Yet another direct-drive TWAK M@g, Li-Ion powered

Yet another direct-drive TWAK 2C Mag-Lite, 18650 Li-Ion powered

Howdy all,

I just finished my first Mag-Lite conversion, on a 2C. I used a TWAK Luxeon, HotLips heatsink and two 18650 Li-Ion cells (1800mAH each) in parallel. Only runs about 800mA direct-drive, so I must have a pretty high Vf on this emitter. Nice white color, and very even beam pattern.

I'm quite happy. I have some pics and more details here, if you're interested. I wrote the text on the following page for some of my friends who aren't "up" on LED technology, so most of you will already know most of this:

My TWAK project

Oops,

I was just playing with my DMM again, measuring the current. It seems that in the 2000mA position, my DMM adds enough impedance to limit current quite a bit.

With the DMM in 10A mode, the current jumps to a little over 1100mA with slightly discharged Li-Ion cells. That's more like it! I was wondering how the light could be so bright at only 800mA...

I think the DMM uses an un-fused shunt in 10A mode, thus the lower impedance. Something to keep in mind when measuring LED current with a DMM...

I'll re-test the current draw once I have the cells fully charged again, and take some beam-shots.

Darron

short the leads on the dmm and see if it gets any brighter. My headlamp on a partially drained 1200mAH li-ion draws 550ma through the 10A DMM, but gets brighter when I switch it on.

Thanks AilSnail.
Yes, that's how I realized the DMM was adding impedance. I had the black DMM probe on the end of the battery pack, and the red one on the bottom edge of the Mag's body tube (on the ring where the anodizing is not present). I then shorted the red probe to the battery, and noticed the beam get quite a bit brighter. That's when I had the "bright idea" to try the DMM's 10A setting, knowing that it used a large copper shunt with no fuse.

Darron

It can be handy to charactarize the shunt+leads resistance on your DMM to get an idea of how much resistance you add.

For instance, I did so on one of my DMMs, and found that it only added 70 milliohms of resistance to the circuit on the 10A setting.

You can characterize your DMM by using a current source (like an LM317 based current regulator), and another DMM's voltage measurement. Force a known current through your DMM, and measure the voltage across the leads. R = V/I. Do this for several current values (several milliamps, several hundred, and 1+ A), and you'll get a good idea of the resistance you add from the DMM.

With the Li-Ion cells fully charged, I measured 1.6 Amps of current. Yikes! Seems OK so far, but I don't know how this thing will hold up. Just incredible brightness and color, though.

I finally got around to taking some beam shots.

The light on the left is a 3D Dorcy, with a 1.7 Amp Carley krypton bulb with lensed end. You can see the filament projected on the wall. It's driven by three 4.0AH Ni-Cd cells. My custom Luxeon 2C Mag-Lite is on the right.







Darron R. Birgenheier
Brantingham, NY

Nice looking mod and great pics on the construction details.

When I did my Mag 2C with the RS KPR112 bulb, I also managed to shoehorn in two 18650 cells; very tight fit.

And you don't have to convince me its frozen in N.Y. - the Mag 2C reflector says it all /ubbthreads/images/graemlins/smile.gif !