08/28/2006- Turning the MagLED into a "Hurricane LED"

Some of you will remember a few of these photos from this review here, it may be good to review this while I'm describing things:
MagLED Technical Review

Before you start, it is good to have someone experienced at soldering regular surface mount components to do the work for you, or yourself, if you have the equipment and skills.

Several folks have asked, how can I turn the module down a little.

Why would a person want to turn down the module, and lower the output, isn't brighter always better?

Well, for starters, they'd like the flashlight to run for a longer time on a given set of batteries. When all the lights are out in an area, you don't need much light to see by. By turning down the module, you raise the efficiency of the electronics, and the batteries deliver their power more efficiently, especially Alkalines. When you start underdriving a Luxeon (which is used in this module), it becomes more and more efficient at lower current levels, and your lumens per watt go up. Additionally, this module doesn't have the best heatsinking, and heat also lowers the efficiency of the LED. Taken together, the increase in efficiency can be astounding, and greatly increase the runtime of your hurricane flashlight.

We will take a look at the MagLite 2D module.

First, you pull the black plastic retainer out of the PR housing, from the rear or bottom, taking careful note of the orientation in reference to the LED. I mark the metal PR can, and the black plastic holder before I pull it all the way out. Pictures can be found in the review, if you'd like to take a look at how it goes together.

Next, mark the side of the PCB as you pull it out, with a Sharpie, so that it matches your mark on the black plastic holder.

So, you should have something that looks like this (I've marked the thermistor as some folks have asked about that.):




The other side, where you'll want to do your modification looks like this, note the location of the part indicated, called a resistor, which is marked R10 on it:




This is the sense resistor. Old timers, will remember Dat2zip's sandwiches, where a person would change the sense resistor, to adjust the output current of the module. Same thing here.

The function of the sense resistor is to sense the output current of the module, and to regulate the current going to the LED.

This is the part you change.

I chose to change mine from 0.1 ohms (R10), to 0.39 ohms.

Once changed, put the module carefully back together, aligning the parts properly as you put them back together, the marks you made will serve as a great guide to help you put it back together. If you didn't mark things, you could put it together backwards, and you will blow up your module.

Thats it, simple as that. Drop it into your MagLite and you are done. Enjoy!


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So, how does it perform? I hit my light meter with it again, and noticed less than a 30% drop in light output. It is still far brighter than most 5mm PR based solutions.

Well, how about runtime? I took a meter, and hooked it up before the mod, and my module was pulling 1.12 amps. After the mod, the module pulled only 0.33 Amps, which only lowers a slight amount as things warm up.

This is a whopping 70.54% decrease in current consumption, and it now consumes less than 1/3rd of the power it did before the mod, with only a 30% drop in light output.

I have not had a chance to do a runtime on the modification, but I am expecting greater than a 100 hour runtime.

You can further reduce the output, by increasing the value of the resistor, if you'd like even longer runtimes. As the value continues to increase, there is a loss caused by it, but at low current levels, it's contribution is minor to the big picture. The bigger piece of the puzzle, is that the Luxeon will pick up a little more efficiency due to less current density, and it will run cooler, plus the batteries will become more efficient at delivering power.

Be aware, doing this mod will cause the beam color to typically shift a tiny tad more green at lower currents.

Oh, and the resistor package size that is used in the module for the sense resistor is an 0603.

Examples of what I utilized:
http://www.mouser.com/search/Refine...ouser_Wildcards
http://www.digikey.com/scripts/DkSe...US&Cat=35193467



I've done two versions of the mod.

The 0.39 ohms and 0.66 ohms. I am still very surprised at how much light still comes out of this with the mod.

I ran a few efficiency plots, and I was wrong, this particular switcher starts loosing a little bit of efficiency as you continue to take the output current lower.

The 0.66 ohm mod draws 0.226 Amps at 3.0V and 0.211 Amps at 2.5V.

This would extend the runtime to beyond 160 hours.




Original question by eebowler
Hi Newbie. Do you think long wires connected to a pot or a resistor and a switch would affect the efficiency/operation of the circuit? I know some circuits have problems with long wires.

I am not sure what you are doing, but if it is to use a pot/resistor to tweak the value for the sense....

You might consider raising the sense resistor, and putting in parallel, your control. You will need a nice low, low value...twist your wires together, tightly, to reduce the lead length inductance.

There are some other techniques, like pre-biasing the FB point that could be utilized, which would allow a higher value pot/rheostat to be utilized, but you are getting into design type stuff.


Original question by jburgett
Newbie,

It seemed to me that using the MagLED with a proper heatsink would allow you to replace the thermistor with a simple potentiometer. Then adjusting brightness is achieved by simply rotating the pot. (I am assuming that you heatsink the luxeon properly, so that thermal control is not an issue.)

This $18 luxeon/circuit combo is a great place to start a mod.

By the way, do you know the part number or room temperature resistance of the thermistor?

Thanks for the info Newbie!



In circuit, I measured 30k (no idea of temp), but it moves around with temperature, obviously...


I finally got a chance to do a runtime plot on the "Hurricane Mod", my light meter has been busy doing runtimes on other lights.

Here is the actual runtime from a module that was modified to pull 215mA off a set of cells when everything is cool. Note how it doesn't turn the current down that much at all, but fades more with battery voltage. If you look carefully, you will notice the line "warbles" a bit, which is the internal thermistor as it senses the variations in my room temperature:




Of considerable note, the runtime didn't turn out as long as I'd expected, as I not considered my own data, and the MagLED's thermistor cranks down the current in the stock module due to too much heat.

Compare to the stock runtime plot:




But, you do get nearly 3x the runtime out of things, without that much of a penalty for light output levels. One of the really nice things about the Luxeon, is that it's Lumens per watt actually increases when you underdrive it- thus the LED's efficiency actually goes up. One of the added benefits is that the lifetime of the LED also increases, since there is less heat. Contrast this to a 5mm, which has to be overdriven to the point of abuse, in an attempt to hit the same brightness levels, which very drastically shortens the life, and also looses a lot of efficency when overdriven. IMHO, an overdriven 5mm is the poor man's way of doing things, as it is an extremely cheap solution, since 5mm LED costs are under the 20 cent range, in volume. But it does increase profit margins.

See my other references for information on long term issues with 5mm, especially when they are overdriven like they are on most flashlights.

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