Safe current for XML2 on Aluminum MCPCB

I appreciate the replies.

I think I’ll just use the 2.8A biscotti driver to play it safe for selling.

If the heat is too much would the output decrease as a sign? I have a lumen tube so I could monitor it. Since each LED varies I think maybe I’ll just use the biscotti driver. This new driver was a few $ cheaper so was hoping I could of used it.

Might be cheaper to buy drivers from Fasttech if you don’t min the standard 3 mode setup? These are the 3/5 mode drivers. Last ones i got where Convoy branded.
https://www.aliexpress.com/item/4000004827705.html?spm=a2g0o.productlist.0.0.3ec1435cNnM0P7&algo_pvid=4f1a5189-884d-4b6c-9f6d-135da0ab0614&algo_expid=4f1a5189-884d-4b6c-9f6d-135da0ab0614-54&btsid=86b4956a-868e-425d-8793-2ca21c75c758&ws_ab_test=searchweb0_0,searchweb201602_1,searchweb201603_53

When i tested my LEDs i direct drive them and they went blue after only a few seconds like maybe 10 seconds max. The XML2 might be able to handle a little more current compared to the XPL because it uses the larger footprint 5050 vs 3535 so that will more heat through. If it over heats to much you will lose output.

The old xlm2s were pretty robust, but the more recent ones seem to burn out much faster.

Grab some ∅16mm 5050 DTP boards and reflow your leds:

Warning: the ∅20mm 3535 board sold in the above ad is not DTP, or at least it wasn't many months ago. Thermoelectric separated ∅20mm copper boards here.

Frankly, the light output between 3A and 4A would be so little as to be almost unnoticeable. Heat, though, not so much.

Already, given the downward-pointing parabola of output vs current, it’s already on the flattening-out part of the curve and could be very well be headed on the downward slope. So, 30% more current for maybe 5–10 more light?

This is so true, i actually downgraded several S2+ lights because of this exact reason.
Now running safe at 2,8A max happily :sunglasses:

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]

The above may not look enticing to you, but let me say the above game was a real crack up in multiplayer due to its insane and bizarre broadcaster quotes. And of course, if you were to be set on fire by someone you would hear your own character shouting “It burns! It burns! Aaah! Aaaaah!” aloud. :-D

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