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



## mailint (Sep 23, 2007)

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?


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## LEDcandle (Sep 23, 2007)

"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.


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## mailint (Sep 24, 2007)

LEDcandle said:


> "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?


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## LEDcandle (Sep 24, 2007)

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.


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## David_Web (Sep 24, 2007)

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.


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## LEDcandle (Sep 24, 2007)

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

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 (Sep 25, 2007)

LEDcandle said:


> 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:



LEDcandle said:


> 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


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## easilyled (Sep 25, 2007)

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.


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## Nereus (Sep 26, 2007)

mailint said:


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


 
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


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## mailint (Sep 27, 2007)

Nereus said:


> 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..


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## biwema (Oct 18, 2007)

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.


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## mailint (Oct 18, 2007)

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.


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## biwema (Oct 20, 2007)

mailint said:


> 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 ).

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?


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## LukeA (Oct 20, 2007)

Nereus said:


> 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.


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## Nitroz (Oct 20, 2007)

LukeA said:


> 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.


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## mailint (Oct 21, 2007)

LukeA said:


> 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?


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## mailint (Oct 21, 2007)

biwema said:


> 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...


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## LukeA (Oct 21, 2007)

mailint said:


> 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.


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## chesterqw (Oct 22, 2007)

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


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## mailint (Oct 22, 2007)

LukeA said:


> 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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## mailint (Oct 22, 2007)

chesterqw said:


> 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


 
Camera flashes use capacitors to obtain those high voltages from 2xAA batteries. There's no need to give them high voltages directly from batteries, that is what you're worried about.


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## evan9162 (Oct 22, 2007)

mailint said:


> 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.



The 50mA had NOTHING to do with the voltage drop of the batteries under load. Even the terminal voltage of AAA alkalines should only drop a miniscule amount under a 50mA load. I don't think you really understand the relationship between current and voltage in LEDs. 

http://candlepowerforums.com/vb/showthread.php?t=77221
http://candlepowerforums.com/vb/showthread.php?t=72528



> 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?



NiMH cells can output a TON of current without dropping voltage very much. You should read up on the performance of rechargable cells as well. It should surprise no one that AA NiMH cells can output 2.5-3A while sustaining a high terminal voltage.


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## mailint (Oct 22, 2007)

evan9162 said:


> The 50mA had NOTHING to do with the voltage drop of the batteries under load. Even the terminal voltage of AAA alkalines should only drop a miniscule amount under a 50mA load. I don't think you really understand the relationship between current and voltage in LEDs.
> 
> http://candlepowerforums.com/vb/showthread.php?t=77221
> http://candlepowerforums.com/vb/showthread.php?t=72528
> ...


 
"Today I received my first LEDs to play with: a Cree XR-E, a Luxeon Rebel, a SSC Z-power P4, all pre-mounted on a star or PCB.

I immediately tested them directly connected to 2xAAA lithium Energizer batteries and I was disappointed by the results.

All were of similar brightness, the batteries went down from about 3.260V without load to 2.850V with the LED connected/turned on.

The currents were about 50-70mA the first time. Then, on a second measurement after a minute they were 40-60mA. Then, on a third measurement after a minute they were 30-50mA.

All the measurements last 1-3 seconds."


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## evan9162 (Oct 22, 2007)

mailint said:


> "Today I received my first LEDs to play with: a Cree XR-E, a Luxeon Rebel, a SSC Z-power P4, all pre-mounted on a star or PCB.
> 
> I immediately tested them directly connected to 2xAAA lithium Energizer batteries and I was disappointed by the results.
> 
> ...




Sounds like dead/bad batteries to me. AAA cells should not drop that much under that kind of load, ESPECIALLY Lithium AAAs.

Where were you measuring the voltage (cells or at the terminals of the LED)? How were you measuring current? What setting on your DMM for current measurement?

This is almost unheard of behavior for fresh cells. Something is amiss.


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## biwema (Oct 22, 2007)

Camera flashs do use a high voltage which is generated from AA cells usind a driving circuit. I think that the efficiency of such a circuit is not optimal and there is quite a loss. Also it might be dangerous if the device breaks in the water. (Never touch charged flash capacitors in cameras)
For my aplication a bright LED would better be suited.

First I wanted to suggest a Luxeon Rebel for running at 2000mA instead of a CREE due to the high temperature limits of 150°C. But when having a look at those two datasheets it turned out that these LED are very similar. Even some diagrams look like an inedtical copy.

When using 2 AAA cells you wont get the voltage needed without any driving circuit. A Energizer Lihium Cell has a capacity of 1.68Ah at 0.5A (link below). Maybe they can even provide 2.5 A at a reasonable Voltage. Some AA cells can even be discharged at 10A and still have a voltage of more than 1V. When using and appropriate circuit, 2000 mA with 2 AAA cells is possible, but not for a long time.

Have a look at these threads about benchmarking Alkaline (including Energizer Lithium) and NiMH cells (AA and AAA).

Alkaline:
https://www.candlepowerforums.com/threads/64660
NiMH:
https://www.candlepowerforums.com/threads/79302


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## mailint (Oct 22, 2007)

biwema said:


> Have a look at these threads about benchmarking Alkaline (including Energizer Lithium) and NiMH cells (AA and AAA).
> 
> Alkaline:
> https://www.candlepowerforums.com/threads/64660
> ...


 
Very useful. Thanks! I understand that the voltage drop of such configuration allows for such currents/voltages.
Sorry evan9162 and thanks biwema.
A doubt: if I measure 3A out from 3 batteries in series, do I have to refer to the 1A line or to the 3A line in those graphs? still 3A, right?


