[mythtv-users] Desk Top Power

[jrh]

> On May 16, 2015, at 1:54 PM, Stephen P. Villano <stephen.p.villano at gmail.com> wrote:
> 
> 
> 
> 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.

For single room purposes, if you have a ~500 Watt power supply, and you draw say 5amps off the 12V rail, and say 10 amps from the 5 volt rail, you’d be using ~110Watts.

I am using this number to represent what would be used from 5 12v wall warts and 6 or 7 5v wall warts.

I know the wall warts will be rated higher than above, but usage would be as above.


Would that be enough to load the 12v/5v rails on the power supply?

Regards!