At 21:00 -0800 2/14/10, Clark Martin wrote: >On 2/14/10 8:14 PM, Bill Christensen wrote: >> At 10:07 AM -0700 2/9/10, Bruce Johnson wrote: >>> >>> If the river is too big (high amperage), the water wheel will work >>> just fine, because it'll only use the amount of water that fits in the >>> paddles...the rest of the river flows on by. >> >> Ok, if the "rest of the river flows on by", does that mean that even if >> your end use device is drawing .9 amps, the wall wart 'river' is still >> going to draw 1.2 or 1.5 or whatever amp rating it has, turning the >> 'excess' to more heat and a slightly higher electric bill? >> >> Or is the metaphor breaking down here? > >Not exactly. > >The components in a wall wart have a linear response (at least idealized >components would), if you reduce the current draw by half, the current going >in is reduced by half. > >The parts are however not ideal but real. That means that the transformer in >particular isn't linear. In particular, smaller transformers tend to more >quiescent power as a percentage of the total power drawn. Quiescent power is >the power the transformer draws with no load.
Methinks the metaphor is a bit mis-stated. The hydraulic analogy, as taught in a first course in electrical engineering, would replace the "river" with the "pipe" that is connected to a large reservoir. The device using the current is analogous to a water valve with a constant flow rate typical of newer shower heads. The water that's not used never leaves the reservoir but it's still limited by the resistance to flow caused by the pipe. It doesn't "flow on by". And modern DC wall-warts, now required in California, typically do not start with a transformer. They are high frequency converters that use a much smaller and more efficient transformer after they convert 60 Hz power to something well above 100 kHz.. Those things are smart enough not to draw current, "quiescent power", from the power mains unless that valve between it and the user is open. And. . . Those new-fangled devices typically draw power from the lines in short pulses 120 times per second. That's called harmonic distortion which is illegal in Europe for larger units like ATX power converters in a desktop computer. We'll hear more about that in a while when California gets a bit brighter shade of green. -- --> From the U S of A, the only socialist country that refuses to admit it. <-- -- You received this message because you are a member of G-Group, a group for those using G3, G4, and G5 desktop Macs - with a particular focus on Power Macs. The list FAQ is at http://lowendmac.com/lists/g-list.shtml and our netiquette guide is at http://www.lowendmac.com/lists/netiquette.shtml To post to this group, send email to [email protected] For more options, visit this group at http://groups.google.com/group/g3-5-list
