Ohm's Law Sine Wave Correction

If it's AC RMS, 1.

If it's peak-peak, that's a different story.

--
Tim Wescott 
Control systems, embedded software and circuit design 
I'm looking for work!  See my website if you're interested 
http://www.wescottdesign.com

Not sure what you're looking for? I=E/R works for AC just as well as DC (as long as I and E are consistent - instantaneous, peak, RMS) Same power? DC = AC(rms)

If one volt DC across 1 ohm produces 1 DC amp of current, then that's what it is.

If one volt AC RMS across 1 ohm produces 1 amp RMS, then that's what it is.

It doesn't make much logical sense to interchange the two units. If what you're asking is how much RMS current flows in some resistor for an AC sine wave of 1 volt RMS instead of 1 volt DC, then just do Ohm's Law using RMS values.

If what you're asking is what AC voltage RMS amplitude you need to apply to get the same average power dissipation in the same resistor as 2A of DC current, then you have to math like this:

(I_dc)^2*R = [(V_rms)^2]/R

On average, you get 1.414. That means if you rectify AC line voltage which is called 120 VAC, you get about 160 VDC out of it. In other countries wher e it is 220 VAC then you get double. In fact there is alot of electronic st uff ade now that simply doesn't care. Plug it into an AC outlet here or in Europe, it simply regulates. And this accomplishment was not like putting a Man on the moon either. Withe better devices it became easier and of cours e they designed equipment so it could be shipped anywhere and just accept t he voltage they have. What would you do ?

Many newer designs seem to use a Sepic convertor or some variation thereof. These devices can increase or decrease voltage as needed.

Anyway, as to the question of the sine wave itself, 120 volts is 120 volts. Its peak amplitude is a bit higher and will rectify to more DC voltage. Th e RMS power is like when it goes to your toaster or whatever. When it comes to your TV or stereo, that might be a little different.

Modern power supplies have done away with most of the iron. They self regul ate and almost do not care the voltage. I have seen SMPSes work on as low a s like 40 volts, and all the way up to 250 volts. Perfect regulation.

Thus this AC power idea is relegated to power distribution. Unless you own an old piece of stereo equipment or something with tubes, all of it rectifi es the AC into DC and that will be 160 volts (in the US). Then usually it g oes into a chopper controlled by a feedback network driven by a correction circuit most likely driven by one of the power supply lags.

The days of real iron are almost over. You get 160 VDC, do with it as thou wilt.

** Ain't it bleedin marvellous:

A question from a retard gets a reply from another one.

Who said usenet was pointless.

.... Phil

It's true, I broke the rule. Thanks for catching that in your sweetheart fashion.

The right hand side must be an integral of

1/(2*pi)*[V_p*sin(omega*t)]^2/R] over 0 to 2pi to compare the average power generated by an AC sine to the average power generated by a DC current.

Once the peak voltage for the required power is known the RMS value can be calculated from that.

What do you want to know? AC is expressed in RMS (which has been gone over moderately well in this thread), peak-peak ('cuz it's easy to measure on a scope), and peak-times-sine ('cuz it's the usual way to mathematically model a sine wave). The "correction factor" is different in each case.

Please give us an example of the problems you're trying to solve, and we can help you out.

--
Tim Wescott 
Control systems, embedded software and circuit design 
I'm looking for work!  See my website if you're interested 
http://www.wescottdesign.com

The weird thing is I talked with a guy who said he worked for Teledyne in a coffee shop last year who was looking for a contract worker. Something about digitizing strain-gauge measurements and transmitting them over Bluetooth or something.

The scary thing is that I think he thought I was qualified for the job LOL

It is also expressable as average, in which case the correction factor is zero.

--

John Larkin         Highland Technology, Inc 

lunatic fringe electronics

True. I forgot that one. Or as a Fourier Series, in which case the correction factor is a vector that varies with the problem :).

--
Tim Wescott 
Control systems, embedded software and circuit design 
I'm looking for work!  See my website if you're interested 
http://www.wescottdesign.com

This is the beauty of RMS and sine waves. The answer is the same.

However, it only works for pure resistors and sine waves.

If the load has capacitance or inductance, then the sine-wave current is not in phase with the sine-wave voltage, and the load has a complex impedance. It is not horribly more complicated, but you have to know the frequency to get the separate components of the impedance.

If the waveform is not sine wave, then you have to do numerical integration to get the power, for instance.

Jon

** Zero ??

Is that because the average value of a sine wave is always zero ?

... Phil

At what frequency?

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Just 60Hz.

Thanks for asking.

Robert Miller

e

h is called 120 VAC, you get about 160 VDC out of it. In other countries wh ere it is 220 VAC then you get double. In fact there is alot of electronic stuff ade now that simply doesn't care. Plug it into an AC outlet here or i n Europe, it simply regulates. And this accomplishment was not like putting a Man on the moon either. Withe better devices it became easier and of cou rse they designed equipment so it could be shipped anywhere and just accept the voltage they have. What would you do ?

f. These devices can increase or decrease voltage as needed.

s. Its peak amplitude is a bit higher and will rectify to more DC voltage. The RMS power is like when it goes to your toaster or whatever. When it com es to your TV or stereo, that might be a little different.

ulate and almost do not care the voltage. I have seen SMPSes work on as low as like 40 volts, and all the way up to 250 volts. Perfect regulation.

n an old piece of stereo equipment or something with tubes, all of it recti fies the AC into DC and that will be 160 volts (in the US). Then usually it goes into a chopper controlled by a feedback network driven by a correctio n circuit most likely driven by one of the power supply lags.

u wilt.

No such thing as RMS power in ac systems, just average power is the definit ion.

ition.

** The term "Watts RMS " is specific to audio amplifiers - and had been mis construed by non technical morons as being "RMS power".

Audio amplifiers work with ANY waveform in the audio range and quite a bit beyond while the AC power supply is strictly 50 or 60Hz sine wave. So it be came necessary to specify that power be measured under sine wave test and c ompute watts by the using RMS value.

However, you do have to measure the RMS value of AC current waveforms to co mpute the VA of many loads and size cables correctly.

.... Phil

inition.

isconstrued by non technical morons as being "RMS power".

t beyond while the AC power supply is strictly 50 or 60Hz sine wave. So it became necessary to specify that power be measured under sine wave test and compute watts by the using RMS value.

compute the VA of many loads and size cables correctly.

You are correct but there is another factor.

The RMS power rating, thought totally incorrect, is established as the de f acto measuerment. As such, if you deny that then you are pretty much denyin g volts, amps ans wats,, possibly even Culombs. Are you ready to do that ?

You might be correct, but all this shit is based on Coulumbbs.

Yesh maybe I did not spell it right but so the f*ck what ?

Whatever.

It does not require sine waves, but only works for resistors. However most inexpensive meters cannot measure RMS of signals other than sine.

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