# LED "module" for DeWalt 18V Light ...



## wquiles (Jul 3, 2005)

*LED \"module\" for DeWalt 18V Light ...*

I bought an extra battery for my 18V DeWalt kit, and since at the time the price of the single battery was the same with or without the light, I bought it with the light, knowing too well that I was going to end up modifying it:






I though about first using a single 3W or 5W, but the pack fresh from the charger was about 21 volts, so that rule out many/most of the converters we have for sale here in the forums. The other point was that I don't need range with this light - this will be exclusively a close range light for work around the car/house so I knew I wanted a floody beam.

I gave up on finding a nice reflector for a single 3W/5W and just put the project a side for a month or two, until it hit me: why not simply use some of the 26K white LED's that I got from Ebay some time back? This should give me a floody light and use very little power (packs are 15x sub-c cells, either 2400mAH or 3500mAH), meaning this light would run for a freaking LONG time!. What I got in the end was close to a 3W light, but with the beam type I wanted: 28 LEDs x 3.2V x 35mA = 3Watts /ubbthreads/images/graemlins/wink.gif

So I got an old piece of perforated board from a project long ago and it just happened to fit perfectly inside the reflector housing:





So I simply put as many as I could, trying to keep 4 in series so that the voltage of the string (3.2V x 4) was close to the drained voltage of the pack (15 x 0.90V):









I used some 1/2 Watt resistors that I had and put several in parallel to get the value I wanted and to spread the heat among them:





I found that about 35ohms or so gave me about 25mA to each of the seven strings of 4 LEDs, and about 25ohms gave me about 34mA (more or less). Here I tested the LED "module" on LOW (25mA):





By the way, it looks really cool from the back:





This is how the module looks like ready to go in:





but I had to use some spacers to get the LED's close to the lens:













Since I wanted to have the ability to go normal and "turbo", but did not wanted to change modes often, I added a simple switch to add additional resistance in parallel to bring it to a lower value and give me the "turbo" mode I wanted:





Here is a low exposure image showing all LEDs lit:





Here is low mode (approx 25mA to each LED):





and this is high/turbo (approx 35mA to each LED):





And finally, some beamshots. First is my U2 on high, about 12 feet from the wall, then the DeWalt on low, then high:













So I am pretty happy that I got the type of light I wanted, for a very small investment /ubbthreads/images/graemlins/smile.gif

Will


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## Sigman (Jul 4, 2005)

*Re: LED \"module\" for DeWalt 18V Light ...*

WOW! How much did it cost in parts? Runtime?


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## redbird (Jul 4, 2005)

*Re: LED \"module\" for DeWalt 18V Light ...*

That is just what I was looking for for my light. Do you think I could talk you into making one for me. This could represent an opportunity to make a couple of extra $$ for yourself to feed your(our)habit.

Let me know by pm


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## Makarov (Jul 4, 2005)

*Re: LED \"module\" for DeWalt 18V Light ...*

Great light! /ubbthreads/images/graemlins/happy14.gif

I've been thinking about a hotwire mod for my Dewalt 18v light, but have found impossible/unpractical (the heat man, the heat...) 

This looks much better, maybe this will be the way to go.


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## greenlight (Jul 4, 2005)

*Re: LED \"module\" for DeWalt 18V Light ...*

I was interested, but the images are a bit large, so I missed most.


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## Lynx_Arc (Jul 4, 2005)

*Re: LED \"module\" for DeWalt 18V Light ...*

I have found that if you grind the bottom lips off 5mm LEDs they will pack together tightly on standard perfboard. My 12LED headlamp mod I did awhile back they are fairly tight together but wiring in series could more difficult when tightly packed.


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## wquiles (Jul 4, 2005)

*Re: LED \"module\" for DeWalt 18V Light ...*

Sigman,
I have not done a runtime test yet, but based on my estimates, this first iteration is not all that efficient in terms of runtime. Here is my math:
battery capacity: 15 cells x 3.5AH x usefull battery life (1.3-0.9)volts = 22.75 wattsH

On HIGH (draw from battery was around 240mA or so):
LED Load: 35mA x 28 LED's x 3.2V = 3.14 watts
R Load: 25ohm * (35mA * 7 LED strings)^2 = 1.5 watts
Approx hours runtime = 22.75 / (3.14+1.5) = 4.9 hours - lets say 5 hours. 

