread of the hot spot.
> 
> BUT; when I noticed it getting very hot on the second run I thought something was wrong so I took it apart and started doing meter checks for a short. The ohms checks found nothing. The checks with the meter set to diode made an audible beep and showed a value on the display via the test leads touching the led solder lead and to the heatsink. When I reversed the test leads no beep. Switch them back and got a beep. I thought something was wrong there so I just pulled the led off the heatsink, which was attached with JB Weld also. I confirmed that I had no shorts and I fired up the led again. That's when it went poof.


The problem was using JB Weld instead of some sort of thermal epoxy. First, JB Weld has lousy thermal conductivity. Second, it ends up in a pretty thick layer which further hurts thermal conductivity. It often ends up with a few air bubbles when you apply it, further inhibiting thermal conductivity. Third, expansion and contraction from heating/cooling undoubtedly caused some air pockets to form, perhaps partially detaching the heat sink. Reason number three was the ultimate cause of failure. Not surprised this happened. You're dealing with a few watts trying to get out via a few hundreths of a square inch. That's a power density well over 100 watts per square inch. The interface has to be very smooth and thin or you'll encounter problems.


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## frenzee (Nov 25, 2007)

I agree with jtr1962. I gave up on JB Weld because it really doesn't make a good thermal interface compund. For one, it is filled with iron particles (hold a supermagnet over the blue tube or some dried pieces and you'll see what I mean). Iron isn't a good heat conductor to begin with and it makes the compound's electrical conductivity unpredictable. Secondly, when heated to high temperatures, it loses it's adesion properties and crumbles like crayon. If you didn't do good surface prep, it will almost certainly just come off and you won't even notice it until it's too late.

I suggest using AA or AS. AA, with proper surface prep (use fine steel wool or Scotchbrite or better yet use a small steel brush to spread the epoxy on both surfaces), makes a very strong initial bond with both copper and silver. I believe the bottom of the K2's slug is copper with silver coating. And if you let AA cure for a few minutes at around 200F, the bond becomes even stronger and it turns into this ceramic-like substance like the stuff Lumileds uses to bond Luxeons to the star's slug. Strong stuff. If you really want to go all out, mix AA with an equal part of fine (50-100 micron) copper or diamond powder. You can make copper powder yourself by rubbing copper tubing or solid-core electrical wire against a diamond file or knife sharpener, and diamond powder can be bought fairly cheaply online ($5-10 for a 2 gram vial) e.g. here. Of course don't use copper if you need electrical isolation.

If you don't care about electrical isolation, soldering the slug directly to the heat sink is by far better than any epoxy, but you have to use a low temp solder (and flux of course).


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## mofiki (Nov 25, 2007)

I just want to thank you guys for taking the time to help me out. I ordered some AA yesturday and I'm halting any more building until I get it. I guess there are no short cuts and I should pay more attention to the details; i.e. heatsinking. 

Heatsinking seems to be somewhat of a science in itself, based on what I've read here. I have no real methods, tools, or enough knowledge to factor proper heatsinking based on actual temps. I have seen some here disregard it by making projects that have such small areas for the heat to escape and state that as long as you keep moving it's ok. I don't want to build projects like that. I've built quite a few halogen lights for biking and sold them to the biking community. I would feel ashamed if I sold junk. Same goes for this new LED technology. 

Thankx again everyone.


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## BentHeadTX (Nov 25, 2007)

Thanks jtr for the warning on JB Weld. I have never used it for electronics as Artic Silver thermal epoxy is something I keep in stock for my weirdness. 

Now for the K2-240 with lower voltage to roll out so I can mod my existing lights. I am not holding my breath.


