Confused with Luxeon

[dw_1984]

I don't know much about electronics but I understand some of the basics. My problem is this.

I connected 3 C cell batteries (Alkalines) to a 1 watt white LS (Q2H) and I measured with a multi-meter connected in series between the negative end of the last battery, to the negative lead on the LS. The MM is set on 10A and it's reading 0.20A.

I thought LS's were supposed to run on 350ma. Maybe my MM is a little off (probably is because my dad insists on using 20-year-old MM instead of getting a new one). Or maybe I'm not measuring in the right place.

Can anyone explain to me what's going on?

Thanks in advance,
Daniel

 

[lambda]

Hmm, with 4.5V (3 cells) you should see close to 1.4 Amps. Typical Luxeon forward voltage is 3.5V, with every 0.1V increase resulting in another 100ma of current.

Suspect the shunt resistor in the meter must be a high resistance, like 10 ohms. Perhaps it was over heated in the past.

Try using a one ohm resistor in series and measure the voltage drop across the resistor (.35V = 350ma). Don't do this with a bare emitter, the Luxeon must have a heatsink for anything over 100ma.

Good luck.

 

[dw_1984]

I'll try that Lambda, thanks!

And I might just buy my dad a new mulit-meter for father's day. I really suspect something's wrong with it given it's older than me but he does likes using all these old gadgets. The soldering iron he uses is from Hong Kong with their different voltage and he's got a transformer or something that's gota weigh 8lbs or so to use it.

I'll be looking for some resistors at school tommorow. Hopefully I can get it to work.

Thanks again,
Daniel

 

[Mednanu]

It might just be the way you are reading the multimeter. I know that some of those older analog-dial style multimeters could get kind of confusing with 7 or 8 different scales on them. You had to know which one to read and how to apply the correct multiplier to the reading in order to get the actual figure the meter was measuring.

Then again, 200 ma isn't that far off of the rated current for the luxeon (350ma being nominal). Both the voltage drop of the Alkalines under load as well as the internal resistor within the Multimeter could easily account for only 200 ma of current draw being reported on the meter. It likely just the larger resistance within the meter that is causing it to report lower currents, though (all my LED's glow a lot Less when I do an in-series current measurement via a multimeter, thus indicating internal resistance of the meter at work in the 'equation').