Direct drive question.

Hello all. I want to build a Space Needle, using a 2c body and a 5w emitter. I was looking at MrBulks website and saw that it was direct drive and that he used 3x 3v cr123's. My question : Is this 5w emitter light direct driven from the 9v supply without the aid of a resister? If so wouldn't this be about 2.5v over the vf of the emitter? Maybe i'm missing something...That's why I'm asking. I tried to search for direct drive posts on the forums but had no luck.
Thanks in advance for your help.

Yes it is. This is overdriving the LED with voltage so its current draw will increase. One thing that Mr. Bulk did is use thin gage wire so there will be some resistance and drop the voltage and current a touch.

A few other members have found out the expensive way that direct driving a 5 watt luxeon this way doesn't always live happily ever after.
A higher than average vf 5 watt and a little added series resistance is a good idea.
Plus most luxeon emitters do lose a bit of thier forward vf with usage for some reason.
If you score a low vf lux5, Try for a downboy 750 regulator if your soldering skills are up to it.
BTW:
If these weren't such good light emitters, I would guess that these are electronically,
some of the worst diodes for electronics use on the market today.

Just like with any direct driving, there are risks. Over voltage is not that much of an issue, it is the heat resulting from high current that kills LEDs. Those 3 x CR123s will put about 1.8-1.9A to the LED with fresh batteries and will taper down in current. Refer to my graph in the MR-X thread below. Heatsinking is the key in reducing the risk of LED damage.

I'm going to try DB1000, Lux V 2 pila 150A's in a 2C /ubbthreads/images/graemlins/smile.gif

Just waiting to get another 150A since one of mine does not work /ubbthreads/images/graemlins/frown.gif

Ctechlite,

The Space Needle will need a lux V with a Vf of "U" or deeper in the alphabet to handle the 9 volts.

Not sure if what I'm about to say is necessarily true, but using a 6AA setup may be less current draw. Any smarty pants /ubbthreads/images/graemlins/wink.gif care to state whether this is true or not?

My direct drive Lux V is a W2W, so I'm about the most 'protected' as one can get unresistored. It's sitting on an O-sink heatsink.

Orion is correct in that 6 plain jane AA alkaline cells will not provide as much current a 3 CR123A cells. Other AA cells (Energizer L91 lithium AA) might provide all the current of the triple 123a and then some.


Adding a resistor is simple to do and will transform the light from a "freakishly-bright-I-Hope-it-doesn't-burn-out-this-time" toy to a wonderfully bright tool that should last for a long time.

A 'W' Vf is still only able to handle 7.83V - 8.31V at it's rated current.

Daniel

Definitely trim it with a resistor. One of the CPFers in B/S/T fried two VV1Us in the process of building a SN2.

I would think it hurts to fry two LuxVs back to back..

[ QUOTE ]
gadget_lover said:
Orion is correct in that 6 plain jane AA alkaline cells will not provide as much current a 3 CR123A cells. Other AA cells (Energizer L91 lithium AA) might provide all the current of the triple 123a and then some.


Adding a resistor is simple to do and will transform the light from a "freakishly-bright-I-Hope-it-doesn't-burn-out-this-time" toy to a wonderfully bright tool that should last for a long time.

A 'W' Vf is still only able to handle 7.83V - 8.31V at it's rated current.

Daniel

[/ QUOTE ]

That is true, but the Rated current for a Lux V is ONLY 500ma, (most people do not drive them this way!) so the additional volt could push it up to around 1000 ma or so but I believe that is still considered safe for a lux V on a Hotlips.

Rated at 500mA? I thought LumiLEDs document DS40 - "Luxeon V Portable" specifies their characteristics as 700mA.

I'm driving one emitter at 917mA /ubbthreads/images/graemlins/evilgrin07.gif so far, so good!

Not to frighten anyone, but every one of my 3 and 5 watt luxeons has dropped a bit in forward voltage with use.
Even a w2w will eventually lose some of it's resistance to current.
Resistored, or regulated are very much the ways to go for a sn2 clone.

I'll just put a dummy AA in place of one of the AA batteries, making it 7.5 volts in, before load. That Lux V should last a long time! /ubbthreads/images/graemlins/wink.gif

Seriously, this talk of drops in forward voltage with these LEDs is a bit concerning. Is this caused from overdriving, or will even underdriven Lux III & V's experience this?

