Effective Voltage And Peak Voltage Difference?

Discussion in 'General Electronics Chat' started by jfl, Oct 26, 2008.

1. jfl Thread Starter New Member

Oct 25, 2008
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Why is effective voltage important? I know effective voltage is a rms between zero and the crest or average votage above/below zero. But, why is that so important in (very simple terms)?

Second, if 110 volts is effective voltage at a wall outlet what happens to the other fifty volts (Peak voltage minus the effective voltage)? What does an electrician read when checking an electrical outlet with an effective voltage of 110v at a wall outlet? Does he/she read effective, crest or some other value?

jfl-

2. mik3 Senior Member

Feb 4, 2008
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RMS is useful to calculate the average power (real power) delivered to a load.

According to your last question, an electrician measures the RMS value out of an outlet. Also, the 50 volts do not go anywhere. You can measure an AC voltage either in RMS or peak values, they are just two different methods of measurements, there is no voltage which gets lost somewhere.

3. Metalfan1185 Active Member

Sep 12, 2008
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Multimeters and DVM's Measure RMS Voltage, you need an oscilloscope to measure Peak to Peak Voltage. If you get 110VAC from an outlet in the house, then that is the root-mean-square, or RMS. This means that if you rectified the signal with some diodes and charged a electrolytic cap with it, you would find that the voltage charge on the cap would be the peak to peak voltage. (or higher considering the properties of the diode and the cap.

110 * 1.414 = 155.54 VAC Peak to Peak

(1.414 is .707 times 2)

Mik3 is right, this is just a different way of measuring, they are the same.

110V RMS = 155.5V P-P

Im no pro, but i hope that helps.

4. The Electrician AAC Fanatic!

Oct 9, 2007
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Metalfan1185, you are confusing peak-to-peak and peak. The peak-to-peak is twice the peak voltage. You said:

"the voltage charge on the cap would be the peak to peak voltage."

The voltage on the cap would be the peak voltage, not the peak-to-peak.

See:

http://en.wikipedia.org/wiki/Peak_to_peak#Peak-to-peak_amplitude

Also, you don't necessarily need a scope to determine the peak and peak-to-peak voltage. Many modern DMMs, such as the Fluke 189, for example, can measure the maximum voltage of a grid waveform. This is the peak, and the peak-to-peak is just twice the peak, in the absence of distortion.