What Happens When You Go Past Max Drive Current?

How much current can you run thru an XM-L or XP-E, etc.? The datasheet says 3000ma/3A for an XML or XML2, 1000ma/1A for XP-E.

Wondering, I have a C8 that runs an XP-E at 1.4-1.5 A measured by removing the cap and using a Harbor Freight DMM with 12ga braided wire inserted for leads. So far so good, will it just not work as long?

Also, I measured an XML C8 with an AW at 3.5A. Is that going to hurt much?

There are all kinds of things that can happen and it depends on a lot of different factors. Match (a member who I haven’t seen in a while) did a ton of work and made some great charts. Sometimes you simply kill the emitters right off the bat. Other times it will stress them and cause an early grave. Other times you will actually see less lumens. If done correctly with enough heat transfer you will often get an increase without damage. Almost all of us modders here are overdriving our emitters well past the factory specs.

Here is a link to some of Match’s great work.

I was trying a spare power supply and turned the voltage selector knob past the lowest to the highest setting by accident, on an XP-E in a light with an external power connector. It got dimmer and bluer for a fraction of a second then went forever dark. So I think I drove it way beyond maximum light output and the heat made the phosphor also not work right. I suppose the bond wires then melted.

That was more probably the die dying, when the bond wires go you do not see any colour change or dimming, it just gets dark instantly.

The blue light of death. You can almost hear those poor emitters crying out for help. :bigsmile:

Regarding out of spec currents, there is a large difference in what maximum current (and output) an emitter can handle, depending on if a special led-mcpcb is used that provided a direct thermal path from the center pad of the led to the metal core of the board (Sinkpad or Noctigon boards).

E.g. an XM-L2 on a normal board can handle between 5 and 6 A, on a Sinkpad it goes over 8A with much more output.

If all you’re asking is whether going above the manufacturer’s stated drive current will destroy the LED then the answer is no, it’s OK to exceed that in many circumstances. There are several ways to kill the LED, but just exceeding the manufacturer’s rating is not a death sentence.

If you have more than a passing interest in exactly what happens, there are probably many considerations. I don’t know much about most of them. The main thing that will be affected by drive current and temperature is “Lumen Maintenance.” The kinder you are to the LED, the longer it will take to become less bright. See here: Cree - XLamp_lumen_maintenance.pdf

As you reach the highest drive currents which do not destroy the LED immediately you’ll find that there may be conditions which cause electrical overstress, see here: Cree - XLamp_Elec_Overstress.pdf. Note that even low-current drivers can do bad things like this!

It’s spaceball1! They’ve gone to plaid!

careful you emitters don’t get jammed.

with good direct to copper bonding and heavy heat dissipating heat sinking, people have pushed over 7 amps through a Dedomed XM-L here on BLF. I have blown up a few of them testing upwards of past 7 amps, but managed to get some to survive no problems past 6 - 7amps. ( as for XP-E, i havent really pushed them very hard yet past 1.5 amps.
close to 8 amps though, there is a high risk that your XM-L will do this below if it dont have good heatsinking:

Like DBSAR said, a GOOD COPPER PATH! Or if you are impatient like me you can make really lousy thermal path and smoke 3 XML’s at a time. The light fades then a yellow to emerald like tint to black. Almost no smoke, just a whisp. I expected more smoke from previous screw ups. But those were different screw ups so different effects I guess. That’s progress right, only make new mistakes.

What happens when you go past the limits? It’s awesome until it sucks. Like riding a motorcycle; faster you go the more fun it is until all of a sudden it’s not fun. But different from a motorcycle because you can keep pushing past the limits and refine what you understand from what you have learned prior to modding. Can’t go back though. You will find all your lights will need tweaking.

more, more, MORE, MORE, less.

Tell them to comb the desert, you hear me, comb the desert!

I said across her nose, not up it!

The sun wont rise tomorrow, watch out…

Mine always do this

more, more, MORE, MORE, off.


We ain’t found S**T

:smiley: :smiley: :smiley:

Classic :slight_smile:

You will open a black hole and all matter and light will be sucked in, typically no light will come back out. Lets face it though death is really just prebirth, power up another. I have run them run to 6 Amp plus on a copper DP with a heatsink, but carefully

Ok so its a big heatsink