# Overdriving the Cree R2 @ 1400mA??



## Scattergun (Aug 13, 2008)

I am thinking of building a D26-module with a Cree R2. I plan on using the AMC1735 1400mA driver since I want all light possible from this setup. 
However I want to know how this affects the LED, since lifeexpectancy probably goes down a bit. 
I can live with a minimum of 100 hours of use on this one, but is it possible or will the LED just burn??


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## StefanFS (Aug 13, 2008)

Use a brass pill and fill the empty space with something like silicon based thermal glue (eg. Fujik from DX and others). I'm running 1.25-1.3A in my Derelight DBS without any problems. It might reduce the leds life some, or not.


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## Scattergun (Aug 13, 2008)

I´ll try that and report back... will probably use either the thermal gooey stuff from DX or some AA..... I´ll start with a R2-module from DX, so the pill is brass from start... 
What does the specs say about output from a Cree R2 @ 1400mA?


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## Der Wichtel (Aug 13, 2008)

isn't aluminium a better thermal conductor than brass?


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## SUBjohan (Aug 13, 2008)

Der Wichtel said:


> isn't aluminium a better thermal conductor than brass?



Yup, it is http://en.wikipedia.org/wiki/List_of_thermal_conductivities

Greetz Johan


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## StefanFS (Aug 13, 2008)

Yes, it is. But brass is denser and heavier and that seem to work better for me in the small dropin pills, the brass pills also have thicker construction than the corresponding alu ones I have used. But in theory alu should be better..
Stefan


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## SUBjohan (Aug 13, 2008)

StefanFS said:


> Yes, it is. But brass is denser and heavier and that seem to work better for me in the small dropin pills, the brass pills also have thicker construction than the corresponding alu ones I have used. But in theory alu should be better..
> Stefan



How about copper than, is also heavy and dense but with better thermal properties than alu.

Johan


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## StefanFS (Aug 13, 2008)

SUBjohan said:


> How about copper than, is also heavy and dense but with better thermal properties than alu.
> 
> Johan


 
Copper would be better, but then you run the risk of galvanic corrosion between the copper and alu if an electrolyte or acid water or whatever comes into the light. Inside a light that's not likely, but I think manufacturers want to be safe rather than sorry. There are also a LOT of different brass alloys available, some with up to 85% copper in them so it's not an easy topic.

As an example the MRV has a massive heatsink made from brass. Compared with the Tiablo A8/A9 that has aluminium heatsinks of about the same volume, the MRV is more effective at keeping an SSC P7 cool and has slightly longer runtimes in identical setups, the MRV design seem to simply be more efficient when it comes to lead heat away. It's also heavier because of the brass..


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## taschenlampe (Aug 13, 2008)

Scattergun said:


> ... What does the specs say about output from a Cree R2 @ 1400mA?


 

335 lumen


tl


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## Nos (Aug 13, 2008)

ive been running my aspheric mag with a dhs heatsink and a AMC1735 1400mA driver for a while now.....without any problems  just....the two 3V rcr123 "fireing the driver become ugly hot.........and after 5 min the thermal protection kicks in :duh2: ....drivin beyond specs :shrug: 

but what can i use instead? with 18650 the driver doesnt regulate to 1,4A.......
only if i feed it with more than 5V :thumbsdow


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## Der Wichtel (Aug 13, 2008)

Yes the current is only limited by the die temperature and the bond wires.

So if you can keep the led cool enough, then you can pump as much current as you wish through the led until the bond wires can't hold the current.


PS @ NOS: Na, auch bei Ledstyles unterwegs :thumbsup:


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## Scattergun (Sep 26, 2008)

I have a similar setup going now with a SSC P4... I know the SSC is not as good as the Cree when it comes to heatsinking, but has anyone tried using it at 1400mA??


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## Data (Sep 27, 2008)

Scattergun said:


> I have a similar setup going now with a SSC P4... I know the SSC is not as good as the Cree when it comes to heatsinking, but has anyone tried using it at 1400mA??



Sure, I run 70 XR-E's at 1800mA plus in the DB70. It has a few hours on it and still going strong. Has it lost max lumen output since being run at that power, I bet it has, but how much, I don't know.

