# LEDS with no driver???



## MTBDaza (Apr 21, 2009)

Hi there, I am a newbie to this site (1st post wahoo!) so bare with me.

I have a Cree XR-E R2 running directly off 3 AA, NiMh, 2600mAh batteries.

Questions:


How many watts is the LED?
What does the tint options mean (WH, WC, WD, WF)?
How long should this LED on these batteries last for?
What are the down falls of running it directly (no driver)?
If driver required what do you recommend?
Cheers in advance
Daza


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## znomit (Apr 21, 2009)

:welcome:


MTBDaza said:


> I have a Cree XR-E R2 running directly off 3 AA, NiMh, 2600mAh batteries.



How many watts is the LED?
3W
What does the tint options mean (WH, WC, WD, WF)?
Different white LEDs have slightly different colours.
How long should this LED on these batteries last for?
Depends on the current draw, and battery. Probably 2-3 hrs. 
What are the down falls of running it directly (no driver)?
No control over brightness, brightness dims as batteries run down.
If driver required what do you recommend?
Depends on your light requirements, your battery and your wallet.


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## LukeA (Apr 21, 2009)

MTBDaza said:


> What are the down falls of running it directly (no driver)?
> ...
> 
> If driver required what do you recommend?



You don't have control over the current. With your current configuration, you're giving too much current to the LED with fresh cells.

The driver depends on the drive current, but a driver based on the AMC7135 chip will serve this application well.


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## MikeRD03 (Apr 22, 2009)

Hi Daza,

One Cree XR-E performs quite well on 3 x AA Batteries or Accu without driver (direct drive) The inner battery restistance will keep the current in accaptable range within the first minutes. After that three AA cells will not bother any 3W LED.

But you will get very different buning times and lightoutput between batteries and NiMH accu. Since I do testing on diving lamps I have one for you for comparison between battery and accu. The lamp here (Tillytec W30 diving backup light) is a 3W XR-E LED direct driven on three AA-cells without electornic or restistor:











Hope that will illustrate the huge diffence between accu and battery without regulator electronic. Note the timeline!
Sorry text in the picture is german.

greets,
MikeRD03


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## Gunner12 (Apr 22, 2009)

1. Depends on how much the LED is drawing from the batteres at what voltage. With your setup, anywhere from 3 watt to 5 watt is a good guess.
2. the "color" of the LED, look at the charts here.
3. Depends on the current, and also what output you think the runtime should end.
4. No control over the current, which leads to no control over output and runtime.
5. How much money, output, and runtime do you want?

:welcome:


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## MTBDaza (Apr 23, 2009)

Hi MikeRD03,

Thank you for your reply. Forgive my ignorance, but what is accu? And also is the runtime in hours? And finally can you please translate the description of the red, orange and white line?

Cheers
Darin


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## MTBDaza (Apr 23, 2009)

Cheers for the reply,

The current draw when first hooked up is about 0.8A.

Cheers
Darin


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## MTBDaza (Apr 23, 2009)

Hi Gunner12,

I basically am wanting to get the maximum light I can out o the Cree X-RE R2 for about 2 - 2&1/2 hrs. I want to run it off 3 x 2600 NiMh batteries.

Should I use a driver to achieve this?

Just so I am sure I understand (and to strip it down ever so slightly):thinking:; if I run it directly I will have a very bright light (say 10 on a scale of 1-10) and then it will fall consistantly in brightness output over 2 hours ending up with about a 2 or 3. However, if I run it with a driver I will get say a 7 or 8 on the brightness scale for the whole 2 hours and then it will die.

Am I roughly on the right track?

Cheers again for your posts, I appreciate you helping out a newbie.
Daza


_


Gunner12 said:



1. Depends on how much the LED is drawing from the batteres at what voltage. With your setup, anywhere from 3 watt to 5 watt is a good guess.

Click to expand...

_


Gunner12 said:


> _2. the "color" of the LED, look at the __charts here__._
> _3. Depends on the current, and also what output you think the runtime should end._
> _4. No control over the current, which leads to no control over output and runtime._
> _5. How much money, output, and runtime do you want?_
> ...


