Lux III & single 123 cell - Which converter?

Hi,
I want to build a single cell 123 light with a Lux III TWOJ. What is the best converter for this app? I thought a DB Nexgen 750 but I am not sure. Thanks in advance.
Chris
.308

A Nexgen converter will be perfect. This may have been a typo, but you said "DB Nexgen". The Nexgen is a type of Badboy converter, not Downboy.

Anyway, you definitely want a BB Nexgen. 750mA should be plenty bright. Enjoy.

Which converter if you want around 750ma but want to be able to go from 2x123 to 1x123?

If you want something that can both boost (raise the voltage of a single cell to the voltage of the LED) and buck (lower the voltage of multiple cells to the voltage of the LED), then you need a Wizard.

Thanks srue.
Chris
.308

Hi Srue,

I got one of those cheapy 3watt
luxeon flashlights on ebay. it runs
on x3 'AAA'. direct drive, not even
a resistor. I measured the current,
it's about 120mA starting at 4.5volts
and slowly drops.

would the nexgen 750mA & single CR123 be much brighter
than what I currently have?

thanks...

[ QUOTE ]
quantum said:
Hi Srue,

I got one of those cheapy 3watt
luxeon flashlights on ebay. it runs
on x3 'AAA'. direct drive, not even
a resistor. I measured the current,
it's about 120mA starting at 4.5volts
and slowly drops.

would the nexgen 750mA & single CR123 be much brighter
than what I currently have?

thanks...

[/ QUOTE ]

It would most certainly be much brighter. Perceived brightness is not a linear scale, but judging by the amperage alone, the Nexgen would appear several times brighter. Some things to consider:

The easiest way to compare the brightness of LEDs in general is to look at the current draw. Now, this assumes the LEDs are similarly efficient (as a function of current), as determined by flux binning (the 'T' in TW0J). A TW0J will be brighter than a SW0J at the same current level, but a TW0J will be the same as a TW0H. (The 'J' and the 'H' represent the voltage forward - lower letters equal lower Vf.)

When an LED is driven at a higher voltage than its rating, it generally starts pulling more current. Depending on the voltage forward of the LED in your ebay light, 4.5V is probably overdriving the LED with direct drive. Assuming your measurements are correct, this means the LED is pulling 120mA after the increase from the overdrive.

The Nexgen will provide a constant 750mA at the natural Vf of LED. Not only will it be much brighter, but the brightness will remain more consistant over the entire discharge of the battery due to the regulation circuit.


So what this all boils down to is that it doesn't really matter what voltage you run the LED at for purposes of determining what will be brighter. What matters is the ultimate amperage going to the LED. So, since 750mA is a heck of a lot more than 120mA, the 750mA will be brighter.

I hope this helps. I've been up all night.

-Stuart

If you want to be able to run 1X123 and 2X123 and anything in between, you'll need a Wiz2 converter. There is a catch though. Running a Wiz2 biased for more than 500mA on a single 123 could be a bit iffy. The Wiz2 will shut down when battery voltage reaches about 2.5v. If the Wiz2 is biased for something like 1A, the the battery's voltage may sag to a point where it won't drive the Wiz2. If you're planning to run a Wiz2 at nothing over 500mA, then it won't be an issue. If you are going to run it at over 500mA, then I'd try to stick to either a li-ion cell or 2X123.

For a straight forward single cell light, then it's a no brainer. Go for the NexGen. 750mA is nice and will allow you to run the light on either a single 123 or a single li-ion cell.

120 or 1200 mA? At 4.5 v even an L Vf binned star should pull about that much.

Hi Stuart/Tony,

greatly appreciate the detailed
info. I ordered the badboy 1000mA.
hooked it up to the lux 3 watt.
I believe it is much brighter, will
compare tonight when it's darker,
between the badboy and the x3 'aaa'
direct drive.

okay, how do you guys measure the current
when using these converter boards. I know how to
use the current meter, just when I tried
to measure, put the current meter in series
on the battery side of the badboy, it get's
loaded down, the led output is dimmer and I measure
about 200mA. so I'm not sure if my meter is
too cheap to measure the current or there is
another method of doing this.

with the x3 'aaa' direct drive, i measure
about 120mA, but then again, I don't know
if it is a meter issue. or the maxium output
of 'aaa' battery is 120mA? how about the max
output of the cr123a battery?

with the same badboy 1000mA and single cr123a, switching
from a lux 3watt to lux 5watt, how would the light
output compare to using 2 cr123's(6volts) and a downboy
1000mA?

I did not go with the nexgen, since it's 3x the cost
of the badboy and i just don't have the funds to justify
the extra cost.

again, I appreciate your great feedback. thanks!

quantum,

I'll take a guess and say that you are getting about 750mA or so to the luxeon with the BadBoy1000. You're probably going to notice that the combinations runs a bit hot. The BadBoy generates a bit of heat when trying to do that much boosting. A single 123 is not capable of supplying enough current to run the luxeon at 1A.

Quantum, one thought I have on your current with your 3x aaa. The voltage of the batteries maybe 4.5 while the light is not on. However, the voltage is likely dropping significantly when the light is on. The voltage is likely dropping below the vf of the lux. Which would expain why the low current. Try measuring the voltage across the lux while the light is on. I'd hazard a guess that it's 3v or less.

As Chop pointed out, about the most you can expect from a single cr123 will be about 750ma to the lux. No matter what the driver is.

Boost driver, that is.

I'll third what Chop and Zulu have said. If your LED has a fairly low Vf then you might be able to get more than 750mA to the emitter, but 1000 might be too high. The nexgen would have been able to do better.

Regarding measuring currents, it sounds like your multimeter is introducing too much resistance. Try measuring the resistance in parallel with the circuit.