Are there any bad brands out there?  Does anyone make one that has Powerpoles built in?

What brand is everyone using?  I want to buy about 3 sets that will work on very long ethernet runs.

Thanks!

Ronny

K4RJJ

Yep that is how it works.  BTW the adaptors I use are about $2 each for a set shipped.  Check eBay.  Not a waste of money at all.  They work great!

I've run WRT54G and GS directly from the 13.8v supply in my motor home (which often is about 14.5v), and I've run them on 9v wall-warts.  Except for WRT54Gv1, they have internal 5v regulators.  The regulator runs a little hotter on higher voltages because it's dropping the input a little more, but I've never had one fail.  Anyway, I wouldn't worry about the losses from a 12v supply working over a couple hundred feet of CAT5e.

The real problem of running PoE on umpteen hundred feet of CAT5e is the inductance!  It causes problems when the current used by the WRT54G fluctuates!  It can AND will vary quite a bit.

This can be fixed by installing a large capacitor in parallel to the WRT54G at its end of the power cable.

Kip, AE5IB, found that a nice large electrolytic around 10,000-uF provided sufficient capacitance. Yes, smaller values were tried with the 180-ft of CAT5 cable that was in use but they didn't keep the router from going a bit nuts.

     -Rusty-

Time to put on my EE hat.  Retired now, I'm an old design engineer.

The inductance is easily avoidable.  The four unused conductors in a Cat5e cable consist of two twisted pairs.  If you blithely use one twisted pair for the positive, and the other for the negative, then, sure enough, the inductance could be a problem.

If, however, you wire it so that the conductors in each twisted pair are carrying equal and opposite currents, the inductance will be reduced by as much as several orders of magnitude.  This occurs because inductance depends upon the creation of a magnetic field surrounding the wires -- and if two conductors are intimately close together and carrying equal currents in opposite directions they don't create a significant magnetic field -- the magnetic field each member of the pair would create is canceled by the other.  Thus they'll have very little inductance.

That's why the wires are twisted in the first place -- in order to avoid magnetic effects, which might couple them to other pairs.  Don't want that.

I'll bet your friend never thought about that, and used one pair in one direction, and the other pair in the other direction.  Bad practice. 

Another thought:  10,000 μF is awfully large, and suggests your friend didn't know that electrolytic capacitors typically have considerable inductance of their own, making them useless for bypassing high-frequency transients.  The load variations you're talking about contain both low frequencies (which you would bypass with an electrolytic capacitor) and quite high frequencies into the GHz (which you would bypass, for example, with a ceramic, mica, or styrene capacitor).

If your friend had used, say, a 100μF electrolytic capacitor and a 0.1 μF ceramic capacitor in parallel, with short leads, he probably would have found that, even with inductance in the supply leads, operation would have been solid.  After all, anyone who ever designed power supplies knows that inductance in power-supply leads is generally a good thing.

Carl,

I agree that running opposite currents in each twisted pair is good and the plan
when running non-DC signals but, bad design or not, one pair in one direction and
one pair in the other is the IEEE standard (802.3af/802.3at) for PoE -- pairs 4&5
are DC+ and 7&8 are DC-. Doing it otherwise would force us to make our own PoE
adapters. Granted, that isn't difficult but not desired.

Not sure if the Kipster used 100μF in parallel with a 0.1μF or not -- that was my
first suggestion (EE Power Supplies 101). Still, I would think that such a combo
was already on the input side of the '54G's regulator and it's hard to drag most
o'scopes up to the top of a water tower to find out if the problem is transients or not.
(No, a small handheld 'scope wasn't available) We can guess/estimate/engineer all
we want but the fact of the matter is that the 10,000μF cap did do the trick and
it was left that way. Thanks for your input nonetheless!

-Rusty-