[mythtv-users] Desk Top Power

[Simon Hobson]

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).