Make a Economical and Practical Rectifier Voltmeter

Buy a magnetoelectric low-voltage DC voltmeter on the market, with unlimited range. Find a potentiometer RP with a large resistance (about 500kΩ) and connect it in series with the voltmeter. At the beginning, adjust RP to the maximum value; use a rectifier bridge (breakdown voltage should be ≥1000V), connect its AC input side to the output end of the inverter, and connect the DC output side to the series circuit of the voltmeter and the potentiometer, as shown in the figure below; connect the inverter to the power supply and adjust the output frequency to 50Hz. At this time, the output voltage of the inverter should be displayed as 380V; slightly adjust the potentiometer RP so that the pointer of the voltmeter points to the maximum range, then the maximum range of the voltmeter is 380V; measure the resistance of the potentiometer, replace the potentiometer with a fixed resistor, and install it in the meter.