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## MTBDaza (Apr 23, 2009)

znomit said:


> _What does the tint options mean (WH, WC, WD, WF)?_
> _Different white LEDs have slightly different colours._





Which of these 4 tints is the brightest? Or best for mountainbiking? I have had a look at the link to the chart below, but it doesn't help answer my question.

Cheers
Daza


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## Egsise (Apr 23, 2009)

MTBDaza said:


> Just so I am sure I understand (and to strip it down ever so slightly):thinking:; if I run it directly I will have a very bright light (say 10 on a scale of 1-10) and then it will fall consistantly in brightness output over 2 hours ending up with about a 2 or 3. However, if I run it with a driver I will get say a 7 or 8 on the brightness scale for the whole 2 hours and then it will die.
> 
> Am I roughly on the right track?



With driver you get what you want, 10 for the whole time if you want.
It all depends on the driver you use.


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## MikeRD03 (Apr 24, 2009)

Hi Darin,



MTBDaza said:


> Thank you for your reply. Forgive my ignorance, but what is accu? And also is the runtime in hours? And finally can you please translate the description of the red, orange and white line?



No problem - here we go:

Red bar ist the Main Burn Time (hours), that means 100-80% lightoutput
Orange bar ist the use burn time (hours), that means 100-20% lightoutput
And white is the whole time where light comes out of the lamp.

Others:
"Helligkeit" = brightness in lux
"Brennzeit" = Burntime in hours
"Maximale Helligkeit" = maximum brightness
"elektronisch geregelt" = electronic regulated

and "Akku" is quite the same word in english -> accu, here three NiMH 1,2V accus AA-cells with 2500mAh.
Hope this helps,

In my opinion the "no-driver" solution is the best with three AA cells cause with driver the burntime is much smaller even the light is a bit brighter running on accus, but the eye will hardly see the differnce. A driver is only usefull with three C-cells and then only on NiMH accus! With batteries AND driver there is also no regulation quite after a short period of time (minutes), cause batteries (even the best) can not stand the current flow of a 3,5W LED!

cheers,
MikeRD03


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## MTBDaza (Apr 24, 2009)

_


[/I said:



With batteries AND driver there is also no regulation quite after a short period of time (minutes), cause batteries (even the best) can not stand the current flow of a 3,5W LED!

Click to expand...




Thanks for reply, sorry I do not understand the above comment. Can you please clarify.:thinking:_


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## MikeRD03 (Apr 24, 2009)

Hi,

This meens, even if u have a driver inside the lamp with three c-cells it would have nearly no effect since the batteries comes down with its voltage very fast (minutes) and the driver shuts down its regulation.
At the end you have a similar brighness curve like WITHOUT driver but less burntime since a driver eats up 20-10% energy.
With other word - with batteries on high output (1000mA) at the LED a driver is quite USELESS in my opinion.

cheers,
MikeRD03


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## MTBDaza (Apr 24, 2009)

Cheers,

So in your opinion it is best that I run it directly off the 3 AA NiMh batts (no driver). And this has no ill effect on the LED or the AA NiMh batts?


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## MikeRD03 (Apr 24, 2009)

Yep, that´s correct


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## yellow (Apr 24, 2009)

yes and no 
(I am no direct drive-guy)

You have to make sure, that there is not too much current passing the led. If the direct drive pushes more than 1 A through the led (initial 1 A might be possible when heatsinking is good), You have to add something to get current down for the few mins, as long as the batteries can give this power (making starting brightness even lower).




> Just so I am sure I understand (and to strip it down ever so slightly):thinking:; if I run it directly I will have a very bright light (say 10 on a scale of 1-10) and then it will fall consistantly in brightness output over 2 hours ending up with about a 2 or 3. However, if I run it with a driver I will get say a 7 or 8 on the brightness scale for the whole 2 hours and then it will die.


*nope!*

With *direct drive *You start with a 10, reducing to 7 within the 1st 10-20 mins, then steady reduction (which decreases over time) for still giving the led a glow after XX hours. Just look at Mikes 1st graph (the one with the primary cells)

With a good *regulation* You start with 10 and stay with 10 (possibly get down to a 9-9.5) - for the time the cells/driver can keep the regulation.
(Your example, in theory: 3 AAs --> 3 hours 15-30 mins, then off)

and this is NOT Mikes 2nd graph, because there it is the same, unregulated direct drive light. He just used rechargeables 
(and I wonder on the relatively flat cuve. At least there is the direct drive initial reduction) 



Problem: Your number of cells.
Can You change to 4 AAs and buck driver? 
Or to 2 AA and boost?
or even get something like a Fenix L2D/LD20 or something? In the end You are cheaper off purchasing better quality light than building one - give or take.

