RMS Power?

@almarg 

And then please where 141 watts comes from. What kind of inbetween power is that to be called?

As I have said, it is the RMS value of a sinusoidal power waveform having a peak value of 200 watts.

Well its not. We have agreed that a 100 watt RMS amplifier supplies 40 volts peak into an 8 ohm load. 40 x 40 / 8 = 200 last time i checked. 

As Monty Python says... say no more, say no more.

Al, I was right (he is not going to get it). RMS value of ANY sinusoidal waveform, having peak at 200 (of any unit) is 141 (of the same unit). 100W would be an average power value corresponding to VrmsxIrms and equal to half of peak power for sinewave (and equivalent to amount of DC power producing the same amount of heat). Guys, please, this is EE101.

@kijanki Al, I was right (he is not going to get it). RMS value of ANY sinusoidal waveform, having peak at 200 (of any unit) is 141 (of the same unit). 100W would be an average power value corresponding to VrmsxIrms and equal to half of peak power for sinewave (and equivalent to amount of DC power producing the same amount of heat). Guys, please, this is EE101.

Lets be a little careful here for those trying to understand this conversation. "RMS value of ANY sinusoidal waveform, having peak at 200 (of any unit) is 141 (of the same unit). Does that apply to watts? Are 200 peak watts the same heating value as 141 watts. They are the same units? I know you dont think so but one could easily interpret any to mean any. Granted going on its fine. Whats all this about average power? Whats the definition. I saw you 3 step calculus but, sorry I dont get it and I did fine in Calculus.

Yes RMS power is half the peak power, but you call it average power without informing us what average power is to you.  Al, who you appear to agree with. thinks 141 watts is the average power of 200 watts peak. He has said so. Still what is this average power? We are talking about a sine wave going on and on. 

Average power as used by most in audio means the average over a long time, playing music and not letting the voice coil get too hot. This is the definition I find most often for average power. I dont see how it applies to amplifiers except for the heat sinking.

RMS power is continuous sine wave in this discussion. Why say it is wrong. Whats wrong with it?

Come on kijanki, lets get this ironed out for everyone else who by now doesnt know what we are talking about. It is important. The early replies to you OP had no idea what to say.

I do think we agree yet use of the term average to describe heating is generally used as RMS. Do you really want to say this. " Prms = 0.61Ppeak "? not 0.5 . P rms= V rms x I rms. does it not. is so .7 x .7 =.5

I am writing a paper on how the FTC got involved, its not the way most people think and its not bad.

Al, who you appear to agree with. thinks 141 watts is the average power of 200 watts peak. He has said so.

No, I have not said that. I have said that 141 watts is the RMS value of a sinusoidal power waveform having a peak of 200 watts. "RMS" in the sense of a mathematically calculated root-mean-square. And in saying that I certainly recognize that the heating which occurs in that example corresponds to 100 watts, not to 141 watts.

On the other hand, though, in citing the 141 watt figure I overlooked the fact that the product of a sinusoidal voltage and a sinusoidal current is not sinusoidal, since it never goes negative in the case of a resistive load. And correspondingly positive power is being delivered to the load at all times, other than at the zero crossings. So I believe the 141 watt figure should be, per one of Kijanki’s posts early in the thread, 0.61 x 200 = 122 watts.

Also, Roger, a **much** better paper on the subject than the Wikipedia writeup Kijanki referred to is the one Imhififan linked to in a post early in the thread:

http://eznec.com/Amateur/RMS_Power.pdf

That author’s conclusions:

It should be noted that the term “RMS power” is (mis)used in the consumer audio industry. In that context, it means the average power when reproducing a single tone, but it’s not actually the RMS value of the power.

Summary:

I’ve shown that:

-- The equivalent heating power of a waveform is the average power.

-- The RMS power is different than the average power, and therefore isn’t the equivalent heating power. In fact, the RMS value of the power doesn’t represent anything useful.

--The RMS values of voltage and current are useful because they can be used to calculate the average power.

Imhififan also provided the following reference early in the thread, which again is highly supportive of Kijanki’s position:

http://www.n4lcd.com/RMS.pdf

In any event, I agree with PTSS that Ralph’s (Atmasphere’s) advocacy of a pragmatic outlook on this issue (see his post dated 6-30-2017) is well stated and appropriate. But in going forward on that basis it seems to me that at the very least we should also acknowledge the legitimacy of Kijanki’s point, that based on a strict interpretation "RMS power" does not equal the product of RMS voltage and RMS current, and therefore does not correspond to the heating effect of a given amount of power.

Regards,
-- Al