# Measuring AC output of variac with DC voltmeter

I have variac (Uin=230V, Uout=0-250V, Imax=5A), where I would like to measure voltage on output on a digital voltmeter. Since I have problems finding digital AC voltmeter 0-300VAC (most of them measure only from ~70V up, but I would prefer form 0V up), I was thinking of measuring voltage with DC voltmeter (these are easy to find to measure 0-300VDC with external power supply of 5-12VDC). What I would like to do is this:

Gretz is used because of DC voltmeter, where I used cap. to smooth the halfperiods into something more likely DC voltage, while resistor is there to discharge (and for faster changes). Voltage divider is there to divide the voltage, for when it's 324V (230V*1.41) to show on DC voltmeter 230V DC.

Is this a correct way to solve the problem?

• your circuit is plausable .You are measuring the peak which is OK .I would go for the average and calibrate it for RMS which is rough enough . Commented Oct 21, 2019 at 10:47
• What is Gretz??? Commented Oct 21, 2019 at 10:48
• @LeonHeller: "Graetz" is another name for a full wave bridge rectifier. "Graetz" from the name of the German guy that invented it.
– JRE
Commented Oct 21, 2019 at 11:27
• Most digital multimeters have high voltage AC ranges that measure from 0 to Vmax VAC. What meters are you using that do not measure below 70 VAC? Commented Oct 21, 2019 at 11:55
• Arguably, the 100k resistor to the left of the capacitor is unnecessary. The voltage divider to the right of the capacitor also acts a bleed resistor to discharge the capacitor. Other than that, it's pretty much the way I would do it. Be aware that, for very low voltages, the volt drop across the diodes will affect the result. Commented Oct 21, 2019 at 12:23