[Tfug] Opine: Bricks, warts or...?

[Bexley Hall]

Hi,

--- On Sat, 8/2/08, Harry McGregor <micros at osef.org> wrote:

> > What would be useful is a universal power supply,
> wherein you could buy
> > one that could serve the needs of multiple devices. 
> Kinda like a
> > standard, but standards are Communistic so I don't
> see the manufacturers
> > going that route.
> 
> I really think we already have two good universal power
> standards, just not too many people using them yet.
> 
> First one is power from USB.  USB is rated at 500ma, 5
> volts, DC, or about 2.5 watts.  Many devices are made to
> take up to 1amp, if provided, 
> and thus go up to 5 watts of charging power (Cell phones,
> etc).  Powered USB hubs work well for this, and you can get
> car USB power adapters, and even 110VAC to USB adapters
> (Apple sells their own cute one for iPod 
> use, but you can get cheap ones for less than $1).

The problem with USB is you can't *rely* on having that
available.  I.e., you, as the designer of a product that
will plug into a USB hub, take a risk when you assume the
user will have a hub that can "spare" that much current for you.

And, if you require the user to buy another hub, you've just told
him to buy a wall-wart-by-a-different-name.

If your customer plugs in his Doohicky9000 and it doesn't
work/charge/spitnickels, he calls you (*if* you are lucky)
or returns it (probably more likely).

Remember, most battery powered devices want a "fast charge".
So, you're usually charging at C/5 or so to keep the device
"portable" (vs. "always sitting in a charger").

> For higher power demands, power over ethernet (802.3af and
> 802.3at).  
> 802.3af is rated at 48vdc, 312.5ma, or 15 watts, and the
> new 802.3at is 
> going to double that to 30 watts.  Single devices that need
> more than 
> 15/30 watts are quite rare for small power supplies.  How
> many wall 
> warts do you run into that are over 12 volt 1.5 amp?

But then you are telling the user he has to have a WIRED
network in his home (?) *and* put the power supply for
PoE *somewhere*.  Note that people use wireless NICs simply
to get away from having to run wires...

Also, both of these (USB & PoE) assume you are talking about
"computer related devices".  Do I have to buy a special
cradle to charge my cell phone from my ethernet jack?
Or, my PDA?  Or, my wireless keyboard?  etc.
 
> Also many PoE devices only use half power, or about 7
> watts, and 3com 
> even makes an in-wall switch that uses less than 7 watts,
> and passes on 7 watts for a VoIP phone.
> 
> http://www.3com.com/products/en_US/detail.jsp?tab=features&pathtype=purchase&sku=WEBBNCNJ220SYS
> 
> I love PoE phones, network cameras, wireless APs, etc.
> 
> If we can just encourage developers to use the standards (I
> have seen 
> way too many passive non 802.3af PoE devices, that I would
> love to use if they were true PoE), we will be set.
> 
> http://www.netgate.com/product_info.php?cPath=60_83&products_id=625
> 
> You could have a small PoE switch and an 7 port powered USB
> hub on your desk, and be rather well setup.

It wouldn't handle my PDA or cordless phone.  It would be hard pressed
to deliver the 36W my scanner needs.  And, would require my (amplified)
desktop speakers to be seriously redesigned (or crippled).

> http://www.newegg.com/Product/Product.aspx?Item=N82E16833122152

Nowadays, you can get a small DC supply directly from the AC line
in a tiny (IC) package.  But, this exposes you to UL and similar
liability issues.  If you need more power, then -- by definition -- 
you need more *volume* for the power supply.  Who do you (manufacturer)
think you are fooling by putting that "volume" in a different box?
Do you think the user doesn't *see* that box??

(I chuckle when I think of the "wall wart" Kurzweil used in his
electric piano -- can you spell "suitcase"?)