Using Power over Ethernet to power two devices from a single ethernet cable

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

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

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

Better way to do this?

--
Bob Alston
Home: 918.494.4913
Lake: 231.893.8044
(E-Mail Removed)
http://members.cox.net/tulsaalstons/


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On Sat, 14 Aug 2004 20:56:44 GMT, "Bob Alston" <bobalston9
(E-Mail Removed)> 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/produ..._id=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 (E-Mail Removed)
150 Felker St #D http://www.LearnByDestroying.com
Santa Cruz CA 95060 AE6KS 831-336-2558

On Sun, 15 Aug 2004 10:17:44 -0700, Jeff Liebermann
<(E-Mail Removed)> wrote:

>On Sat, 14 Aug 2004 20:56:44 GMT, "Bob Alston" <bobalston9
>(E-Mail Removed)> 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.

Have you tried decaff? ;-)

>
> Have you tried decaff? ;-)

Never touch the stuff. Need the kick.

--
Bob Alston


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>>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.

Humm..... I am pretty sure my WRT54G is a version 2 - as I recall looking on
the bottom of the unit a while back. So that makes it 12 volt. But I
recently installed WAPPOE - and it still works.

Difficult to verify version 2 - cause I got to get out the extension ladder
and take it to the 2nd floor of the building.

Wonder why it is working??????

Have a message in to Linksys.

Bob Alston




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On Sun, 15 Aug 2004 20:22:45 GMT, "Bob Alston" <bobalston9
(E-Mail Removed)> wrote:

>>>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.

>Humm..... I am pretty sure my WRT54G is a version 2 - as I recall looking on
>the bottom of the unit a while back. So that makes it 12 volt. But I
>recently installed WAPPOE - and it still works.
>
>Difficult to verify version 2 - cause I got to get out the extension ladder
>and take it to the 2nd floor of the building.
>
>Wonder why it is working??????

Easy. The guts of the WRT54G runs on 3.3VDC. The low dropout
switching voltage regulator probably can handle anything down to about
1VDC between input and output, Therefore, it should work on 4.3VDC.
My guess(tm) is that the original version was designed to operate from
5VDC but was marginal over the usual distribution of what actually
comes out of a 5VDC wall wart, or the efficiency of the regulator
operating at the low end of its operating range was rather crummy.
So, they simply raised the voltage rating of the input cazapitors so
that they could handle a higher voltage and change the specifications.
They could have used 9VDC but there was probably a large demand for
10-15VDC battery operation, so 12VDC made more sense. The regulator
is possibly good up to perhaps 40VDC so it could probably be convinced
to run on 24VDC. Oh yeah, the higher the voltage input, the higher
the regulator efficiency. Just one problem with this theory. I'm not
sure exactly what chip is used for the switching regulator.

http://seattlewireless.net/~mattw/ph...e/IMG_3425.JPG

There's still an open question whether the WAPPOE box has enough
current handling ability to run two WRT54G. My guess(tm) is that each
box sucks about 1.5A at 5VDC. So, ask Linksys why the hell there are
no techy specs on the WAPPOE on their web pile, and whether the box
will handle a 3A load at 5VDC.

>Have a message in to Linksys.

They'll probably just recommend decaf.


--
Jeff Liebermann (E-Mail Removed)
150 Felker St #D http://www.LearnByDestroying.com
Santa Cruz CA 95060 AE6KS 831-336-2558