# "Burn-in" of SST-90 significantly lowers Vf



## Techjunkie (Jan 20, 2010)

After experimenting with different direct drive solutions and resistance mods in my SST-90 4500K torch, I noticed that even when the emitter has cooled down, it now draws more current at the same Vf than it did when first assembled. It's now possible for me to get 9A+ draw from 3 NiMH C cells. Even more after it has heated up.

I made a video demonstrating the current draw now that the emitter has been burned-in:

http://www.youtube.com/watch?v=C5vrmCCxwcQ

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///___UPDATE: Please watch this response video as well: http://www.youtube.com/watch?v=D9WaHtmDrFM&feature=response_watch ////////////////////////
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///___In it, I explain and demonstrate how & why my tailcap current measurements are so high compared to the results that others get.//////
///___I also demonstrate the lower current draw measured using the method most others are using.______________________________//////
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By the way, the SST-90 4500K mounted with Arctic Silver Thermal Adhesive in the Brightlumens Deluxe Mag D heatsink starts to turn blue around 13A current draw, in case anyone was wondering.


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## Linger (Jan 20, 2010)

Interesting. Is this first report?


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## Packhorse (Jan 20, 2010)

Thats really interesting.

Has anyone else noticed this?

How long do you estimate the burn in process took?


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## Techjunkie (Jan 20, 2010)

I searched for "LED burn-in" and discovered that wquiles reported a lowered Vf of SSC P4 emitters after a 24 hour burn in at 1000mA years ago. Here, the differences in this giant emitter seem much more drastic because I'm measuring the change in draw at a given voltage in Amps, not milliAmps.

Will's old SSC P4 thread here, and another thread started by Jerry B about a similar observation with MC-E here.


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## HarryN (Jan 20, 2010)

This used to be a common aspect of power LEDs, and there were extensive comparisons done on Lux IIIs, Cree packages, etc. I used to commonly burn in Lux Vs for 24 hours to knock down the Vf a full bin code. A CPF member in ID used to post a lot of graphs on it - perhaps someone will remember his name.

This "feature" is not so common now in die produced by the leading firms (Cree + Lumileds) so it is an indication of where the die are likely not coming from.

BTW - if you "burn in" an LED die for 24 hours at full drive current, usually it will not drop significantly after that. The effect is a sort of annealing / recombination / crystal defect related.


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## Packhorse (Jan 20, 2010)

So we are talking about a 1 off 24 hour burn or will 48 half hour burns do the same thing?


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## Techjunkie (Jan 20, 2010)

Who knows what's the safest or most effective. In the case of my experience it was much more aggressive. More like a series of near death experiences for the emitter. It worked though. I just took it for a spin outside and on the three C cells, the image it casts on the bare tree 450 feet to the North, looks as bright as it ever did with the Lithium cells that now overdrive it.


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## Linger (Jan 20, 2010)

Harry N, any suggestions what variables are for this?

Techjunkie - help me out, so if 'burn in' is successful the vf should drop and lumen output maintained or increases right?
As opposed to 'hurting' the emitter where we're going to have a series of mishaps and output degrades?

Is heat a variable in this or is 'burn in' a bit of a misnomer?

I recall a thread a few months ago where a person had 1 dead die in 4 on an mc-e: cpf'er suggested hitting it with a whack of over-voltage and it activated and began normal function.


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## Techjunkie (Jan 21, 2010)

Linger said:


> Harry N, any suggestions what variables are for this?
> 
> Techjunkie - help me out, so if 'burn in' is successful the vf should drop and lumen output maintained or increases right?
> As opposed to 'hurting' the emitter where we're going to have a series of mishaps and output degrades?
> ...


 
I'm not 100% sure, but I suspect heat is the catalyst for whatever change the emitter undergoes to cause it's Vf (even while cold) to be reduced after the burn-in. (Reduced Vf means that less voltage is required for the emitter to draw the same amount of current as it did peviously.)

