Carlos E. R. wrote:
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The Thursday 2008-02-14 at 13:07 -0500, James Knott wrote:
But I don't see how a transformer primary, which is an inductor, can be anything _but_ reactive.
An unloaded transformer is inductive, which limits the current to a low value and lagging voltage by 90 degrees. As the load increases, the voltage and current come closer into phase. When the transformer is at maximum load, the phase angle will be 0, assuming a resistive load on the transformer.
The problem in this case is that the load is neither: it is "switched". To calculate the real power used you need to sample the waveform, at least 15 samples per period, both voltage and current, then multiply and integrate (root mean square, RMS). You need some type of cpu. Actually, there is a chip that does all this, and I guess it is why these measurement gadgets have appeared in the market.
Quite so. I was just replying to that transformer comment. With switching supplies, transformers are often not used on the input. The incoming AC is rectified, filtered and the resulting DC is used to power the switching regulator that provides the desired output voltage(s). This process results in a lot of noise, that has to be filtered from the power line & load as well as shielded, to prevent interference.. -- Use OpenOffice.org http://www.openoffice.org -- To unsubscribe, e-mail: opensuse+unsubscribe@opensuse.org For additional commands, e-mail: opensuse+help@opensuse.org