[mythtv-users] Desk Top Power

[Stephen P. Villano]

On 5/16/15 12:59 PM, Simon Hobson wrote:
> Michael Watson <michael at thewatsonfamily.id.au> wrote:
> jrh <jharbestonus at gmail.com> wrote:
>
>> Regarding power imbalance or however it is called, is this still an issue for power supplies built today?
> Yes I would say for a typical PC PSU.
> The multiple outputs typically come from multiple secondary windings and rectifiers from one transformer. The feedback control operates on the primary output - it's only possible to accurately regulate one output without secondary regulators. The other rails will more or less follow the main one - the relationship between output voltages depends on the ratio of the number of turns on the transformer, and the voltage drop in the rectifier diodes and windings.
> If you keep the load on the primary output constant, then varying the load on one of the secondary outputs will vary the voltage on that output - increase load and the voltage will droop, reduce it and the voltage will rise.
>
PC power supplies have long been switched mode power supplies, with a
"chopper" duty cycle being controlled by output voltage of the various
outputs.
Many have multiple "chopper" circuits, in order to follow the demands of
the various outputs, such as the 5 volt and 12 volt lines. They're
literally independent power supplies within one box.
The end result of insufficient loading can be nothing or one can end up
with a bad odor and "popcorn" from blown electrolytic capacitors,
depending upon the design of the power supply. Some can handle no-load
conditions, some cannot.

As for whole house distribution, that is a non-starter due to resistive
losses in long wire runs. An intermediate voltage run might be feasible,
but one would be more fiscally responsible by leaving mains voltage to
each room and place higher demand capable power supplies in multiple rooms.
Otherwise, you'd be slinging large gauge cables around, just to lower
resistive losses from the wires (larger gauges tend to have lower losses
than small gauges).

Tesla and Edison had a longstanding argument, Tesla advocated for
alternating current, Edison advocated for direct current. As alternating
current has less losses in long transmission lines than direct current,
Tesla's argument won by means of feasibility.