On Sat, 29 Sep 2007 16:32:29 -0400 kony <spam@spam.com> wrote:

| The difference would be negligible, when a PSU uses a
| roughly 360VDC input to the chopper transistors it is merely
| a bridge rectifier followed by capacitors. Active PFC units
| have to maintain a level above the peak rectified DC so 360V
| wouldn't be enough margin. The PSU will still need
| capacitor(s) for this 360V so the only thing removed would
| be the bridge rectifier, roughly 1% efficiency difference
| and practically no difference in PSU size.

So standardize on 400V or more if needed. I do believe a bit more than 1%
of the power loss comes from the initial upconversion in a typical PSU,
based on how hot I've seen said parts get (and in a couple of my many PSU
burnups, on those parts).

Where there's dissipation, there is efficiency gained if that part can be
eliminated without incurring that cost elsewhere (but that may be an issue
in the data center to convert its incoming 3 phase 480VAC to 400VDC and
managing the paralleling with the battery banks).


| Further, commodity grade electrical supply line wire is not
| very expensive relative to most other components, the loss
| on the (existing AC, or per your idea going to DC) supply
| wiring is also negligible.

It's not too bad at 120VAC, though a it better at 240VAC (which I would
prefer to use). But a design around 12VDC would be some very big wires.
It's both the cost of the copper and the heat loss, which is proportional
to the _square_ of the current for the same size conductor (no, you would
not do that), which means it is proportional to the current when the wire
size is also proportional to the current (e.g. much more wire with the
same current density).


|>But such a setup would be far too hazardous for typical home use
|>(that is, not something sold commercially for a consumer market, even
|>though an engineer hobbyist might have no problem with it).
|
|
| It would be impractical and expensive, but the hazard not
| significantly different than present 110/220V AC delivery
| systems. All that to save a trivial amount of power.

Such a system can be made safe by competent electricians. But for homes,
the standards have to consider do-it-yourself-ers doing the wiring. DC
is not as easy to interrupt as AC. And your fault current from a central
PSU might not have enough to work the breakers properly.

Even common DC to 120VAC inverters are dangerous for homes because such
inverters can't properly trip circuit breakers when there is a short on
the AC side.

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| Phil Howard KA9WGN (ka9wgn.ham.org) / Do not send to the address below |
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