Does it Really Only cost $14 to Operate my TV for a Year?

Remember that with resistors, Power = Volts * Amps? Well, inductors and capacitors take current too, but ideally don't consume power. That is why with motor loads, VA (volts * amps) exceeds power:

power factor == (real power) / (volts * amps).

Ideal resistors have pf=1, ideal inductors and capacitors have pf=0. Motors fall in between, and small cheap motors can have very low pf.

I used 'real power' because some engineers also speak of reactive power, which is an inductive or capacitive or 'imaginary' component. 'Imaginary' is used in the same sense as Complex numbers, which are based in including the square root of minus-1 as an actual number.

Power factor gets even more complicated because of harmonics, which create non-sine-wave currents. These are seen in many electronic power supplies, both old-style linears with diode rectifiers and more modern switch-mode systems. These currents now cause enough problems that they are often regulated, requiring high powered equipment to include power factor correction.

 

Yes, this is sort of the idea. But tip the incline up, not down, causing the water to stop and reverse. But the water keeps flowing for a short time due to momentum, not viscosity. This is similar to inductance.

 

Good gawd. There's so much I don't know about electrictity. So... the real power is something you measure (which indirectly measures all of that non-idealness you spoke about) and then you divide it by V*A to determine just how non-ideal the widget is. If the PF is near zero, the widget is shite (loaded with some very non-ideal components). If the PF is near 1 you've got an better widget (in the sense that it's bits and pieces are pirating too much power)?

 

What is the wave aspect of the current? I don't understand what that means. To say that the current has a sine wave shape, (forgetting the vile, loathsome harmonics for the moment) I'm not picturing it. I think of current like water moving through a pipe. Obviously, electrons moving through a wire (in the opposite direction... thank you very much Benjamin Franklin!) is different to water in a pipe, but that's how I think of it and it doesn't seem like you'd talk about the sine wave of water flowing through a pipe.

 

Alternating current AC ranges from ~120volt + to ~120 volts- alternating between the two 60 times a second,,, hence alternating current. If you look at the wave form through a scope, it forms a perfect shaped wave between the 2 extremes.

Picture a perfect ocean wave, measured between the peak and the trough, The height (and depth) of the wave is the voltage,, the distance apart is the cycle,,, HZ.

Is that clear as mud?


Icarus

 

Alternating current AC ranges from ~120volt + to ~120 volts- alternating between the two 60 times a second,,, hence alternating current. If you look at the wave form through a scope, it forms a perfect shaped wave between the 2 extremes.


Slight correction, common household 120VAC is 120VAC rms and has peak values of plus and minus 120 times the square root of two. Approximately 170 volts peak plus and minus, or 340 volts peak to peak on the sine wave.

 

ds71,

You are right,,, I only understand it,,,a little bit! By the time you add in RMS you get things even more confused more most laymen. (Myself included!) It is much easier to explain ~120+ 120-, even though it is not technically correct.

Icarus


Now explain to me RMS watts!

 

I don't think we want to go there, it will make the audio people go crazy.

Anyhow watts is always the instantaneous product of current and voltage but this gets confusing when the current and voltage aren't in phase, or you start talking complex waveforms. I imagine the killawatt meter does some kind of summing of the volts amps product over time to calculate the kilowatts and kilowatt hours.

 

No, they could easily be ideal components. But low power factors are very unfriendly to the power system. The extra current causes extra wire losses, for which the utility does not get paid. The harmonics are unfriendly to transformers and neutral wires in 3-phase systems. All your household single-phase gets bundled with others somewhere into a 3-phase system.

 

Perhaps I shouldn't have brought it up. I'm not a very good teacher, and it's difficult for me to explain obscure items in easy to understand terms

I originally brought up PF as a lot of electronic loads in the home, eg those power bricks and tv's etc, have very poor PF performance. PF problems create a lot of issues for utilities and - as a result - unnecessary cost to us

Nice graphs help, since my artsy-fartsy ability is zero, here we go

AC Power Factor Principle - Wolfram Demonstrations Project

http://www.ab.com/drives/techpapers/Harmonicsbasics.pdf

If you want to think about it in terms of phasor diagrams - or simply phase

Phase Relationships in AC Circuits

This one from the University of New South Wales explains it very clearly. The phasor animation they have very closely resembles the phasor display on my AEMC power qualtity meter

AC circuits, alternating current electricity

This paper details the effects of standby losses

FSEC-PF-344-98

Ok, did this help or only serve to further confuse the issue?

 

You could also look at it this way. DC power is always "on", +12volts one wire -12 volts on the other.

AC goes from positive to negative 60 times per second (HZ) The voltage doesn't just stop, but rather it builds, peaks and then falls, falls below zero until it stops falling (exactly as far below zero as the peak is above zero) creating an average of ~120 vac. The "True" measurable" voltage is the RMS of that peak voltage (if I understand it correctly)

(If you buy a cheap "modified sine wave inverter" at you local auto parts store so you can plug it into your car battery to get 120 vac,, what you get is not a clean sine wave form, but some form of a modified square wave. That is, instead of a clean "wave" dropping from positive to negative, the voltage is suddenly "turned off and reversed" 60hz. This is a very much inferior wave form that induces noise in things, and can burn up sensitive electronics and motor loads)

For the layman,,, We don't really need to know What RMS is, or even what AC voltage is and how it works. All we really need to know is that AC is different from DC and the two don't play well together.

We need to know that our light bulbs run on 120vac and our car battery is 12vdc. (although even that gets more complicated than that)

Clear as mud.

Icarus

 

All I know is Tony is buying his Chicago land watts for nearly 1/2 of what So Cal pays (rip off!) . . . but more than, the Flathead Valley MT.
Life is only fair if you're the big fish.

 

I will now send us off the rails - surprise!

A large solar flare or coronal mass ejection can interact with the earth's magnetic envelope - magnetosphere- and auroral electrojet

Space Weather News

Magnetosphere, HAARP, ionosphere, Simulations of ELF radiation generated by heating the high-latitude D- region

and introduce Geomagnetically Induced Current into pipelines and power transmission lines. This is quasi-DC being introduced, and can lead to fairly damaging half-wave saturation at transformer stations

http://www.ansoft.com/workshops/altpoweree/David_Cope_Engrg_Matters.pdf

http://www.labplan.ufsc.br/congressos/PowerTech07/papers/445.pdf

Ok, back to topic. Ummm .... PF=1.0 is good

 

RMS is Root Mean Square. You take the AC voltage, square it, find the mean, and then take the square root. You can think of it as the DC equivalent of AC voltage, or the effective value of AC for power calculations and such.

Tom

 

Last time I checked, Manitoba Hydro was charging 6.1 cents a KWH, with a service charge of around $16.

http://www.hydro.mb.ca/regulatory_a...ctricity/electricity_billed_rate_schedule.pdf

One can still heat a home here with electricity for about the same cost as with natural gas

 

alreet, jayman. I will read those links and comment back. probably more than I really want to know, but I'm curious enough to have a go.

 

Only if you want to. On this topic, I think the correct word to describe my nitpicking is "pedantic"

 

I tried reading through this thread and it reminded me why I dropped out of electronics

 

Sorry bout that!



I really do not mind explaining how things work. Where did I lose you??

 

I fear it is too complicated for me to grasp. I will look at it someday when I am better rested. Maybe I will be able to understand then