# Rectifying ac increases voltage?

I have a transformer that outputs 16 volts ac. I built a 4-diode full wave rectifier and added a 4700uF 35 volt smoothing capacitor. Now my dc voltage measures 21 volts? I thought the voltage would drop because it has to pass through diodes. What explains this voltage increase?

RMS being "Root Mean Square" is a math' way of getting something meaningful out - you square the voltage so that -ve becomes +ve (-2 x -2 = +4), then average it and square-root it (root +4 = 2).

As AC is "lumpy" the peak voltages at the top of the sine-wave are above the RMS average, and if you're not applying heavy load the rectified DC voltage is closer to these peaks than the RMS (math' for AC) value.

L

Re-design gave you the numbers, but not the math.

When you measure AC "voltage", what your meter reports to you is the RMS (root mean square) of the sinusoidally oscillating voltage. For a sine wave, the RMS value is 1/sqrt(2) of the peak amplitude. In the U.S., the RMS is nominally 117V, for a peak value of 165V.

A simple rectifier bridge essentially flips the negative-going half of each sine wave to become positive, which moves the RMS value much closer to the peak.

Diodes don't introduce any significant voltage drop.