Help me understand Light Engines

Lonely Raven

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I'm a smart dude. I taught myself how to build and service vintage tube amps (not enough to build from scratch, but I can copy pretty well :) and it's bugging me that I don't fully understand these light engines.

I'm starting to get the difference between the bins, I'm pretty sure I understand how the multi-level clicky works, but I'm not sure I follow how different light engines can/can't handle certain battery configurations.

Keep in mind, I don't even own a common SureFire yet, I'm shopping for my first real light now. So I've not taken a light apart and rebuilt it (like I normally would with anything I'm interested in). So, is there a primer somewhere that could get me up to speed on how this works, or more specifically what configurations of light engines are compatable with what battery options?

I'd really like to snag the raw aluminum aleph that's for sale, and eventually figure out how to get a 2X123 body for it, or a 1X1.5 body since that's more the size light I'm looking for, but I really don't know if I can do that without having to rebuild/swap a light engine and start fresh. I don't know if I can simply pull the Lux out of there and drop a U-bin or Cree in it's place. I have the skills to do all this work, I'm just not sure what I can get away with, and don't feel like throwing money away killing hardware to find out! :)

Again, I'm looking for a primer to get me started. I don't expect anyone to write up a book for me in this thread if the information is already out there for me to digest on my own. Though any guidance is greatly apprecaited!
 

wasBlinded

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If you are interested in the Aleph series of modular lights, look at the sticky threads on the McGizmo forum. There is a lot to absorb there, I'll admit. The problem with the Alephs now is that they are no longer "in production" so it can be hard to score exactly what you want, though the convertor boards and light engine parts are still available.

As a general guide, a convertor circuit that boosts the voltage of a single CR123 cell (like the Badboy or Nexgen BB) to drive a single LED will not accomodate more than one cell without damaging the LED. Usually with that kind of circuit you can use a single Li-ion rechargeable cell, but the light will initially be driven at a pretty high current regardless of what the boost convertor is set to deliver.

A convertor that drops the voltage and limits the current of two or more cells is called a downconvertor or buck convertor. The Downboy is an example of this, and it will comfortably accept 4 to 12 volts of input to drive your LED at a desired current.

The Wiz2 is kind of in a gray zone. It is a buck-boost convertor best suited for use with single Li-ion cells or two CR123 cells.

Each of these Aleph system convertors can be built to deliver a fairly wide range of current, depending on your needs.
 

Lonely Raven

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I found one of the FAQ's in the Shoppe that explained some of that. I do apprecaite it!

My question is, if we have quality boost/buck converters, why don't we just use them on all light engines for more battery options? Is it a matter of boost circuits being more efficient in single battery usage then a buck/boost in a single battery conversion?

I'm kinda thinking it might be fun to build a sandwich myself, but I don't have a single body to work with yet. I wish I had $600+ to throw around so I can buy one as EDC and example of how the circuit and overall design works, then the rest for buying parts and building a couple of my own to truely understand the circuits. That's what I did for the vaccuum tube amps...I simply bought a few, took measurements, repaired some that were out of spec, then cloned a couple...got bored and sold it all to get into photography. :)

I'm a hobby whore.
 

wasBlinded

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It is apparently hard to build a stable and efficient buck-boost circuit with a wide enough voltage range and in a small enough form factor to be useful in a small flashlight. The Wiz2 will accept from 2.5 to 6 volts input and it is pretty efficient. Unfortunately that 2.5 volt requirement keeps you from getting the maximum use out of a single CR123 lithium primary cell. Another disadvantage to the Wiz2 is that it isn't rock stable with a resistored low. The flickering with a low low bothers some people. A Wiz2 with the capability of multiple current regulated levels has been designed, but switching between them requires a more complicated light.

I really like the Wiz2, particularly since my preference is for single Li-ion cell lights. I don't like using CR123 primaries except as backup.
 

Lonely Raven

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I prefer rechargeable myself, and I also prefer bodies that are slightly larger then my fist (4"-5" which I think is a 1.5X123). What seems popular now and days is smaller and smaller. Which is fine, but CR2 just isn't for me. :)

I appreciate your words of experience. It looks like I'll have to buy/build a couple and learn as I go. Those FAQs I found in the Shoppe do help some, but assumes people know more then they do. I'm still trying to figure out what all the abbreviations and acronyms mean!
 

wasBlinded

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With the 1.5x123 body you can use a single 17500 Li-ion cell or two CR2 cells. The Wiz2 would be the convertor of choice for that size.
 

greenLED

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Some of it depends on how the board components are rated. Some can take a wide range of voltages, some can't. Also, I'm guessing the topology of the converter (and IC's, etc.) affects which batteries can be used.
 

