Some Direct Drive questions

Some Direct Drive questions

Looking to build some DD Mag light mods. I have three hosts, a 2C, 3D & 4D. All will be using Hotlips or O-Sinks. The 2C will become a space needle. The D mags, I hope to run of D Alkaline or rechargeable. The questions I have are with respect to the acceptable Luxeons that should be used. I prefer not to have to use any resistors.

For the space needle, at 9V from 3 123's what would be the best binned 5 watter with
respect to Vf? Is it realistic to find such a bin?

For the 3D would you guys suggest a J, K, or L binned Lux III?

The 4D is open for suggestions, I may not be able to DD this one, possibly a down boy with a Lux III?

For all lights I am looking for maximum safe (overdriven within reason) output.

Any advice would be greatly appreciated.

Thanks,

Matthew

needle - Vf of "U" or deeper in the alphabet

3D - "K" or deeper

4D - El Negatori.. /ubbthreads/images/graemlins/grinser2.gif

HTH'd...

I'm not sure about the 5W mod, but with the Lux III, going with the L Vf will get you a good DD on the alkalines, about 900mA to 1A. It should also be safe to run with NiMH cells, without resistance.

The 4D with a downboy would be nice for a Lux III, but might be nicer with a BadBoy and a Lux V.

Thanks guys,

Tony, how do you calculate the .9 to 1 A? from experience or do you know the resistance of the average mag body?

As a follow up if I got this right, for the 3D a L Vf would provide ~1A, so a lower Vf, say K, the light output would increase at the expense of overdriving the emitter, would the current also be increased then? ie. > 1A?

By this rational for the needle the U Vf should then be the brightest (providing all other factors are constant)however for longevity of the emitter, V or W Vf would be preferable.

Is this right?
Thanks,

Matthew

M R,

You've about got it right. The reason that I like the L Vf with the mag mod is that most inevitably go to NiMH cells. The rechargeables have much less internal resistance a typically provide more current to the luxeon.

The numbers that I quoted were from memory. I got the numbers from experience.

I have directly driven a LuxeonV with Vf of T with 3 x CR123s and a Luxeon III with a Vf of J with 3 x Lithium AA's with no problems. The key is the heatsink. Any Vf above those is OK, based on my past mods and Luxeons received.

I run a few K & L binned Lux3s on Hotlips in 3 cell DD lights using both Alkalines and NiMh. All have been used quite extensively without problems. J bins are pushing it. A few here have killed J bins, while others are getting away with it.

I'm in about the same boat as illumigeek, having used K & L binned Lux3s on Hotlips in 3 cell DD lights using both Alkalines and NiMh. I've had 950-1200ma (K bin) with 3 NiMH in mag 3c or 3D and fresh alkalines start about there, too. D cell lights in my experience seem to draw about 50-100ma LESS current with the same bin stars.

J bins draw more like 1.4-1.6 amps, and will probably hold up on a hot lips, however, IMO anything over 1.2a with a LuxIII gives very little extra light for the extra juice. There's plenty of room for a .2 or .3 ohm resistor in the hotlips, tho.

Given the LL (Luxeon Lottery) is still alive and well, please do not rely strictly on Vf bin codes to guide you through the Dead-Luxeons graveyard, nor the dozen or two anecdotal experiences of the lucky few. As Illumigeek said, some have worked and some have not, and they're not even talking long term, just that it worked for them at the time.

Over the last two years or so I myself have built a couple thousand DD lights and it is on this that I base my comments. To the naked eye, differences in brightness between a J and K may not be readily apparent, yet the difference between a lit Luxeon and a dead one becomes Very obvious indeed... /ubbthreads/images/graemlins/naughty.gif

Thanks for all the input guys, I've got some nicely binned J's and L's, will go with the TWOL for the 3D and save the others for something else. Now all I need to do is source a 5 watt Lux for my space needle.

Thanks,

Matthew

/ubbthreads/images/graemlins/crackup.gif

Yea, what Mr. Bulk said.

The L's are the safest way to go. Besides, the size of the reflector has more of an impact on performance than a couple hundred mA. As you go beyond about 700mA or so, increases in output become less noticeable as you increase current.

Fellas, to me DD means from the batteries straight to the emmitter, no resistor. Is that the way you see it?

That the way I see it. Typically, if you taylor the Vf of your luxeon to the power source, you shouldn't need resistance.

Until the Vf of the luxeon changes...

Yes. Luxeons are known to go somewhat lower in VF as they age. Another reason the J bins are a little iffy for DD.

It would be pretty simple to add a little resistance if you want to run a J bin. You could even get fancy and rig a switch to the resistor, so after your Alkalines fade a bit you could bypass the resistor. Just remember to switch it back in when you change batteries or run Nimh cells.

I would personally consider a resistored solution 'direct drive' even though in the purest sense it really should be called 'circuitless' or something.

I had thought of making a circuit with tiny little switches that automatically cuts out the resistance as the battery drops akin to ilumigeeks idea above, i even got some samples.. the chips are quoted to be 'the smallest spst switches in the world'.. they are in-fact about 1mm square, so pretty small no doubt.

Problem: dangit.. they have 3ohms closed resistance, what good is that? /ubbthreads/images/graemlins/wink.gif

question: could a few FETs be used in parallel to make such a circuit.. say... if you pick an FET with an Rdson of an ohm... put three in parallel and you should get 1/3 ohm.. bias each differently so that at higher voltage one FET turns off and you get 1/2ohm... and with a little higher voltage you get 1 ohm. I'm dying to make a ckt like this, that basically is a 'switched resistor bank' but don't know if there is any advantage over the LDO type ckt mr. al. came up with for my latest design.

-awr

Andrew,

Basically, what you're describing is exactly what an LDO linear regulator does, except it works as if it has a near infinite number of switches and resistors. Unless you were looking to switch brightness levels, an LDO would be a better choice anyways.

yeah, evan i think i came to realize that... maybe not coincidence that's the driver going into my nano mod. FET LDO.. did you check it out yet? it's really cool, and tiny tiny tiny.. designing it to have a settable brightness (set n forget).. here it is