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## Gryloc (Nov 27, 2007)

I ordered 4 of the 0180 parts last week, and I never had the chance to test them out. I tested 2 out of the 4 tonight and here are the measurements that I got:

```
LXK2-PWC4-0180

Current   Voltage
  (mA)      (V)             <Update:>
         #1       #2       #3       #4
  50   3.149    3.089    3.055    2.88
 100   3.28     3.222    3.184    3.011
 150   3.38     3.30     3.26     3.102
 200   3.456    3.37     3.33     3.176
 250   3.52     3.42     3.38     3.236
 300   3.57     3.48     3.44     3.27
 350   3.62     3.52     3.48     3.31
 400   3.66     3.56     3.53     3.35  
 450   3.70     3.60     3.56     3.39 
 500   3.73     3.63     3.60     3.42
 600   3.79     3.70     3.67     3.48
 700   3.84     3.77     3.73     3.53  
 800   3.90     3.82     3.78     3.58  
 900   3.95     3.84     3.84     3.62  
1000   3.99     3.89     3.88     3.66  
1100   4.03     3.93     3.93     3.70  
1200   4.09     3.96     3.97     3.73
```
In my test rig, I have a Fatman boost regulator powered from a battery pack. The Fatman has an external potentiometer attached so I can change the amount of current going to the emitter. The small sense resistor on the Fatman was used like a shunt resistor where I can measure the current with my volt meter by measuring the voltage drop. 

So, I will try to get the voltages of the last two K2-0180 emitters and update this post later.

I am a little saddened by the high Vf of the new K2 emitters, but this isn't the end of the world. I have a certain application for all four, even if it means that a fraction of a watt more will be consumed compared to other emitters to produce the same amount light. If I needed a more efficient emitter, I would have grabbed a few of the older P4 XR-Es. Then again, the beam pattern of the lambertian emitter will work better than that of the XR-E. All that matters is that these emitters work, and they are still better than the old LuxIII and K2. Besides, I really like the tint of the batch of new K2s that I got. They are very white. Since the Rebel 0100 is so hard to find easily, these will do...

-Tony


<Update:
So, after too many days, I got around to testing the other two. Just a reminder, these are fresh from the cut reel packaging. Vf may drop, but maybe for just a select few of the K2 emitters and only a small fraction of a volt. Emitter #3 was used for more than 30 minutes over the last week in the test rig, and I found that the Vf did not drop one bit since the initial testing. Too bad.

I was rather amazed by the low (or maybe normal) Vf of emitter #4. At 1500mA, I measured a Vf of 3.83V (this is the only emitter out of the four so far that I went to 1500mA since I do not want to ruin my only test rig). This Vf is close to the Vf of the first K2 0180 emitter at 700mA!!! Wow! Good thing that these will be used in series in an application where heat and efficiency is not the most important. As I find anything more about these emitters from my testing, I will post somewhere in this thread. I ordered another K2 0180 with another Future order, so I may get some more variety of color and Vf due to the good 'ol "Luxeon Lottery".>


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## TorchBoy (Nov 27, 2007)

I never knew diamond powder was so inexpensive. At (from memory) ten times the thermal conductivity of aluminium, and an electrical insulator, a big solid diamond would be the ideal stuff to make a heatsink from... if only it wasn't so expensive. :sigh:


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## SemiMan (Nov 28, 2007)

I got my K2s fired up and did some testing tonight. I am running strings of 4 in series, 2 neutral and 2 cool. I have not done any detailed testing, but when I run these strings of 4 at 700mA, I got forward voltages of 13.7 for one string and 13.8 for the other. This was right after they were turned on with just about no time on them. I would expect the Vf to go down with temperature and a bit of burn in. 13.7 and 13.8 represents 3.425v and 3.45v respectively per LED. I double checked the current and the voltage and everything looked good. 3.45 at 700mA is pretty good.

Semiman


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## Curious_character (Nov 28, 2007)

So at 700 mA, we have. . .

evan9162: 3.85 - 4.12 v.
Gryloc: 3.77 - 3.84 v.
SemiMan: 3.425 - 3.45 v.

Looks to me like if we wait a few more days, Vf'll be down to a couple of volts.