Cheers
Dave


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## wechnivag (Sep 27, 2008)

SUBjohan said:


> Yup, it is http://en.wikipedia.org/wiki/List_of_thermal_conductivities
> 
> Greetz Johan



Not to be cheeky, but diamond has awesome thermal conductivity, just sucks the heat away...


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## CampingLED (Sep 27, 2008)

wechnivag said:


> Not to be cheeky, but diamond has awesome thermal conductivity, just sucks the heat away...


 
Wonder why my wife thinks that the 10 carrat diamond on order is for her. :lolsign:



taschenlampe said:


> 335 lumen


 
Two driven @ 700mA each = 1400mA = 421 lumen


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## CM (Sep 27, 2008)

The lumen figures you guys are throwing around is with the LED die temp at 25C. I guarantee you that you'll be far from that when you drive the sucker at 1.4A, especially with a setup like a drop-in where you get very little heat transfer. I bet you will not see any increase in output driving at 1.4A since the heat generated will diminish the light output so much that it will probably be no brighter than driving it at 1A.

I'm sure to get flack for this but Surefire has done the right thing driving their drop in moderately. I think even 1000mA is on the verge of too much.


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## saabluster (Sep 27, 2008)

CM said:


> The lumen figures you guys are throwing around is with the LED die temp at 25C. I guarantee you that you'll be far from that when you drive the sucker at 1.4A, especially with a setup like a drop-in where you get very little heat transfer. I bet you will not see any increase in output driving at 1.4A since the heat generated will diminish the light output so much that it will probably be no brighter than driving it at 1A.
> 
> I'm sure to get flack for this but Surefire has done the right thing driving their drop in moderately. I think even 1000mA is on the verge of too much.


And I'll probably get flack for this but Surefire has done the wrong thing in even using those drop-ins for LEDs. Like you say their heat transfer ability is less than optimal. I know people like to be able to easily switch them out but there is a much better solution. It is not a big deal with incans where the heat goes out the front of the light but LEDs are a different animal and need a different solution.


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## CM (Sep 27, 2008)

saabluster said:


> And I'll probably get flack for this but Surefire has done the wrong thing in even using those drop-ins for LEDs. Like you say their heat transfer ability is less than optimal. I know people like to be able to easily switch them out but there is a much better solution. It is not a big deal with incans where the heat goes out the front of the light but LEDs are a different animal and need a different solution.



LOL, I wasn't going to go to such extreme but I hear you. At least Surefire drop-ins seem to behave like they have thermal protection since they drop back to a lower (regulated) level in plastic lights like the G2's. You can greatly enhance the heat transfer of the cheap modules by using foil. I do this with the ones driven to 1A. 

Now to all that want to drive the ****ens out of these drop ins, listen up. I modified one of the cheap R2 drop-ins from 1A to 465mA. The output was much flatter and runtime went to 2 hours 45 minutes compared to one driven at 1A. The 1A one had nice output the first few seconds (about 2x brighter) after which it dropped off big time and settled to about 1.35 times that of the one biased at 465mA after a few minutes of cooking itself. My guess is that you'll get similar results when driving it at 1.4A since the driver is even less efficient and you'll heat up much faster, driving the output lower faster. Using foil helps a lot but you still won't improve efficiency and you'll just delay the drop off in output.


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## Scattergun (Sep 28, 2008)

The SSC P4 I plan on driving at 1,4A is going to be mounted to a H22A heatsink... will this do any difference? And will three Alkaline D-cells be able to sustain a regulated 1,4A to the LED through a 7135-circuit?


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## TigerhawkT3 (Sep 28, 2008)

I gave a light to a friend that runs an SSC P4 at 1.2A on max, and he hasn't reported any problems yet. It's on one of H22A's DHS heatsinks in a D Mag. It's not quite 1.4A, but pretty close.

The alks might be able to do that, but I'm not confident of that. If you want, you could try an unregulated light with three D NiMHs. And heck, if you're doing that, you might as well use a P7 instead of a P4 and get about four times the output. However, the P7 will then want a glass of milk...


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## kurni (Sep 28, 2008)

Scattergun said:


> The SSC P4 I plan on driving at 1,4A is going to be mounted to a H22A heatsink... will this do any difference? And will three Alkaline D-cells be able to sustain a regulated 1,4A to the LED through a 7135-circuit?



