Luxeon Saber - to drive, or not to drive?

[Olos Nay]

This thread is intended to be for technical discussion regarding luxeon saber blades, more precisely "how should I connect the thing in order to get the most out of it".

If you are still trying to figure "should I get EL or LED" please look at some other threads in the prop electronics section... if you know you want LED, this thread is to discuss about the various ways of making this.


I personally "make" my luxeon sabers. To this end, I like to get the "lightsaber luxeon driver" from Corbins Components. It makes a nice bright blade and its fade-in, fade-out makes good retractions of the blade, that's without the "Clash and Lock" flashy effect.

However, I recently started to wonder about making the blade glow without the driver for various reason, but mainly to reduce the parts count on a stunt saber.

Therefore, I went the "direct connect" route of making a 4-AA battery pack pass trough a 2.2 ohm resistor to a 3W luxeon led.
I was surprised to see that the possible 80 lumen of my 3W cyan led wasn't brighter then what I get with the final result...

I strongly believe that the AA batteries cannot supply the necessary current to fully operate the luxeon LED. I know there are drivers for that, and am thinking of experimenting with them, but it would void the idea of having less components...

here's a pic of 2 different sabers:

the top amber one is a 1W amber luxeon star/o driven with a corbin driver - that led is rated 45 lumens.
the bottom one is a 3W cyan luxeon star driven direct from 4 AAs with a 2.2 ohm - this led is rated 80 lumens.
From my point of view, the amber saber really uses the led's 45 lumens output, while the cyan doesn't emmit all of its possible 80 lumens.

I know that the corbin driver uses "PWM" and technically generates the best of the luxeon led, but I checked the voltage out of the 4 AA batteries, and it drops to 4.23 Volts when powering the led.
I really thinks that the AA batteries just cannot supply ennough current to completely light the luxeon.

I most likely will start to look about trying out some buck driver or something specific in order to get the most out of the 3W led, even if it means cranking up the number of components in my duel saber.

does anyone else in here have experience in various ways of driving the luxeons?

[Jeffrek]

As youve discovered direct drive via a resistor works, but nowhere near as well as a proper driver does. The direct drive method also has another disadvantage. The drivers work by delivering a constant current to the led(s) regardless of voltage. In effect this means that the led stays at full brightness even when the batteries start to become depleted.

The direct drive doesnt. Batteries as they run out of power drop in voltage. With a fixed resistor you have to know your working voltage to calculate its value to supply the desired current to the led. This is fine when the batteries are new but as they progress their voltage drops which means the led receives less current. This in effect means your led drops in brightness.
This becomes really noticeable near the end of the batteries life, you will see a gradual fading off of intensity. With a driver like Corbins the transisition is more abrupt, more like works to doesnt work rather than any fading of light intensity.

An intermediate technique commonly used to make leds brighter is pulse operation. This is where you drive them at higher currents than the led is rated for but for very short lengths of time (a few milliseconds). In effect you flash the led ON and OFF very quickly. Usually the off time is 2-20 times longer than the ON period. This gives a brighter output and a longer run time too as the led is only on for a percentage of the time.
This method does have a few things to watch out for though. You have to flash the led very quickly. If you dont flash it fast enough then then you move the sabre blade rapidly it will appear to 'flicker'. Taking a picture is usually best for catching this, the arc of light produced by the blade will have bright and dim sections where the high speed camera electronics catches the pulsing of the led. In effect you need to flash the led at 20khz or more. As this is still a direct drive method you will still get the fading problems as the batteries die too but less noticeable than the pure battery/resistor method.

It also doesnt help with your component count Olos as you need the electronics to control the flashing speed. Of course it can be done with a modern 8 pin microcontroller, a mosfet transistor and a few resistors so once built and programed it would be quite small.

