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H Steve Thanks for the comments. We are at the process of addressing them. Yair From:
owner-stds-802-3-poep@xxxxxxxx [mailto:owner-stds-802-3-poep@xxxxxxxx] On Behalf Of I've read the paper by John Siemon and Dean Stoddart on the subject of
RJ-45 reliability for PoE, and I have some comments: 1. I agree, the damage appears to be
from arcing. But the paper doesn't seem to distinguish between the two
causes of arcing: a. On insertion,
the arcing is due to inrush into the capacitor. b. On extraction,
the arcing is due to kick-back from the inductor 2. The experiment used a DC power
supply in place of a PSE. This causes arcing on connector insertion that
wouldn't happen with a PSE, because the PSE in detection mode has a minimum of
45kohms source impedance. I did a quick SPICE simulation of the RLC
circuit with a step voltage input to estimate the peak inrush current. I
assumed 0.1 Ohms series resistance to approximate the wiring (something the
Siemon/Stoddart paper doesn't seem to mention). I observed a peak of
about 13A. This is probably where the damage is occurring, and it
wouldn't happen with a PSE. 3. The arcing on extraction probably
causes little or no damage since it's energy is so low. The test was at
57V, with 105 Ohms load. This means 543mA thru the 100uH inductor just
before extraction. The energy stored in the inductor is
0.5(0.543^2)(1e-4)=14.7 micro Joules. (By contract, the energy that the
5uF cap sucks up after insertion is 8.1mJ, or 552 times higher.) For these reasons, I think the results
were invalid. I recommend the experiment be repeated using an actual PSE
instead of a bench supply. I predict the amount of damage observed will
be dramatically reduced, perhaps even imperceptible. |