Seriously, does anybody have a clue about the cause of the apparent wide variation?

c_c


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## SemiMan (Nov 28, 2007)

Technically it is all within the specification of the forward voltage of the product which is quite broad. My measurements are just at the typical. The die is the same as the Rebel and some Rebel-100's I had had a Vf of approximately 3V at 350mA, so I imagine we are seeing process variation and things will get better as they start cranking of manufacturing. I am interested to see what happens with burn in. I may get less voltage drop than those with higher Vf bins.

Semiman


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## soffiler (Nov 28, 2007)

SemiMan said:


> Technically it is all within the specification of the forward voltage of the product which is quite broad. My measurements are just at the typical. The die is the same as the Rebel and some Rebel-100's I had had a Vf of approximately 3V at 350mA, so I imagine we are seeing process variation and things will get better as they start cranking of manufacturing. I am interested to see what happens with burn in. I may get less voltage drop than those with higher Vf bins.
> 
> Semiman


 
Just a thought (and I may be off base here, as I am well behind you folks in my knowledge of both Rebel and K2):

Is it possible that, if both Rebel and K2 are using the same die, that they are binned and Rebel is getting all the lowest-Vf bins? That would mean Rebel has less waste heat to deal with for a given drive current, which is consistent with the small package size. Then the higher-Vf bins have to go _somewhere_ - voila, K2.


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## SteveDavis (Nov 28, 2007)

Curious_character:

Thank you for the insight on Vf in relation to total efficiency. You're certainly correct that a buck or a boost is almost always more efficient than a buck-boost, and also certainly cheaper.

However, I think it's important to point out that this data could be very suspect. The range of Vf's for a die is extremely high. The new K2 is spec'd to have a Vf between 3.03V and 4.71V at 1A. 

When I recommend to a flashlight manufacturer a driver circuit, I look at the entire Vf range for this reason.


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## SemiMan (Nov 28, 2007)

Technically they should not be able to do this...put the high Vf bins into the K2 as they would violate their typical Vf number by doing it. We are currently working with a sample size of <20 which may have been only two reels worth. It looks like we all got them about the same time, so it is possible that they were broken off the same reels. Gryloc, Evan did you get them from Future?

The max on the data sheet is pretty high. I wonder if under burn in this would come down? Cree does not list the max at 1A, but based on the max at 350mA and typicals at 350ma and 1A, it is likely in the 4.3-4.4V range. SteveDavis....you distribute Cree, can you find out what the max for Cree would be at 1000mA?

Semiman




soffiler said:


> Just a thought (and I may be off base here, as I am well behind you folks in my knowledge of both Rebel and K2):
> 
> Is it possible that, if both Rebel and K2 are using the same die, that they are binned and Rebel is getting all the lowest-Vf bins? That would mean Rebel has less waste heat to deal with for a given drive current, which is consistent with the small package size. Then the higher-Vf bins have to go _somewhere_ - voila, K2.


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## evan9162 (Nov 28, 2007)

Yep, got them from future.

The wierd thing was that, for every other order I've ever made from future, I've had a bin code on both the invoice, and package label on the anti-static bag.

For these, there were no bin codes to be found anywhere.


Anyone else have bin codes on their package labels/invoice for these new K2s?


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## SteveDavis (Nov 28, 2007)

Max Vf for an XR-E at 1A is 4.3V


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## mofiki (Nov 28, 2007)

I got my K2's form Future also. No bin codes on mine either. Something else I noticed though, product must be mounted within a certain period of time upon openning the bag. What!... Why?


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## SemiMan (Nov 28, 2007)

mofiki said:


> I got my K2's form Future also. No bin codes on mine either. Something else I noticed though, product must be mounted within a certain period of time upon openning the bag. What!... Why?




Standard procedure for surface mount LEDS. You have to run them through a reflow oven within a given amount of time from opening the moisture sealed bag or rebake them to get the moisture out. If you order from one of the large distributors, they will follow the proper handling procedures. You tend not to get that from the smaller dealers.


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## blesbok (Nov 29, 2007)

I just received six K2 -0180s and tested one for Vf at 10mA increments up to 1A. These were labeled SVNG bin (180 lumen, VN color, 3.75-3.99V). This sample measured 3.85V @ 1A, just below the middle of the specified range.