The result of lowered Vf should be the same light output at the same current as before but now with lower input voltage, or conversely, more light output at the same input voltage as before, but now with higher current draw. It does not increase the maximum possible output, but does reduce the total Wattage necessary to achieve maximum output, due to the reduced input voltage at max current.

In support of my suspicion that heat is a factor, I offer that the torches in which I have surface mounted MC-E emitters to MCPCBs myself by using the hotplate method, all appeared to have the lowest Vf MC-Es that I had encountered. I had originally assumed that was because of the source of those emitters, but now I suspect that the heat applied to the emitters during my crude surface mount soldering may have had a burn-in effect.

Also, from Wikipedia: For electronic components, burn-in is frequently conducted at elevated temperature and perhaps elevated voltage. This process may also be called *heat soaking*. The components may be under continuous test or simply tested at the end of the burn-in period

As for the MC-E resurrecting the dead die with a blast of power, I don't think that phenomenon applies to burn-in.


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## ma_sha1 (Jan 21, 2010)

Techjunkie said:


> The result of lowered Vf should be the same light output at the same current as before but now with lower input voltage,



Lowering vf is great news for single cell DD of SST/SSR. 
But you will reduce lumen/amp also, that's hard to measure unless you do a controlled experiment. There are some article talk about head speed up the reduction of lumen maintainance (Eventually LED will put out 70% initial lumens at the same drive current vs. when new) 

http://lsgc.com/downloads/AN_01_Life_Lumen_Maintenance_and_Reliability.pdf


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## Techjunkie (Jan 21, 2010)

Accellerating reduced lumen maintenance is expected whenever running LEDs at max current. To me, that's a fair price to pay, especially considering that there will be more powerful LEDs out every year.

I'm just happy that now that this LED has been broken-in that it's much brighter running on 3 NiMH batteries than it was when I first got it.



ma_sha1 said:


> Lowering vf is great news for single cell DD of SST/SSR.
> But you will reduce lumen/amp also, that's hard to measure unless you do a controlled experiment. There are some article talk about head speed up the reduction of lumen maintainance (Eventually LED will put out 70% initial lumens at the same drive current vs. when new)
> 
> http://lsgc.com/downloads/AN_01_Life_Lumen_Maintenance_and_Reliability.pdf


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## Techjunkie (Jan 21, 2010)

I thought it was important to point out that because of the drastic effect that the smallest amount of resistance has on voltage these currents, and in turn the drastic change in the amount of current that is drawn by the emitter when voltage drops due to that slight resistance, that I have taken special steps to ensure as little resistance as possible is introduced into the circuit while taking current draw measurements.

In a second video (http://www.youtube.com/watch?v=D9WaHtmDrFM&feature=response_watch), I demonstrate the difference between taking the direct drive tailcap measurement with an in-line DMM using 16AWG copper leads (good), versus taking the measurement with a clamp meter with that same low resistance lead (better), versus taking the measurement using the clamp meter and replacing the 16AWG stranded copper lead with a sheet metal conduit (best).

The difference with a fully charged 4.2V pack is literally 8A->9.4A->11.9A by varying the method. Even the best method does not capture the actual current draw with the tailcap in place.

By rough estimate, I'd say most people are direct-driving their SST-90 several amps harder than they are measuring with their DMM at the tail.

The true test will be a clamp meter test around one of the wires between the emitter and the driver (or switch in the case of direct drive). If I ever remove my heatsink again, I'll grab a video or snapshot of that clamp test.


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## HarryN (Jan 22, 2010)

In the past, 24 hours at the factory rated LED current was nearly ideal - very well heat sinked. There was very little change after that. In electrical devices, there is plenty that happens from electrons passing through crystals - heat or no heat. I don't have any idea about 48 cycles of 30 minutes, but if you think about it, that is a pain.

There could also be a thermal effect, and here is why. At the end of growing the LED at the wafer level, the final step is a thermal anneal. Some firms are better at this than others, and some simply do this to a minimum level to save money.

