Safe current for XML2 on Aluminum MCPCB

And even at that, if you let it tailstand even 5-10min or so (ask me how I know), it’ll get too hot to even turn it off, let alone grab it.

It was like grabbing a curling-iron by the wrong end, that it fell to the ground, still on. Had to use a shirt as an “oven mitt” to just grab it long enough to click it off, and even then, had to let it air-cool a loooooooong time before I could pick it up.

@PiercingTheDarkness, Simon has been using DTP MCPCBs for a long while.

Just use them normally, and don’t exceed 3A on them.

Okay, 3A limit it is or I’ll have a go reflowing.

Cheers

No questions asked. I know how it feels, they can become burning hot, i have lended some of my lights when someone asked for a light, and exact the same thing happened.
Now i try only to hand over lights which are safe for persons not knowing the power of Li-ion operated lights. (a.k.a. noob lights)

See Djozz his temperature measurements with a S2+ over here

Dumb question…

Why is running at 4 amps a problem? Is it just because it’s an aluminum board? There’s plenty of FET-driven C8 lights that work perfectly fine at probably 4A-5A (mostly using XPL, though). I presume they’re likely using copper head sinks. Do all of them? And, are they all safe at the higher amps? I haven’t noticed any issue, myself, for stock lights.

The difference in output between Convoy’s 2.8 amp driver, and a FET driver, is very noticeable (about 50% brighter by my measurements). Yes, the FET light gets hot quicker and eats up the battery faster, but it would be a shame to limit the current to 2 or 3 amps if it’s safe to go higher.

The thing is, since you are planning to sell these lights, we are just giving the advice not to run them on very high current, just because of safety reasons.
Djozz his test shows the light with a standard 2,8A driver already hits 90 °C, which is already sky high.

if you are planning on running 4~5A, these lights will even exceed 90°C, which is just not smart because of safety reasons (burning wounds)

I added the wrong link damn it. Check out these drivers.
https://www.fasttech.com/p/8727400

My next answer would be a very unpopular opinion in BLF…
Running any LED beyond manufacturer’s max rating is bad for LED lifetime. Even if you can make the LED base temperature cool.
The reason manufacturer use conservative max current limit is the thermal path bottleneck at the LED substrate level. There’s thermal build up in the die. This heat will degrade the light produced by the die overtime. I tested many LEDs and the result always the same: after overdriving beyond max rated current the voltage and the output permanently reduced. And this doesn’t take many hours to happen, only few seconds. Permanent output loss is very prominent past 1,5x max rated current. High CRI and warmer CCT suffer more than low CRI cooler CCT due to thicker phosphor layer (hotter die).

[Clemence]

I’m surprised you say it’s only a few seconds (or even hours) at high current before LED damage is noticed.

I have plenty of FET-driven lights, that generally max out at somewhere around 5A per XPL with a high-drain cell. With throwers (like a C8), I exclusively use them on max. Even smaller lights I do that with, at least until they get too hot to hold (which I admit isn’t that long). They’ve had many hours at full output, and I don’t see any noticeable drop in output.

I totally understand that over-driving will decrease the expected usable lifespan of the LED. But, my assumption was that it would drop from 50,000 hours to something like 10,000. Or even if it was only 1,000 hours, that would likely be more than I’d ever use.

But just a few hours? Or seconds?!? I’m not seeing that.

Get yourself a decent lux meter and 5 digit volt meter. And see for yourself. Initial drop from “virgin” output is the fastest.
I discussed this with Djozz few months ago. And he got the same conclusion too. After few hours resting, the output back to normal but requires more current. All damaged LEDs needs higher input current to get the same output/voltage/temp reading.
In your case with FET driver, as the LED voltage gets lower, the current input gets higher. This is why you don’t see much reduction in output, the driver compensates by increasing the current.

[Clemence]

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I do not think the high temperature thing is much of a problem because any resonably common sensed human being will notice the flashlight getting hot in his hands. He/she should know that is going to happen much faster if not hand held…

Anyway, I refuse to lend my flashlights unless the recipient is sufficiently knowledgeable or he/she's within vigilance range.

