XM-2 churning out 1.3amps! Which Lux will survive?

dimwatt

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I got a super deal on an ElectroLumens XM-2 with a bad Lux3 so wanted to repair my first "real" light! I have a couple of Waion's clones so decide to pop one off the sink and drop it in the XM. All went well and I twisted the tail cap with sweet anticipation and was rewarded by beautifull, bright white light!!! Ah, the sweet joy of success!!!

WAIT!!!! WHY IS IT GETTING DIM AND TURNING BLUE AFTER ONLY 20 SECONDS OR SO!!! TURN IT OFF!!! TURN IT OFF!!! WHAT DID I DO WRONG?? OMG! I MUST HAVE SCREWED UP THE LED!! QUICK!! RUN THROUGH THE STEPS IN YOUR MIND!! NO, IT WON'T WORK AT ALL IF I SWITCHED THE ANODE AND CATHODE!!

Ok, the adrenaline is starting to burn off but confusion still reigns! Logic says try it again but I'm almost afraid to! Will it even come on again?? A very slow and cautious turn of the tail cap and nice bright, white light appears!
I shake the flashlight, no rattles! I try to stick it in my ear, it won't fit! I then taste it, hmmm, needs more salt!
OH, CRAP! I realize I have a DMM stored away in an inaccessable location! Oh good, the battery is still good after 34 years 137 days and some odd hours since I last attempted to figure out how to work this modern and highly sophisticated piece of technology! /ubbthreads/images/graemlins/grin.gif

After unscrewing the bezel and clumsily holding the test probes in all the right(?) places, I push the tail switch downward against my leg (as I don't happen to have been as lucky as my Brother who was born with three arms and hands) and the meter reads.......$#@*! I can't see because the light slipped and got me dead center in both eyes!
Ok, Ok, the spots are starting to go away and the readout says... (I don't wanna get flashed again!)/ubbthreads/images/graemlins/awman.gif....the stinking leads slipped!

Any way, enough foolishness! I read 1.3 amps at the Luxeon! It has to be that the poor clone was over heating and the 1.3 amps is likely what did in the 3 watt Luxeon that was in it.
Now I need help figuring out what to put in there that will survive. I think I remember reading somewhere that Red Luxes are tolerant of higher current but am not sure.

Any suggestions from experienced Mod people will be much appreciated. Any color, wattage or combination will be considered but I hesitate to do anything that requires a new board due to the cost factor.

Thanks, all!

dimwatt /ubbthreads/images/graemlins/au.gif
 

knifebright

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Hey arlen
You've got a direct drive light going there. I never used the clones but i can tell you your significanly over driving the lux. When you overdrive=heat. Heat causes the lux's to change color and dim. Now you have a couple options. Put a lux3 T**K. For the mean time you need to add some heat sink material under the slug. I"m assuming that you put the whole star in there?? you need to add some heat sinking material to make sure there is thermal path out of the light. does the light get hot when you run it??? if it doesn't and your dimming then you've not made a good thermal path.
hope this helps
jimmy
 

dimwatt

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Re: XM-2 churning out 1.3amps! Which Lux will surv

Hi Jimmy,

Thanks for the info. I had to remove the emitter from it's base as the XM 2 has a countersunk space the emitter sits in. It is a tight fit and must be pushed in rather firmly. The dome of the emitter does not get more than warm to the touch, even against the cheeck while running. I made sure there was adequate thermal grease on the mitter and in the recess before soldering the tabs.

I have a TWOJ emitter in the Mini Pro kit from Lambda that I have not assembled yet but didn't want to take a chance of damaging it. I guess I could get some thermal epoxy and make it permanent but hesitate to do that because of the recess it sits in. If it ever had to be changed again, it would have to be drilled out. /ubbthreads/images/graemlins/str.gif /ubbthreads/images/graemlins/aaa.gif

dimwatt /ubbthreads/images/graemlins/au.gif
 

knifebright

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Re: XM-2 churning out 1.3amps! Which Lux will surv

thermal grease would work just fine. It's the lux that your using is similar to a 1 watt and that means that it can take about 3 volts and be driven at spec at about 400-500ma. Put the twoj in and you be very happy.
jimmy
 

dimwatt

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Re: XM-2 churning out 1.3amps! Which Lux will surv

Thanks for moving this and sorry I posted under "general" flashlight questions. My bad! /ubbthreads/images/graemlins/whoopin.gif
 

HarryN

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Re: XM-2 churning out 1.3amps! Which Lux will surv

A 1 or 2 ohm resistor will help a lot as well with the LED lifetime, and will make the whole light be a more consistent brightness over the battery life.
 

dimwatt

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Re: XM-2 churning out 1.3amps! Which Lux will surv

[ QUOTE ]
HarryN said:
A 1 or 2 ohm resistor will help a lot as well with the LED lifetime, and will make the whole light be a more consistent brightness over the battery life.