PS: brightness is measured, so the same _bin_ is the same brightness. 
The _tint_ is how it feels. The more blue, the brighter but also the more awkward. I like WD best.
With the thread Gunner posted, 1st post, chart for the XR-E (Cree X-Lamp): 
in the middle - total white (WC, WD), around that the other possibilites:
white with a tend to blue, purple, yellow, green


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## Egsise (Apr 24, 2009)

MikeRD03 said:


> In my opinion the "no-driver" solution is the best with three AA cells cause with driver the burntime is much smaller even the light is a bit brighter running on accus, but the eye will hardly see the differnce. A driver is only usefull with three C-cells and then only on NiMH accus! With batteries AND driver there is also no regulation quite after a short period of time (minutes), cause batteries (even the best) can not stand the current flow of a 3,5W LED!
> 
> cheers,
> MikeRD03



Accu, akku, accumulator(?) = rechargeable battery

*Professional flashlights use drivers* and rechargeable batteries, not direct drive the led with 3xAAA or 3xAA batteries. 

*If you mus*t use direct drive, take a look of Led Lenser P7 and P14, they use resistors instead of drivers, and they are powered by *4xAAA* and *4xAA* alkaline(manufacturer does not recommend rechargeable batteries).

With rechargeable batteries and without driver the led is overdriven, causing overheating.



> _With batteries AND driver there is also no regulation quite after a short period of time (minutes), cause batteries (even the best) can not stand the current flow of a 3,5W LED!_



*Alkaline* batterys, *ALKALINE. (Direct drive or not)*


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## MTBDaza (Apr 25, 2009)

yellow said:


> Problem: Your number of cells.
> Can You change to 4 AAs and buck driver?
> Or to 2 AA and boost?


 
Hi Yellow, cheers for reply - I am starting to get the picture - thanks for your patience.

I can go to 4 AAs (and it makes sense why). Can you recommend an appropriate buck driver? As I am in New Zealand, getting stuff posted here from abroad can be a problem. I currently source my bits from Cutter Electronics (Australia). Heres the link to their available drivers http://www.cutter.com.au/categories.php?cat=27
If you have the time to have a quick look and make a suggestion I would greatly apreciate it.

Thanks again
Daza


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## MikeRD03 (Apr 25, 2009)

hi yellow,

The inital question was how to drive a led with 3 AA cells. If u can use 4 cells a driver is a must have - certainly. A resitor solution with 4 cells will definilty lead into at lest one deep discharged rechargable cell!

And yes, with accu I mean a NiMH rechargable, sorry german expression.

You wounder about the flat graph when running on NiMH rechargables? Well I have tons of this graphs here from different lamps and it it absolutly normal with this cell type. It is a normal discharge curve. They hold up their voltage of 1,2V quite about 80% of their capacity and this is the reason why a driver with rechargables nearly has no advantage in comparision to direct drive - you will hardly see it. And never mind about the first minutes where a LED get up to 1,2A. All LED will take this without any damage so no reason not to do it and the internal resistance of a AA cell will limit the current without trashing the LED.

On the other hand you will have much less burntime with a driver circuit AND you do not have such a long emerengy burntime with low lightoutput. And this is a very import thing when u are a diver and perhaps your life pepends on your light. 

greets
MikeRD03


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## carbine15 (Apr 25, 2009)

Scale is important visually too.


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## Egsise (Apr 25, 2009)

MikeRD03 said:


> hi yellow,
> 
> The inital question was how to drive a led with 3 AA cells. If u can use 4 cells a driver is a must have - certainly. A resitor solution with 4 cells will definilty lead into at lest one deep discharged rechargable cell!
> 
> ...



First i corrected one "truth" from your post, then second, third... after that i wiped everything and i'm just going to say wrong wrong wrong fail doublefail faaaiiiil.


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