Simple LED circuit help

[cjarmst]

Ok guys I need some serious help here.. I am feeling very stupid at the moment. I decided I would put together the most basic of LED circuits, measure things out, then build on it.. it's just the way I like to learn .
So I purchased a standard blue 3600 mcd LED with 3.6V fv, and 20 mA requirements.
Plugged that into the LED resistor calculator with 6V source voltage and it tells you that you need a 120 ohm 1/8 watt resistor. That should give an actual LED current of a perfect 20 mA.
I grabbed a 4 AA battery pack, and a package of 120 ohm 1/4 watt resistors (they were out of 1/8) and wired them up like this:

Battery(+) ---> 120 ohm R ---> (+)LED(-) --> (-)Battery

The LED lit right up.. cool. Pulled out the multimeter and started probing on things.. voltage at the battery pack is 6.22.. well thats a little annoying but ok. Voltage after resistor at LED terminals is 3.5V.. hmmm.. current is 48 mA.. argh, wtf??
So just out of curiosity I wire a second resistor in series with the first so now it looks like this:

Battery(+) ---> 120 ohm R ---> 120 ohm R ---> (+)LED(-) --> (-)Battery

Current between resistors, still 48, current after 2nd at LED terminals is 25. That makes sense in my head.. but why aren't the numbers lining up with the voltage calculator?
Just as a sanity check I also measured the resistor and it reads as 119.5 ohm.

Any ideas??
thanks!
Chris

[Do-Clo]

I am going to ask a really dumb question so please don't be offended, but when you measure current are you inserting the current metter into the circuit between the led and the negative side of your battery? This is simple point to measure current because it only requires a break in the circuit between the battery and the led. I did a quick caculation of the resistance needed to get 20 ma and it comes up 120 ohms.

Do-Clo
Don't make me destroy you...

[cjarmst]

No offense taken! Here is where I am inserting the two leads from my multimeter. PB = probe black, PR = probe red

Battery(+) -> Resistor -> PR -> (+)LED(-) -> PB -> (-)Battery

Am I measuring incorrectly?
thanks!

[cjarmst]

OK nevermind I am an idiot :) I knew it had been too long since college lab days. I was not breaking the circuit and putting the MM in series.
I re-hooked like this and everything read ok.

(+)Batt -> Resistor -> (+)LED(-) -> PB PR -> (-)Batt

Please ignore my rambling for the day.
These aren't the droids you are looking for. Move along. Move along.

[Do-Clo]

It happens sometimes you stare at something and just can't see the problem, then you walk away for a while and come back and there it is.

Do-Clo
Don't make me destroy you...