LED flashlight question

[Perd Hapley]

Old maglites still make good thumpers  

This one, according to the original owner, was occasionally used to knock heads, in brawls between drag-racers armed with automotive tools. Hence, it needs a new spare bulb for the tail cap. Unless I go with the LED, of course.

Most likely, its new role will be to serve as a vehicle just-in-case light, where its thumpiness may also, God forbid, be appreciated.

[Perd Hapley]

I also have one of the mini mag light LED jobs. It rides in my back pocket every night. The 4 function switch is kind of over kill though. I can appreciate the high setting and the low mode. I can even sort of understand the strobe mode but the S-O-S mode is kind of a waste.

It doesn't seem to hurt anything, though. I'd be OK with a simple on-off switch. The low power setting may come in handy someday, though. I'll probably never use the strobe or SOS, except to mess about with it.

[Chuck Dye]

Problem is, you may also be risking the Maglite.

 What is the risk to the Maglite?



The Terralux gadget arrived along with a new battery.  I threw the new components into the flashlight, slid the flashlight into the charger, and waited for darkness.

WOW!

I bought the dimmable version providing 600 lumens, 300 lumens, or "<100" lumens.  I will need to take care where I aim when I turn the thing on.  The unit starts on high and steps down as you hit the switch repeatedly.  I suspect I will mostly use the middle and low output options.

Worth $40?  Hard to say 'til the gadget fails,but I am pleased for now.

[GigaBuist]

What happens if I run a 3 volt LED on 3 D cells?

Nothing all that good it seems.

You could try fashioning a D-cell sized "battery" out of aluminum foil, wrap it in electrical tape except for the ends, and shove that in there.  Put in a D cell battery, the spacer, then another D cell.  Now you're only running around 3V.

Haven't tried anything like that since 1st grade though... and that was back around 1986.

[Hawkmoon]

  What is the risk to the Maglite?

The risk is that the heat created by the LED will damage the light.

I'm willing to take the risk. I typically don't run a flashlight for prolonged periods, and I'm usually at home where I have access to at least one (or more) others, so I'll spend $15 for the Terralux conversion rather than $30+ for a new Maglite LED, just because I think Maglite's attitude stinks. If I cook my old Maglite, I'll have to buy a new one ... but I don't think it's likely.

And the difference the 3-watt Terralux maks in my 3-D-cell Maglites is nothing short of phenomenal.

[Chuck Dye]

Apparently I am out of my depth.  I would have thought that, even with the 50% overvoltage Fisty is looking at, an LED would not throw the heat of an incandescent bulb.  I think I have an old disposable key chain light the kids overlooked.  If I find it, I'll test it on the car battery, see what happens.

My favorite publican worked in LED production years ago, says the final step before packaging was a few seconds at 20 volts.  Survivors shipped, burnouts were trashed.  He mentioned nothing unpleasant in the process.

[Perd Hapley]

I attended a meet-and-greet with a lighting supply company a few months ago, and they said heat dissipation was quite a significant issue for LED replacement lamps for incandescent/fluorescent fixtures. It depends on the lamp, though. In one of our elevators at work, I installed screw-in LED bulbs, with 4 diodes a piece. They are finger-burning hot, like an incandescent. When we were ready to put LEDs in the other elevators, Phillips had changed the design to 3 diodes, and those don't get hot enough to cause any discomfort. (Not that I'm saying the number of diodes made the difference; just that it shows they had changed the product.)

[Brad Johnson]

Chuck's link takes you to the Streamlight version of the TerraLUX product line.

Here's the MagLite-specific products...

MiniMag conversion
http://www.terraluxportable.com/product/tle-5ex/

MagLite 4-6 D cell conversion
http://www.terraluxportable.com/product/tle-310-m-ex/

Rechargeable MagLite conversion
http://www.terraluxportable.com/product/tle-310mr-ex/

(Both the 4-6 cell and rechargeable conversion are 1000 lumens on high! )

Maglite 4-6 cell direct-bulb-replacement conversion
http://www.terraluxportable.com/product/tle-6ex-cnc/

MagLite 2-3 C/D cell direct-bulb-replacement conversion
http://www.terraluxportable.com/product/tle-6exb-cnc/

Brad

[erictank]

Apparently I am out of my depth.  I would have thought that, even with the 50% overvoltage Fisty is looking at, an LED would not throw the heat of an incandescent bulb.  I think I have an old disposable key chain light the kids overlooked.  If I find it, I'll test it on the car battery, see what happens.

