I wanted to do some work with battery charging and powering a 100 W load. So I bought a couple of combination panel meters that will measure voltage, current and power as well as an energy running total. One came with a 50 amp shunt the other a 100 amp shunt. It has been a while since I got them and I seem to have mixed up the shunts and panel meters.
The strange part is the meters seem to be the same! They have the same part number PZEM-051. The shunts are 50 amp at 75 mV and 100 amp at 75 mV. So clearly the resistances are different and so the meters need to be different to account for the different voltage they will see for the same current in the shunt.
What am I missing? Am I misinterpreting the spec? 100 amp 75 mV means it will drop 75 mV at the rated current, right?
I thought there might be a setup in the meter as it does have a button, but that seems to only be for clearing the energy reading, toggling the back light and setting a voltage range which I believe makes the display flash to alert you to a problem. Nothing to set the current range.
I'm using the 50 amp shunt at the moment and I suspect my current readings are doubled. I guess I'll have to try the other shunt and then the other meter to see what the heck is going on. Lots of wires to mess with.