Christexan

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Hopefully I can keep this brief (not my style admittedly)...
Vf = Forward Voltage (Vf(min), Vf(max), Vf(nom) are maximum, minimum, and nominal abbreviations that I use, nominal is the typical factory rating of either batteries or LEDs in operation, DD is "direct-drive (off batteries).

The LEDs have a minimum voltage they'll operate at (and either plummet in output or simply won't light at all), below this no harm will come to them, they just won't work... they have a max they'll operate at SAFELY (due to heat buildup, beyond a certain point they'll literally fry internally, either the die, the epoxy, the epoxy, or everything...)... look at some of the datasheets and you'll find lots of 'derating' curves and such (so if you know an LED will be sealed in a hot environment, you can cut back other parameters to stay in the safe operating envelope of the LED.

Now that's the voltage range, however LEDs are actually "current driven" devices... the voltage is a by-product of the current they are operating at (as current increases, the voltage increases as well, but you can increase voltage and current might drop, depending on your source)...

So to optimize designs, you need either a voltage source that is in the operating range of the LED and can generate a suitable amount of current for operation (you can have a 3.2V LED, running off 3 NIMH cells (3.6V nominal) that are discharged, but still showing 3.2V, and the LED may not light up due to the internal resistance of the batteries preventing the current from flowing.

Most direct-drive (battery driven directly) LED lights are based on the nominal cell voltage falling within the LED ranges.

The biggest design problem with direct-drive is "thermal runaway"... an LEDs resistance (which isn't big to start with) drops as it's temperature increases (unlike most electrical parts).... if you run an LED near it's Vf(max), and it can't get rid of heat to ambient fast enough (enclosed, no heatsink, etc)... it'll start to heat up and the resistance to current will decrease... as this happens, the current increases, causing the heat to rise further, lather rinse repeat... the LED "runs-away" until you get a "friode" (fried LED)... these can short "closed", causing more current increase in neighboring LEDs, eventually blowing the entire set if it's an array.

Resistors in each voltage series helps avoid this for direct drive operation, as the resistance of a resistor increases with heat and higher current, it more than negates the drop from the LEDs, cancelling out this problem.

Regulators maintain a "constant" current to the LED array (array of 1 or more units)... in this regard, as the LED heats up, although it's resistance drops, the regulation circuit senses the change and adjusts to maintain a set current, essentially preventing any chance of runaway. If you have an array of parallel LEDs, thermal runaway is still possible, if run near limits and one starts to runaway, it'll take current away from other parallel legs, so to prevent this, small resistors can be added as well even in regulated circuits... however if designed reasonably within limits, this problem isn't likely to happen. Also, most regulators vary voltage to limit the current, and this will negate again thermal runaway (the Vf of each parallel leg is always the same, if an LEDs Vf starts to rise, it would require other Vfs in it's parallel leg to fall, but they must all share the current in that series, and act as "mini-resistors" to each others changes in Vf, and will basically "parasitically" take the current they need and thus stabilize the current, which will box in the misbehaving LED, so long as the regulator stays constant. It's not foolproof, and if you mix LEDs of significantly different Vfs, or push them right to the limits, stability can suffer and fail, but it's pretty reliable up to the operational and environmental limits. Exceed "mA max" and "Vf max" ratings at your own peril though.

Okay, the reasons regulators aren't used more often are numerous, however some of the most obvious...
1 - They take space, valuable especially in small AA lights
2 - They consume some power and drop efficiency:
A> Linears are (typically) 70-90% efficient (based pretty much on matching Vf of LEDs to Vin of batteries, the wider ranges needed (for instance, to accomodate alkaline and NiMH cells), the more it suffers
B> Switchmodes depend on types... buck/boost models (can handle a wide range of inputs above and below the output needed) are the least efficient but most flexible, typically 60-80%... boost models are typically 80-90%, but have to have the input a certain amount below the output, and buck models are the most efficient (90%+), but require the input to be some amount above the output
3 - They add complexity to design
4 - They add cost

Advantages are pretty obvious in most cases...
1 - Regulation - constant brightness over time until Vin drops below regulation capabilities
2 - Control options - most have brightness level, strobe, etc controls.
3 - Extra maintained brightness - These can be made to maintain higher brightness than direct driven lights, at the expense of runtime (using all available source power)... this can be a disadvantage also if a "cutoff" isn't programmed in, battery damage can result.

