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

Simon Hobson linux at thehobsons.co.uk
Sun Aug 21 11:24:45 UTC 2011


Jay Ashworth wrote:

>  > 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.

...

>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.

Let me guess, you have high neutral currents ?

>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.

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 !).

-- 
Simon Hobson

Visit http://www.magpiesnestpublishing.co.uk/ for books by acclaimed
author Gladys Hobson. Novels - poetry - short stories - ideal as
Christmas stocking fillers. Some available as e-books.


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