[GLLUG] Want to learn PoE
chrisbell at chrisbell.org.uk
Thu Oct 24 10:14:08 UTC 2019
On Thursday, 24 October 2019 09:31:25 BST nickmount91 via GLLUG wrote:
> Hi everyone,
> I have some Cisco CP-7911G VoIP Phones that I want to use on a fibre
> broadband connection. Some of them have PSUs, but some don't. Can anyone
> point me towards resources where I can learn about Power over Ethernet,
> Sent with [ProtonMail](https://protonmail.com) Secure Email.
If they are using 10/100 base ethernet they will only be using two of the four
pairs, and PoE could be supplied via the other two pairs, which is what I do
with CCTV cameras, I just separate the unused pairs and provide close to 48v
DC correct polarity via self re-setting fuses and let them take whatever
current they require via their own switchmode regulator.
However I assume they are using gigabit ethernet.
The full procedure is fairly complex, with the PoE sender chatting to the
device and increasing the output on demand over up to all pairs, so the
easiest method is to use a commercial PoE inserter or a PoE enabled bridge/
switch. Expect non-PoE ethernet devices to link transformer centre-taps to 0v,
and short PoE.
They are listed at millsltd.com and cpc.farnell.com
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