Re: What is Rms?

My short version

If a voltage is DC or even if it is always positive and pulses then
you can get its effective voltage by taking an average. The average
of a sinewave (AC) which spends half of its time positive and half of
its time negative is zero but it does carry power!

The RMS is the DC voltage you would need to supply to provide the same
power as the given AC signal. The RMS of a sinewave is the amplitude
divided by sqrt(2). The amplitude is half of the peak to peak
voltage. sqrt(2) is 1.41. Conversely if you want to know the peak
(say if you intend to recify it then multiply the RMS by 1.41.

So if you have a sinewave of 100v it has an rms of 100/1.41 = 70.9v as
this is the equivalent DC voltage you can find the power disipated in
a load by doing P = IV or I^2.R or V^2/R

And if you were building a PSU and your transformer halved the applied
voltage you might get 120v(rms)/2 after the transformer and once
recified 60X1.41 = 84.6v assuming you have a nice big smoothing
capacitor anyway.

Graham