Do not let the LED overheat - that just causes LED death. Guess how I know - lol.

I still do this on my Lux Vs, although I am not sure if it is really necessary. In the meantime, when I am burning in the LEDs, my garage is really bright. 

It would be interesting to see what a modern Cree or Lumileds Rebel does under those conditions. I don't have the equipment for that testing, but if you have a proper voltage / current power supply it it is not that hard.

I am pretty sure that the main CPF poster of this info was evan9162. If you do a "theads started by him", it will likely be in his list, assuming that info has not been lost over time.


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## flashfiend (Jan 24, 2010)

OMG! This thread is awesome. Now to temper my excitement although there will be some difficulty, are you guys trying to tell me I can get my sst-90 to draw more amps after a 24-hr burn in process? I just purchased a nailbender direct drive sst-90 and was a bit underwhelmed by the output. After further digging on this forum I discovered that my sst-90 may only be pulling 3.5-4.5 amps from my 26650 Battery Space battery. But now with this thread, it seems you guys are saying I can get it to pulls amps at spec or even more. Granted with a great increase in heat. I am very interested in how to do this and am wondering is this just a matter of amassing 24hrs of runtime on this LED or is there a specific process I need to follow?


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## JohnF (Jan 24, 2010)

flashfiend said:


> OMG! This thread is awesome. Now to temper my excitement although there will be some difficulty, are you guys trying to tell me I can get my sst-90 to draw more amps after a 24-hr burn in process? I just purchased a nailbender direct drive sst-90 and was a bit underwhelmed by the output. After further digging on this forum I discovered that my sst-90 may only be pulling 3.5-4.5 amps from my 26650 Battery Space battery. But now with this thread, it seems you guys are saying I can get it to pulls amps at spec or even more. Granted with a great increase in heat. I am very interested in how to do this and am wondering is this just a matter of amassing 24hrs of runtime on this LED or is there a specific process I need to follow?



I wouldn't get too carried away... I have a nailbender SST-90, and have never seen more than 3.2a at the tail with a fresh 26650, and it drops quickly to 2.8. There are other limitations. I believe the direct drive PWM driver he uses max's out at 6a, but other factors come in to play - the tail switch & spring of the host, etc.

On the bench, I don't see enough difference in output running the SST-90 at 9a over 4a to make it worth it - but the heat gets out of hand unless you are using a great heat sink. 

John F


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## flashfiend (Jan 25, 2010)

I understand there are many other factors at play here and I didn't realize nailbender used a pwm driver, but seriously I would be very happy to get my sst90 to pull just 6amps. Heat be darned I want my output. Will burn in help me get closer to achieving this? And if so, how do I go about burning in my LED? If not I may change to a different LED.


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## Techjunkie (Jan 25, 2010)

flashfiend said:


> I understand there are many other factors at play here and I didn't realize nailbender used a pwm driver, but seriously I would be very happy to get my sst90 to pull just 6amps. Heat be darned I want my output. Will burn in help me get closer to achieving this? And if so, how do I go about burning in my LED? If not I may change to a different LED.


 
Based on my observations, yes, burn-in will get your emitter to draw more current. Also, being that a PWM only driver is in effect direct drive, reducing resistance at every contact point will raise Vin sent to the LED which will also increase current draw. Try using a deoxidizing contact cleaner on all the battery contact points and inside the switch. (I used Deoxit, but it's expensive.) 



JohnF said:


> I wouldn't get too carried away... I have a nailbender SST-90, and have never seen more than 3.2a at the tail with a fresh 26650, and it drops quickly to 2.8. There are other limitations. I believe the direct drive PWM driver he uses max's out at 6a, but other factors come in to play - the tail switch & spring of the host, etc.
> 
> On the bench, I don't see enough difference in output running the SST-90 at 9a over 4a to make it worth it - but the heat gets out of hand unless you are using a great heat sink.
> 
> John F


 
How are you measuring current draw? Unless you're using a clamp meter on the wire going directly to or from the LED, then you're introducing additional resistance into the PWM/Direct Drive circuit, which is lowering Vin and reducing current draw because of the lower Vf.

