two stage switching: strategies

Hi guys,

As some of you may know, I have caught the multi output level bug and have been doing some L1-PRT mods as well as a few X200's and working on my own design for an E series LOTC retro-fit. Of course many others are working in the same areas as well as two and three stage levels on other lights.

I was just working on an e-mail response to a fellow CPFer in regards to options and strategies on a L1 mod when I realized that more could be better served if I started a thread here and posted some of my thoughts and observations as well as getting the comments and considerations of the rest of you.

I'll try real hard to keep this post short but it seems that there is a lot to consider and learn. /ubbthreads/images/graemlins/icon15.gif

First, let me just throw out some observations.

A resistor value in the range of 50 to 80 ohms seems to provide a great low beam on both buck and boost circuits for 1W, Lux III's and the 5W's. This low is typically a "low" low but very viable. The stock L1/A2 switch only uses 10 ohms and although this works great on the L1, The low is "higher" than I want on say a downboy system or even badboy system. Those who mod or have mods made for them will have a choice to some extent in picking their "low" level. This seems to me to lead to a discussion of strategy.

Presumably, one will want an ideal or typical "normal" level and then an additional, less often used level of output. To get the most out of one of these dual level lights, I think you want to decide if you are a "normal-High Beam" user or a "normal-LowBeam" user. For instance, with a LuxIII LED, a normal-HighBeam user might go for a low resistor value so that the low beam would drive the LED just out of regulation but at say a level of 500 mA whereas the buck circuit might be biased at 1 amp or even higher. A normal- LowBeam user might want a higher resistor value driving the LED at 30 mA on low with a buck circuit biased at 500 -750 mA. This discussion is probably more significant for lights that will be used in somewhat extended constant on situations. At the very least, it seems to me that we will want some data in regards to how differing resistor values effect various battery, converter and LED systems in terms of output. As a modder, I know I would like more information and data on this but I sure don't welcome this variable added to a build discussion! /ubbthreads/images/graemlins/icon15.gif None the less, it is a variable with effect on both output and resulting performance.

I have been more involved in the design and function of a two stage switch than in experiments with its use so far. In checking some schemes out, I have been surprised at just how versatile a two stage switch is and at the options it will accord us. For instance, I just put a PR-T-DB917 (TV0J) on an E1e to see what level of light I would get from essentially driving the TV0J in direct drive. As expected, the output was useable but certainly not real bright. What I hadn't considered was the fact that I could use a two stage switch on this setup and get a resistored low level that was still useable and noticibly lower than the DD of the TV0J! For the heck of it, I put a L1 head on the E1e with two stage switch and observed the same thing; two distinctly different levels of useable light.

With a two stage switch, one could design a DD system whereas the DD mode would be an overdriven HighBeam and the resistored LowBeam could be used as a normal or long run time mode with the LED driven at a reasonable or even reduced current level. I get more excited at the range of possabilities everytime I think about this and get a chance to play with more combinations! With the same front end (converter and LED) one could even have interchangeable tail switches with different resistor values for different strategies; not to mention a pedestrian clickie switch as well. /ubbthreads/images/graemlins/tongue.gif /ubbthreads/images/graemlins/grin.gif

As an ignoramous when it comes to understanding the magic of these circuits, I would like to comment on an observation that I believe is correct but don't understand. In some brief bench testing, I found that the resistor seemed to dictate the current level of the complete circuit (LED in series with resistor and battery) regardless of the Vf of the LED. Is this right???? With a given Vin, does the resistor set the current regardless of Vf? This does not compute?

To avoid some e-mails and PM's that I suspect this post might generate, I am just about done with the design of my E series LOTC module and have already gone out to bid on the key components. The module is based on the E series LOTC and I am looking into a guarded tail cap that could be used in lieu of the standard SF tail cap if one were so inclined. My design is based on using single or multiple SMD resistors (0805). Initially, I had designed the module to work in the Z57 shell as well but I have reason to believe that soon, the Z57's will not be provided in a dismantable state. That's cool, the Z57 is a great clickie and should be kept as such. It is my hope and plan that I will be able to assemble complete two stage switches as TK's as well as customize and build to suit, using existing LOTC's provided. Further, I hope that the various components and parts will be available on the shop for DIY. It is all too early to tell and the costs for components are not known yet. This particular program goes beyond the scope of a hoby for me, both in terms of expenses and time. I hope that I can see a return on investments as well as provide a useful part at a reasonable price for for the gang at CPF.