Design considerations...
Direct drive will give long-life but with steadily decreasing output... a resistor also needs to be added to prevent a too-high voltage input from blowing the LED, but the resistor will always be wasting some power in the form of heat as a result. Best designs put the Vin(nom) closest to the Vout(nom)... so if you have a 3.6V battery source (LiIon), and a 3.6V LED, it's a good match (and why you see so many LiIon flashlights on this website, as both are pretty much the nominal figures, so minimal to no resistors are needed).

If you got an abnormally strong LiIon battery (say 4.2V fully charged) and a LED with a real Vmax of 3.8 (kind of low for most power-white LEDs), you might blow it, and you'll see some people recommend slightly discharging the LiIons before using in certain flashlights for this reason (the 4.2V off a strong charge quickly drops below 4.1V when used for just a few minutes). A small resistor can protect against this, at an efficiency penalty.

Linear regulation will give safe regulation (too much Vin won't blow the LEDs), at the expense of efficiency, and runtime will be shorter than direct drive.

Switchmode regulation can be designed for many scenarios... long runtimes (using PWM or PFM switching to "dim" the LED for example can greatly extend life over either above method, especially in a buck converter), brightest output possible, brightest maintainable output for a given interval, etc... the simplest are nothing more than a pre-programmed current regulator though, if you have a 700mA LED that you want max rated brightness from for as long as the source can support it, buy/build a 700mA constant current regulator, linear ($2) for cheap, switchmode ($20+) for optimal efficiency.

Okay, not brief, hope that gives a quick 101 on the question.
 

Christexan

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Oh yeah, and it is hard to maintain a "low voltage" regulator off one or two cells, mainly because the components needed to operate the regulators (transistors and diodes internal to the devices) require some voltage of their own to operate obviously, so that doesn't leave much for the regulator to output to the LED to work with.

For instance the micropuck...
http://www.ledsupply.com/02009a.php
can output 8.0V off a 3.0V supply, for several hours (while totally killing the batteries, keep rechargeables away from such a device if you value their lives or stop them as soon as dimming begins to increase noticeably). At 80% efficiency to run LEDs fairly brightly for 3 hours that the batteries wouldn't even get a spark out of on their own, is still pretty darn amazing.
 

Lonely Raven

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Very interesting info, and helps clear up some things. I see now that CRC123 are a good match for theses Luxeons due to the voltage match, and if I follow you correctly the rest is balancing out current with desired output and desired runtime. Add to that the "tint" as I'm seeing it called can vary slightly from it's BIN'd due to current choices.

OK, this all makes this much easier for me, Christexan. I do apprecaite the time you've taken to write all that out.

I still don't understand how the tail switches can induce a dual mode (electrically I figure it's just resistors) I'm sure it's something physical that I'm just not getting since I've not taken one apart yet.

I've just purchased a McLux III with a U-bin that I hope to have this weekend for my birthday. I think I may save up some extra cash and pick up a used Aleph 2 and some parts and see if I could build up a LE myself.

Thanks again, everyone!
 

Lonely Raven

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I was just thinking about that MicroPuck.


Am I correct in thinking that using protected cells I wouldn't have to worry about killing cells dead, dead, dead? They would cut off properly on their own (assuming the protection circuit works).

And on that thread, using unprotected cells with a buck/boost circuit, the circuit itself would cut off before the Li-on cells were damaged? Or is that really design dependant?
 

wasBlinded

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Lonely Raven said:
I was just thinking about that MicroPuck.


Am I correct in thinking that using protected cells I wouldn't have to worry about killing cells dead, dead, dead? They would cut off properly on their own (assuming the protection circuit works).

And on that thread, using unprotected cells with a buck/boost circuit, the circuit itself would cut off before the Li-on cells were damaged? Or is that really design dependant?

A protected cell will shut off the current before it drops into cell damage territory. The Wiz2 can be run with unprotected cells, since it has a 2.5 volt cutoff. That is just the way it is designed, and is not a typical characteristic of buck-boost circuits.
 
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