You would not visually notice a difference up close, but the amount of brute force throw is noticibly increased at 7A vs. 4A. Also, I've noticed that the color of the 4500K tint emitter loses its sickly yellow look at higher currents. I've heard others complain that the 5700K version also has a yellow hotspot in most reflectors. I imagine that would also be remedied with burn-in and higher currents.


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## flashfiend (Jan 25, 2010)

Thanks for the help and very informational videos techjunkie. Now this is where I'm a little confused because I'm running my sst-90 direct drive so in effect there should be no PWM unless I'm using a dimmer mode. Is this assertion correct? Btw, I should be getting some DeOxit today. Also as far as current measurement, I would seriously be happy 'just' getting 6 amps which I don't believe I'm getting from the visible output from my sst-90. I won't know until later this week when I get my new multimeter. If I am getting 6 amps then I am very disappointed with the sst-90.


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## Magic Matt (Jan 25, 2010)

The burn in is lowering the Vf, and so pulling more current.... and I realise that more current increases the output and also affects the tint slightly according to the specs. Is this burn in also affecting the tint and brightness, or is it just pulling more current to achieve the same output as it was new? - if it were restricted, to the same current as before, would it have dimmed down and colour shifted slightly after burn in?


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## Techjunkie (Jan 25, 2010)

flashfiend said:


> Thanks for the help and very informational videos techjunkie. Now this is where I'm a little confused because I'm running my sst-90 direct drive so in effect there should be no PWM unless I'm using a dimmer mode. Is this assertion correct? Btw, I should be getting some DeOxit today. Also as far as current measurement, I would seriously be happy 'just' getting 6 amps which I don't believe I'm getting from the visible output from my sst-90. I won't know until later this week when I get my new multimeter. If I am getting 6 amps then I am very disappointed with the sst-90.


 
I would assume, as you have, that on the brightest mode, the PWM that controls the FET is at 100% duty cycle, so the circuit is constantly closed. The FET itself adds some resistance though, and as we've seen in the video, the slightest amount of resistance changes the numbers significantly in this high current, low voltage application. In other words, compared even to your high mode, direct drive without the driver would draw even more current.

I built a few keychain torches with MC-Es and observed the same difference between the direct drive ones without the PWM only driver and the ones with it (and an MCE only pulls 2-3A at the same Vf that the '90 pulls 5-9A).

Short of unassembling your torch and getting a clamp meter between the PWM driver and the heatsink, the closest to actual measurement that you can take (by introducing as little extra resistance into the circuit as possible) is to test as I have with a piece of Aluminum sheet metal or some very heavy gauge copper and a clamp meter. Whatever number you measure, you can safely assume that without the test equipment in your circuit, the emitter is drawing even more current than you measured.

If you find that you are seeing 6A or more to the emitter and you are still underwhelmed, then you should consider trying different reflectors or optics. That big giant emitter makes getting a tight focus a real challenge (especially with the dome in tact).


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## easilyled (Jan 25, 2010)

I wonder why the "burn-in" isn't done by the manufacturer.
They could then claim lower Vf, and greater efficiency.


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## Techjunkie (Jan 25, 2010)

Magic Matt said:


> The burn in is lowering the Vf, and so pulling more current.... and I realise that more current increases the output and also affects the tint slightly according to the specs. Is this burn in also affecting the tint and brightness, or is it just pulling more current to achieve the same output as it was new? - if it were restricted, to the same current as before, would it have dimmed down and colour shifted slightly after burn in?