Regardless of my personal situation and plans with a E series LOTC, the door *is* open on varible output levels and we have only just begun to factor this varible into our wants and needs! The main point of this thread is to discuss this last comment, hopefully, in more general terms; not how it relates to a specific switch or light . /ubbthreads/images/graemlins/thumbsup.gif

/ubbthreads/images/graemlins/popcorn.gif /ubbthreads/images/graemlins/popcorn.gif /ubbthreads/images/graemlins/popcorn.gif

I'm in line when you're ready to sell them. Keep up the excellent work and thanks for keeping us abreast of your thinking. /ubbthreads/images/graemlins/thumbsup.gif

Britt

count me in, too. I am sure your investments - both in time and cash - won't be in vain, at least for us /ubbthreads/images/graemlins/evilgrin07.gif
/ubbthreads/images/graemlins/thumbsup.gif Don !
bernhard

Hello Don,

Switching strategies are not easy to define. You have identified two users, the normal high beam user and the normal low beam user. I think the area where you are using the light is also a factor.

I am a high beam user in high levels of ambient light. I am a low beam user in low levels of ambient light. In the middle of the night if I get up to go to the bathroom while camping, I become a very low beam user.

I have carried an EternaLight while camping for quite a while. I doubt that I need 12 levels of light, but find that I often use more than 2.

I am not sure how this fits into you concept, but perhaps you need to address light output levels from various sources. You could offer a whole kit of dual powered lights covering the whole spectrum of lighting conditions.

Tom

Don, thanks for your thoughts. /ubbthreads/images/graemlins/wink.gif

Regarding that resistor vs. Vf question, the changing Vf would cause differences in output current, assuming we're talking about a simple resistored circuit (power source through a resistor and an on/off switch to the LED). However, the range of Vf is relatively narrow, going from roughly 3V to maybe 4V (educated guess, too lazy at the moment to lookup specifics)... this means a fairly narrow band of output within that range. Also, the higher the current flow, the higher the Vf, so to some extent the circuit's output level is "self-normalizing" (my term, not a technical name for it).

I think the final piece of the puzzle is the fact that human eyesight is non-linear in terms of brightness perception. In other words, an output difference of 50% in terms of current flow might look like a perceived difference of only 10-15% or so to our eyes. So the bottom line might be that the LED's rising Vf as current flow increases makes the output differences fairly small, and our eyes make that small difference look like essentially no difference at all.

There ya go, dude! Two cents from an electrical engineering wannabe. /ubbthreads/images/graemlins/ohgeez.gif

well ... as different user types go ... I am a high beam junkie /ubbthreads/images/graemlins/grin.gif
if the low beam is too low it would be useless in an urban enviroment, meaning Arc AAA brightness is the minimum setting for me.
also, quick access to the high beam is important for me, since I am using this one far more often than the low beam.
bernhard

P.S.: how will your wonder switch work? will it be able to speak to me and say nice things about me? /ubbthreads/images/graemlins/evilgrin07.gif will I have to supply the original tailcap?

Well thanks Britt and Bernhard but the point to this thread is really to discuss the implimentation of the two and multiple stage, switches.

Anybody with a LED light and removable tail switch can do some experimentation on their own by using a standard resistor to close the circuit (connect the - terminal of the rear battery with the battery tube lip).