3 D Alks won't cut it.

1.4A LED current means at least 1.5A input.

Alks voltage will drop under such current, and the driver will try to suck more current resulting further voltage sag.

Another Alks drawback is capacity drop when discharged at high current.

See Energizer datasheet.

You better use D or even AA NiMH.


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## saabluster (Sep 28, 2008)

kurni said:


> You better use D or even AA NiMH.


energizer e2/ultimate lithium AAs will work for this as well.


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## Scattergun (Sep 28, 2008)

Would it be better to run three Eneloop AA´s in D-A-converters instead of the three Alk D´s??? And what would runtime be in that case?


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## kurni (Sep 28, 2008)

Scattergun said:


> Would it be better to run three Eneloop AA´s in D-A-converters instead of the three Alk D´s??? And what would runtime be in that case?



The benefit of NiMH including Eneloop is its ability to _*raesonably*_ sustain high current discharge; Alk D is not designed for high current discharge. Notice in the datasheet Energizer only tested Alk D at 500mA in comparison to 4000mA NiMH AA or 1000mA Lithium E2 AA.


3 Alk D capacity would be unpredictably low, note that at 25mA it holds 21,000mAh but at 500mA it holds only 11,000mAh; I have no idea how much it holds at higher current but I don't like the trend.
I have 6D [email protected] with BuckPuck pushing 1A through Q5; with 6 Alk D I see 500mA * 9V = 4.5W, 5 Alk D I see 600mA * 7.5V = 4.5W, 4 Alk D I see 800mA * 6V = 4.8W (BuckPuck efficiency went down), I can't test with fewer cells because BuckPuck minimum input is 5V.

2000mAh NiMH will give you at least 1 hour in practical use; the datasheet infers 1.5 hour runtime but notice the voltage sag; your circuit will draw more than 1500mA as the voltage drops (just like my BuckPuck setup).

I just did a _*naughty*_ test, a fresh Alk D could actually push almost 9A, yes 9000mA  Not so fresh Alk D could only push 2A. I wouldn't dare to do this with LiIon fearing explosion but Alk is safe  I have no idea what the voltage was because I only have 1 DMM, theoretically it's near-zero volt because the DMM would have little resistance.

So in theory 3 Alk D should be able to sustain 1500mA draw but nobody know what sort of capacity it would have; note that at the capacity is halved when you increase the discharge from 25mA to 500mA; I can't imagine 1500mA because it's too far from the specification.

To get the most of your 3 D [email protected] body, I suggest you use 3 NiMH D, or 9 Eneloop paralel holder (3 * 3)


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## Bullzeyebill (Sep 28, 2008)

kurni said:


> The benefit of NiMH including Eneloop is its ability to _*raesonably*_ sustain high current discharge; Alk D is not designed for high current discharge. Notice in the datasheet Energizer only tested Alk D at 500mA in comparison to 4000mA NiMH AA or 1000mA Lithium E2 AA.
> 
> 
> 3 Alk D capacity would be unpredictably low, note that at 25mA it holds 21,000mAh but at 500mA it holds only 11,000mAh; I have no idea how much it holds at higher current but I don't like the trend.
> ...



Check out SilverFox's Alkaline shoot out. Scroll down to D cells. https://www.candlepowerforums.com/threads/64660

Bill


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## kurni (Sep 28, 2008)

Bullzeyebill said:


> Check out SilverFox's Alkaline shoot out. Scroll down to D cells. https://www.candlepowerforums.com/threads/64660
> 
> Bill



Thanks Bill, I missed the good-old thread  Very informative.


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## TigerhawkT3 (Sep 28, 2008)

AFAIK, the AMC7135 and other LDOs and linear regulators have Iin=Iout. The energy loss comes from reducing the Vin down to Vout without reducing Iin below Iout (which is what a buck converter would do). So, a Vin of Vf+Vdropout+Vdrop, with Vf being the LED's Vf at whatever current you chose, Vdropout being the regulator's minimum voltage drop (which is very small for LDOs like the 7135), and Vdrop being any additional dropped voltage, would waste (Vdropout+Vdrop)*I watts for an efficiency of Vf/Vin. As Vin falls due to sagging battery voltage, Vdrop will decrease, resulting in a more efficient regulator but, of course, reduced cell capacity. If Vin falls below Vf+Vdropout, the light will basically DD with as much voltage as it can muster, with Vout (no longer a fixed value, but determining the emitter's Vf, and therefore its If, as well as Iin from the battery) being equal to Vin-Vdropout. At that point, efficiency would be Vout/Vin or, equivalently, (Vin-Vdropout)/Vin.

