Need help: Underdriven Lux3 on 3C NiMH

This one has got me /ubbthreads/images/graemlins/Christo_pull_hair.gif

Normally the recommended configuration for direct drive is a K-bin Vf Luxeon 3, 3C NiMH or 3C alkaline. I have that.

Problem is I'm getting only 400mA through the Luxeon with freshly charged cells hot off my Maha C777 or fresh alkies from the pack. It's a star, so I confirmed bin on the back, and I've even managed to take a Vf measurement by powering everything up, and touching my DMM to the positive and negative leads of the emitter itself (the emitter sitting on the star MCPCB that is).

I completely don't get it at all. I've tried isolating every possible point of failure to the extent of soldering the star directly to the battery pack with the only break in the connection for my DMM. I've even tried changing chemistry to lithium ion (3.7V nominal) only to get the same result. What's going on?

The only possible fix to the problem is to switch to 4C NiMH, which yields a working current of 700-800mA, which is exactly what I want. However, my housing can only accomodate 3C cells.

The stars themselves have had around 5-6 power-on hours in order to try and break them in, too.

Any /ubbthreads/images/graemlins/help.gif welcome...

Have you tried another emitter with the same batteries? Maybe you have a bum LED, could happen.

This is actually the troubleshooting phase of Project Mag3X with 3 Luxeon TWAKs. All of them exhibit the same behavior whether driven together or independently. Unless the whole batch is a mis-labeled "L" bin, but I've checked the Vf with a DMM and it is 3.49V.

If you're measuring 3.49V at the emitter, and you're only getting 400mA, then there's about 1V being dropped by resistance. So you have 4 ohms of resistance that has crept in somewhere.

With the light turned on, start measuring for voltage drops where you can. The easiest is the negative of the emitter to the negative of the body tube. Use a long rod of metal to check positive through the switch (to contact the positive spring at the switch).

I guessed that it might be the light, or the adapter I was using, so I pulled everything out and soldered wires directly onto the LED, took the batteries out and hooked them up directly. The strange part is that the numbers aren't a whole lot different whether the LED is mounted in the Mag3C or directly wired.

That's kinda why I'm so stressed out, because it's not resistance. It's something else. I'm using 24AWG solid copper which is good for up to 3A, and I have run another light which was running 2A over this same 24AWG.

Measure everything. If your cells are maintaining full voltage (measure directly at the cell terminals), and the Vf is what you say it is, then there must be resistance somewhere. Either in your battery holder, wires, or soldering job. Do you have a constant current power supply? If so, measure the Vf of your Luxeon at various current levels to be sure.

[Edit] One more thing - how's your DMM? Maybe try to characterize the current shunt resistor by using a CC power supply and measuring the voltage drop across your meter (including probes).

I have just done this as my first mod.
SYOK bin, LuxIII, direct drive ( no resistor ) and 3 Alkaline C cells. With brand new cells I am pulling 1.3 amps for the first few minutes. I have a massive heat sink so no overdrive problems so far. After 15 minutes of random use. the output has settled around 950 ma.

KevinL
I STRONGLY suspect your ammeter is lying to you. This doesn't all add up. question; is the LUX star getting hot when it's run off the heatsink? That would indicate it's getting sufficient power. Also, is it dim or bright?
Somebody suggested testing the meter. You can take a known resistance and a known voltage and predict what the current should be. The meter can be compared to the computed value.
Let us know what the problem is.

Hmmm...

I just did a little bit of checking. With a 3.1V source (Fresh CR123), and a 1.8+0.9 ohm resistance load I should get 1.11A. The meter indicates 1.18A. 0.9 is caused by the hackjob repair I did on the probe when the tip snapped for no good reason. Cheap crap meter...

Kevin,
CY had some jeers for those titanium c cell batteries a while back.
Most magg hosts have very little added resistance.
If you can get hold of some battlebot grade batteries,
That should end the problem and start another with heat generated /ubbthreads/images/graemlins/mpr.gif and complaints from the neighbors about a bright light coming from your direction. /ubbthreads/images/graemlins/grin.gif


www.battlepack.com

I have some of thier teeny little N cells slamming 1.3 amps through an Ledlenser v2 "1 watt" light.

Any chance you are getting some kind of effect from the star being grounded ? BTW, I have some TWOK emitters that I damaged from a DD from 3 x D. It was really bright - for a little while. Then, much dimmer. My voltmeter went south, otherwise I would offer to measure them.

Hmm..

I think it may be the meter. I even changed chemistry to bare 18650 lithium ion cells, which can put 8 amps through this DMM on the 10A scale. I'm only getting 1.4A.

However, as I said..

A fresh CR123 at 3.1V should deliver 1.66A with a 1.8 ohm load. The meter measures 1.18A. However, when I try to measure the meter's own resistance by touching the probes directly together, it says 0.9 ohm. Working backwards, 3.1V, 1.8 + 0.9 = 1.11A. Very close to the metered reading.

Is it the meter?

As an aside, what are your opinions on the Wavetek Meterman series? I need something with 10A DC capability (as demonstrated), DC voltage, resistance and HIGH PRECISION measurements so that I don't freak out /ubbthreads/images/graemlins/mpr.gif over this issue again.

PS: I know Fluke because of their DSP-4000 system and would love to own a Fluke 189, but the lights have eaten the whole budget.

Kevin,

The best way to measure your meter's resistance is with a constant current power source and another meter. Use an LM317 in current mode and pass several different test currents through the meter in question. Use the other meter to measure the voltage drop across the test meter's probes. Then use Ohm's law to figure out resistance.

Thanks evan... Nope, no constant current power supply here, not even a second meter. I'm thinking if I'm going to invest in another meter I might as well go all the way and get a good one, too. Appreciate the help /ubbthreads/images/graemlins/smile.gif

I posted in your other thread, that the stars may be mis-labled or just way off spec.

Can you measure 3C's or whatever to a single luxeon other than the TWAK's you have now? See if the DMM reads 1amp or so. If so then I'd say it's your stars... Time for new ones... :|