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I have a 19.4v/2.37A power adapter. I have 5 LEDs (3.2v-3.4v 20mA) connected in series. When I measure the current, the reading says 0.08A, which is total of 4 LEDs, not 5, but close enough. Strangely, when I add another LED to the chain, the reading says 0.02A instead of 0.10A. All I'm trying to do is measure how much amps all 5/6 LEDs use together.
When I adjust the units, the decimal places do not change, regardless, if I set 10A or 2mA, it always says 0.08 or 0.02, is my multi-meter broken?
Since you dont have a current limiting resistor, the current going through the LEDs is regulated by the sum of their I/V curves:
By luck you did not fry your LEDs and by coincidende they added up to 80mA (which you thought was 20mA * 4).
The current in series does not add up, so if you have 4 LEDs that are rated for 20mA, you should be running them at 20mA. Your reading of 80mA actualy indicates that you are running the 4 of them at 80mA each.
When you added another LED, you added its forward voltage to the bunch and hence move the current further down in the I/V graph of your combined LEDs, hence now you have 20mA.
You should really add a resistor in series with your combination. I'll add that you'll probably have to run 2 in series and 3 in series if you want 5 LEDs with this 19V PSU.