After composing this post, I figured there was one configuration that wouldn't work with a resistored 2 stage switch and that was a DownBoy with LuxIII on 3x123. I figured that the converter would still be in regulation but just running less efficiently. I was wrong. The light output dropped noticibly. I am hoping that some of the electronic whizes can shed some light on the nature of this beast. What are the dynamic current ranges one can shoot for in simply using a resistor in series with the common converters we are using in our mods and production built flashlights? As I understand it, with constant current converters, the resistor needs to drop the converter out of regulation by limiting the Vin. What does a resistor do with a voltage regulated circuit or more to the point, how effective is such a scheme? These switches are being brought into play by the modders but what do *we* want them to accomplish? What is it that they can accomplish? I understand that there is always compromise and questions of efficiency. However, after hearing that Roy got 30 hours run time from a resistored DB917, I could care less about the inefficiency of the system in this particular example.

I have been on vacation with blinders on so maybe I'm just late to this party. I believe I saw where the Fireflys are being modded or equiped with two stage switches. What are the findings? What drivers and resistor values are prooving to be most effective and what has the exploration and testing yielded so far? If these questions have already been hashed out and understood, then forgive this post and thread and point me and any other late commers in the right direction. /ubbthreads/images/graemlins/blush.gif

For instance, it seems to me that I could build a 3x123 light with a buck driver set at a 1.5 amp bias for a LuxIII. Now I think this would be silly if 1.5 amp were the only level available. However, if I could use a resistor to limit the current (via voltage drop) to say 750 mA for the low level, then such a light might make sense? This would be a light with a "nitrous oxide" or "panic" button if you will.

Resistor limiting at 750 mA would waste a heck of a lot of power. That kind of limiting should be done with PWM and not resistors. I think it's time to have some discussions with dat2zip about some new boards that let you bring out a wire for brightness control. The regulator chip already has the capability so it's just a matter of making it accessible.

Man, I am just too slow at my posts. I see good input while I was hunting and pecking.

SilverFox,

Of course you are right and I have over simplified the situation. A dual switch is no magic bullet but it does double the possibilites (OK some statistician will probably shoot this comment down). SInce I use lights in momentary mode more often than not, I prefer the greatest range between the two levels.

Bernhard,
The way my simple switch design works is the same functionality as the SF L1 or A2 switch. That is that you can push the button in from the rear for first low and then high momentary activation. You can screw the cap down for first low and then high constant on. The switch can also be locked out.

Paulr,

If you build it, they will come! Integrating a method of controlling the circuit (switch mechanisim) is not trivial to my way of thinking. The Arc4 and soon to be released VIP's and U2's have what you are after, I believe. In the meantime, a simple tail activated 2 stage is a heck of a lot better than a single stage; efficiency be damned! Roy I believe got 30 hours out of an inefficient resistored DB917. I can live with that! Sure, 60 hours would be twice as good if you can get it!

EDIT: Scott, thanks for your 2 cents! /ubbthreads/images/graemlins/grin.gif (from a ME wannabe /ubbthreads/images/graemlins/tongue.gif )

ah ... this sounds good /ubbthreads/images/graemlins/smile.gif
from a user standpoint of view with no technical knowledge IMHO the best approach would be to have the high beam of choice as the standard beam and a really low beam (about Arc AAA brightness) for extended runtime and usage in really dark enviroments, just like you mention it.
I do not think that a setting with a standard beam of choice and a super-bright boost mode (750 to 1500 mA) would make much sense since it will not drastically augment the usefulness of the light and looses a lot of energy in inefficient overdrive settings.
A true merit would be a true low beam like said above since this setting opens new doors (runtime and night-adapted eyes) and might be an asset to reduce the number of ights one might need to carry or, simply put, makes the carried light more versatile and useful.
I'll shut up now and let the technic experts truggle this out ... /ubbthreads/images/graemlins/tongue.gif
bernhard

EDIT: the limited efficiency in this low beam wouldn't be too horrible since the runtime will nevertheless be very long AS LONG AS the efficiency of the high beam is not compromised.

Excellent post Don.

I agree that the future looks very bright,,, is dim, for multi-level mods.
I have Gadget_lovers dimmer for the Arc LS, and it really made me realize just how much more useful a light can be if make dimmable.

