NEEDED: Resistors. 5Watt or higher.

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jtice

jtice

Flashaholic
Joined
May 21, 2003
Messages
6,331
City & State/Province
West Virginia
I am just about done with my LuxIII TWAK 3x123 2C maglight.
But I need some resistors for it first.

I went to my local Radio Shack, but the only ones they had above 5W were HUGE.

I need about 5 Ohms at 5 Watts.

Does anyone have any resistors close to this?
Or know a place I can order some from?

Thanks alot. I am dieing to get this thing working.
 
I don't understand why you need a 5W resistor. You should recheck your calculations on the power you need to dissapate in the resistor.
For source, Digikey or Mouser will have anything you could possibly need.
 
Doug S,
I am posting this question in this thread because I believe jtice will also be interested...

I recently added a Luxeon III (bin SVOK) to one of Elektrolumen's Blaster Jr.'s. Since I didn't notice a significant increase in light, I then removed the resistor, making it direct-drive. This achieved a very noticeable and significant increase in brightness. Of course, being a flashoholic, I had to convert the original 3-to-D power source to a 2 X 123 as soon as I read Elektrolumen's "Blaster Jr. On Steroids" description. The amount of light produced at this point was absolutely AWESOME!

Up until now, I have only run this light for brief periods of time (probably a minute, or less), and the LED has been giving a very bright and white color (no visible trace of the "angry blue"). Being worried that I might be overstressing the Luxoen III, I then added a 2.7 ohm resistor to the circuit. The 2.7 ohms, however, just took too much away from the brightness I was getting from the direct-drive. I then found a 1 ohm resistor that I had liberated from a previous Blaster II (there were two of these connected in series). After substituting the 1 ohm for the 2.7 ohm, I am very happy with the light output. It is very, very close to what I get with direct-drive.

Having said all this, can anyone attempt to speculate what the ma's might be? In brief, if I continue to run this light this way, should I go ahead and prepare an envelope for DougS (to send a dead Lux to)? Or might this Luxeon be spared a sudden and early demise? With the outstanding heatsinking of the Blaster series, is only 1 ohm resistance enough?

Thanks for any responses.
 
[ QUOTE ]
bucken said:

Thanks for any responses.


[/ QUOTE ]
Can you access the resistor with the light operating? If so, just measure the voltage drop across it and calculate current. Since it is 1 ohm, 1V=1A.
 
[ QUOTE ]
jtice said:
Nope, thats right.

TWAK LuxIII ~3.6 Vf 3x123



[/ QUOTE ]

Whoops, I didn't notice the 3 X123! Why this source for a Lux III? You throw away half the battery energy as heat. 2X123 is bad enough.
 
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bucken,

That sounds interesting.
I am wanting this light to be as bright as possible, but I dont want to worry about killing the led.
So I was thinking about 1.2 amps.

The bad thing is, I really hate to order just a few resistors, cuz shipping will be as much as the resistors, lol

Anyone have anything I can use?

Also, my configuration is alittle different, sence I plan to use 3x123 instead of 2x123. (more runtime)
 
DougS,

You really think I would be better off with 2x123?
I was just wanting to get more runtime out of it.
Although, this lights main purpose isnt runtime,, its Bright throw.

Well, let me ask this then. I have a TWAK, and a 2C mag, what should I do, if I am looking for max brightness? (without killing the LED)
 
Doug S,
Measuring the voltage drop across the resistor would be very difficult. Even if I figured out an easy way to access those points, I only have one of those cheap multi-meters to measure anything with.

Sounds like variation within individual LED's is enough that you almost have to measure it somehow to get good information.

I think I remember reading somewhere that you can drive a Luxeon III direct-drive with 4.5 volts (providing you have a really good heatsink). With this in mind, I am guessing that my light may be running somewhere between 1200 - 1500 Ma.
 
[ QUOTE ]
jtice said:
DougS,

You really think I would be better off with 2x123?
I was just wanting to get more runtime out of it.


[/ QUOTE ]
Assuming that you resistor it for similar current. 3X gets you no more runtime than 2X.

[ QUOTE ]
jtice said:
Well, let me ask this then. I have a TWAK, and a 2C mag, what should I do, if I am looking for max brightness? (without killing the LED)

[/ QUOTE ]

I'll leave this to others to answer as it is not my style of mod. I am sure that many can offer suggestions.
 
[ QUOTE ]
bucken said:
I think I remember reading somewhere that you can drive a Luxeon III direct-drive with 4.5 volts (providing you have a really good heatsink.

[/ QUOTE ]
4.5V at the LED terminals?? Keep that stamp and envelope handy! /ubbthreads/images/graemlins/wink.gif

[ QUOTE ]
bucken said:
With this in mind, I am guessing that my light may be running somewhere between 1200 - 1500 Ma.

[/ QUOTE ]

If I had to guess, I would think you are likely in the high part of your 1200-1500mA range but as you note it is rather LED dependent.
 
Ahhhhh yes,, very good idea, forgot all about the dummy cell route.

Now I just need to find the darn resistor.
 
Why you want to start from 3x123 (9V) and then waste nearly 6V on the resistor and feed only less than 4V to a TWAK? You would be a lot better off using 2x123 and a smaller resistor, plus a spacer to take up the missing length; or use a 5W X-binned LS instead.
 
Yea, I have come to realize the 3rd batt does no good.
I will use a resistored dummy cell,,, or break down and get a DB1200. /ubbthreads/images/graemlins/smile.gif And then use 3x123.

No Fry's nearbye. /ubbthreads/images/graemlins/frown.gif
I know of one place, but they probably dont carry small stuff like this.
 
jtice,
I would normally offer you my extra 1 ohm resistor but, under the current (current, get it) uncertainty, I may need it to safely run my Lux III.

Doug S,
Thanks for your help. I think that I will leave my light as is, at least for the moment, and perhaps try to acquire a couple of nice binned spare Lux III's. If this one goes out, then I will know to double the resistance, next time. I will keep that stamp and envelope handy, though.
 
bucken,

No problem, I will find them somewhere.

I am actually thinking about doing a 3x123 DB1200 now.
Might as well go alllll out huh? /ubbthreads/images/graemlins/wink.gif

Thanks for the help guys.
 
If you really end up wanting 1.5 Ohms at 3 Watts as someone suggested, I'd suggest six ten Ohm half watt Radio Shack resistors in parallel (total 1.66 Ohms, 3 Watts).

If you still have trouble sorting it out, PM me, I'll find something for you.

Doug Owen
 
Well, no matter what, unless I cut down the 2C mag, its still that long,, so, theres no sence only putting 2x123 in it,, and taking up space with a dummy resistored cell.

To utilize all the length, it really should have 3x123.
And for that, the best solution is to use a DB1200.
No sence it half assing it. I will just cough up the extra $22 and buy a DB1200.

I want this as bright as possible, without running the risk of killing the TWAK. 1200 mA is probably right on that edge.
I have a large heatsink, so it should be ok.

Thank you all for your help. This is why I love this forum soooo much. /ubbthreads/images/graemlins/smile.gif

I will post later to let you all know how it came out.
 
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