For 220V could you take 2 kill-o-watts and put one on each hot wire? On Thursday, September 27, 2012, Jim Cathey wrote:
> And then there's the fact that watts do not equal amps times >>> volts when working with sine wave AC. >>> >> >> Watts = Amps x AC Volts RMS, regardless of the waveform... >> > > Exactly. A little more background: A non-true-RMS meter > is usually actually a peak-reading meter. For a sine wave > the RMS voltage is 0.707 times the peak voltage, and so > your AC range is calibrated to this value. For sine waves > you then read RMS (assumed) directly, but what you're really > reading is peak voltage times the fudge factor. This can be > useful to know, if you need a peak reading voltmeter for > a periodic (but non-sinusoidal) waveform. Such a number is > useless for wattage numbers, though, since you need RMS. > Same for current. > > There are true-RMS meters out there, the Fluke 87 is one such. > (My favorite Fluke 83 is not one. I have both. The 83's > batteries last longer, it has one less IC in it.) > > For paid-for power you need wattage, and for that you need RMS > voltage, current _and_ the power factor correction. That is > not a number you will get, not easily unless you actually have > a wattmeter. (I've got a couple, including the highly-useful > Kill-O-Watt, but nothing that could measure a 220V heavy-duty > appliance.) With a current clamp and a dual-trace oscilloscope > you could probably map out a pretty good guess, though. (You > have to integrate the instantaneous product of current and > voltage across a cycle. Tedious, by hand!) That is, in fact, > what a true wattmeter actually does, by some fashion. (Power > factor is calculated by taking the ratio of watts to the RMS > voltage multiplied by the RMS current, ignoring phase.) I > know of three competing technologies for doing watts: > emf-based meter 'motor' (vane, or actual spinning thing), > analog multiplier/integrator, or digital integration. > All are the same solution, just implemented with different > technologies. (Integrating the instantaneous product of > voltage and current.) > > If EV chargers became widespread I'd expect the charging circuit > to be somewhat elaborate, and power-factor corrected. On a > nationwide scale that would matter quite a lot. > > In fact, power factor itself isn't a very good number. It > assumes that essentially there is an inductive or capacitive > phase shift, only. The kind of thing that happens with > motors, and inductive/capacitive loads. With these, power > factor is corrected, reducing unpaid-for losses in the transmission > network, via compensating capacitors or inductors. (Once upon a > time this could be done with a synchronous rotating machine. > The power savings alone would pay for a sinning installation > to have this special machine installed and 'idling'. Or a big > capacitor bank; whatever was needed.) A SMPS, though, can have > a truly wretched power-draw cycle, essentially un-compensatable, > and one that could give the rotating machinery nature of the > power grid fits if it were large-scale enough. Rotating AC > sinewave sources really like feeding resistive loads, like > heaters and incandescent lights, and rotating machinery. > Anything that diverges far from that results in wasted > energy, or at least wasted generating capacity. > > -- Jim > > > > ______________________________**_________ > http://www.okiebenz.com > For new and used parts go to www.okiebenz.com > To search list archives > http://www.okiebenz.com/**archive/<http://www.okiebenz.com/archive/> > > To Unsubscribe or change delivery options go to: > http://mail.okiebenz.com/**mailman/listinfo/mercedes_**okiebenz.com<http://mail.okiebenz.com/mailman/listinfo/mercedes_okiebenz.com> > _______________________________________ http://www.okiebenz.com For new and used parts go to www.okiebenz.com To search list archives http://www.okiebenz.com/archive/ To Unsubscribe or change delivery options go to: http://mail.okiebenz.com/mailman/listinfo/mercedes_okiebenz.com
