500 mA ARC LS mod not regulated ?

Hi,

I have switched the 1W LED from my ARC with aTX0K and added a .33 Ohm Resistor so it works with approx. 500 mA.

Then I did a runtime test and put the readings (1 sample per minute, later 1 sample per 10 minutes) into some charts.

According to the charts, the ARC doesn't seem to be regulated. The brightness steadily goes down during the test time of 10 hours:





I also charted only the first 1.5 hours, and here I'm not sure if it is regulated or not:






Can you tell from these charts if the ARC is regulated or not ?

Would it be better regulated if using the stock resistor, running with 334 mA ?

abolite, if the first part of your graph shows fractions of a minute, and the later part full minutes, you get an artifact of scale obscuring the pattern. I use same units on a graph.

From you second graph, I see that it takes your light about 45 minutes to go from .85 to .80 brightness. This is before it drops to a lower plateau around 55 minutes.

I'd say this is regulating somehow.

You do, however, have a problem with the vertical scale on your graphs. I don't see how the 0-1 scale on the first graph corresponds to the 0-1 scale on the bottom graph. Does the vertical scale in the first graph correspond to the first 10 minutes and the one on the second graph to your entire run?

greenLed, you're right, I should have explained the scales of the graphs, here it goes:

The first graph (red) shows the entire runtime of 10 hours, the X-axis is in scaled hours (0 to 10,0).
Every vertical grid line in the first graph is 10 minutes.

The second graph (blue) shows the first 1.5 hours of the first graph.
Every vertical grid line in the second graph is 1 minute.

So the second graph (blue) shows that part of the first graph (red) that goes from 0 to 1,5 hours.

The Y-scale (brightness) is the same in both graphs.

It's possible the K vf may be too high for the light to start out in full regulation from the very start.

I'm with Billson. That could be contributing to the situation. I've only ever used J's for my LS mods. An H would be sweet now wouldn't it?

Ah! I was not understading the graphs properly. Thanks for clarifying. I guess my answer changes now, but I can't explain the pattern.

Thanks for your answers, guys.

Billson, do you think that regulation can be achieved by reducing the current to the stock 334 mA ?

How long would it probably be regulated in that case ?
I think that the brightness would drop if using the stock resistor, but I'm wondering how much ?

I also thought of some mistakes I probably made during soldering the parallel resistor. It could be possible that I accidentally short-cutted the resistors. Could that explain the graph ?

I would think so. Most of the stock LS's had K vf and ran in regulation for 1.5 to 2 hours. A better solution would be to use a lux with a lower vf.