Underdriven do it too.
I have some that started off at 650-700 milliamps that are now approaching 800-950ma on the same nimh batteries.
I can just see where some TWOJ bins would eventually sink down to TWOH forward vf after a while. /ubbthreads/images/graemlins/thumbsup.gif

I think I was the first to offer extremely overdriven DirectDrive lights for general sale.

To date no LGIs, Classic, Super, or otherwise, have come back to roost because of burned out Luxeons (and we're talking over 600 units during a most exciting two year span).

The Space Needle was simply an evolution of that all-risks-be-damned concept, and although about three (yes, 3 total) have indeed "burned out", it was a mistake on my part for pushing the boundaries and risking "T" Vf-binned Lux 5s in them, after which I only used "U" and deeper-into-the-alphabet (higher Vf) bin codes.

If you are looking for forever durability, then drive them at spec or even underdrive them. You will fall asleep while getting just acceptable light levels, and yet nothing really "wow" will jump out at you unless you stick it in a big reflector (for example a Lux3 driven at ~700mA in a big Maglite will throw nearly as far as a direct driven one, but again this is a function of the reflector size).

BUT - if you are looking to show that LEDs are indeed knocking on the proverbial incandescent door, or would like a crowd to gather round seeking the source of that super-white alien-like beam reaching up into the sky, or wish to drive a solid-state light at virtually 100% efficiency, look no further than a Direct Drive Luxeon light to get you there.

AND - if you think of this as a way to push the envelope in LED development, then the Very occasional "bulb changes" involving desoldering/resoldering two wires is simply a small collateral cost for the pleasure of participating in leading-edge lighting development, the first real advance in portable lighting since Thomas Edison first literally burned a sliver of bamboo used as his bulb filament - and then it almost even begins to make just a little sense... /ubbthreads/images/graemlins/naughty.gif

You only live once, so ignore the sphincter-squeezers and BUILD that Space Needle. You will never regret it.

(but use 30- or even 32-gauge wire...) /ubbthreads/images/graemlins/grinser2.gif

[ QUOTE ]
KevinL said:
Rated at 500mA? I thought LumiLEDs document DS40 - "Luxeon V Portable" specifies their characteristics as 700mA.

I'm driving one emitter at 917mA /ubbthreads/images/graemlins/evilgrin07.gif so far, so good!

[/ QUOTE ]

Oh your right 700ma. if thats what the docs say I think someone told me 500 I have never looked. I'm going to drive mine at 1000 anyways. hell for $10 more you might as well regulate it!

Thanks for all of the help! 'Specially you Mr Bulk. I need to gather some parts now...

With all due respect to Mr Bulk (and I do respect him a lot), you really should go with properly sized wire and a resistor. The use of 32 guage wire is meant to be an imprecise low resistance resistor. The exact resistance will depend on the length and the guage, and whether it's stranded or not.

The advantage of the resistor (even a low value one) is that 1) it is an exact amount of resistance and 2) it will disipate the heat where you want it instead of at random spots inside the light.

Mr Bulk is right, though. If you want a light that blazes brightly but briefly and one that will wow people, direct drive is one way to do it. Personally, if I want to overdrive something I'll use a converter to explicitly abuse it. That way it does not dim as quickly as the battery dies down.

Daniel

I made a couple kick-arse DD lights for laborday and they really did the wow-factor.. but i'm putting 1200-1300mA into the lux3s.. http://rouse.com/flash has the lights.

for the nano project i'm doing we developed an LDO driver that holds back the voltage while the battery drops, so it acts like a DD with an inline resistor, but that resistor changes smartly... it ended up that i can max out the battery's suggested current max and have an absolutely flat brightness output for the entire usuable runtime.

It was not hard to build the driver, it only has 4 components and i put it into an 8mm circle.. look for 35mV LDO driver in batteries not included.

-awr

Is it worth it building a space needle with two 150As and a downboy of some sort (like 1200)? Realistically, how long will that converter actually be doing something? Just the first five minutes? I wish there was a better option. As far as I know, the wizard2 can't drive 5ws yet. I've had a a w3u (and C hotlips) sitting here for the past 8 months because I haven't decided how do drive it yet...

But now that I have two 150As on the way, its time to do something.

Mark