On LOW (draw from the battery was about 175mA or so):
LED Load: 25mA x 28 LED's x 3.2V = 2.24 watts
R Load: 37ohm * (25mA * 7 LED strings)^2 = 1.13 watts
Approx hours runtime = 22.75 / (2.24+1.13) = 6.75 hours.

I should note that these are not hours of constant brightness, but rather of very slow dimming (given the high capacity of the NiHM cells). Of course, with an efficient circuit the pack will last even longer, but this is pretty nice for this first iteration /ubbthreads/images/graemlins/wink.gif

Note: The 4 resistors (150 ohm, each 1/2 watt) in parallel have a total thermal capacity of 2 watts. In this project, maximum is about 1.5 watts, so we are within the "safe" range for continuous operation.

redbird,
You are too kind /ubbthreads/images/graemlins/blush.gif. These were all parts I had laying around and I don't have enough parts to make another one, so for now this is one-of-a-kind /ubbthreads/images/graemlins/frown.gif

Cost-wise, it was the PWB (I don't even rembember how much was it from Rat Shack - lets say it was $3-4), the LED's (like 40-50 for $20 or so?), switch ($1-2) the resistors ($1-2 bucks at Fry's), and the screws and spacers which I had in my spare parts bin (say $2-3) = $3 + $10 + $1 + $1 + 2 = $17-18 bucks in parts (more or less), so for $20 of less, anyone with patience and a soldering iron should be able to build one as well.

greenlight,
These were 800x600 which are actually very small. The originals are from an 8MP Canon - you definitely won'd want to try to see those /ubbthreads/images/graemlins/wink.gif. 

If somebody would point me to a link that shows how to insert pictures with a small picture showing but when you click you can see the larger picture, I would be more than happy to edit this post and add the even smaller pictures /ubbthreads/images/graemlins/smile.gif

Makarov,
Yes, this flood light seems pretty reasonable for the intended use, specially given the relatively easy construction and low cost. I used it last night within the house, and it will also make for an excellent emergency light if one were to loose power given its relatively wide coverage /ubbthreads/images/graemlins/grin.gif


Will


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## andrewwynn (Jul 4, 2005)

*Re: LED \"module\" for DeWalt 18V Light ...*

that's a really nice mod... very practical light too... especially useful for lighting up a work area. 

-awr


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## HarryN (Jul 5, 2005)

*Re: LED \"module\" for DeWalt 18V Light ...*

That is a very nice mod - very practical and cost effective.

A couple of driver alternatives for you in case you are interested - Resistors - I have some custom made power resistors in the range you are using. They are 1206 size, and will easily handle the power levels you are using here.

The other, more conventional - georges80 (taskled.com) sells a driver that will handle you battery voltage range just fine and drive Lux IIIs or Vs from it.


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## andrewwynn (Jul 5, 2005)

*Re: LED \"module\" for DeWalt 18V Light ...*

interesting thought... with that many LED.. you could easily use an nFlex to supply a constant current to the LEDs.. just use branches of them and put the bunch of branches into parallel so their current adds up to a reasonable level of current and voltage.. i.e. 7 strings at 25mA = 175mA.. the bonus.. you can dim... the nFlex has a standard of 350mA for the lowest level though so maybe you'd need more strings.. but also very doable.. 10 strings at 35mA is 350mA and then you could have it dimmable.. the nFlex will work up to 24V input i think... the only 'trick' with that is dealing with low volt cutout which the drill batteries don't usually have.. don't think there is a shutdown pin on the nFlex so it's something you'd have to be aware of so you don't damage your batteries.. you could build a very simple low-voltage alarm with an LED and an opamp and a few resistors.. come to think of it.. you coudl use the same opamp solution to run the gate on an FET that supplies power to the nFlex and that'd shut it off as well. I think part of the charm of this solution is not using Luxes... i would love to see the output levels from this light compared to 3-lux solution for example but for a flood light it's marvy.

-awr


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## wquiles (Jul 5, 2005)

*Re: LED \"module\" for DeWalt 18V Light ...*

Andrew,
HarryN,

From a technical point of view I like using something like the nFlex. Seems like the max. voltage is 24 volts, and fresh from the charger these packs hit 21 volts, so this might work. It worries me that even the 350mA would be too much for my LED module - I wouldn't want to go back and add more LEDs at this point, plus I like the theoretical runtimes that I calculated. Cost-wise, I would hate to put a $25 converter to raplace $2-3 of resistors and a switch to get about 240mA's /ubbthreads/images/graemlins/wink.gif. 

