Meter and Shunt Wiring Question

BFL13 wrote:
In diagram #2, the IN+ is on the outer end of the shunt and COM at the inner end, so it would show the amps from the battery to run the motor?

If the thing is a battery charger instead, you put IN+ on the battery end of the shunt and COM on the outer end, and it will read amps into the battery from the charger?

Yes and yes.

It may help to understand that the ammeter part is really just measuring voltage and applying some scaling factor, and the shunt is really just a low-value resistor. The current through the resistor causes a voltage drop, and the meter part measures that voltage drop and shows it in numbers that (hopefully) correspond to the current flowing. The COM lead is the negative lead for the ammeter's voltage measurement, and the IN+ lead is the positive lead. (The PW+ lead is the positive lead for the voltmeter part of the meter, and the COM also its negative lead. Apparently COM and the power supply - are internally connected together. The + power supply lead is, of course, the positive supply for the meter circuitry.)

When current is flowing from the battery to a load, the battery negative terminal is the most negative side of the resistor, so the COM lead goes there. When a charge current is flowing, the sense of the current and the voltage across the resistor is the opposite—the battery really is the load in this case, and the charger the power supply—so the end of the resistor opposite the battery is the most negative and gets connected to COM.