?'s about DD, .5 ohm resistor, and 1 ohm resistor?

4x4Dragon

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?\'s about DD, .5 ohm resistor, and 1 ohm resistor?

Now i know it may vary depending on the bin of the luxeon, but how much difference will each make compared to one another in terms of brightness and runtime? Im curious because Im wanting a 3D Maglite LuxIII mod(done by someone else) and would like it tweaked to my likings. Im basically wanting something with say.........?????? around 7,000-8,000 lux AT LEAST and AT LEAST a solid 8 hours of lights, and I would want to stick with Alkaline batteries. also looking at using a sputtered reflector and UCL.(if that matters) Im shying away from DD as I just got the Blaster 3P and would really prefer a resistored light for some "super" runtime on a light with a nice beam.(one with a good hotspot and decent corona/spill)

any help would be appreciated.
 

evan9162

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Re: ?\'s about DD, .5 ohm resistor, and 1 ohm resistor?

it really depends on the Vf of the particular luxeon you get, but 1 ohm should give around 700mA on fresh batteries (diminishing somewhat linearly to about 200mA after 14 hours, down to about 100mA at 24 hours). 0.5 ohms will start you around 1-1.2 amps, diminishing even faster.
 

4x4Dragon

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Re: ?\'s about DD, .5 ohm resistor, and 1 ohm resistor?

[ QUOTE ]
evan9162 said:
it really depends on the Vf of the particular luxeon you get, but 1 ohm should give around 700mA on fresh batteries (diminishing somewhat linearly to about 200mA after 14 hours, down to about 100mA at 24 hours). 0.5 ohms will start you around 1-1.2 amps, diminishing even faster.

[/ QUOTE ]

weren't the the Blaster III's being run with 1 ohm resistance and seeing around 900 ma?
 

evan9162

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Re: ?\'s about DD, .5 ohm resistor, and 1 ohm resistor?

perhaps - it totally depends on the Vf of the particular luxeon, which varies on an individual basis.
 

4x4Dragon

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Re: ?\'s about DD, .5 ohm resistor, and 1 ohm resistor?

[ QUOTE ]
evan9162 said:
perhaps - it totally depends on the Vf of the particular luxeon, which varies on an individual basis.

[/ QUOTE ]

yeah i understand it varies, but i what about for comparative purposes only, for example: take 3 Maglite 3D LuxIII mods all with the same Vf, (1) with no resistance/DD, (1) with .5 ohm resistor, and (1) with a 1 ohm resistor. i wonder what the lux difference would be as well as runtime difference.

i guess i liked the ol' claim made by Wayne J. about the Blaster III having 24 hrs of bright light, and from what i remember it had a 1 ohm resistor??? (900 ma ?)
 

evan9162

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Re: ?\'s about DD, .5 ohm resistor, and 1 ohm resistor?

Allright, let's take your 3 examples and give assign current values for them (with fresh alkalines)

DD - 1.8A
0.5 ohms - 1.2A
1 ohm - 800mA

due to the diminishing returns you get when pumping extra current through an LED, the 0.5 ohm light will give you maybe 20% more light for the 50% greater current. The DD light may only give about 10% more light for the 50% greater current than the 0.5 ohm light. In the end, you may get 30-40% more light from the DD than the 1 ohm light.

So that's the perspective on just what's coming out the front of the light - we have 2 more things to consider - what these various drive levels are doing to the batteries, and what they are doing to the luxeon due to heat.

First, drawing 1.8A from alkaline D cells is going to kill them off quick! I would say that you'll kill them down to a dim level in only a few hours. Of course, the current is decreasing from the get-go, as an alkaline's voltage is relatively proportional to their life, spread out from 1.5-0.8V.

I would say that doubling the current draw will cut battery life to less than half, because alkalines don't like high discharge current at all. I said the 1 ohm light would give acceptable light level till about 14 hours - so the 0.5 ohm light would give the same to about 6 hours, and the DD light, the same to about 3-4 hours.


Finally, theres the issue as to what you're doing to the LED with those drive current levels. If we assume the Vf of the LED is 3.6V at 800mA, 3.8V at 1.2A, and 4V at 1.8A, then the power being dissipated by the luxeon in those three lights is 2.88W, 4.56W, and 7.2W respectively.

