Direct drive a lux3 with a pila 150/168?

I would like to know which special safety measures should be taken to drive a lux3 in direct drive mode using a Pila battery. (150 or 168)

My main concern is the fresh charged pila that outputs 4.2v instead of the nominal 3.7v

Links to previous threads are welcome!


Thanks


Pablo

all depend on the voltage of the led:

with a L bin absolutely no problem

with a K bin slightly overdrived but only with a fresh battery

with a J bin the led is hard overdrived and when the battery is fresh you risk to blow all. but if you think the total output... /ubbthreads/images/graemlins/cool.gif

I guessed an answer like that, K or L bin should be the solution, but a L one will be borderline with its lower Vf spec and K with it higher.

So whats the best choice? K or L ?

a L bin should drop is Vf in the first hours according to this Thread so its a safe bet.

I wonder what will happen to the J binned Lionhearts /ubbthreads/images/graemlins/confused.gif


Pablo

PEU,

I'd go with the K Vf. It'll run nicely on the Pila. I've done lots of them.

just in time for the huge batch of TX1J & TWOJ's coming...

/ubbthreads/images/graemlins/jpshakehead.gif /ubbthreads/images/graemlins/smile.gif

Pablo

If you go with a J Vf and a 168S, you'll be seeing about 1.2A to the luxeon, IIRC. Shouldn't be a problem with good heat sinking.

See this thread for reference Thread

I used a 0.6 Ohm resistor in the tailcap to limit fresh charge current to just under 1 amp. And yes it gets warm. But it is my favorite light. MonoLith+

i can't understand why you have fear of overdrive your luxeon... i drive a lux-I at 900ma, a lux-III at 1600, a lux-V 1400...

ok they can't last thousand hours with this overdive but where is the problem? how much time can pass until you decide to upgrade further the led? /ubbthreads/images/graemlins/grin.gif we are flashaolic don't forget /ubbthreads/images/graemlins/wink.gif

I have a design in the drawing board, and want it to work for a long time without the need of user replacements.

I know that if posible, flashaholics like us, will go the extra mile(s) to find a TWOH for it /ubbthreads/images/graemlins/grin.gif


Pablo

[ QUOTE ]
PEU said:
I have a design in the drawing board, and want it to work for a long time without the need of user replacements.


[/ QUOTE ]

IF that's the goal, you might want to rethink DD. Think about it, how many guys have lost their LED in DD and how many is resistored or regulated lights?

The thread we just had on how Vf (the very factor you're counting on to keep current under some control) goes *down* with time is also a factor. Meaning current will go up....on it's own, later.

Doug Owen

[ QUOTE ]
Doug Owen said:
[ QUOTE ]
PEU said:
I have a design in the drawing board, and want it to work for a long time without the need of user replacements.


[/ QUOTE ]

IF that's the goal, you might want to rethink DD. Think about it, how many guys have lost their LED in DD and how many is resistored or regulated lights?

The thread we just had on how Vf (the very factor you're counting on to keep current under some control) goes *down* with time is also a factor. Meaning current will go up....on it's own, later.

Doug Owen

[/ QUOTE ]


That can be a rather significant factor.

Also, with the Vf bin width there will be variation from light to light.

Then the Vf drops as the emitter heats up. Basically it drops by -2.0mV per degree C. So, say the flashlight body heats up by 30C, there is another 0.06 V drop in the Vf.

Of course, the LionHeart is DD at full brightness, and it is praised. I wonder how things will hold up when the emitter Vf drops by 0.3V over time. The current will go up alot, then if the light is allowed to heat up, more issue. Time will tell...

The LionHeart is a good test of the DD concept, maybe you could watch how it holds up over time.

Direct driving a luxeon with a Pila really isn't rocket science. When ever I've driven a K Vf Lux III with a Pila 168S, I get between 800 -900mA to the luxeon. Even if the Vf shifts a whole range over time, you might wind up with something over 1A getting to the luxeon. That's still no big deal, as long as you have proper heat sinking. If you go with an L Vf luxeon, the output will be too low to satisfy most.

Sorry, I'm just a big fan of direct driving luxeons with Pilas. With proper heat sinking, current isn't a problem as long as it doesn't get crazy. The output of the Pilas is so flat that the light almost runs as though it was regulated.

What really needs to be done is to charactarize a Pila cell at various current levels to see what its terminal voltage is at those current levels. Then you can definitively see what kind of danger you will be in with DD.

Lets say the Pila maintains 3.7V at 900mA (mid-life), and your Luxeon's initial Vf is 3.7V at 900mA. Then for the majority of battery life, the current will be around 900mA, excepting the first few minutes (which is really the most critical, since it's when damage can be done).

Anyways, if the Vf drops by 0.3-0.4V (which I've observed with K Vf luxeons running at 1A), then the Vf of the Luxeon will be around 3.4V-3.3V at 900mA, and 3.7V at about 1.5A. Now, you won't get 1.5A, because the extra current will pull the cell voltage down, but, you may get around 1.2-1.3A, which may not sound like a whole lot more, but consider that your design just shifted by 40%, and power dissipation in the emitter went from 3.33W to 4.5W (+35%). Even with perfect heat sinking, junction temperature jumped from about 70C to about 85C (when the body is at room temperature). Initial current has changed in a similar manner, which means with a fresh charge, you could be slamming the luxeon with nearly 2A, for about 8W of dissipation, for an initial junction temp of 130C (5C below absolute maximum)

So you really should characterize your power source, and calculate the conditions of the worst case scenario. So that means measuring cell voltage at various current levels, both freshly charged, and about half discharged. Is this something that SilverFox has done with his battery testing?

Just some food for thought.

[ QUOTE ]
evan9162 said:
What really needs to be done is to charactarize a Pila cell at various current levels to see what its terminal voltage is at those current levels. Then you can definitively see what kind of danger you will be in with DD.

Lets say the Pila maintains 3.7V at 900mA (mid-life), and your Luxeon's initial Vf is 3.7V at 900mA. Then for the majority of battery life, the current will be around 900mA, excepting the first few minutes (which is really the most critical, since it's when damage can be done).

Anyways, if the Vf drops by 0.3-0.4V (which I've observed with K Vf luxeons running at 1A), then the Vf of the Luxeon will be around 3.4V-3.3V at 900mA, and 3.7V at about 1.5A. Now, you won't get 1.5A, because the extra current will pull the cell voltage down, but, you may get around 1.2-1.3A, which may not sound like a whole lot more, but consider that your design just shifted by 40%, and power dissipation in the emitter went from 3.33W to 4.5W (+35%). Even with perfect heat sinking, junction temperature jumped from about 70C to about 85C (when the body is at room temperature). Initial current has changed in a similar manner, which means with a fresh charge, you could be slamming the luxeon with nearly 2A, for about 8W of dissipation, for an initial junction temp of 130C (5C below absolute maximum)

So you really should characterize your power source, and calculate the conditions of the worst case scenario. So that means measuring cell voltage at various current levels, both freshly charged, and about half discharged. Is this something that SilverFox has done with his battery testing?

Just some food for thought.

[/ QUOTE ]


Yes, but re-do the numbers for an aged emitter, and with heating of the flashlight. Also consider a K bin has what, a 0.3 V range to start with....Try it with emitters on the low end of the bin, dropping the Vf for age and for temperature...

will do the test when the pilas are with me, with my soon to be working CPF logger /ubbthreads/images/graemlins/smile.gif


Pablo