# MAX real current for CREE LED emitters?



## Uldzha (Oct 12, 2012)

Hello all,
I am interested in what is MAX real current for CREE LED emitters?
OK, in CREE data sheet can reed:
MAX DC Forward Current for *XR-E *Cool white is: *1000mA*, Warm and Neutral white: *700mA*
MAX DC Forward Current for *XP-E*: *1500mA*

But in real life has seen thet emitters driven at much higher forward current... (for example, XP-E @1400mA, XP-E @2000mA and XM-L @ 5A)... and they works...
I have a question - how exactly is? 
Whether I can add a 4x1735 chips driver(1400mA) to XR-E (cool White), if it have a good cooling? Or 3x1735 chips driver(1000mA) to Warm white XR-E? ...it certainly will work, right? but for how long? What actually will happen? :thinking:


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## Epsilon (Oct 12, 2012)

Cooling is everything.

And the most critical part is the LED mounting to the star. The thermal path of the LED to the star needs to be good, and then the start itself needs to be good. 
The best option you have, are leds directly soldered to copper PCB's, like the XM-L that Led-tech.de is selling. They are difficult to find for other led types though.


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## Uldzha (Oct 12, 2012)

Ok, thanks Epsilon!
but is it so that Warm white XR-E (P4) heats more than Cool white (Q5), if Q5 is officially allowed higher current?
for example: XR-E Q5 normal Current is 1000mA... and it no heat and so much...
If I connect the same current(1000mA) to XR-E P4 Warm white - or it is heated more than the Q5?
I want to know because I want to build two C8 throwers - One with XR-E P4 warm white LED (on 16mm round aluminium board from DX),
and the second with XR-E R2 WG (on 20mm aluminium star from DX).
Or they will work well, if the first one will be driven @1000mA, and the second one @1400mA? (of course, I will use the thermal glue)
Or they will last a long time?


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## Th232 (Oct 12, 2012)

It's vague. As Epsilon has said, how well you cool it is essential, without knowing exactly what your "good cooling" is it's very hard to say. Effects from overheating include destruction of the bond wires, burning of the phosphor and probably a couple of others. I think I saw a thread somewhere about a P7 that was run at 10 A with water cooling, worked fine until it was powered up without the water flowing. No info on long term effects though.

Also, how much lifetime are you willing to sacrifice? Are you fine with the LED having a nominal lifetime of only 2000 hours if you run it at 125% of the official maximum rating?

Yes, the P4 will heat up more than the Q5 since the Q5 is, by definition, more efficient, so less energy is turned to heat.


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## Optical Inferno (Oct 12, 2012)

I saw some interesting data on an XM-L that was pounded with 8A and 10A. It was done by a company that designs fire alert systems for buildings. As the others have said cooling is the key, but you can also help cooling with PWM at a relatively high frequency.


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## Uldzha (Oct 12, 2012)

2000 hours actually sounds acceptable... it is several years even if used as EDC flashlight...
But these will be used as Hunting lights, the most frequent in winter...
by looking at these charts: http://www.candlepowerforums.com/vb/showthread.php?192925-AMC7135-Specs-Inside-**UPDATE** can conclude that the MAX current is only in the first minutes, then it drops gradually and soon the LED is no longer overdriven.
and more... since R2 is more effective than the Q5, in the theory, the less heat, right? difficult decision...
I just want to build a very bright thrower for Hunting, but also do not want to fail after a few weeks...


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## Uldzha (Oct 15, 2012)

_DC Forward Current - white ≥ 5000 K, royal blue, blue mA 1000
DC Forward Current - white < 5000 K, green mA 700_

Looking at the following Flux Characteristics table, can see that the cool white P4 an warm white P4 have the same brightness (80.6lm). So the efficiency and heat also must be the same... but allowed current is different...
Maybe Max current is calculated by weakest emitter on group? In this case - 700mA is max current for Warm white XR-E N3... but Warm white XR-E P4 is more effective, so it could hold a larger current...
The same with cool white's:
P4 and R2 - both have 1A MAX current... if P4 MAX current is 1A, then theoretically R2 can hold more.

Or my theory is correct? Or I'm not really understand it all?


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## AnAppleSnail (Oct 15, 2012)

A brightness bin has little to do with current rating.The LED structure is more important.


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## blasterman (Oct 15, 2012)

Yup.

Longevity is also a key part of the equation and what your expectations are. I just finished a test running some XP-Gs at 1.4 amps for 2500 hours at around 45C and they were visibly dimmer than the control emitters. Not a huge amount, but there is some visible loss of brightness. Had I been using high performance stars I'm sure they would have tolerated it better. 2500 hours is a long time though for hand held use. Short form - get good stars if you plan on running at high currents.


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## Uldzha (Oct 15, 2012)

Ok, it seems that: if emitter mounted on the copper star, then I can use the 1.4A current. But if it mounted on the 20mm Aluminium star, than should be used only @1A, otherwise it will not work long and well.
Ok, will stay with aluminum star an 1A current... anyway, R2 @1.4A gives only ~60lm more than @1A. Maybe really is not worth risking with LED health.
P.S.
And if the LED is cooler, it gives out more light, right? So if it does not have so good cooling, then R2 @1.4A will not be so much brighter as well-cooled R2 @1A.


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## AnAppleSnail (Oct 15, 2012)

Some copper stars are no good as well. Some copper stars have the equivalent of foil under fiberglass PCB layer. Validate your thermal path by building or measuring it.


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## HugeOne (Oct 21, 2012)

I tested the XM-L to 7A using water cooling, blow up point is 8A.
LED heat pad directly soldered to a 5/32 copper tube with flat spot grinded into it.

Hugo


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