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On 10/02/2015 01:03 PM, John Vaughters via TriEmbed wrote:<br>
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cite="mid:813261844.298371.1443805415553.JavaMail.yahoo@mail.yahoo.com"
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<div id="yui_3_16_0_1_1443721524175_63698">From a product
specification perspective, PoE is going to take into account
the full 100 meters and then you could factor in about a 10
times safety ratio. You could engineer the amps based on type
of wire and the current limits relative to length, but realize
that the insulation is pretty thin as well. Based on the
information from this email string, I suspect you could easily
use PoE in a custom engineered standard and have plenty of
power to spare, while maintaining safety. But that statement
is based on much shorter cable runs than 100 meters, which I
feel confident most of us will not use. If you DO use the full
100 meters, I would definitely not violate the specification.
CAT 5 was never designed for power and the ratings are more of
a limitation based on the minimum CAT 5 specifications. </div>
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<div id="yui_3_16_0_1_1443721524175_63696" dir="ltr">Concerning
the high voltage and switching DC-DC supply idea, you would
have to run the calculation on the efficiency curve of voltage
drop and power supply given by the DC-DC converter. The more
voltage you drop the more power you loose, so this could be a
self-defeating plan and more costly in upfront costs as well
as operation costs. Although, most of us could care less about
the operation costs; being so little. There would probably be
an optimum power draw combination in that situation, which
would depend on the characteristics of the DC-DC converter. If
you are sticking to the PoE specification, for sure you will
never see 13W of power at your Pi, but you could probably make
it work.</div>
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<div id="yui_3_16_0_1_1443721524175_63696" dir="ltr">John
Vaughters</div>
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<br>
You're right, it would be a silly, frustrating exercise (risking the
escape of magic smoke) to have the DC-DC converter on the "source"
end of the cable without another regulator on the sink end with a
Raspberry Pi, so why not just use one on the sink end. I also think
that following the PoE limits for both power and voltage would tend
to keep your house insurance company happier.<br>
<br>
Another issue we haven't touched on (here, but it's been extensively
discussed in the past) is the (mostly economic) hazard of having
expensive equipment hanging off 100 meters of unshielded wire during
a lightning storm. I'd have to be willing to replace the RPI
periodically to explore anything like this. <br>
<br>
<br>
-Pete<br>
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