 
Higher current draw and the brightness/tint changes that come with it are achieved at a lower Vin for a burned-in emitter. This can be an advantage when direct driving the emitter and battery sag and resistance were keeping the circuit from achieving optimal Vin prior to burn-in. If supply/resistance were optimized for maximum current prior to burn-in, disaster could occur in the form of thermal runaway after the emitter as burned-in and Vf is then lower than Vin.

A constant current driver would simply have to deliver less voltage to the emitter after it has burned-in than it did before it was burned-in, but there would be negligible change in brightness as current would remain the same.

A burned-in SST-90 being driven to 9A will yield the same lumen output immediately after it was burned-in as it did when it was driven to 9A before it was burned in. Over time, the "lumen maintenance" of an LED drops, meaning that at a given current, less lumens are output than at an earlier time in the LED's life.

Running a high-output LED at high currents reduces lumen maintenance faster than running it at low currents. It is arguable that aggressive burn-in accellerates the initial drop in lumen maintenance, compared to a prolonged burn-in.

I would only recommend intentionally burning-in an LED if it were to be used in a direct-drive setup, to achieve a desired battery/resistance configuration against a more predictable Vf. If a constant current driver were used, then burning-in would only afford the small advantage of less total Wattage consumed by the LED and is probably not worth the time invested to perform an intentional burn-in.

I have heard that the yellow phosphor that coats the LED to change it from blue to white is slightly consumed over use, so it is also arguable that at the same current, a burned-in LED may have a slightly cooler tint than prior to burn-in. By my own experience, I thought that the hotspot of my 4500K SST-90 was too yellow when I first began to experiment, but no longer find that to be the case. I attribute that change more to the higher current, different reflectors and my own perception than phospor consumption though.


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## flashfiend (Jan 25, 2010)

So you are saying my 3-mode direct drive sst-90 does have a PWM driver in it and it is adding resistance to the circuit? I thought in high mode it would just be completely direct driven with insignificant amounts of resistance introduced into the circuit. Btw, I'm doing a burn-in right now and it 'feels' like it is drawing more current mostly indicated by heat and not output.



Techjunkie said:


> I would assume, as you have, that on the brightest mode, the PWM that controls the FET is at 100% duty cycle, so the circuit is constantly closed. The FET itself adds some resistance though, and as we've seen in the video, the slightest amount of resistance changes the numbers significantly in this high current, low voltage application. In other words, compared even to your high mode, direct drive without the driver would draw even more current.
> 
> I built a few keychain torches with MC-Es and observed the same difference between the direct drive ones without the PWM only driver and the ones with it (and an MCE only pulls 2-3A at the same Vf that the '90 pulls 5-9A).
> 
> ...


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## Techjunkie (Jan 25, 2010)

easilyled said:


> I wonder why the "burn-in" isn't done by the manufacturer.
> They could then claim lower Vf, and greater efficiency.


 
Over time, the manufacturer could improve the manufacturing process to reduce or eliminate the need for burn in. Burning in the LEDs would require heatsinking, time and other costs, which would raise the unit cost.



flashfiend said:


> So you are saying my 3-mode direct drive sst-90 does have a PWM driver in it and it is adding resistance to the circuit? I thought in high mode it would just be completely direct driven with insignificant amounts of resistance introduced into the circuit. Btw, I'm doing a burn-in right now and it 'feels' like it is drawing more current mostly indicated by heat and not output.


 
No amount of resistance is insignificant in a low voltage high amperage circuit. Consider the three different readings I got in my second video. The reason each measurement differed greatly was becaue each different method of measuring introduced a different (slight) amount of resistance to the circuit.


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## flashfiend (Jan 25, 2010)

So have I shot myself in the foot by getting the extra modes? Meaning, with the modes I won't get full output or even have a chance to get the 6 amps I'm looking for? Hopefully the DeOxit w/ LED burn-in can get me close. I'm bummed.


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## Techjunkie (Jan 25, 2010)

flashfiend said:


> So have I shot myself in the foot by getting the extra modes? Meaning, with the modes I won't get full output or even have a chance to get the 6 amps I'm looking for? Hopefully the DeOxit w/ LED burn-in can get me close. I'm bummed.


