[mythtv-users] OT: Standard LVDC power (was: HDHomeRun Prime iPad app)

Jay Ashworth jra at baylink.com
Sun Aug 21 21:10:38 UTC 2011

---- Original Message -----
> From: "Simon Hobson" <linux at thehobsons.co.uk>

> Jay Ashworth wrote:
> >Now, that said, you're right; it would be really nice if there was a
> >companion standard for +12VDC at, oh, 2-3A maybe? That would service
> >everything except full size laptops, which would require one more standard:
> >+24VDC at 5A. Those three VCC sources, which could all be provided on
> >one jack, would service 98% or so of all portable electronics.
> >
> >The real problem, as it happens, is that switchmode power supplies --
> >the lion's share of all small LVDC power supplies, as they're much more
> >efficient than linear ones (albeit noisy, and with crappy power factor;
> >this matters when you have 500 of them in one building, ask me how I
> >know this :-) -- tend to be unhappy unless they're loaded to at least
> >50-60% of peak load.
> Let me guess, you have high neutral currents ?

Well, probably, but it's more that the power company gets pissed at you
because your meters read low.

> >That makes it difficult to design one that would service between 1 and 12
> >outputs at random, and still be in the zone. You'd almost have to make
> >the supply linear, and heat dissipation becomes a problem.
> Actually, they aren't hard to design or make - just hard to design &
> make **very very cheaply** - ie for a halfpenny or whatever most
> vendors want to pay.

I'll buy that.  But not for much.

> What I have observed is that some equipment actually works over a
> wide input range and this is specified in the manual. Even for
> equipment where it isn't specified, when you open them up they have a
> switch mode regulator and so could take a wide voltage range. There
> really isn't an excuse for the variety of power supplies used by
> vendors these days - nor the variety of plugs - and especially not
> the range of proprietary plugs (yes Apple !).


-- jra
Jay R. Ashworth                  Baylink                       jra at baylink.com
Designer                     The Things I Think                       RFC 2100
Ashworth & Associates     http://baylink.pitas.com         2000 Land Rover DII
St Petersburg FL USA      http://photo.imageinc.us             +1 727 647 1274

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