You just cant beat a proper constant current driver though Like yourself I like Corbins driver, its a good design and has the fade in/out and also the clash effect if you want to use it. It does however have one problem.
Its bloody big.
There are quite a few sabre designs where I cant fit it in due to its width.
For those sabres Ive found a physically small series of drivers from Konlux, they are about an inch square. While they dont have a fade in/out, just off and on they drive the leds just like Corbins. They do drivers with output currents from 350ma all the way up to 1400ma for the K2's. Just choose the current needed to match your led.

I get mine from a German company www.dotlight.de/shop/index.php?currency=USD&cPath=79_181&sort=2a but im sure you could find a supplier in the US or something similar (and cheaper).

Ive just got a couple of small drivers from a canadian company that I will be fitting to a new sabre at some point (after Ive finished the 4 others I have to make first).
On paper they look good, you can easily fit a brightness control or interface to a microcontroller to get a fade in/out etc and they are small too. Prices were reasonable to buy but by the time they had arrived in the UK they ended up costing 2x as much as the original order once shipping and import duties/fees were added on (US$82 for the parts, $43 for the shipping and another $42 for import fees once they hit the UK). I'll let you know what they are like once Ive fitted one to a sabre.

[Starkindler (The Naked Jedi)]

good info here. Thaks!

also of note is the fact that whatever the Lumen rating, certain colors will look brighter than others. There was a chart somewhere (maybe at TCSS) that illustrated the difference. Green will look the brightest and Cyan always looks a bit pale to my eye.

[Olos Nay]

Tenric: I understand about eye perception of colour... but a blue 80 lumens will definately have a brighter-to-the-eye output then a red 55 lumens.

But I agree cyan isn't all that brightness I was hoping for.

I measured the current drawn in my circuit. I must be hollidays tired as I totally didn't think of looking at it before. Anyway, with my 4 AAs, when the led is on, I draw 460 miliamps... even with 4 brand new duracell batteries, I cannot get most out of the blade.

Regardless of lower light emission, the blade is still bright compared to other types of saber. Its still impressive, it just **** when you know its not up to its full potential.

Jeffrek, I was aware of the direct current not being efficient, but I was really expecting "over time" to be "after some usage"... I still haven't found a way to light the blade to the full brightness even for one sec.

I think "THE" way will be to have "some" driver, and I am all up to trying other drivers then Corbon's for that saber.

Could you point me out that canadian company for the latest driver you're trying - I'm in Canada, it should have the opposite effect to you regarding shipping. I might want also to check at the ones at lumileds.

I might decide to go 5W for this saber, the cyan 5W are 160 lumens... interesting...

[Jeffrek]

Olos Im surprised its only drawing 460ma. Either the batteries cant supply an amp of current which for duracells really really surprises me as Ive used them in high draw circuits before or theres some resistance elsewhere in the circuit. Have you checked how much resistence the wire and battery holder has ? Sometimes the contacts on a battery holder can get a little oxidised so need a light abrasive polish with a poliblok or simlar to remove it.

If its the batteries then you could try 4x rechargeables. While they dont have as great a capacity they can supply a greater peak current under load. IIRC they would use a 1.5ohm 2W resistor for a 3w led.

The canadian company is luxeonstar. Looks like they do everything, leds, optics and drivers. The ones I ordered are www.luxeonstar.com/item.php?id=863&link_str=240::241&partno=3021DE1000
Mainly due to their small size but the ability to swop them from sabre to sabre by making/using a wiring harness for the connector pins and the fact that at a later date I can integrate them easily to a micro if I want to control things like brightness etc.

[Starkindler (The Naked Jedi)]

can corbins driver handle a 9v battery?
Perhaps with a resistor?
might that provide enough "Umph" for the LED?
if so it would solve the power problem and take up less space.

[Olos Nay]

Tenric, the problem with 9V battery is the duration... I really prefer keeping with AAs or AAAs to have 3 times the battery life. (you're happy to get 900 mAh with a rechargeable 9V, so about 1 hr of light)
Also, note that the corbin driver can take from about 3.5 to 12V, but the problem I am experimenting isn't with corbin's driver, but direct connection of the LED to batteries.

