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

[Jay Ashworth]

----- Original Message -----
> From: "Ken Truesdale" <kat at tiac.net>

> Wouldn't it be nice if there could be some standard for DC power input
> to devices? All of them at 12 VDC or 5 VDC or something. And then
> you'd be able to buy a low voltage "power strip" that had a series of
> these low voltage connectors on it so that you didn't have a string of
> 7 wall warts fighting for space on a 120VAC outlet. You'd have a
> single block doing the transforming and each device could just pick up
> that output. 

There is.  But you have to be satisfied with 5VDC at 500ma peak: MicroUSB
is the new DC charge standard for cellphones.  In practice, some DC adapters
with that plug will supply more than 500ma, up to 8-900, and while the device 
is *strictly* supposed to negotiate for that much power, and will if on an
*active* USB jack, on an adapter, it will just draw what its load requires, 
up to the limit of the adapter.

So if 2.5W is enough for you, go.  :-)

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
lions 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.

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.

Cheers,
-- jr 'IANBP[1]' a
[1]I am not Bob Pease[2]
[2]RIP
-- 
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