16 LED, 3 'D' Cell Flashlight (torch) problems

[HarveyH42]

For christmas, my younger brother gave me a flashlight, apparently a very cheap one... Anyway, put batteries in it, worked okay, not real bright. Last night had a raccoon in the backyard, and wanted to check it out. Grabbed the flashlight. It seemed to be dimmer this time, turned it up a saw that several LEDS weren't lit.

This morning, counted 5 LEDs burned out (have a yellow tint compared to the neighbors). So took it apart, thinking to just replace the LEDS (got 74 from strings I bought on sale). Anyway, there is no protection, just 16 LEDS in parallel. So, as is, I can expect to be replacing LEDs pretty much everytime I use it.

It has a heavy, thick, skull-crusher metal body, well machined, so not total garbage, just poor electical design. I need to make it better. Don't think my PCB software does anything but retangular boards, but can work around that. The origional board is about 2" in diameter, and there is a plastic reflector with 16 holes for the LEDs.

Don't have any specs on the christmas light LEDs, so a series resistor on each LED would be a guess at best. Figure I can check some specs for bright white 5mm LEDs, and use an average. Just wonder if any suggestions on getting this going. No idea how I'm going to cut a circular PCB. Wondering if it would be better to get a 3 watt LED instead. How bright could I go off 3 'D' cells? Basically a good flashlight body, would like to use it, the electronics is wide open. Have the parts and materials to do something with 5mm LEDs, but could afford to go a little crazy and buy insanely bright. Any input?

 

[Hero999]

Just replacing the burnt out LEDs and add a series resistor to each of them, hopefully won't won't even need a PCB, just use tinned coper wire.

 

[mvs sarma]

Hi,

I have a basic doubt, generally LEDs (even though wide angle) are not emitting light in reverse direction. that being the case what advantage we will get by using a reflector for a multiLED torch, as compared to incandecent bulb torch?

I am trying to modify one of my torches with LEDs.

 

[Sceadwian]

They emit light in all direction's, just less in reverse, as it's usually absorbed if by nothing else the leads of the LED package itself, or refracted from the plastic. If you're going to put a piece of backing plastic in it anyways, might as well make it round and throw some chrome on it, in bulk it's an afterthought and so cheap it adds only pennies to the design.

 

[mvs sarma]

Thanks Sceadwian

Then perhaps the manfacturers could have a chance of improving the brightness with a very minor midification of the body incorporating a sort of reflector.

 

[HarveyH42]

Haven't played with the PCB software to see what it will do for me yet. I'm a little hesitant remember how much fun I had with IR iluminators for my security cameras. At least the plastic reflector would be handy for holding the LEDs in place while I soldered them.

There are so many flashlight mod hits from google it's almost worthless. Guess this is sort of an obsession for some people. Think I'll go with one or more high output LEDs, and make this blinding bright.

So, which LEDs give the best output for the $$$? And what kind of driver am I looking at? Haven't really been that interested in the past, seemed that these LEDs fry pretty easy, and a series resistor alone is useless for protecting them. At $12.00 or more a pop, just never seemed like something I'd want to play with (so many other projects, and too little spare time).

 

[audioguru]

Three alkaline D cells will quickly drop down to 3.6V which is the minimum voltage of most white LEDs. Forget about using Ni-Cad or Ni-MH cells which will average only 3.6V.

A good LED flashlight steps up the voltage then regulates the current for the LEDs.

 

[justDIY]

Harvey, if you're feeling ambitious check out this design:

inital design write-up
https://projects.dimension-x.net/archives/74

actual gizmo
https://projects.dimension-x.net/archives/79

revision two
https://projects.dimension-x.net/pictures/smps/tps61040_cc_2.jpg

I'm up to revision three now, but didn't photograph it yet, onyl difference is I fixed the problem with the separated grounds.

anyway, the gizmo will turn 3 volts into 'up to' 28 vdc. I've got it rigged as a constant current driver. for 16 leds, you'd have to do two series strings of 8 with a small resistor on each string to balance the current.

it should provide a smoother light output, not to mention extend your runtime, since it'll keep going until the batteries are sucked dry.

 

[Oznog]

Replace all the LEDs, not just the bad ones. They need to match.
Actually there are much better LEDs than those use. I just got some 10mm "jumbo" white LEDs rated at 150,000mcd! And cheap off of eBay, I paid a little over $5 for 5! One of those may outdo such a cluster. The Luxeon and similar emitter devices are even better performers when a focusing lens is used. Not many configurations use reflectors.

You're correct in noting the reflector does little. Even for the light it does capture and send forward, it will fail to focus it into the central beam area so it does little to make the flashlight more effective.

The reflector problem is one reason for the development of the unusual "side emitter" Luxeon LED package. At first this looks like a useless emission pattern. But actually it works quite well with specially designed reflector optics to make a tighter beam than a normal package can do.

 

[HarveyH42]

Harvey, if you're feeling ambitious check out this design:

inital design write-up
https://projects.dimension-x.net/archives/74

actual gizmo
https://projects.dimension-x.net/archives/79

revision two
https://projects.dimension-x.net/pictures/smps/tps61040_cc_2.jpg

I'm up to revision three now, but didn't photograph it yet, onyl difference is I fixed the problem with the separated grounds.

anyway, the gizmo will turn 3 volts into 'up to' 28 vdc. I've got it rigged as a constant current driver. for 16 leds, you'd have to do two series strings of 8 with a small resistor on each string to balance the current.

it should provide a smoother light output, not to mention extend your runtime, since it'll keep going until the batteries are sucked dry.