My readings with a Neutral White at 4A

1050 lumens - turn on
900 - 30 sec
860 - 1 min
765 - 3 min

Max temp was 62 degress

Neutral White with 2.8A 7135 biscotti

820 - turn on
780 - 30 sec
767 - 1 min
737 - 3 min

Max Temp 53 degrees

Measured with my calibrated lumen tube

Lasers (vcsel chips, particularly fussy) can go “pouf!” in microseconds with hit with slight overcurrent.

In some cases, lasing current and overcurrent isn’t all that much (eg, 1.5:1 or 2:1). Even transients like a flashlight’s “pre-flash” can kill a laser.

I’ll let laser mavens go into more detail, as I generally don’t get into laser design.

Do you still have any of the test data for this? I’d be interested in looking through it. I’m not surprised that there is a loss in brightness, but the fact it’s rapid does surprise me slightly. The sinkpad marketing videos show the die being much cooler with a DTP board when viewed through an IR camera, and one might expect that to carry on when the LED is overdriven. That’s just an assumption though, I’ve never seen it tested. Next time I get a new LED for a FET light I might test the output before / after the first turbo run

I never really write it down because crash test any LED in my opinion, is a one way destructive test. The first time I noticed this was when I skipped a current setting (yes I do all the test manually). For example, let’s say I plan to test an LED from 100mA all the way to 5A with 100mA resolution. Then at 3,3A I forgot if it was 3,3A or 3,4A. So I wait several minutes and rerun the test from 3A, in all cases, whenever I passed too far outside max rated current, the second reading always reads lower.

I don’t think you will get accurate reading with FET based driver. As I mentioned above, damaged LED (by over current) has almost always suffer reduced forward voltage. Lower forward voltage means higher current in FET driver. It’s self balancing.
My measurement done with constant current DC power supply in a controlled total loss cooling system.

[Clemence]

That is very surprising. With all the FET-driven lights that BLF users love, there should be more complaints about damaged LEDs. Whether it’s higher current consumption, or lower output, this board should be full of complaints about all the high-output lights people buy.

Even if the output is compensated with reduced forward voltage, that can only give a little more time before the problem is noticeable. It’s not like you can shove 10 amps through one of these LEDs.

You’re talking about damage in seconds. Everyone should notice that.

Okay, you’ve got me interested enough that I’m going to dig out my test results on some of the FET lights I reviewed when new, and re-test them now that I’ve used them for a year to two.

My guesstimate is at 4A your L95 = ~2000 hours, and at 5A L95 = ~500 hours. Output depreciation is not an on/off process, everything starts as soon as there’s current flowing.

[Clemence]

Okay, I did a quick test of my most-used FET light, the Astrolux C8. I’ve had it for about 1.5 years, and put on about 15-20 hours of “full output” usage on it (just a rough estimate). It does have a timed step-down, but I always bump it back up every time it steps down. So, it does get hot, though not too hot to hold.

The output is exactly what I tested on it when it was new, a little under 1300 lumens. No current measurements, though.

Okay, I know you say you can’t tell with FET lights, but if the damage is so quick, it’s got to show up as decreased lumen levels eventually. Unless the damage stops after a certain point, and lumen and current levels stabilize.

Is the damage you’re seeing, possibly due to improper heat-sinking?

Okay, from that chart, it looks like the damaging factor is heat at the junction point, not the amount of current flowing. Current plays some role, but it appears if you properly heat-sink things, most of damage is mitigated.

And even worst-case, it doesn’t seem the L70 lifetimes are affected much at all; just the L95 lifetimes.

I’m not sure if we can extrapolate accurately past Cree’s 3 amp testing, but if you’re right that 5A gives 500 hours until the LED is only 95% as bright, then that’s why I’m not seeing any drop at all after 15 or 20 hours.

I’m okay if I get 500 hours at almost “new” output levels. That would explain why people aren’t complaining.

Please check if you think my setup wasn’t cool the LED enough:

[Clemence]