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## mofiki (Dec 3, 2007)

I've got my tripple K2 light pod lit right now. I have it hooked up to a BK Precisson regulated power supply with no resistors or driver. I'm pushing exactly 500mA into it and my voltage meter is showing a wee bit under 10v DC. The amount of light is wowing, no way to measure actual lumens, but I'm pleased. I really don't see the need to burn this thing any brighter. It's been running for about twenty minutes and it's lightly warm. I made a donut shaped aluminum heat sink appoximately 1 5/8" diameter by 3/8" thick which fits perfectly inside aluminum tubing and I got a tripple lense from Future. The color makes this light seem brighter than the tripple Cree XR-E I built a few weeks ago. I guess it's because it's more of a cool white and the Cree's seem more warm. I'm going to get myself some more equipment to measure the light and other tools for Christmas.


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## Gryloc (Dec 4, 2007)

Here are my updated findings. I also updated/edited my original post, which this post is similar to.


```
LXK2-PWC4-0180

Current   Voltage
  (mA)      (V)             <Update:>
         #1       #2       #3       #4
  50   3.149    3.089    3.055    2.88
 100   3.28     3.222    3.184    3.011
 150   3.38     3.30     3.26     3.102
 200   3.456    3.37     3.33     3.176
 250   3.52     3.42     3.38     3.236
 300   3.57     3.48     3.44     3.27
 350   3.62     3.52     3.48     3.31
 400   3.66     3.56     3.53     3.35  
 450   3.70     3.60     3.56     3.39 
 500   3.73     3.63     3.60     3.42
 600   3.79     3.70     3.67     3.48
 700   3.84     3.77     3.73     3.53  
 800   3.90     3.82     3.78     3.58  
 900   3.95     3.84     3.84     3.62  
1000   3.99     3.89     3.88     3.66  
1100   4.03     3.93     3.93     3.70  
1200   4.09     3.96     3.97     3.73
```
So, after too many days, I got around to testing the other two. Just a reminder, these are fresh from the cut reel packaging. Vf may drop, but maybe for just a select few of the K2 emitters and only a small fraction of a volt. Emitter #3 was used for more than 30 minutes over the last week in the test rig, and I found that the Vf did not drop one bit since the initial testing. Too bad.

I was rather amazed by the low (or maybe normal) Vf of emitter #4. At 1500mA, I measured a Vf of 3.83V (this is the only emitter out of the four so far that I went to 1500mA since I do not want to ruin my only test rig). This Vf is close to the Vf of the first K2 0180 emitter at 700mA!!! Wow! Good thing that these will be used in series in an application where heat and efficiency is not the most important. As I find anything more about these emitters from my testing, I will post somewhere in this thread. I ordered another K2 0180 with another Future order, so I may get some more variety of color and Vf due to the good 'ol "Luxeon Lottery".


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## Lightingguy321 (Dec 6, 2007)

What was the bin code on your K2-0180s?


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## mofiki (Dec 7, 2007)

Today is my lucky day. I just figured out more functions of my tripple power supply from BK. If I switch it to parallel I get double the current, so I can run led's at 1 amp now. I also found that I don't have to buy a new multimeter because I forgot that my Fluke 73 has an upgraded board which makes it a 77. I can measure current. So I had to play to see what the Seoul P4 I built would do. :twothumbs I'm impressed. Looks like about a third more light output. I ran the tripple K2 setup I built to use as a helmet light at 1000mA and the voltage drop across the led's started off at 11.8volts then as it warmed up, about ten minutes, the voltage droped and leveled off at 10.8 volts. I stuck an ice pack under the housing and the voltage worked it's way back up a couple of tenths of a volt but that's about it. At least I can do accurate calculations on run time and battery options without having to guess now.

Would one of you guys recommend a light meter for me now so I can get data. I need data.