The juntion-slug thermal resistance of an L3 is 13C/W. Assume 1-2C/W slug-heat sink resistance, and the J-HS thermal resistance is 15C/W. Let's assume that for the first few seconds, the heat sink doesn't heat up at all, so we can use the heat sink as a 25C reference. So the junction temperature is calculated as 25+15(P), so we have junction temps of 68C, 94C, and 133C. The maximum junction temperature allowed for an L3 is 135C. Also, LED life decreases exponentially with increased temperature, so the combination of excessive current and excessive heat will cause the Luxeon on the DD version to have a relatively short lived life before it begins to dim.

If the heat sink heats up to 40C in the flashlight body (rather warm), then this is a 15C increase over the previous temperatures, so the junction temps are now at 83C, 109C, and 148C. The junction temperature of the DD version has greatly exceeded specifications, and will have a very short LED life, and also may be dimming quite a bit due to temperature. The 0.5 ohm version is also getting pretty hot, but is still within maximum specifications, however, it will also experience a much shorter LED lifetime than the 1 ohm version.


My take would be to go with the 1 ohm version. You likely won't notice the initial brightness difference between it and the other two configurations, but the light will run cooler, longer off a set of batteries, and the LED will have greater longevity.
 

IsaacHayes

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Re: ?\'s about DD, .5 ohm resistor, and 1 ohm resistor?

I'm DD'ing a SW0K off of 3C's and I find it started at 1.5, and dropped to 1.2amps within 15secs. It stabalized there for a while and slowly droped. I ran it for a good ~2hours on the 4th, and it's still just as bright to my eyes. At least it still has the same useable throw as it did before. It may not light up a few less feet of distance, but it throws so far that I can't make out the details unless I use binoculars (does anyone do that here at night?). Right now it's running at 800ma.

So mine doesn't ramp up the current too bad (1.2amps is what it sees mainly for a decent amount of time, perhaps 20-30mins around there on fresh batts). So 200ma over max spec I'm not too worried as it only see's that for a short while. If you had a J Vf, I would put at least .5 ohms.

Mine would probably perform just as good in actual use with .5ohms and get a little longer battery life, but I've already assembled it. I don't use NiMH in it, which would more than likely cause a problem (too much current)
 

4x4Dragon

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Re: ?\'s about DD, .5 ohm resistor, and 1 ohm resistor?

/ubbthreads/images/graemlins/ooo.gifthank you sir! /ubbthreads/images/graemlins/thumbsup.gif /ubbthreads/images/graemlins/bowdown.gif thank you for taking the time to explain all of that.
 

4x4Dragon

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Re: ?\'s about DD, .5 ohm resistor, and 1 ohm resistor?

[ QUOTE ]
lambda said:
One other option you might want to look at ProMagnum 700

[/ QUOTE ]

okay, that is nice! wouldn't mind another 1000 lux or so with a couple hrs less runtime, but i ain't complainin' /ubbthreads/images/graemlins/grin.gif

so with regular alkaline D cells would the still be pretty flat?
 

3rd_shift

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Re: ?\'s about DD, .5 ohm resistor, and 1 ohm resistor?

The only way I can think of to maintain "showroom brightness" with a 1000 milliamp led for 8 hours would be to run it with 8500 mah rated or higher d cell batteries. /ubbthreads/images/graemlins/thumbsup.gif
As a security guard working in some of the creepiest parts of town at night, I have to have full performance from my light for the whole shift whether I'm armed or not. /ubbthreads/images/graemlins/eek.gif
When the nimh batteries start to run down, I then change to a waiting, fully charged set of batteries for the remainder of my shift. /ubbthreads/images/graemlins/smile.gif
Once you have the 8500+ mah rated d cells and smart charger, you only need to fine tailor the added resistance to the led to bring it to about 1100 ma starting, and then it should settle down quickly to about 800 ma to 1000ma, or thereabouts for the remaining 8-10 hours of discharge.
If you would like a slightly higher starting amperage, I have had both my ledlenser v2 powerchip "1watt" lights survive up to 1600 milliamps going through with www.battlepack.com nimh n cells! /ubbthreads/images/graemlins/ooo.gif
Good luck. /ubbthreads/images/graemlins/smile.gif
www.batterystation.com www.batterymart.com and www.amondotech.com are but a few who can help you get started on obtaining your stable, rechargeable power sources.
This and this may help you out too with figuring out your resistances.
 
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