As Tom said, I do find that more than 2 levels is what is REALLY nice.
Take the SF L4 for example, its super bright, well great, /ubbthreads/images/graemlins/smile.gif
But, if made to dim really dim, say close to an Arc AA, that makes it sooo much more useful,
The problem I run across is, thats ussually alittle too dim sometimes.
So, that middle level, say, 500mA, makes it great, then you have all the levels covers.
All out bright, night time use dim, and LS type bright for average use.

Of corse three stage is alot harder to do vs. two.

Your LOTC is a great idea, and I hope it pans out for you, I would love to have one of those.

I think, to make things the way we eventually want them, we need to get this actually incorporated into the circuit itself.
Similar to the Uflex.

-John

one last thing:
another merit of this tailcap Don proposes lies in modularity: it will run on every E-series light / McLux light combo of your choice and might enlarge your combination possibilities quite a bit !!!!
In addition to that, we could use all the heads we already have and run them 2-stage without any further costs!! This is a big big oplus IMHO.
bernhard

hmmm...

But isn't that what the convertor boards are set to do?

They will try to maintain the set output using every available electron until those electrons are no longer available, where they will then revert to DD mode. The exercise may be to only restrict electron flow to the point that the convertor drops out of regulation. So long as there is adequate electron flow, the convertor will remain in regulation and maintain the set output. By relying on controlling the power going into the convertor, you have only one choice: resistor to drop the convertor out of regulation. (unless you try two convertors, one downstream of the other or another such config)

It seems to be a very difficult task unless the convertor is microprocessor-based, or a separate level switch is used at the head to control the vSense resistor of the convertor board.

Good thread to start, Don!

I haven't played with the light meter much yet, so this is just subjective and influenced by my preferences. I find the Arc AAA "level" about nominal for "low beam." My first try was with 25 Ohms/BB750/CR2/R2H and other than the R2H turning a little green, the level was perfect for me. I loaned it to Wayne as a proto, and got it back with a 33 Ohm which was on the dim side for me. That module died /ubbthreads/images/graemlins/mecry.gif and it did lead a hard life (190degF once /ubbthreads/images/graemlins/grin.gif ) Next came 25 Ohms/MM Lite/CR2/TVOJ for His Supremeness which seemed to me to be pretty nice. I made a replacement module for my EDC using 20 Ohm/MM+ WFO/CR2/TVOJ and the low is brighter than I want and "whiter" on low than hi. (The 2 TVOJ's I've tried so far both semed to be a little bluish.) I guess my only point is that different drivers/batt configs will require different resistor values for differing "tastes." I suspect that Vf does matter with boost drivers. /ubbthreads/images/graemlins/icon3.gif

Larry

I've had a bit of experience with two stage switching. I've sold about 120 hi/low springs for the ARC LS line. /ubbthreads/images/graemlins/smile.gif Here's my "key learnings" as they used to say in post-project review sessions.

The majority of Boost and Buck converter boards drop to direct drive once the voltage drops to a certain level. The exception so far is the madmax and Dorcy boards, which keep trying to boost until it's dead.

The madmax and Dorcy boards have a maximum amount that they can boost, so as the Vin drops the output drops too. The two stage trick works with these boards, but the end result is shorter run-time but brighter output when on low.

The wizard buck/boost keeps trying to draw more current as the voltage drops so that it can provide a constant current. When the voltage drops below a set level (1.4 volts??) it just stops.

The use of a resistor in series with the battery limits the current available to the converter, and thus the LED. This is basic electicity... E=I*R . Example:

Add a 10 ohm resistor between the converter and the battery. If the minimum resistance of the converter is 3 ohms, and the supply voltage is 3 volts the maximum current is 230ma. Even if the converter's resistance drops to 1 ohm, the circuit's total resistance is still 11 ohms, so the current is limited to 270ma.

The higher the battery voltage the higher the resistor value is needed.

The higher the current you want at the converter/LED, the bigger the resistor has to be physically (wattage).

The Vf and bin of the individual LED makes a world of difference. I find a Q bin at 50ma with 3 volt supply is fairly bright, but the same 50ma with an M bin is way too dim. The lower the LED Vf, the more likely it will be better at using the current that is available.