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## evan9162 (Oct 22, 2007)

The 3A line

I just did a test of my own. Using 2 Eveready Gold alkaline AAAs (pretty generic quality) in a crappy 2AAA battery holder (so plenty of extra resistance).

I measured current with the 10A scale of a DMM. 
I measured the voltage of the batteries at the ends of the 4" leads attached to the battery holder. 

Open circuit (no load) the batteries measured 3.22V
Directly connected to a P4 XR-E, the batteries measured 3.08V, and the XR-E was getting *180ma*.

So, with crappy alkaline AAAs, in a crappy battery holder (introducing extra resistance and extra voltage drop at the point the battery voltage was measured), the battery voltage still didn't drop anywhere near what you reported, at over twice the current level that you reported. 

There's definitely something wrong with your batteries, connections, or both.


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## mailint (Oct 23, 2007)

evan9162 said:


> There's definitely something wrong with your batteries, connections, or both.


 
Consider that they were used batteries...


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## biwema (Oct 23, 2007)

mailint said:


> I immediately tested them directly connected to 2xAAA lithium Energizer batteries and I was disappointed by the results.
> All were of similar brightness, the batteries went down from about 3.260V without load to 2.850V with the LED connected/turned on.
> The currents were about 50-70mA the first time. Then, on a second measurement after a minute they were 40-60mA. Then, on a third measurement after a minute they were 30-50mA.
> All the measurements last 1-3 seconds."


 
In this point I agree with evan9162. Those Lithium cells are bad. With AAA Energizer Lithium you should still have more than 1V after 2 hours at 500mA; at 70mA it should run 18-20hours.

- When you measure 3A at 3 cells in series, every cell has 3A. Their Voltages sum up.

- When you measure 3A in parallel, every cell is discharged at 1A, on average. The trongest one a bit more, the weakest one a bit less. The Voltage equals the voltage of one cell.

Currents are measures in series (with a low internal resistance of the DMM), voltages in parallel (with a high internal resistance of the DMM).

Important:
If you run a LED on 2-3 AAA cells and you measurea high current, there will be a voltage drop ober the Multimeter. Maybe 0.1V to 0.5V depending on the internal resistance. Without the Multimeter in series the voltage over the LED would be higher and the current much larger. £This could destroy the LED. Try using a clamp-on amperemeter which supports DC.


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## mailint (Oct 24, 2007)

biwema said:


> In this point I agree with evan9162. Those Lithium cells are bad. With AAA Energizer Lithium you should still have more than 1V after 2 hours at 500mA; at 70mA it should run 18-20hours.


 
Yes but the problem is that the Vf of the LED at 500mA is much higher than 1V. The Vf of a Cree XR-E at 500mA is 3.4V so I'ld never reach 500mA from 2xAAA batteries except, perhaps, for some seconds...



biwema said:


> - When you measure 3A at 3 cells in series, every cell has 3A. Their Voltages sum up.
> 
> - When you measure 3A in parallel, every cell is discharged at 1A, on average. The trongest one a bit more, the weakest one a bit less. The Voltage equals the voltage of one cell.


 
Ok, got it. Thanks for the confirmation.



biwema said:


> Important:
> If you run a LED on 2-3 AAA cells and you measurea high current, there will be a voltage drop ober the Multimeter. Maybe 0.1V to 0.5V depending on the internal resistance. Without the Multimeter in series the voltage over the LED would be higher and the current much larger. £This could destroy the LED. Try using a clamp-on amperemeter which supports DC.


 
0.1V to 0.5V of error due to internal resistance seems huge to me. Are you sure that the internal resistance can be so much relevant?


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## evan9162 (Oct 24, 2007)

Yes, it can

Many DMMs use an 0.1 ohm current shunt. Add in contact resistance for the leads, and that can be even higher. If you're not using the highest scale on your DMM, you could be introducing even more resistance. If your current meter has a 2A and 10A scale, then the 2A scale probably has an 0.5 ohm current shunt. Or worse, if you're using the 200mA scale, it uses a 1 ohm current shunt. 

You need to measure the voltage drops across all parts of your circuit to see where extra resistance is creeping in. You'd be surprised.


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## mailint (Oct 24, 2007)

evan9162 said:


> You need to measure the voltage drops across all parts of your circuit to see where extra resistance is creeping in. You'd be surprised.


 
Incredible. I never thought it was so significant. I will try with different positions next times... Thanks for the info


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## evan9162 (Oct 24, 2007)

Cheap battery holders are the worst offenders. Then contact resistance with things like alligator clips. 

I was doing some testing last night. The setup was like this:

Power supply -> DMM -> LED+resistor -> Power supply

Each step used alligator clips. Between the connections and wires, I had almost 0.3 ohms of resistance creep in. At one point, the power supply output was 4.5V, while the LED+resistor combo only had 4.2V across it.


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## biwema (Oct 24, 2007)

mailint said:


> Incredible. I never thought it was so significant. I will try with different positions next times... Thanks for the info


 
You can calculate the voltage drop ot the Multimeter that way:

Voltage = Resistance * Current

Example:
Shunt DMM: 0.1 Ohm
Resistance leads of Multimeter: 0.1 Ohm
Connections of Multimeter, LED and Batteries: 0.2 Ohm (maybe even more)
Current: 2A
(0.1 Ohm + 0.1 Ohm + 0.2 Ohm) * 2 A = 0.8 V

At such currents you have a reasonable voltage loss even without multimeter. Try your best to reduce all resistances of the circuit (Clean contacts of the battery, careful soldered connections (instead of alligator clips and thick wires).

If your batteries provide 3.4V, that will not be enough and will drop even more in use.


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