driving your LED(No resistors allowed)? Read this

[Novastar]

Ambo... now WHY did you resurrect this sad, pathetic thread? :P

Welcome back Ambo... and... hmm--you may need to remove your link below to ambosabers...

[Silverwing]

It's like the misnomer of Corbin's board as a "3W driver"... it leads people to think it'll only work for a III and the other misinformation that III=3W (Red III anyone? 6W K2's?etc...).

After reading over this conversation (being a padawan of sorts when it comes to sabersmithing) I have learned that you cannot correctly power an LED through a driver without AT LEAST matching the LED's required forward voltage. But what about the other way around?

But just to clarify X-Wing's statement for my fellow newbies and padawans, I CAN power say, a Lux V with the "Luxeon 3w driver V2" currently sold at TCSS. True, it runs 1000mA constant, but assume that I WANT to overdrive the LED, since it needs only 700mA.

The LED will only take what it requires as far as voltage is concerned, and therefore if you use a driver you can use a battery pack HIGHER than the LED's forward voltage without incident, provided the voltage is underneath the driver board's maximum voltage.

Any problems with that statement?

Obviously this topic has come and gone, but since I'm trying to learn and this thread is stickied, I figure it's easy to de-mystify the question here and save myself and others time and questions.

[Novastar]

Silverwing... the entire point of (most) LED drivers is the following:

* They (generally) accept a range of voltages (let's say ~3.7v to ~7.2v)
* They will either spit out a "fixed" current... or have options (again--as a range) in order to regulate. So maybe 700mA, 1A, 1.2A, 1.3A, 1.5A
* They are attempting not to require tons of the voltage/current THEMSELVES in order to run. In other words--the driver board itself shouldn't be sucking down 2.5v & 500mA of current...
* They often adopt a style of driving called "Pulse Width Modulation" (PWM). Look it up to get a general idea of how it works... in favor of extending runtimes, and keeping the LED somewhat cooler during such runtimes...

Comparing a "resistor to LED" and/or "direct drive" setup... ... to a driver setup... is just not really apples to apples comparison-wise.

It's true:

* With a direct drive / resistor setup... MATCHING THE BATTERY VOLTAGE to the LED FWD VOLTAGE is fairly smart + efficient

but...

* With a driver... you need to consider the following:

~ How much does the driver take to run? Likely around 0.5v to 1v... and a little current.

~ How does the driver actually WORK? Does it burn off "excess" voltage as heat? Or is it "smarter"? (for example, Force FX boards aren't really "smart" LED drivers... whereas CF handles current fairly intelligently)

~ How much voltage can the board handle? If you have a Luxeon V (~7v fwd) and you plan to use a board that can't handle such voltage... errm... what's the point? You're just going to kill the board.

So... a lot of stuff enters the equation.

Now ULTIMATELY... if you feed an LED "somewhere around the right voltage and/or current"... meaning give or take 0.75v and give or take around 500mA... really...

...you won't see THAT much of a visual difference. Whether you use a board... whether you direct drive... whatever. Current is current is current, and voltage is voltage is voltage.

You just don't want to feed 9v into an LED that is "looking for" ~3v. That would be pretty stupid. Relationally, same for current. Don't feed 1500mA where only 700mA is the max rating. DUH.

Finally though... high powered LEDs (HIGH powered LEDs)... are fairly hardy. You can "abuse" them a little bit with the right heat-sinking and care not to leave them on for 4 hours straight.

But... caveat emptor... and mise en garde! You push one too far... and it's gone. Oh well. Get another one.

[Silverwing]

Thanks, Novastar!
That was a great piece of... theory? if you will...

So once again, the key phrase here is "within reason."

Obviously, if an LED wants 700mA at 6.8v, you dont want to shove 2.2A at 12v through it; that's just asking for trouble. I was just unsure if I should be getting my current and voltage to an exact science here (I.E., using resistors or regulators before the board). I just dont want to be wasting perfectly good electronics, especially since high grade sound cards seem to be so elusive these days.

[KuroChou]

I think the point was confirming the thought process

if sound(regulator)maxV > battV > LEDfwd
then LED lights (without burning) for batt mAh/LEDmA hours.

I think that pretty much sums it up....

if you're using a regulator that makes it's current adjustments based on a static reading of the batteries' voltage, then the LED will always get dimmer when the supply voltage drops... unless:

you overshoot your minimum voltage (board Vdrop+LEDfwd) significantly, and use a separate voltage regulator BEFORE the current regulator.
This is more prudent and practical in direct drive, or relay drive circuits.
e.x. a white P4 wants 3.25V @ 1A; using a zener diode/transistor+resistor regulator, you can set an output voltage at 3.25, and then have a current regulator to keep the output at 1A, meaning that as long as your supply voltage is greater than 3.25@1A= 3.25W you will always have a fully lit saber.
This means that if you have a supply of say 4AA NiMH, you have a total power supply of (1.2v*2600mAh)*4=12.48W/h; 12.48Wh/3.25W=3.84 hours theoretical runtime.
Of course this is assuming that the batteries can make a complete drain cycle, which as has already been stated, can't be done without scaling the voltage.
Instead let's assume that the batteries lose their charge at a rate of 20% (or .96V) per hour, that means that our run time is actually reduced to an effective 1.61 hours maintaining maximum brightness, and completely failing to run afterward.
Considering that's without special packs or cells, it's not too shabby.

