Loren - For the staight scoop on power over ethernet, visit www.poweroverethernet.com. DC/DC converters imply using Power over Ethernet, which is formally kwown as 802.3af-2003. I've been using "my standard" for 3 years now to power outdoor ethernet devices - but all I do is put 48VDC on the spare pairs and use a standard dc/dc converter to create either 5VDC or 12VDC (or both) inside the device. I use whatever brand of converter is cheapest on the surplus market- some from vicor (www.vicr.com), at&t/lucent, tyco, and others. I normally pay $5 for a small converter. (note - the "standard" for POE has 2 forms, as well as handshaking to turn the power on, etc - I ignore all that and do it the brute force method. If you buy 802.3af-2003 compatible h/w expect to pay a bundle for the convenience)
I get the 48VDC from my telecom power supply & battery system, which adds a layer of UPS capability to the network hardware. It also means I have a single fully redundant supply instead of dozens of wall worts that are each single points of failure. If you like building your own power supplies - you can split your own design upstream of the regulator, after the rectifier, and place capacitors at both ends of the cat-5 cable (it now carries the unregulated DC) - install your regulator circuit near the load (even inside the case since there's normally room for it) and you have the same result. Because of the low power requirement for 802.11 hardware, even linear regulators work with tiny heatsinks. This is fair game for any load up to 1A - above that range is where DC/DC converters are really required. POE simplifies outdoor and mezzanine/roof installations - a single low voltage cable handles everything. Unfortunately the 802.3af-2003 standard seems to raise the price of the end product over one without POE. This should change as POE is adopted by more vendors. Everett > > Danf wrote -- > and install a dc/dc > converter for the +5VDC they want so you can use POE > > Is there a DC/DC converter you would recommend? > > For an inexpensive POE, I've used a pair of lawn sprinkler timer > transformers (24 VAC at around 1.25 Amps). One transform plugs into the wall > outlet and the 24 VAC is placed on the unused CAT5 pairs with a homemade > power injector. The second transformer is placed at the radio end and wired > as a step-up transformer. A female-female power socket is used to connect > the AP's own 120VAC powercube to the step-up transformer. Be careful!, the > exposed male prongs on the transformer have 120 Volts on them. In > California, Orchard Supply Hardware carries the transformers for around $13 > each. Ace Hardware has the same product at $16. There is a few volts drop on > the 120 Volt end at the access point with a 10 - 15 watt load. I have five > radios being powered by their individual transformer pairs and they seem to > work fine. > > Loren Zemenick > > -- general wireless list, a bawug thing <http://www.bawug.org/> [un]subscribe: http://lists.bawug.org/mailman/listinfo/wireless
