Downboy VS Badboy to run a Lux3 on a Pila 168s?

[Kabible]

A buddy just got a PRT-HA-NAT-917 from McGizmo. He's using it on an L4 body. Impressive! /ubbthreads/images/graemlins/bowdown.gif
My question is this; to run a Lux3 in this head with a Pila 168s, which would do better? A Downboy 917 that Don used to take advantage of two 123s or a Badboy 650, 750, Etc. that would be limited to the use of the Pila in which case the only danger would be if someone else or maybe one my other personalities used 123s in it.
I have two BB750 Lux3s in Minimags. The one I mounted an SWAK on is pulling 1.5 to 1.6 amps. The other one with a Wayne's T rated emitter pulls up to 1.9 amps!! /ubbthreads/images/graemlins/ooo.gif It's pretty bright for a 2.4v Mini but I never run that one more than a minute or two. I'm afraid it will overheat & pop /ubbthreads/images/graemlins/icon23.gif.

Opinions?

Thanks, Brian

 

[Klaus]

Hmmh - the jury is still out on this it seems - the voltage from a single Li-Ion (what the PILA actually is, a pretty good and protected one) covers a range from 4.2V when full to 3.0V when depleted. This also is the range a LuxIII is well within. IMO the perfect driver circuit would be a combined buck/boost like the circuit used in the SF KL1 or WYs Wizzard series, but these aren´t driving a Lux3 fully though. The drawback of a buck/boost typically is less efficiency. I think there really is a need for such a high efficiency high current buck/boost driver circuit (next gen wizzard ?) for exactly this application - a similar situation does exist for 3 NiMh/NiCd cell applications as well.

As of today with the avaible circuits one of the relevant points discussed lately was the actual Vf of the LED in use. If you have a pretty low forward Voltage (Vf) LuxIII like a "H" or "J" the use of a buck circuit (downboy) seems advisable, if your LuxIII is towards the higher end of the range like a "L" or "M" the use of a boost (badboy) looks better then. For a middle range LuxIII like a "K" one might get away direct driving it but I caution against just throwing things together without measuring the actual current draw then as Lux3s still vary widely even inside the same Vf bin.

Overall I think you could roughly follow these guidelines unless one of our resident gurus ™ jumps in - use a downboy with low Vf Lux3s, use a badboy with higher Vf Lux3s. If you have both type of LEDs avaiable I personally would favour the low Vf and downboy combo as the runtime should be longer and efficiency better and you can set the Downboy to higher currents too. The Nexgen Badboy might change this then.

Just my 2 Euro cents and YMMV

Klaus

 

[balrog]

I run a Badboy1000 on a TV0J Luxeon III on a Pila 168S. Fully charged, I haven't had any problems and it appears to be regulating fine (current draw on the Pila is just over 1A). I think that the combination of innefficiencies in the convertor, plus internal resistance of the Pila mean that in practice the convertor isn't "seeing" the full 4.2V of a fully charged Pila. Vf of the Luxeon is 3.7V so I guess it's seeing at least 0.5V less than the open circuit voltage of the Pila. Also, given that the current draw from the Pila is just slightly more than the current the convertor is outputting to the LED fits well with this guess. I haven't had the opportunity to try this with a Luxeon with an H forward voltage.

If you do use a Downboy, I highly suspect that it will be regulated for a very short period of time, or not at all.

Just my 2 Australian cents worth, which is worth less than the usual 2 cents worth /ubbthreads/images/graemlins/grin.gif

 

[dat2zip]

Re: Downboy VS Badboy to run a Lux3 on a Pila 168s

You can safely add 0.3V to the Badboy when driving near Vf.

That is to say, if your Vf is 3.5V, you can add 0.3V and that would be the absolute tops (according to me /ubbthreads/images/graemlins/smile.gif ) that you are safe to operate the Badboy and stay withing acceptable limits.

Of course, you might get by with more margin or differential than that.

If the battery sags a few tenths of a volt from 4.2V (let's say 0.3) of which I was corrected before on these batteries and my mind fails me what the numbers were. Then you could get by with a Luxeon with a Vf of say 3.9V - 0.3V or ~3.6V @ 1A.

If you could use a Luxeon or select one with a Vf of 3.7, you would be safer.

The revision 4 has less margin utilizing a different diode that sets this 0.3V margin. The older boards had probably a margin of 0.4V. So, be careful if you are using a revision 4 board.

Setting it up outside the flashlight is not too difficult to setup and test your exact configuration. If it works /ubbthreads/images/graemlins/thumbsup.gif if not try a different Vf LED.

Wayne

 

[Kabible]

Re: Downboy VS Badboy to run a Lux3 on a Pila 168s

Ok, I get most of this. Great Info BTW. Thanks. Klaus, I'm also curious about just direct driving an emitter with the Pila, considering the proper Vf. I've changed the 1 watt in some SL 3 AA Luxeons to DD 3 watters and had no problems with alkalines or NiMH cells. I know that two of the Lux3's were SWOK's but the others I modded where of unknown values. Wayne at Elektrolumens doesn't usually say.
Now I know there's a big difference between 3 NiMH AA's at 3.7V and a Pila at 4.2V.
I'd like to know more about using a Pila to DD a Lux3 and which Vf would be a good choice. The K sounds like a good starting point.

Brian

 

[Klaus]

Re: Downboy VS Badboy to run a Lux3 on a Pila 168s

Kabible,

IMO its all about proper heatsinking and some stress tolerace on your and the emitters part /ubbthreads/images/graemlins/grin.gif

I did some DD-ing with a LiIon with a TYAL and its nice and at reasonable current levels depending on cell used - based on that I would say a "K" would be a good starting point.

Based on differences in actual Vf of the emitter used AND varying internal resistance of different Li-Ions as well your result may vary a lot and measuring the current is advisable.

Don´t confuse the "mid-point" voltage of NiMh/NiCd of 1.2/1.25V or 3.6/3.7V for three cells with the "fully loaded" voiltage of a LiIon at 4.2V - actually a single Li-Ion looks pretty much the same as 3 NiCd/NiMh cells and has a mid-point voltage of 3.6/3.7V too, the "fully loaded or fresh of the charger" voltage for 3 NiMh/NiCd is ~4.2V as well.

Using a current regulated circuit definetely is much easier

Klaus

 

[Chop]

Re: Downboy VS Badboy to run a Lux3 on a Pila 168s

I've built many lights around Pila cells. Both direct drive and regulated. I won't pretend to know the first thing about electronics, but I have survived a lot of trial and error with the help of gurus like CM.

When I DD a lux III with a Pila 168S or 150 A, I usually use a lux III with a "K" Vf. IIRC, this will yield about 1.5A to the luxeon which it will handle with proper heat sinking. The circuits that I usually use are the BadBoys. I haven't had any problems with even "J" Vf bins. They run really well, albeit hot.

A Pila WILL NOT run a Lux III in regulation, or if it does, it won't do so for long. It does, however, run well. For the greatest flexibilty, you could use a downboy so that you could run a Pila or 123's. With the Pila you will get a sort of a DD mode at about 700mA getting to the luxeon.

Hope this helps.