Cree XR-E Q5 at 2000mA with 2xAAA lithium batteries

mailint

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I read that someone here reached 2000mA with a Cree XR-E led...

Well, I need to obtain the best brightness, even for short time, from a Cree XR-E Q5 (or other top-class) led necessarily using 2x AAA lithium batteries (those of my laser pointer!).

I read that for obtaining the highest current (mA), and therefore the highest lumen, I need to use "direct driver". What does it mean? that I have to connect the batteries directly to the emitter? what mA value can I expect from 2xAAA lithium batteries?
 

LEDcandle

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"Direct driver" probably refers to a single output driver that pushes 2A to the LED... I'm not sure if any off-the-shelf drivers push that high.

Direct driving with 2 x 1.7v lithium batteries probably will get you less than 1A, very much depending on the Vf of your particular Cree and other resistance calculations of your host.

I'm just giving a guesstimate based on direct driving several Crees with a Li-on batt (3.7v - 4.2v) and getting around 800ma - 1.2A in different lights.
 

mailint

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"Direct driver" probably refers to a single output driver that pushes 2A to the LED... I'm not sure if any off-the-shelf drivers push that high.

Direct driving with 2 x 1.7v lithium batteries probably will get you less than 1A, very much depending on the Vf of your particular Cree and other resistance calculations of your host.

I'm just giving a guesstimate based on direct driving several Crees with a Li-on batt (3.7v - 4.2v) and getting around 800ma - 1.2A in different lights.

Thank you for the informations LEDcandle.
Out of curiosity, what happens if I connect the 2xAAA lithium batteries directly to the emitter?
 

LEDcandle

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Theoretically, it should light up without incident. If its Vf is around 3.6-3.7v or more, it will be very dimly lit. If it's low 3v, it will be brighter.

However, please note these type of LEDs heat up VERY QUICKLY, especially if its Vf is lower than your combined battery voltage. A quick flick just to test the LED is usually ok, but not prolonged connection. You need some kind of heatsinking if you want to turn it on longer.
 

David_Web

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Direct drive is when you drive the led directly from the battery or through a resistor.
NOT when you use a driver.

I guess that around 1A it the max you can get with 3.5V
The batteries will sag at that current so you would probably see less.
 

LEDcandle

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Well, I read 'driver' and it seemed like the person achieved a 'controlled' 2A, so I didn't think it would be direct drive :D :stupid:

Yes, direct drive actually means connecting directly, but I'm not sure in this case how the 2A was achieved . It would be very random without knowing the Vf of the LED, the resistance of the wires used, battery resistance etc... might get magic smoke instead :) But it is very unlikely with the batteries in question.

A fully charge li-on (4.2v) directly connected to the LED might have a good chance of pushing almost 2A (depending on the LED Vf). Some of the older luxeon Jetbeam MkIs with an average Vf of 3.4v or so saw 1.8A to the LED when direct driven through the flashlight.
 
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mailint

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Well, I read 'driver' and it seemed like the person achieved a 'controlled' 2A, so I didn't think it would be direct drive

Sorry LEDcandle, I intentionally wrote "driver" because my italian inexpert mind remembered "driver" instead of "drive" and indeed I had a doubt on what of the two to choose when I wrote it. :ironic:

Yes, direct drive actually means connecting directly, but I'm not sure in this case how the 2A was achieved.

To be exact I only read that someone achieved 2A. With 2xAAA is only my dream, not a fact that I read :)
 

easilyled

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I am not an expert but I think that 2 AAA batteries are too small to provide
2A for any length of time even if you could find a driver that regulates
that current.

You'd need something much bigger, more like a li-ion C-sized or D-sized cell.
 

mailint

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You may be referring to this post of mine? If you do, I can tell that I have experience on only short bursts (1-2 minutes) of 2+ amp input currents. I do not know how much faster the XR-E takes damage if run longer at 2+ amps.

-N

I was referring to a post of a person who wrote that someone did it. Now I guess that that someone are you :)
Thanks for the information!
I wrote a message for you on that thread..
 

biwema

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I intend to build a similar construction: A light weight strobe which emits a flash every 2-3 s which can easily be seen in a bright environment. A traditional stroboscope is too heavy for that purpose.
A bright LED which is driven by a high current that is powered by one or two AAA cells would be much better suited.

Unfortunately the voltage of 1-2 AAA cells is not high enough for a Cree. Even when using 3 AAA cells, the voltage varies in such a large area, that a direct wiring is difficult.

