Using Power over Ethernet to power two devices from a sing..

Archived from groups: alt.internet.wireless (More info?)

On Sat, 14 Aug 2004 20:56:44 GMT, "Bob Alston" <bobalston9
NOSPAM@aol.com> wrote:

>I need to find out if it is possible to use Power over ethernet to power two
>devices from a single ethernet cable.

OK, you're cheap. I can understand that.

>I forsee a relatively standard POE
>setup at the injector end. Then at the location of the first device needing
>ethernet connection and power, put in an ethernet hub before the power is
>split out. One ethernet output (with power ) from the hub goes right into
>the POE splitter and then provides ethernet (w/o power) and power to the
>first device. The second ethernet (with power ) from the hub goes on to the
>second device and connects to a standard POE splitter to provide power and
>ethernet to the second device.
>
>Plan is to use Linksys POE devices to power two WRT54G Access Points.

OK. Which WRT54G mutation? Only the original one run on 5V while
others require 12V.
http://www.linksysinfo.org/files/WRT54G%20Versions.htm
The Linksys WAPPOE only duz 5V so that will only work with the
original WRT54G.

I'll assume the 12V version which draws about 0.5A (measured in
haste). Therefore the real question is whether the WAPPOE will power
it. Well, the WAPPOE box only does 5V and not 12V power, so that
won't work. So, your options are to either find a 12V PoE system,
use an older pair of WRT54G, or build your own.

This might be worth reading:
http://www.keithl.com/Linksyspower.html

I've built a few PoE system. I'll leave out the details but basically
it's a DC-to-DC power converter, with a 24V or 48VDC input (to keep
CAT5 DC resistance losses to a minimum), and a 5V or 12V DC output. I
have one built that's running 3ea WAP11 access points on top of a
tower. I prefer Astrodyne DC-to-DC converters as some are shielded
(for low EMI/RFI) and are reasonably priced.

For running two WRT54G 12V boxes, you need at least 12V 1A output plus
whatever the hub burns. Hopefully, you can find a 12VDC powered hub.
Methinks a 20watt unit will suffice. See:

http://www.astrodyne.com/astro/pro [...] 6&watts=22
http://www.astrodyne.com/pdf/ASD20.pdf
Digging through the pile, methinks an ASD20-48S12 ($36) will work.

>1) Will a passibe two port hub handle all wires in the cable including the
>ones with power?

What's a "passibe two port hub"? For that matter, where are you gonna
find a 2 port hub (with the proper bypass wiring)? I usually buy some
random hub (in this case, must be 12VDC powered), and add my own power
bypass wiring.

>2) Does the Linksys POE injector supply enough power to power two WRT54G
>devices?

Nope. WAPPOE does 5V. Most WRT54G run on 12V.

>Better way to do this?

Of course. See above on DC-to-DC converters. Don't forget the fuse
or current limiter. Input source can be unregulated (i.e. solar
powered). Learn by Destroying works, but can be expensive.



--
Jeff Liebermann jeffl@comix.santa-cruz.ca.us
150 Felker St #D http://www.LearnByDestroying.com
Santa Cruz CA 95060 AE6KS 831-336-2558

Archived from groups: alt.internet.wireless (More info?)

>
> Have you tried decaff? ;-)

Never touch the stuff. Need the kick.

--
Bob Alston


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