This is AFAIK and I could be wrong, but I hope not.


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## kurni (Sep 28, 2008)

TigerhawkT3 said:


> AFAIK, the AMC7135 and other LDOs and linear regulators have Iin=Iout. The energy loss comes from reducing the Vin down to Vout without reducing Iin below Iout (which is what a buck converter would do). So, a Vin of Vf+Vdropout+Vdrop, with Vf being the LED's Vf at whatever current you chose, Vdropout being the regulator's minimum voltage drop (which is very small for LDOs like the 7135), and Vdrop being any additional dropped voltage, would waste (Vdropout+Vdrop)*I watts for an efficiency of Vf/Vin. As Vin falls due to sagging battery voltage, Vdrop will decrease, resulting in a more efficient regulator but, of course, reduced cell capacity. If Vin falls below Vf+Vdropout, the light will basically DD with as much voltage as it can muster, with Vout (no longer a fixed value, but determining the emitter's Vf, and therefore its If, as well as Iin from the battery) being equal to Vin-Vdropout. At that point, efficiency would be Vout/Vin or, equivalently, (Vin-Vdropout)/Vin.
> 
> This is AFAIK and I could be wrong, but I hope not.



Hmm, you might be right; I've never understood what "linear" regulator means.

Any regulator will cause power loss; hence Pin > Pout; I won't be wrong about this 

P = V * I; this must be correct also 

Do you mean that "linear" regulator simply "chops off" excess voltage to maintain constant I?

nFlex and bFlex are not "linear", are they? You can feed 20V to power 4V LED without having to heatsink nFlex and bFlex; if it's "linear" then 16V * 1A = 16W has to be converted to heat, which has to be released through a massive heatsink.


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## TigerhawkT3 (Sep 29, 2008)

Yep, that's right.

If a circuit is "buck" or "boost" (or both) then it's not linear. For an explanation of buck and boost, see the Electronics/Electrical section of the Welcome Mat.

Was my explanation of linear regulators clear and accurate? If it was, I might add it to the Welcome Mat.


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## kosPap (Sep 29, 2008)

Scattergun said:


> I am thinking of building a D26-module with a Cree R2. I plan on using the AMC1735 1400mA driver since I want all light possible from this setup.


 
hmmm shouldn't we also discussing proper module-body contact? one cannot 100% expect proper fit so heat dissipation-transfer should be a better problem that heat-sinking of the board-LED.

I recall a member using tight wound aluminum foil between module and body and he got much better heat tranfer.

till latter, kostas


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## Scattergun (Sep 29, 2008)

From post #18 in this thread


> You can greatly enhance the heat transfer of the cheap modules by using foil.


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## Drewfus2101 (Sep 29, 2008)

I have done a test or two on a P4 where I ran it at 700mA and 1050mA (through AMC driver) and I got a higher value in my light box with the 700mA one. This was after they warmed up a little. I imagine the problem was the heat of the 1050mA one. So more current isn't _always_ better.


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## FLT MEDIC (Feb 4, 2009)

kosPap said:


> hmmm shouldn't we also discussing proper module-body contact? one cannot 100% expect proper fit so heat dissipation-transfer should be a better problem that heat-sinking of the board-LED.
> 
> I recall a member using tight wound aluminum foil between module and body and he got much better heat tranfer.
> 
> till latter, kostas


 
We use aluminum foil tape for roofs sometimes called roof flashing tape (Sello brand from New Zealand). It's as wide as duct tape but made of aluminum. Just cut to about 7 inches and about the same width as the flat portion of the R2 drop in reflector. Peel off tape backing and stick aluminum foil around the reflector until it's snug inside the flashlight. 

It really transfers a lot of heat from the drop in reflector to my C1's bezel, right up to the tailcap switch! :twothumbs


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