In my case I only need short flashes of maybe 1/20s. After that, the LED has 2-3 seconds to cool down.
For delivering a high current in a short time, a capacitor is the ideal device. First I have to measure at which voltage the current through the Cree is 2.5 A.
The Capacitor in the device should be charged up to that voltage. After switching the capacitor to the cree, the current should drop down to 1.5A in 0.05s. Using these values the capacitor can be sized. At this point the current can either be interrupted or continue until it stops automatically (That would not harm the LED).
When the flash is finished, the capacitor will be recharged to the initial voltage. (The capacitor will never be discharged below 3 V during operation and hence need less energy to recharge).
Nevertheless a driving and timing unit is necessary to trigger the flash and charge the capacitor using a lover voltage (DC converter). The charging can be done continuously that the current from the battery does not get too high. (Is there such a driver already available?)

Maybe a similar construction can also be suitable for your application if the driver and battery are strong enough to keep the capacitor at that voltage which correspondents to 2A.
Or might it be possible to wire two (already existing) 1A LED driver in parallel? Some AA cells are able to keep the voltage above 1V at 10A (for a short time). Probably similar AAA cells are available.
 

mailint

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Hi Biwema

I can't help in your precise requirements but have you evalued a 125mW laser or an off camera flash?
I had an off camera flash that keeping a button pressed continually emitted the flash after the 10-15sec. charge from 2xAA batteries.
 

biwema

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I can't help in your precise requirements but have you evalued a 125mW laser or an off camera flash?

Do you mean I should use these devices or just have a look at those circuits?
I assume you meant the former.

I think i will go for a LED flash because camera flash do need a too high voltage.
I was already thinking about a flash from the camera of a mobile phone. maybe they are strong enough for my purpose. (I now ordered some emitters and other stuff from DX where i can do some experiments and empirical tests)
In my application the product should be not too large. An example is a signal strobe which people can put un the cap when going swimming in a lake that the swimmer can be easily be seen by the boats.

At the moment I am reasoning about a circuit of this form. A LED is powered by capacitors in series. Between these capacitors there is a transistor that triggers the flash. Between the falshes, the transistor seperates these 2 capacitors that they can be charged to 2.something Volts each independantly from 2 AAA cells. When both are charged, the flash can be triggered again. (It can even be that this architecture does not work - it just appeared in a dream :whistle:).

If such a circuit works, it might also be suitable for your application. Just use 2 sets of capacitors. When one set is charging from 2 to 2.01V, that other set is discharging from 2.01 to 2V. If you toggle maybe at 10000 or more Hz, the capacitory could be small. Of course it necessary that your AAA cells can provide 4A at 1V. For Lithium no problem, maybe you can do it with LSD NiMh?
 

LukeA

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You may be referring to this post of mine? If you do, I can tell that I have experience on only short bursts (1-2 minutes) of 2+ amp input currents. I do not know how much faster the XR-E takes damage if run longer at 2+ amps.

-N

I got about 3 hours total life in 1-3 minute bursts running a P4 off 3 AA NiMHs (looking at the chart from the datasheet, about 2.5-3A). Then it started to flicker. The flicker got more severe and eventually it just stopped.
 

Nitroz

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I got about 3 hours total life in 1-3 minute bursts running a P4 off 3 AA NiMHs (looking at the chart from the datasheet, about 2.5-3A). Then it started to flicker. The flicker got more severe and eventually it just stopped.

Wow, to think that something like this with a Lux III would fry immediately, not that I ever fried any Lux IIIs.:whistle:
 

mailint

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I got about 3 hours total life in 1-3 minute bursts running a P4 off 3 AA NiMHs (looking at the chart from the datasheet, about 2.5-3A). Then it started to flicker. The flicker got more severe and eventually it just stopped.

Luke I'm very interested in your experiment. What driver circuit did you use to reach that amperage from the 3xAA Ni-Mh batteries?
 

mailint

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Do you mean I should use these devices or just have a look at those circuits?
I assume you meant the former.

I think i will go for a LED flash because camera flash do need a too high voltage.

too high voltage? I believe that most camera flashes take standard AA batteries...
 

LukeA

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Luke I'm very interested in your experiment. What driver circuit did you use to reach that amperage from the 3xAA Ni-Mh batteries?

Direct drive from 3 cells in series. They were about 4V all together. That's off the chart from the Cree datasheet.
 

chesterqw

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ummm... camera flash do use high voltage...

the xenon flash wun be able tor un from those pity low voltage batteries gives.

it needs thousands of volts :)
 

mailint

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Direct drive from 3 cells in series. They were about 4V all together. That's off the chart from the Cree datasheet.

The data sheet at http://www.cree.com/products/pdf/XLamp7090XR-E.pdf doesn't show the curve after about 3.6V, and - most important - don't give any idea of the voltage drop of AA batteries.
With 2xAAA lithium batteries in direct drive and Cree XR-E P4 I only reached about 50mA because of the voltage drop of the batteries when connected to the load.
I'm stunned that you obtained such an higher voltage with 3xAA Ni-MH under the very heavy load of 2.5-3A. What was the total voltage of your batteries without load? 5V? from 3xAA Ni-MH?
 
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