I'm trying to measure current on a cheap multimeter. It has an unfused 20A port and a fused 200mA port.
I'm using a simple circuit with an LED, a resistor and 5V DC and setting the multimeter dial to read maximum of 20mA DC input.
If I use the fused mA port I get the correct reading of about 2mA. If I use the same setting with the unfused 20A port I keep reading 0 even though the LED turns on. Is this normal or is the multimeter broken?
This is the multimeter:
The lower current settings usually only read the current through the fused, low current jacks.
If you want to use the 20A jack, you have to set the meter to the 20A setting.
You probably won't be able to get a good reading for the LED current when using the 20A setting. 2mA is probably too low to register on the 20A scale.
Assuming a 3.5 digit DMM, the lowest digit would be 10mA (19.99A FS), so you would expect it to read zero with 2mA.
Also some newer chipsets for low-end DMMs are not quite as good from an accuracy pov as the older ones based on the ICL7106 (and its many clones) and have more nonlinearity etc. but require fewer and cheaper/smaller external components.
If you put it (on the 20A range, briefly only) across a reasonably fresh 1.5V AA alkaline battery it should read a couple amperes, and maybe half that for an AAA cell.
