[mythtv-users] Desk Top Power

Daryl McDonald darylangela at gmail.com
Sat May 16 15:17:03 UTC 2015


On Sat, May 16, 2015 at 11:08 AM, jrh <jharbestonus at gmail.com> wrote:

>
> > On May 16, 2015, at 10:21 AM, Mike Perkins <mikep at randomtraveller.org.uk>
> wrote:
> >
> > On 16/05/15 14:45, jrh wrote:
> >>
> >>> On May 15, 2015, at 3:53 PM, Simon Hobson <linux at thehobsons.co.uk>
> wrote:
> >>>
> >>> Mike Perkins <mikep at randomtraveller.org.uk> wrote:
> >>>
> >>>> I think you're missing the point slightly. If he has a spare +5v or
> +12v supply available from his PC, you're suggesting using it to switch a
> relay turning on or off an auxiliary mains supply which would feed a power
> supply to another device... at +5v or +12v.
> >>>>
> >>>> So why not just cut out the middle man?
> >>>
> >>> No, I'm not missing the point.
> >>> His aim isn't "to run stuff from the PC PSU", it's "to switch stuff
> off automatically".
> >>>
> >>> So yes, he could run stuff from the PC PSU - as long as it runs from
> 5V or 12V, and it's not dependent on any form of isolation*, and it doesn't
> imbalance the loads on the PSU**, and he makes the adapters, and ...
> >>>
> >>> Or with an off the shelf device (or simple modification), he can use
> use the PSUs that come with the kit and not have to worry about any of
> that, and not have any issues buying new kit.
> >>>
> >>> Neither is right or wrong - just different approaches.
> >>>
> >>>
> >>> * I recall reading a blog post a while ago about some problems someone
> has fitting out a yacht (floating gin palace) for WiFi. He was using PoE
> powered APs and stuff that worked fine on the bench for setting up didn't
> work once installed. Eventually he figured out it was lack of isolation,
> and the PoE got shorted out with the APs screwed to the metal structure.
> >>> Probably not an issue with most kit likely to be found in a home
> network, but can't be ruled out.
> >>>
> >>> ** Don't know whether they've improved much/at all - but going back it
> could be a problem if the loading on the different rails was too much out
> of balance. The PSU doesn't independently regulate each output, and back
> when I was working at that level, it was the 5V rail which was fully
> regulated - the other rails could drift somewhat depending on relative
> loadings. So adding several amps on the 12V rail could well result in that
> voltage drooping.
> >>> Again, it probably won't affect the connected equipment which will
> regulate the 12V down to other voltages internally, but it might affect PC
> components such as the hard disk(s).
> >>>
> >>
> >> Regarding power imbalance or however it is called, is this still an
> issue for power supplies built today?
> >>
> >> This is interesting to me, and could be an exercise in supplying whole
> house 5v/12v outlets!(Looking at all the wall warts I have in this room
> that are either 5 or 12 volts).
> >>
> > I thought of doing something similar many, many years ago, but with a
> monster transformer and some serious silicon rectifiers.
> >
> > The drawback to wiring a house for 5v / 12v is the power law: at 12v
> you'd need to supply a significant number of amps to your outlets, which
> means thick, expensive cable. If you don't then you'll have power losses in
> the walls and voltage drops at the outlets.
> >
> > There's a good reason why mains supplies run at 110v or 220v. That's to
> save copper. Unfortunately, modern devices like LED lamps all need lower
> voltages. Hence, wall warts everywhere.
> >
> > --
> >
> > Mike Perkins
>
>
> Agreed regarding current draw.   I was thinking just one room since that
> is where most of my wall wart problem is.  .. 2 hdhrs, 2 switches, 2 rasp
> pis, 2 external hds, magicjack, etc… We(as a group) probably have the same
> collection of wall warts plus or minus as i do!
>
>
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I'm going to go with something like this:
http://www.instructables.com/id/A-USB-Power-Controled-Plug-Strip-With-Isolation/

again thanks to everyone who entered the discussion.
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