[/ QUOTE ]

How does a resistor help make the brightness more consistent over the life of the battery? /ubbthreads/images/graemlins/thinking.gif I knew that a board to regulate current would do that but I was under the impression that all a resistor does is absorb some of the current before it gets to the LED. I also think/thought a resistor is very ineffecient and actually wastes power and creates heat in the process.If I am off track here, someone please enlighten me. (hence, the CPF name, dimwatt)LOL

dimwatt /ubbthreads/images/graemlins/au.gif
 

matrixshaman

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Re: XM-2 churning out 1.3amps! Which Lux will surv

If the resistor is just in series with the power provided to the LED you are right - all it does is suck some of the power from your battery and wastes it as heat. But if the resistor is part of an IC regulator circuit than you will be reducing the actual output as well as drain from the battery.
 

Ctechlite

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[ QUOTE ]
dimwatt said:


After unscrewing the bezel and clumsily holding the test probes in all the right(?) places, I push the tail switch downward against my leg (as I don't happen to have been as lucky as my Brother who was born with three arms and hands) and the meter reads.......$#@*! I can't see because the light slipped and got me dead center in both eyes!
Ok, Ok, the spots are starting to go away and the readout says... (I don't wanna get flashed again!)/ubbthreads/images/graemlins/awman.gif....the stinking leads slipped!

Any way, enough foolishness! I read 1.3 amps at the Luxeon! It has to be that the poor clone was over heating and the 1.3 amps is likely what did in the 3 watt Luxeon that was in it.
Now I need help figuring out what to put in there that will survive. I think I remember reading somewhere that Red Luxes are tolerant of higher current but am not sure.

Any suggestions from experienced Mod people will be much appreciated. Any color, wattage or combination will be considered but I hesitate to do anything that requires a new board due to the cost factor.

Thanks, all!

dimwatt /ubbthreads/images/graemlins/au.gif

[/ QUOTE ]

When you measured the current, from the way I read it anyway...you put one lead on one side of the emitter, and the other lead on the other side? If so you just shorted the battery to run thru your meter instead of the emitter. To correctly measure current your meter must be in line with the load.

Hope this /ubbthreads/images/graemlins/help.gif
 

HarryN

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Re: XM-2 churning out 1.3amps! Which Lux will surv

More info on the resistor comment

- If you have V bat = Vf + 1 or more volts, then the battery is essentially in a dead short through the LED.
- Under these conditions, the circuit resistance is mostly the internal resistance of the battery, and the battery will supply current in a very non ideal way. This makes for rapid voltage drop off of V bat, and a lot of wasted power (and run time) that could have come from the batteries.

If you add a resistor, yes, there are looses from the resistor, but in many cases, you make up for this loss in circuit efficiency, with much better battery operating efficiency.

A good example is 2 x 123 running a Lux III with a Vf of 3.5 volts. If you run it "direct drive", the current will try to reach nearly 2 amps, the Lux III will be very hot, the cells will be hot (due to internal resistance) and the run time will be perhaps 20 - 30 min.

Brightness will not be as much as expected within minutes of the start of the run due to temp.

If you add a 2 ohm resistor to the circuit, V bat will be pretty steady at 5.4 + volts, current approx 700 - 800 ma for most of the battery life, and run time will be more like 1.5 + hrs. (at these currents, the Li 123 has a very flat discharge curve) Efficiency will be nominally 3 watts to the Luxeon and 1.5 watts to the resistor, which sounds bad - right. - but - look at run time.

Brightness will be perhaps 30 - 50 % less than in the DD case, which is not that much different to most peoples eyes.

The resistor needs to be rated for at least 2 watts, which is kind of hard to buy off the shelf if you want a small resistor. This is exactly the reason I had some 12006 size 2 ohm resistors made. They are small (3mm long x 1.5mm wide) but rated at MUCH higher than the needed wattage.

If you run the numbers, you will find that the exact same effective relationship holds for running 3 x 123 and either a Lux V or 3 x 123 and 2 x Lux III in series.

Two great places to see this effect - look at the post by Silverfox in Nov 2004 comparing 123 cells (compared at 0.5, 1 amp, adn 2 amps) and the duracell web site - tech info on the 123 cells.

Of course, you will obtain even better run time with pretty much any of the switching circuits from the Shoppe or Georges80, but nothing is simpler or cheaper than a resistor.
 
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