Direct drive "J" Vf on lithium ion

Direct drive \"J\" Vf on lithium ion

Have I had too much to drink or does a "J" Vf look good for direct drive on a 3.7V lithium ion? If I do follow thru on this idea, I'll be using the Hotlips heatsink - we know how much THAT one can take /ubbthreads/images/graemlins/happy14.gif

... specifically, has anybody blown up emitters doing this /ubbthreads/images/graemlins/grin.gif

I'm shooting for a current level of around 1A sustained through the majority of the lithium ion's discharge curve.

Re: Direct drive \"J\" Vf on lithium ion

If you do, can you monitor its lux and Vf over time? /ubbthreads/images/graemlins/grinser2.gif

Re: Direct drive \"J\" Vf on lithium ion

Kevin, I DD a TWAK with a Pila168S without a problem. Max current was only a tad above 1A. If you used an unprotected li-ion, I think you will get more juice through the emitter. I don't have a bare cell, so can't offer you any mA figure.

Re: Direct drive \"J\" Vf on lithium ion

Charlie uses the TYAJs in his LionHeart and it's just controlled thru PWM. So with full duty cycle it should be just like your DD /ubbthreads/images/graemlins/grin.gif

What's the host for your latest project? Remember to include it in your uFAQ. I read it every other week /ubbthreads/images/graemlins/wink.gif

Re: Direct drive \"J\" Vf on lithium ion

I am direct driving a Lux III SYOL off of a pila 168S in a L2 bezel. Very bright, but does heat up fairly quickly. I would imagine that a J bin would suffer a much shorter life driven directly off of a 3.7 volt battery.

Re: Direct drive \"J\" Vf on lithium ion

i'm driving a txoj in a cmg infinity off a 3.7 volt li-ion aa 14500 cell. I'ts got a madmax+ but for the first couple minutes its in direct drive. the vf is measured at 3.40 so with a freshly charged cell there is a bit of OD. No problems yet.
jimmy

Re: Direct drive \"J\" Vf on lithium ion

Very cool.... thanks for the suggestions. I don't have a luxmeter but I'm working on that /ubbthreads/images/graemlins/smile.gif

Re: Direct drive \"J\" Vf on lithium ion

My TV1K on a fresh R123 runs 1.2 amps direct drive. On a fresh Pila 168, it runs 1.4 amps. My TYOL on a fresh R123 run's 1 amp. I have not put a J bin on it yet, but I imagine it would be pretty high. That's been MY experience.

Re: Direct drive \"J\" Vf on lithium ion

I have heard tell that a fresh Li-Ion can provide 4.2V to the LED. This I do not know form experience. For the heck of it, I just set my bench supply to 4.2V and for safety (relative term! /ubbthreads/images/graemlins/tongue.gif ) I set the current limit to 2 amps. I took a TX0J I have mounted on an E-screw and hit it with the power leads. It hit 2 amps at 4.1 volts!

I suggest you do some testing on the LED you plan to use with the batteries you will be using!

Re: Direct drive \"J\" Vf on lithium ion

The reason I ask is that fresh NiMh can also deliver 4-4.2V. Lithium ions, hot off the charger will start at 4.2 then sag, but I don't want to blow up $15 worth of LED to find out whether they sag in time.....or not! /ubbthreads/images/graemlins/grin.gif Thanks for the little 'experiment' and glad you did not sacrifice another to the blue smoke gods in the process. That took guts. I'd limit at less than 2A myself. /ubbthreads/images/graemlins/clap.gif

I notice 3rd_shift uses a 0.2 ohm resistor to trim down J bins for direct drive on NiMH. Maybe that's a good idea I need to think about too.

Re: Direct drive \"J\" Vf on lithium ion

Go with a K Vf luxeon. It's safer all around, since the Vf of the lux will drop over time. BTW, I've cooked a few J Vf luxeons DDing them on li-ions.

Re: Direct drive \"J\" Vf on lithium ion

Since the LH uses J bins in DD, what prevents the leds from being cooked? Is it down to heatsinking?

Re: Direct drive \"J\" Vf on lithium ion

LH is DDing its lux? i just heard that now

Re: Direct drive \"J\" Vf on lithium ion

Thanks Chop. All I have are two TY0L stars and one TX1J (thanks - that was one of five from you) left. I'll probably look into the resistor idea. Don't feel like sacrificing a Luxeon to the photonic gods /ubbthreads/images/graemlins/smile.gif

Re: Direct drive \"J\" Vf on lithium ion

On the LH, the juice is still going through a PWM for the dimming function, so some is getting soaked up there. You just have to remember that heat and time work against you in a DD Li-ion setup with a J Vf luxeon. The Vf of the lux will drop over time. Then you have the heat issue. With proper sinking you will probably be OK, but I tend to really run my lights. I'll leave them on until the batt dies and then pop another batt into it and run it some more. The J Vf luxes that I killed were in a KL1 head that I modified. It got mighty hot and that's probably what killed the luxes.

In any case, my opinion still stands. If you are going to DD a luxeon with a li-ion, a K Vf is the best way to go for a dependable, trouble free light.

You just have to take what I say with a grain of salt. I'm really not into pushing things to the limit. I like to stick with what works and keeps on working.

KevinL,

If the TX1J is what you have to work with, then just use a little resistance. You might just want to run two 2 ohm resistors in parallel and that will get you a good amount of light. 1A is a good target current. Luxes start to get really inefficient above 1A and the return above 1A isn't worth the heat and runtime sacrifices.

As for my statements about performance gained by going over 1A not being that great, I'm talking about practical performance, or what the eye can see or discern, not what a meter will tell you.

Re: Direct drive \"J\" Vf on lithium ion

[ QUOTE ]
Chop said:
On the LH, the juice is still going through a PWM for the dimming function, so some is getting soaked up there.

[/ QUOTE ]
As I understand it, on *high* there is no pulsing - so on hight there is only insignificant loss of going through the driver. For all intents, high is full-on DD.