Of course 20% is a random hypothetical number, and we're also neglecting any voltage drop, resistance, inductance, or heat from the regulating circuits, sound board, and hilt in the equations.
Round it down a little and we're still hitting in the 1.5 hour range people on the forums have been reporting.

....I'm no expert, but I think that pretty much covers it for a best case hypothetical scenario.....

[Novastar]

Kuro, I think you're over-complicating things in some parts of your last post... and over-simplifying some others. One in particular regarding battery discharge...

Differing cells output the whole "less voltage over time/drain" in differing ways. A real-world example is the Li-Ion cell... which tends to have a "flat" discharge curve: the Li-Ion maintains a fairly solid voltage up until something like the last 10% of its charge... and then drops significantly (and a PCB protection circuit should be there to "save it"). Ni-Mh cells do not perform as such. Ni-Cd... different too. Alkalines... behave differently as well. Also, all of these cell types behave dynamically/differently under "heavy" drain (let's say =>2.5A)... or even "spikes" of drain (suddenly drawing ~4A, then back to ~1A).

Additionally, you have the fact that the human EYES can't truly tell the difference between LED type "X" driven @1A... vs. that very same LED "X" driven @1.1A... or possibly even @1.5A. Same goes for the voltage, as it is relational to current. Running @ 3.3v will often yield "the same" visuals (for HUMAN EYES, not light meters) as would running @3.5v or 3.6v. Possibly more, too.

Finally, although the theoretical runtime of a cell (let's say "2600mAh" rating) is a good ballpark figure... you AGAIN (as my previous post mentions) have:

* How does driver work... PWM? Fast "blinking" of LED? Basically direct-drive?
* How much juice does driver take/want?... 50mA? 87. 66mA?? How many volts, too...?
* If you have a speaker... how much is it draining?
* Ok, although the LED "specs" say "3.85v fwd" or whatever... when it ACTUALLY is being driven... is it sucking away MORE? Less? etc.

So, by the time you attempt to figure in all of these things... it's just a bloody mess, and it's a crude "guestimate".

To me--direct drive is pretty much the closest way you're going to see a GENERALLY "more predictable" runtime when you're considering that it's simply LED + possible resistor + cells. Then... sure... it's easier to a point.

But for example--on my CF sabers... between the LED driving (PWM, and btw it's a 4-die RGGB w/ FoC setup) and the speaker, and the board, and the indicator LEDs and the motor...

...well my the little "2600mAh" rating on my Li-Ion packs... really don't count for squat!! I consistently draw "PWM'ed" ~1.21A... plus the motor, plus the little LEDs, PLUS the speaker... and SOMETIMES we have the flash-on-clash (FoC)!!!

So... once it gets THAT complicated... good LUCK on trying to make a guestimate on runtimes!!! It lasts as long as it does. Something like 2 hours I guess. Who cares, I just recharge it, and actually I've never "run out" on any given day of usage... I throw it back on the charger.

[KuroChou]

Yeah... as I said, none of those figures were taken into account in the simple calculations, and by no means did I intend to, because then we're dealing with umpteen variables, entirely based on the builders preference.
I'm not the kind of expert to be giving that kind of advice anyway.
The limit of my electronic knowledge comes from a year of Electronics 1, my freshman year in high school, and whatever tinkering I've done since then.

Like everything else in this thread, I hoped my figures would be more of a guide than a rigid plug-and-play, and could be taken with a grain of salt and some personal directive on the part of the reader.
Anyone who has taken the time to read all the way through it, is likely more than just a casual builder, and is actually looking for some more advanced help.
As long as someone had the effort to look up the datasheet for their components, they could get the constants they need to solve their power and driver requirements pretty easily.
I agree that I severely oversimplified the matter of drain rate, but that's why you're here to correct the inadequacies of my posts.

I still feel like it's useful information so that, between the two of us, people with less electronics experience understand that even in a relatively static circuit, the saber electronics are practically a living breathing thing, and subject to constant change. Even things as obscure as the operating temperature of the saber can make a huge difference when calculating drain rates and voltage off of unregulated chemical batteries.
That being said, If they follow what I did, substituting with their own batteries, LED, and voltage curve, then they at least have a minimum ballpark, that they can add more complicated components to.
Most electronics calculations are fairly simple algebraic conversions, but they're a little harder to formulate off the top of your head.
I know in my personal experience, it's easier if I've at least seen what it looks like and how it works.
Once you start messing with thermal runaway, variable resistance, and drain curves, the it gets a lot more complicated, throwing exponentials into the equations, and making it less worth your time.
That said, it's again, more for a ballpark reference of what you'll need if given your specific components and desired runtime.

I kinda feel like the site needs a collaborative guide to advanced electronic mathematics. A kind of textbook or reference sheet of all the necessary terms and equations.....of course maybe I'm getting carried away again, as most people visiting for the first time don't even have the whole concept of Ohms Law.

EDIT: At this point I'm posting in the wrong thread anyway... I get a little sidetracked when it's too far past my bedtime.

[SithDuelist45]

I hate to take sides but i have to admit i agree with X and Novastar about the over complicating things. its like telling an 8 year old before he walks to school: "dont deviate from your default path to school". when instead you should say: make sure you go strait to school, dont stop for anyone or anything." not that im saying were all 8 year olds but you get the idea. lol and again im not trying to take sides, but as far as the Volts and mA's go im just starting out im am ordering my first electronics kit rightnow, so for a complete noob like me, i am getting quite confused lol...