I would love to replace the resistor with a constant current circuit that would be more efficient than the resistor for the range of currents that I am using, and that would preserver the two-levels I have today. A downboy circuit (about $12) might be OK, except that its maximun voltage is 16.0 volts -> 21 volts would kill it instantly /ubbthreads/images/graemlins/icon15.gif

Any other alternatives available?

Will


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## legtu (Jul 5, 2005)

*Re: LED \"module\" for DeWalt 18V Light ...*

[ QUOTE ]
*wquiles said:*
I would love to replace the resistor with a constant current circuit that would be more efficient than the resistor for the range of currents that I am using, and that would preserver the two-levels I have today.

Any other alternatives available?

[/ QUOTE ]

How 'bout using a LM317T in CC mode? You'll only need a regulator, 2 resistors(1 for each level) and a heatsink.


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## andrewwynn (Jul 5, 2005)

*Re: LED \"module\" for DeWalt 18V Light ...*

that's a great idea... i don't know what the voltage limits on the chips i'm using on my LDO ckt but it's mighty nice to have such a simple solution... i build my LDO ckt for like $2.. go to http://ldo.rouse.com and see if i posted the exact parts i use.. you can go to digikey.com and figure out the voltage limits.. they are likely within tolerance of what you need... since only the FET has to handle the voltage difference from LED to battery.. if you set it up right so the difference is basically zero when bats are dead.. you could even add in an op-amp to pull the gate on the FET low when batteries are dead. you could build the whole ckt custom to your light for about $10. 

-awr


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## HarryN (Jul 5, 2005)

*Re: LED \"module\" for DeWalt 18V Light ...*

Your setup is really pretty good. I know that constant current setups are ideal, but a "reasoned out design" using resistors is actually pretty good. I use resistors for lights a lot more often than true constant current converters.

I am more of a power LED sort of person, so I probably would have used 3 x Lux IIIs or 3 x Cree Xlamps and run them at low current with a resistor, but that is mostly because I am too lazy to do that much wiring.

I had a major fit problem for power resistors for one small light I was building, and had to have some small ones made in 2, 10, 25, and 30 ohm for the project. By the time I was finished, it might have been cheaper to use a true CC setup, but size can be a problem for inductors sometimes.

If you look at the typical voltage range you are working in, nominally 15 - 17 V, your efficiency is actually pretty good.

George does sell a package for dome lights that is a prebuilt CC board and Lux I for around $ 30. Still, it is hard to beat a homemade setup and almost free components.


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## andrewwynn (Jul 5, 2005)

*Re: LED \"module\" for DeWalt 18V Light ...*

harry's the resistor expert... i think.. that if you consider a relatively large limit resistor (37.5ohm for one of them)... will keep the voltage rather stable.. i would bet for the vast majority of runtime you can't even tell the difference.. if you do the math.. it might be just as efficient as a driver.

My RT4 with 4 lux 4s spends about 1.8W on heating the driver board.. and i'm powering from a 10.8V LiON battery pack. 

i love to see the type of creativity shown here... if you wanted a pre-fab light of simliar concept.. they have those flood board high-power leds similar to luxeons but they are like $70 to 100.

harry's little resistors are a sight to see.. mind blowing power dissipation... need to heat sink them if you push 'em but they can really be pushed.. way past anything of it's size.

-awr


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## wquiles (Jul 6, 2005)

*Re: LED \"module\" for DeWalt 18V Light ...*

HarryN,
Andrew,

Thanks. It looks like it not that bad as it is today. I think I will just leave it alone for now and work on other projects. This one does what I want, and except for the resistors a Fry's, I did not had to buy anything else to get it running /ubbthreads/images/graemlins/smile.gif

Will


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## andrewwynn (Jul 6, 2005)

*Re: LED \"module\" for DeWalt 18V Light ...*

that is so cool to build with parts on hand.. two thumbs up on the build... you can always re-work things later... even with those LEDs.. be careful about over-draining the battery... 0.9V/cell is a critical value.... i shut mine down at 1.1V/cell.


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## wquiles (Apr 22, 2006)

*Re: LED "module" for DeWalt 18V Light ...*

To this day, many, many months later, this is "still" my most useful light in the house. Great flood, LONG running time, easy to re-charge 

Will


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## divxdude (May 10, 2006)

*Re: LED "module" for DeWalt 18V Light ...*

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