All the Luxeons work at reduced current, including the LuxIII and LuxV. The color shift is not too noticable.

Some batteries will last a very long time if the drain is way under normal. 1/10th the power drain can mean 15 times the run-time.

The LuxV work well at lower and medium current too. I have one that uses 3x123A that has the second brightness level set for a 75ma battery drain. The math comes out to 2/3 watts used, and probably 1/3 watt at the LED. It is plenty bright enough for most things.

No two people will see the same output level the same way. It depends on if they are in a bright room or a dark one. It also depends on whether they are used to 200 lumen lights or mini-mags with alkaline cells.

The best way to dim a light is to use PWM. Few converter boards give the modder a way to vary the output without hacking the board.

As the battery drains, the low stage of a two stage light will get dimmer as the battery voltage drops.

You will not please everyone. I'm lucky in that only 5 or 6 people were dis-satisfied enough with the hi/low springs to say anything. On the other hand many were ecstatic.

For the mods I'm doing for the L4's I'm asking that they send me their whole light to ensure that the resistance is suitable for the LED and battery choice. I've only blown that once.

A 1 watt light is hard to distinguish from a 1/3 watt light if you have not seen the other setting in a while. I sometimes suprise myself by trying to go to low mode when I'm already there.

And the MOST important thing: Manage the expectations of your customers. Make sure they understand that a 1/8 watt low beam will be great for examining sparkly things or walking around the house at night and will run for 20 hours , but will be barely visible in a well lit room. If you set the low at 1/2 watt, make sure they understand that it will only run for 5 hours, not 24.

We need better switches. They should be operated by one hand, not two. They should allow momentary as well as off/on, off/low, off/high, lo/high and high/low. Special morse code type sequences should not be necessary to select an output level.

OK, I'm done.

Daniel

Okay, now that the bug has been planted in my head, I can't ingore it.

So, the riddle is how to provide a lower output setting without relying on dropping the circuit out of regulation.

This would mean (given current convertor boards available) re-biasing on the fly. This is as simple as adding a switch to one of the resistor pairs in a DB or BB.

The trouble is with a single tailswitch as the control, it requires a separate pair of wires running between the tailswitch and the convertor board.

Some ideas as I was driving home from work: (based on the Shoppe's parallel resistor settings)

1) Two convertors in parallel, with some sort of interrupt on one convertor

2) One convertor with second bias resistor/bypass in tailswitch

3) reverse the orientation of the batteries and move the convertor to the tailcap. CON - makes for a larger tailswitch and fitting it within the dimensions of an E-series tailcap is very unlikely

CON for 1,2, and 3: all require separate wires running between the head and tail switch

A week ago I took my McGizmo modifed L1 (the same one Roy plotted the runtimes for) down to Quintana Roo in the Yucatan for a few days and nights. I was primarily checking out some locations and accommodations for a couple of hunts I'll escort next fall.

The High output was used as frequently, if not for as long durations, as the low output. When walking in very dark and unfamiliar terrain, I have to check out what's ahead as often as what is within a few feet of my steps.

Being able to select one output or the other with no more than how much pressure I exert on the same switch makes it easy and quick. When I moved about at night and needed to use the light, I switched back and forth constantly.

I'm willing to give up the clickie feature on a Z57 in order to obtain two-stage output managed by the same switch. Though I'd like to have my cake and eat it too.

Britt

A possible probelm with re-biasing on the fly; the added wiring may change the capacitance of the circuit enough that it no longer works properly.

It would be nice to locate the hi/low switch near the head, and leave the tailcap for on/off.

Daniel

Daniel,

Agreed, I was merely throwing out ideas that I would not have to act upon. /ubbthreads/images/graemlins/grin.gif It could still work if the convertor was moved to the tailcap, but a separate -ve wire is still required to run between the head and the convertor.

Running a separate set of wires would be a logistical nightmare. Fitting the individual components would have to be precise and repeatable. Even the simple task of changing batteries would become surgery.

I like the idea of the switch in the head near the convertor, the only functionality you would sacrifice would be single-handed operation.