My favorite publican worked in LED production years ago, says the final step before packaging was a few seconds at 20 volts.  Survivors shipped, burnouts were trashed.  He mentioned nothing unpleasant in the process.

I've blown small (consumer-grade Radio Shack) LEDs instantaneously on application of 9VDC (< 3x rated forward voltage) - I expect your key-chain light will make a nice bright flash, once.

Easy fix....disassemble your current flashlight.....then drop it in the trash can and buy one of these....

http://www.walmart.com/ip/Coleman-3AAA-LED-RWG-Flashlight/13029916

....you'll never miss the old one..... 

That looks nifty.

[S. Williamson]

I connected a Surefire P60 lamp assembly to a "small" aircraft ELT battery once.

Once. 

[Fly320s]

I thought LEDs didn't give off heat, only the power supply or transformer does.

[bedlamite]

I thought LEDs didn't give off heat, only the power supply or transformer does.

They still get hot, but the light output per watt is much greater. The light I linked to on page one is about 9 watts, but it throws as much light as the 90 watt spotlight behind my garage.

[2nd_to_one]

Sorry for the late reply, but since no one else mentioned this, I thought I'd chime in.  LEDs are actually current mode devices so it is primarily over-current that will take them out, not over voltage.  It is possible to blow them up with a sufficiently high reverse voltage (ask the poor high-school electronics class substitute ) but you should be just fine at 4.5 volts (nominal) as long as the LED module has a proper current-limiting resistor.

Steve

[Nick1911]

The retrofit LED kits have resistors to get the proper voltage to the element.

Got a source?

Resistor is great for claming down the thermal runaway problem inherent with LED's, but I don't see how it could be used to get the correct voltage to the LED.  The basic "Luxeon star" LED found in most flashlights spec a very minimum turn on voltage of 3.0 volts. [1]  Alkaline batteries state 1.5 volts each, but quickly drop below this.  Combined with the clamping resistor providing some voltage drop, this would make the flashlight very useless when it still has plenty of battery life.

I believe there almost has to be a small buck/boost circuit and voltage regulator in place to maintain the correct amount of voltage and current at the element over the life cycle of the batteries.

[2nd_to_one]

To Nick1911,

As I stated, voltage is not particularly important to an LED, it is current (which a resistor will limit) which kills them.  Since you asked, however, here is a "source" (aside from my EE degree) which may persuade you http://support.luxeonstar.com/customer/portal/articles/175525-how-do-i-power-luxeon-leds-.

Steve

[Nick1911]

Thanks for the link.  It notes:

The output voltage of the DC power supply is not important, as long as the voltage is at least a few volts higher than the forward voltage rating of the LED.

The minimum forward voltage of a white LED is 3.0V.  How can such a device be powered from a two cell battery pack with just a resistor to clamp down the thermal runaway?

Note that Luxeon has their own driver circuits.  http://www.luxeonstar.com/350mA-Low-Voltage-LED-Drivers-s/52.htm I picked the first one that was able to run from one or two cells and... yup, boost driver.  http://www.luxdrive.com/download/?dmid=1243  It has to be to make the correct forward voltage.

Really, I just wanted to point out that inside an LED light, you will find more then just an LED, batteries, and a current clamping resistor.  Sure, this arrangement works great when designing circuits with stable power input - but it will not work where there is less then the forward voltage requirement of the LED; and it will not work well in a circuit where the voltage tapers off over time.

[Jim147]

I still think a pair of diodes in the circuit would be a simple solution. Get about .70 drop on each one.

A dummy battery was mentioned also and that would really make it simple to drop it to 3 volts.

jim