Thanks alot! That Worked
I'm understand now. Probes becomes a part of the sercuit
And yes, i'm not measuring AC from the wall here. On the right side of the Buck Converter it's 12V and it's 24v on the left side (input).
A picture is worth a thousand words... See attached picture --- but, it requires explanation still. There is something missing that may affect your measurement.
To measure voltage, it is done in parallel (see
top left picture). To measure current, it is done in series (see
top right picture). But
NOT SO FAST. There is one very important thing called
burden voltage.
Your 12 Volt first hit the DMM, when it comes out of the DMM, it is no longer 12 Volt , it dropped a bit. The amount it drops is called
burden voltage. Say the burden voltage is 1 Volt for easy math, 12Volt dropped by 1Volt meaning your LED is going to powered by only 11 Volt. The Current at 11 Volt
will not be the same as the Current at 12 Volt. It doesn't matter whether it hit the LED first or the DMM first, it can "eat" the 1V at the top (DMM first) or the 1V at the bottom (DMM after), you are still left with only 11 Volt for the LED.
Burden voltage varies from DMM to DMM, and it varies from DMM setting as well as from amount of Current. The larger the Current, the larger the burden voltage drop. On some DMM and when set to mA,
it may drop so much that the number becomes meaningless.
Typically, when your DMM is set to the highest current setting, there is minimal stuff in between (lowest value shunt) and the burden voltage drop is the lowest. The highest current setting is of course DMM dependent. On mine, the max is 10A max and the burden voltage drop is 1 Volt at 10A (measurement done via 0.1ohm shunt). So, if it is running 10A, the 12V input is really only 11V to the LED. I don't know what mine is at 220mA-Max setting, but I know the drop is so big that the mA reading is fairly meaningless.
If you
only have one DMM, try using your DMM's max current setting (note: it looks like from the picture of your DMM that
your probe needs to be plugged to a different socket in your DMM), that will typically minimize your burden voltage drop and gets a number that would be closer than otherwise.
For better measurement, you need to use two DMMs. (see
bottom picture). The second DMM will show you exactly what voltage is fed into the LED - at least you know what the damage is, so to speak. If you are reading say for example something like 9Volt powering your LED, you know the Current reading is
probably not very meaningful.
Since you are using a buck convertor, may be it is an adjustable buck. If you can
adjust the output carefully increasing the voltage until your second DMM (measuring voltage) is reading
12Volt after the burden voltage drop, now you know for sure what your Current will be at 12 Volt. (Don't forget to adjust it back after measurement - otherwise, once DMM1 is removed, you no longer have the burden drop and you would be over 12V now if you don't change it back).