[MLB-WIRELESS] PoE, was WRT54G Bulk Buy

[Dan Flett]

As far as Power-over-Ethernet (PoE) goes, it depends on how much money
you want to spend, and how much time and motivation you have to DIY.
PoE is not rocket-science, electrically speaking.  Personally I think
some of the PoE solutions out there are way over-priced.  But if you
shop around you might find something cheap.

PoE comes in two flavours - regulated and unregulated.  Unregulated
simply relies on the DC voltage drop of the Cat5 to get the correct
voltage at the DC power inlet of the Access Point.  If there is too much
voltage drop over a given length of Cat5 then you just increase the DC
voltage output of the power supply.  Doing this is dangerous because if
you for some reason shorten the Cat5 cable run and don't lower the P/S
output you could blow up your AP.

Here is an oft-linked site that is a howto for unregulated PoE:
http://www.nycwireless.net/poe/

Regulated PoE uses a voltage regulator at the AP to drop the incoming
voltage level down to the exact voltage required.  A voltage regulator
simply dissipates the excess voltage as heat.  Or you can use a
switchmode DC-DC converter to make efficient use of the incoming voltage
- much less heat is generated by a switchmode converter.

Jaycar has a few kits, both assembled and with assembly required, that
are either voltage regulators or Switchmode DC converters.
This one is a 24vDC to 12vDC @ 1Amp:
http://www1.jaycar.com.au/productView.asp?ID=AA0265
and this one, 24vDC to 12vDC @ 3Amp:
http://www1.jaycar.com.au/productView.asp?ID=AA0266

They seem pretty appropriate.  I think they're switchmode but I'm not
sure.  Running 24v over the Cat5 will reduce your voltage drop and
therefore reduce your overall current draw.  Unregulated 24vDC power
supplies can be bought pretty cheaply.

Some Googling found this site that sells some very nice looking, and
reasonably priced Switchmode DC-DC converters:
http://www.computronics.com.au/meanwell/sg/dc.shtml
They are based in WA.

> -----Original Message-----
> From: Tony Langdon (ATC) [mailto:tlangdon at atctraining.com.au]
> Sent: Wednesday, 23 June 2004 10:12
> To: 'nick.sibbing at arts.monash.edu.au'; 'dflett at bigpond.net.au';
> 'melbwireless at wireless.org.au'
> Subject: RE: [MLB-WIRELESS] WRT54G Bulk Buy - cheaper again!
> 
> > Gday Dan
> > Keep up the good work! I was about to buy 3 more minitars but
> > the WRT54Gs look tempting. I'm after a bit of info to be sure
> > I'm on the right track.
> 
> I must admit that I'm tempted.  Have an opportunity to throw something
up
> the mast too in the next couple weeks...  What's the best option for
> access
> points for mast mounted PoE?  At this stage, I'll be looking at purely
for
> client access, throw it up and see who connects. :)

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