Jeffrec, I was running the batteries by a 2.2ohm resistor.
since the 6V/2.2ohm resistor don't give out what I was expecting, I decided to do some trial-and-errors on new years day. By removing the resistor and running the same batteries, I can get up to about 650 miliamps... but I don't have anymore new Duracells to try out, I would expect to get at least a little better. The thing is, the batteries don't stay fully charged very long, and the current tends to drop quite quick.

However, I tweaked a bit, and with noname batteries, if I put 8 of them I get the nominal 900 miliamps necessary to get a nice brightness. Problem is (aside from room available) that the batteries tend to overheat as they are discharging. and I really say overheat - within 15 minutes its burning to the touch.
I have given initial tests for rechargeable batteries and I get the necessary power... I'll have to put back a resistor ;-)
I am happy I decided to use a 9V connector for the electronics, it gives me a huge advantage for experimentations...

[Jeffrek]

What sort of MM are you using ?

[Olos Nay]

Its a old school radioshack brand digital multimeter I got prior of getting my EE, but it works OK when you know how to get the most of it.

I remember I chose the model because it has a 9600 baud serial port in it ^_^ ain't I the software guy??

[vortextwist]

I have heard of people using a buckpuck or micropuck. I believe it is like a driver where it keeps a steady supply of volts. I think I am saying this right. There are alot of stuff on this over on the tcss forums.

[Olos Nay]

I agree there's a lot on constent current drivers discussion at TCSS, but not much on direct battery connection.

After a few days of on-and-off trying the saber with my NiMH batteries, I measured again, and the current drawn by the led has dropped from a nice 950 miliamp (the 3W likes 1000) to a lower 750 miliamp (lower brightness as well) 2 conclusions I have from there.

1- I compared it at that point with an Obi-Wan MRFX - the brightness is similar, so at full current I believe the 3W luxeon to be brighter then the MRFX sabers.

2- even with NiMH, the battery won't hold full current long ennough for our needs. While its working on a suboptimal level, one might want to go with some sort of constant current or PWM driver.

I'll dig out what can be done in the ways of cheap PWM drivers for Luxeon, and constant current drivers as well. Whatever driver to be used must be able to drive the luxeon at optimal efficiency...

My goal is to find "the cheapest efficient way" to drive the led, to attract more people in the luxeon sabermaking. (I already have something interesting but suboptimal)

[Starkindler (The Naked Jedi)]

I am all ears since I have decided the 3 sabers I plan to build for my kids and I will be LUX. Theirs will be as simple as I can get them (ie; no Corbin driver). Mine may be more elaborate (since I would love rechargeables and a port along with sound), but we will see.

I am not very knowledgeable in electronics but am a seriously fast study so "teach" away!!

[Olos Nay]

What you need to remember when you use a luxeon is that its powerful ennough to burn itself. The key is to cool it down, using an heat sink. I suggest using thermal compound between the LED and heatsink.

Apparently the new K2s don't need much cooling, but I haven't tried them yet.

If you want a rechargeable port, I think corbinscomponents have the wiring diagram for that... for sound, besides gutting commercial sabers, I haven't found a good solution so far.

Hope this info prooves being useful.

[Starkindler (The Naked Jedi)]

yanlauzon said:

What you need to remember when you use a luxeon is that its powerful ennough to burn itself. The key is to cool it down, using an heat sink. I suggest using thermal compound between the LED and heatsink.

Apparently the new K2s don't need much cooling, but I haven't tried them yet.

If you want a rechargeable port, I think corbinscomponents have the wiring diagram for that... for sound, besides gutting commercial sabers, I haven't found a good solution so far.

Hope this info prooves being useful.

a number of those at TCSS use K2s.....I think there is even a new heatsink as well.

they are also working on some possible sound alternatives... including a custom/programmable board.

Corbin has been very helpful with info.

[vortextwist]

the thing I have heard about the k2's is the bubble on the led is not hard it is soft, James3 from tcss was saying they messed one up trying to put the lenz and holder on. I think there is a few guys on tcss that did recharge ports.