 
Not necessarily. If you eliminate as much other resistance as possible and the emitter's Vf drops after a burn-in period, you might even find that you're sending 7-9A to the emitter after it warms up, provided that your battery pack is up to the task.


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## vestureofblood (Jan 25, 2010)

Thanks for the info, and I love that you added vids:thumbsup:


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## mvyrmnd (Feb 16, 2010)

Just a quick point about your tailcap measurements...

I used a second multimeter today to measure the resistance of the measurement circuit of my primary multimeter, to compare it to the tailcap resistance.

For example, the tailcap in my Solarforce L2 provides 5 milliohms resistance.

The measurement circuit of my multimeter provides .5 ohm resistance.

That's a full 100 times greater resistance than the tailcap!

Using a multimeter to measure tailcap current is a VERY rough guide at best!


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## Techjunkie (Feb 16, 2010)

mvyrmnd said:


> Just a quick point about your tailcap measurements...
> 
> I used a second multimeter today to measure the resistance of the measurement circuit of my primary multimeter, to compare it to the tailcap resistance.
> 
> ...


 
Exactly. Also, bear in mind that your tailcap has a switch in it. Mine is a deanodized Mag tail with a gold plated short spring, both treated with deoxit gold.

Even the aluminum sheet metal bridge that I used in the clamp meter tests has more resistance than my tailcap, which was obvious when it didn't turn the emitter blue but the tailcap did.


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## zelda (Feb 16, 2010)

from my sst-50 with 3 SCHR cells observation:

When I measure at the "tailcap" with a quality 1mm2 multimeter-cable I got 3.2A.
The same way with a 4mm laboratory cable without test probes like this one: https://www.distrelec.com/ishopWebF...r/is/102651/and/id/is/01/and/series/is/1.html
I got 5.7A 
Put enough force to the plugs with multiple cells when measuring!

zelda


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## uluapoundr (Jul 11, 2010)

I just put together a DD SST-90 3D Mag. I initially tested the amps at the tailcap using a Sperry MM. Using 3 Tenergy NiMH, got only 2.0-2.4 amps. Slipped in 4 C-cell Tenergy NiMh and was getting 9.0 amps. Been doing 15-30 seconds burn-in sessions, using the 4 cells and running on the MM, then letting it cool down. Using the tailcap immediately turns the light blue. Prior to Deoxit the 3 cell was pulling 3.4 amps and the 4 cells 12.0 amps. With deoxit treatment, the 3 cell is now at 3.9 and 4 cell 12.8. Looks like the emitter is burning in. At 12.8 amps, this light is super bright, brightest single LED I've ever seen, makes my P7s look like stock mag bulbs. This bin is only WM bin, what an awesome emitter!


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## Illum (Jul 11, 2010)

its natural for LEDs to lower their Vf when heated...but considering in how short time these LEDs lower its Vf draws more concern about the current regulation of the power supply overtime, as well as the longevity of these LEDs in a fixed lighting configuration


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## mvyrmnd (Jul 11, 2010)

So just to clarify something... If I wanted to burn in an emitter, what would be the best procedure?

Would I hook a battery directly to the emitter and feed it 4.2V, and keep it heatsinked well enough that it doesn't burn up?


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## uluapoundr (Jul 15, 2010)

Another update. Continued running the SST90 3D mag build using 4 C NiMh with measurements at the tailcap at about 10-12A using standard MM wires. Would run in 30 second sessions till the head of the mag heated up, then let cool. Couldn't use the tailcap as the currents were too high and light would turn blue in a few seconds. Used the MM to create some resistance for the cycles. Did a dozen or so cycles. Took measurements with the 3 D NiMh and was getting almost 5A at the tailcap. Switched out the MM wires for thicker wires and took measurements again, it's 5.8A. Light OTF looks about twice my P7 D bin, pretty awesome!


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