Wow, that sound like one sweet little circuit. Is the TSP61040 SMP only? I haven't done surface mount, a little too small for me to work with. I like the idea though, could be useful for some of my solar projects. For the flashlight, there is plenty of space for additional PCBs, so normal sized parts would fit.

The more I look into this project, the more I'm drawn toward making this thing abnormally bright, instead of 'just useable' bright like it is/was (still have 11 LEDs burning). Pretty sure I'll need some sort of switching regulator, those big LEDs pull 200-700 mA, so guessing batteries will get drop within minutes. It's not to bad, since I only use flashlights for a couple minutes (except huricane season...).

 

[mvs sarma]

Hi HarveyH42,
recently i purchased a 8 LED table light (mini and cute) works with 3 AAA ordinary cells. Lighting was really good. i was thinking the cells might work for 15 mts or so. one night i switched on and left. next morning it was still glowing --ofcourse celss have come down from1.5 to 1.2. wondered, i opened and saw thereis nothing--noelectronics. straight parallel lamps with switch and batteryof 3*aaa

the current measured at 3.6V was around 100mA. the cells were just ordinary chinese make-- i mean not DURAcell. i only wonder how you cold estimate 200 to 700 mA ?

 

[audioguru]

I don't know about el-cheapo Chinese battery cells, but Energizer has datasheets for theirs. The little AAA alkaline cell is too small for much current for much time. You can nearly see the LEDs dimming with a 100mA load.

 

[justDIY]

Wow, that sound like one sweet little circuit. Is the TSP61040 SMP only? I haven't done surface mount, a little too small for me to work with. I like the idea though, could be useful for some of my solar projects. For the flashlight, there is plenty of space for additional PCBs, so normal sized parts would fit.

that particular part, the TPS61040 is smt only, in the SOT23-5 package. However, there are a lot of other chips out there that do the same thing. Maxim has a bunch in an eight pin DIP package. Usually the larger the part, the lower the frequency, which means a larger inductor but also cheaper capacitors.

an oldie-but-goodie is the mc33063a (aka 34063a), its very low frequency makes it easy to breadboard.

 

[HarveyH42]

Hi HarveyH42,
recently i purchased a 8 LED table light (mini and cute) works with 3 AAA ordinary cells. Lighting was really good. i was thinking the cells might work for 15 mts or so. one night i switched on and left. next morning it was still glowing --ofcourse celss have come down from1.5 to 1.2. wondered, i opened and saw thereis nothing--noelectronics. straight parallel lamps with switch and batteryof 3*aaa

the current measured at 3.6V was around 100mA. the cells were just ordinary chinese make-- i mean not DURAcell. i only wonder how you cold estimate 200 to 700 mA ?

Your 8 LEDs in parallel, 100 mA? That's around 12 mA each, how bright are they? Anyway, I could repair or replace the LEDs, but it was kind of a weak light. Better 5mm LEDs might get me 2-3 times more light, functional. I decided that if I'm going to rebuild this thing, might as well make it much better, like spotlight bright.

The 200-700ma is what 3-10 watt LEDs run, Lumiled Luxon, Prolight. I have very little knowledge, and these monster LEDs are relatively new, and constantly improving, new driver ICs for them, different techniques for getting the best performance. Only been searching through the web a few hours, and there is tons of information to sort through for just modifying a flashlight. Started this thread to help narrow things down to something a little more manageable, and hopefully learn what to avoid.

 

[justDIY]

Harvey, be careful, don't fall victim to flashlight psychosis. Many of the regulars at candlepowerforums.com suffer from this affliction, costing them $100's if not $1000's to support their habit buying and building very tiny and very bright flashlights.

If you want something bright, grab a 6D maglight nightstick and run it with Duracell batteries - you'll be all set for a long time, no hardware hacking required.

 

[HarveyH42]

Yeah, there are thousands of hits on google, it's a sickness. This is a one time deal. I have a very nice, strong flashlight body, but worthless electonics. Would be a shame to just pitch the whole thing in the trash. Not to mention it was a christmas gift from my brother. Only had it a week...

Guess price wise, thinking no more than $50 to super power it (led(s), driver board, lenses...). I think as a spotlight, I'd get better use from it. It's much too heavy for working on the truck (got a flouresent that clips on the battery for that...). Although it would make a nice weapon...

 

[justDIY]

grab the MaxStar 3 and figure out how to mount it in your flashlight body ... it includes a three watt luxeon emitter and constant current driver circuitry, in a package the size of a standard maglight halogen bulb.

**broken link removed**

there's also the maxstar 5, which has the same brightness as the maxstar 3, but uses the new K2 led, so it doesn't suffer as badly from thermal degradation

 

[HarveyH42]

Tempting, under $20... Have to look into it a little closer. Not sure what 'lambertian' refers to, and my flashlight doesn't focus. Then again, for another $10 or so (shipping) I could swap out the emitter with a 10 degree Luxeon.

 

[justDIY]

lambertain is the beam pattern

there is no such thing as a 10 degree luxeon, there's the lambertain lens, the batwing lens and the side-emitting lens, and all of them are extremely wide-angle. you can buy collaminating optics for a few dollars which will give you anything from a 6 degree beam to a 20 degree beam. these optics sit on top of the emitter and are glued to the board or heatsink the emitter is attached to.

 

[HarveyH42]

Well, just order it, $27.32 with shipping.
The 10 degrees is with optics installed. This might have it already, checked this bulb replacement on other sites $32-$40. Guess we'll see in about a week.