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## SemiMan (Dec 9, 2007)

mofiki said:


> Today is my lucky day. I just figured out more functions of my tripple power supply from BK. If I switch it to parallel I get double the current, so I can run led's at 1 amp now. I also found that I don't have to buy a new multimeter because I forgot that my Fluke 73 has an upgraded board which makes it a 77. I can measure current. So I had to play to see what the Seoul P4 I built would do. :twothumbs I'm impressed. Looks like about a third more light output. I ran the tripple K2 setup I built to use as a helmet light at 1000mA and the voltage drop across the led's started off at 11.8volts then as it warmed up, about ten minutes, the voltage droped and leveled off at 10.8 volts. I stuck an ice pack under the housing and the voltage worked it's way back up a couple of tenths of a volt but that's about it. At least I can do accurate calculations on run time and battery options without having to guess now.
> 
> Would one of you guys recommend a light meter for me now so I can get data. I need data.




Was just reading this and I think you may want to check your numbers/heat sink. If you started out at 11.8 cold, then dropped to 10.8 warm, and there was no long term voltage shift, then these LEDS are running a good 100-110 celsius above ambient. In my triple-K2 implementation at 700mA, my LEDS only drop by about 0.4V and that is after hours. I think you may still be in the K2 spec for long term at 110C over ambient (with 25C ambient), but it cutting things thin.

Did you check the voltage again once they were cold?

Semiman


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## mofiki (Dec 10, 2007)

I'm a bit worried about the heat too. Let me run these again tonight at 700mA and see what happens. The housing did get so hot I couldn't handle it and had to wait for it to cool.


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## mofiki (Dec 10, 2007)

Tripple K2 still running after 30 mintutes at 700mA. It started at 10.9 volts and is down to 10.5 volts.


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## SemiMan (Dec 10, 2007)

Looking at your enclosure, you do not have a lot of surface area. That could create some troubles for getting the heat out. You would do better if you could cut some grooves into it to increase the surface area. I have a significant amount of fin surface area on my set up.

Semiman


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## mofiki (Dec 10, 2007)

There's a big difference in the heat between running at 1amp verses 700mA. I can handle the enclosure at 700mA. It burned me at 1amp. It's cooler than the halogen setups I was building with the same encloser. I pushed 20W bulbs 20% and you could smell em. The internal heatsink is almost 1/2" thick. I'd be interested in seeing how you heatsinked your setup and if you could tell me how you calculate area verses heat.


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## SemiMan (Dec 11, 2007)

For my "playing" ... not work, I use CPU heat sinks which are cheap and have lots of surface area. They are perhaps a bit of overkill, but they work, do not way a ton and keep the LEDS nice and cool. For work we have thermal modelling software which fortunately I do not have to run...we have someone for that. Y

On the coolers, you used to be able to buy round ones (that were small, not like the monsters they make now) that were great for making LED lights, but you can not get them any more. Have you seen "tube" coolers, these are used for cooling vacuum tubes, they fit around the tubed. I wonder if you could use that with your set up?

The problem I see with what you have is even with airflow, you do not have a lot of surface area to take advantage of it.

I am looking at your set up which you indicated 700mA, but I only see one of the power supply outputs connected which I think will give you only 350mA will it not?


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## mofiki (Dec 11, 2007)

If you look at the power supply above right corner, the switch for parallel, series, and independent, the supply switches internally. I have it set to parallel so the current meter display is actually double but voltage is the actual. Just to be as sure as I can be I set the current using my Fluke DMM first for accuracy. It was supplying 700mA. Again just to be sure of the voltage reading I connected the Fluke to the outputs of supply to get the voltage drop of the leds.

That program sounds interesting but unless I was to make a business of selling lights I think best guessing will do for heatsinking. I'm currently sourcing suppliers of copper stock. That other little light you saw in the picture has a Seoul P4 installed and runs cool at 1000mA I think because I used a solid copper fabricated heatsink.

I think I'm going to build another housing for the next set of K2's only this time make it about one inch longer and use copper for the heatsink. I know the output of light at 1000mA won't be much more but it will be more and it will be safer from accidental 1amp settings when driven with a Maxflex or bFlex driver board.


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