LED torches

[RODALCO]

Question ?

These LED torches, with 21 or xx or 68 LEDs and operate on 3 or 4 AAA cells.

Do these work on the joule thief principle too ?

I haven't had the time to strip one apart into pieces or do a current measurement on them.
They work well but are power hungry on the little AAA batteries.

The best one I have has only 3 LED's and gives the best performance.
I think the AAA batteries are under capacity to furnish the current required to run those torches for more than one hour.

In those torches appears to be a section in between the battery and LED's, which may have a type of coil in it.

The LED's appear to be series parallel soldered on the LED circuitboard.

Hope anyone can shed some light on this topic.

Thanks Raymond

 

[kchriste]

These LED torches, with 21 or xx or 68 LEDs and operate on 3 or 4 AAA cells.
Do these work on the joule thief principle too ?

They could, but really don't have to if you have 3-4 cells because most white LEDs need around 3V when they are at their nominal operating current. Using 3 cells you have 4.5V with alkalines and 3.6V with NIMH/NICADs. If you feed the LEDs with a 3.2V low drop out regulator and an array of 10hm: current balancing resistors, you can get pretty good brightness over the life of the batteries. This is simular to how I converted an incandesant flashlight to LEDs.

 

[spondootre]

I have an LED torch with 16 white leds, it runs from x3 LR1 batteries. I bought it a couple of years ago, I left it on for 3 days once by mistake and I still haven't changed the batteries since buying it!!

 

[RODALCO]

I did a load check on my 31 LED torch.
It draws 1.00 Amps at turn on and drops to about 0.88 Amps after 20 seconds.
Now i see why the AAA batteries don't last that long.
I'm modifying the torch handle now to take AA or C size batteries.

The LEDs appear to be all soldered in parallel with no equalising resistors.
That becomes more noticeable when the batteries run down and certain LED's are a lot dimmer than other LED's.

 

[Sceadwian]

The current drop after 20 seconds is just the heat building up.
That torch seems to rely on a brute force light creation method =) More LED's = more light, they make em simply by making sure the voltage never exceeeds the limits of all the leds. You could make the torch probably two or three times brighter by regulating the current into each LED but it's likley not worth it. Tacking on bigger cells sounds like a good way of getting more life out of the torch.

 

[Hero999]

I don't see the point in just adding more LEDs, when it will be more efficient and possibly cheaper to use one high power LED maybe even with a smps current source.

 

[audioguru]

Are you serious about using tiny AAA alkaline cells with a 1A load?

I played with Energizer's graph because they don't show a current so high. I think it is correct:

 

[RODALCO]

No , audioguru, I bought one of those torches on trade me (our local Ebay in NZ).
It has 3 AAA batteries in it what i found already under rated for the job.

Now i'm in the process of modifying it to 3 C cells.
The light output is great.
The white LED's run at about 25 mA's each. which is probably a little over for dc operation.

 

[mamun2a]

dr,
rodalco give me ur diagram i wanna make a headlight for bike with flash LED,
how many LED I need ?

i've lot of red LED to do so, but i guess red LED is not perfect for head light.....:-(
thnx

 

[RODALCO]

Flash light

For a white flash light the, white LED's run at about 3.4 volts.
Take your battery supply at 4.5 volts and 20 mA per led then each led will have its own resistor of 55hm: nearest E12 value is 56hm: or 68hm: . (¼ or ½ Watt)

It is better to provide each LED with its own resistor to allowe for minor differences in LED threashold voltages, so that the LED with the lowest threashold voltage doesn't take most of the current in parallel operation.

You have to experiment a bit with how many LED's versus battery usage.

Also you can make the LED's pulse on and off to reduce the loading on the battery.

Some high efficiency LED's give already an enormous light output at 10 mA so increase the R value to 100 or 120hm: and your battery life will double.

I don't know if they sell those bicycle lights in your country and it may be cheaper and easier to buy one from the shop.

 

[HiTech]

I have been doing quite a bit of reading and research into these LED flashlights (torches for some of you!) and other than the type of LED employed, the lens and reflector assy. is crucial as well. I have compared large arrays of white LEDs tested against a single or 3 LEDs in a quality, properly designed reflector and lens assy. The large arrays performed poorly in comparison to even a single LED torch of proper design. Before I'd go wasting my time and money on a handful of super-brite white LEDs, I'd opt for a single 1.5w Nichia or Luxeon Star, or even their 3watt versions coupled to a good reflector and lens. Properly done, you'd end up with a "tactical" quality flashlight over something that merely floods a small area with bluish-white light. For around $35 US, MagLite sells a three D cell flashlight w/ 3watt Luxeon LED, housed in a CNC milled, aircraft aluminum grade housing with a real glass lens and adjustable reflector.

 

[Sceadwian]

Reflectors are easy, chrome on plastic is a piece of cake. The lens is a little more tricky, as the LED aragment has to be designed with the lens in mind or vice versa.

 

[HiTech]

Reflectors are easy, chrome on plastic is a piece of cake. The lens is a little more tricky, as the LED aragment has to be designed with the lens in mind or vice versa.

WRONG! Reflectors come in a variety of qualities, material construction, etc. Cheapo reflectors are polished aluminum foil bonded to plastic. Good reflectors are polished metal with the proper curvature and placement of the LED. it makes a BIG difference... then the lens can do the rest to enhancing light output.