Hi,
quote=Roland,Aug 11 2005, 07:01 PM]
Side note: 11 PM and I have to be packed and on the road in ~9 - 11 hours, tops, for my vacation. God I hate the night before. :P
[right][snapback]85804[/snapback][/right]
[/quote]
Ain't that the truth. It's been my experience that by the time you get everything settled at work and home so that you can leave for vacation, you really need one. Sort of the zero sum law of recreation :)
Have a good time, wherever you go. See you when you get back.
--Pete
P.S. {added in edit} I think I see where the efficiency issue comes from. It looks like THG measures the wattage by simply multiplying the voltage times the current. This is fine for direct current, since the two components are always in phase. But for alternating current, one must include the effect of the 'power factor'. The correct formula for AC power is voltage times current times the cosine of the phase difference between voltage and current. Only if the two are in phase will this reduce to the simpler formula. Since, IIRC, switching power supplies are an inductive load, the two *will* be out of phase. Thus, since the efficiency is power out over power in, we can calculate the phase angle from
cos(PA) = E_ignoring_phase/E_including_phase.
So a power supply which I'd call 90% efficient and which THG calls 70% efficient has a phase angle of about 40 degrees. Not an unreasonable value IIRC. However, the 90% value more truly represents what that watt meter on your wall would measure and what the power company would charge you for :)
P.P.S. Later saw that THG *is* taking the phase angle into account, but the power factor (cosine of the phase shift) they seem to get is more like .97 than the .8 to .5 of highly inductive (or capacitive) loads. So, for the time being, I'm puzzled. However, I will probably go with a PS that has a better pedigree and lower nominal wattage (say, about 500W if at least 450 of them are in the 3.3 5, and 12 lines).
quote=Roland,Aug 11 2005, 07:01 PM]
Side note: 11 PM and I have to be packed and on the road in ~9 - 11 hours, tops, for my vacation. God I hate the night before. :P
[right][snapback]85804[/snapback][/right]
[/quote]
Ain't that the truth. It's been my experience that by the time you get everything settled at work and home so that you can leave for vacation, you really need one. Sort of the zero sum law of recreation :)
Have a good time, wherever you go. See you when you get back.
--Pete
P.S. {added in edit} I think I see where the efficiency issue comes from. It looks like THG measures the wattage by simply multiplying the voltage times the current. This is fine for direct current, since the two components are always in phase. But for alternating current, one must include the effect of the 'power factor'. The correct formula for AC power is voltage times current times the cosine of the phase difference between voltage and current. Only if the two are in phase will this reduce to the simpler formula. Since, IIRC, switching power supplies are an inductive load, the two *will* be out of phase. Thus, since the efficiency is power out over power in, we can calculate the phase angle from
cos(PA) = E_ignoring_phase/E_including_phase.
So a power supply which I'd call 90% efficient and which THG calls 70% efficient has a phase angle of about 40 degrees. Not an unreasonable value IIRC. However, the 90% value more truly represents what that watt meter on your wall would measure and what the power company would charge you for :)
P.P.S. Later saw that THG *is* taking the phase angle into account, but the power factor (cosine of the phase shift) they seem to get is more like .97 than the .8 to .5 of highly inductive (or capacitive) loads. So, for the time being, I'm puzzled. However, I will probably go with a PS that has a better pedigree and lower nominal wattage (say, about 500W if at least 450 of them are in the 3.3 5, and 12 lines).
How big was the aquarium in Noah's ark?