[Soekris] Max distance for PoE

Dave dave at cc0.net
Sun Nov 30 05:42:07 UTC 2003


Ethernet aside...

I have one of my 4521 boxes about 800 feet away from the power source over
18 gauge zip cord. Power source is one of the 15V/30V Radio Shack models
running at 30V although at the transformer (5') shows 36V with no load.
Never done any load/voltage measurements after installation and after
800'...just connected a 4521 (actually 2 for a while) and it has been going
for about 5 months.


-Dave



> Thanks for the help, I did realize that the voltage drop can be
> calculated.  I have one of the PoE power supplies you can order direct
> from Soekris, which I believe is 48v.  I didn't know the theoretical
> "cut-off" point at which the Soekris would refuse to power up.  I don't
> really know how far I'm going to have to go to get to an electrical
> outlet, so I figured I'd just ask how far other people have gone to get
> a real world best guess.
>
> Thanks
>
> -----Original Message-----
> From: soekris-tech-admin at lists.soekris.com
> [mailto:soekris-tech-admin at lists.soekris.com] On Behalf Of Chuck Yerkes
> Sent: Saturday, November 29, 2003 9:01 PM
> To: soekris-tech at lists.soekris.com
> Subject: Re: [Soekris] Max distance for PoE
>
>
> Quoting Fred Weston (fred at daytonawan.com):
> > For those that are using PoE with their 4511/21, what's the longest
> > ethernet cable run you've used?  Have you ever had a problem with
> > using too long of a cable?
>
> 1) ethernet will likely have limits before proper RFC/Cisco complaint
>    48VDC PoE.
>
> It would be easier if you just said:
> I have THUS challenge and think I'll meet it THIS way and let us address
> actual numbers.  But in the abstract: It's basic electricity.
>
> Voltage drops over distance using wires.  My Pocket Ref isn't handy and
> I never remember the numbers, but at 200M, you lose maybe 4 or 6 volts?
> (don't hold me to those numbers). At 48VDC, that leaves you with 42
> volts.  Not a problem.  At 15VDC, your Soekris won't come up.
>
> Lower power also means more amperage means more heat and perhaps issues
> with the 24(?) gauge wires in CAT5.
>
> Now, I wanna find out about Power over fiber :)
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