Is there any "standard" way to provide power that is more than 802.11af (PoE) specifies at the power consumer end..?
Asfaik cat.5 cables use AWG 24 which should allow .8 Amps per wire. By useing them in parallel one should be able to transfer .8 Amps * 2 wires * 48 Volts = 76.8 Watt. Useing not only the spare pairs in a 10/100 setup. 153.6 Watt should be possible.
If 802.11af is followed then limit is 12.95W. Which is to little. If a normal dc/dc converter is used then the required power is supplied (large lcd). But it will not follow specification.
Multiple links in parallel? A separate Cat-5 power feed?
There is a revision in the works to accommodate higher-power endpoints, but that will take some time to reach market.
The whole PoE thing is quite a challenge on the head-end, where the PSE's may have hundreds of ports pulling 13W each. It's driving re-designs of power backplanes, supplies, chassis and facility cooling, dedicated line power, etc. I suspect this influences the pace of the spec changes too.
The main scenario is 10/100 Mbps setup with the 4-5 and 7-8 pairs for power. The second one is all four with frequency seperation. And possible 1000 Mbps operation.
Know anything about it?, seems PowerDsine.com is the one actually doing it. But I only find PSE chips.. Seems the current solution is to simple attach an dc/dc converter and be done with it (for now).
One thing that pussles me is why not have the endpoint simple tell how many Watts/Amps it wants with 0.25 Watt granularity. And then the PSE grants the request if possible. One could also signal power requirements for power outages. Useing something like a slow bitstream instead of complicated measurements.
So, there appear to be two wiring options, including the one you list. The other seems to be level shifting of the signal pairs. I'm not sure which one is proprietary vs. the official "standard" (maybe both are). Designs often include a selector for the input power pairs.
The newer spec? I don't think it's official yet.
ISTR that Linear is quite big in this space; they've advertised it a lot in the trade rags. And, they make both ends of the link (PSE and PD controllers).
Only for the older style, where there was no sensing of the powered device. Problem is, you plug in the wrong thing (like a non PoE Ethernet card) and the endpoint goes POP! This was a problem with early proprietary solutions, because some of the Ethernet card vendors (a la
3Com) didn't leave the extra pairs unconnected.
Well, they do, I believe. There are several levels of power negotiable, and the device signals the power requirement to the head-end during init before power is applied (so the PSE can decide if it has capacity). There's a signature resistance at the end device, and capacitance IIRC.
Check out
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Power Management | Hot-Swap | PoE Controllers | View Table
The standard way is to have a voltage between the differential pairs. Some safety concerns limit this voltage to a value far lower than the undamaged isolation would allow. It now depends on your cable and the treatment of it, on how high you can go with the voltage. If you treat the cable well, eg don't pinch it in a door or such, I guess
200V would be doable if you don't tell anyone, for one-of, in a guarded environment, eg your lab.
For a product being used in and given to the public, I wouldn't exceed the PoE rating, since these guys thought a lot about everything.
The PD must be able to handle both options. But the PSE is the one choosing.
Meaning senseing is needed.. ;), but the non-standard dc/dc approach to PD should be workable at least. The PSE end might be different due it's the one powering things and thus responsible to not blow things up.
But the current power levels are to coarse. And there's no support for >12.95W. Or backuppower specification.
Seems
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have problems with their webservers today.. (Linux/WebLogic XMLX)
Exactly. I think you need the PD chip to do this signaling, so the PSE knows to a) energize the line, and b) the power rating to supply. If you were using the spare pairs and hacked the signature specs, you could probably cobble a simple dc converter tapped off the line, but what if the PSE is configured to level-shift the signal wires?
It seems to me that the PD controller is also needed unless you roll your own solution (incl a discrete version of the PD controller), in which case you decide how it works (but at the risk of creating a hazard for anything else that might be connected to the port).
True, the specs are very coarse. I'm sure it had something to do with trying to keep it simple, probably due to limitations on the signaling capabilities (rather than trying to actually create a simple standard).
I've heard there's a high-current version of the spec in the works, but I don't know it's progress.
Unless you control both ends of the link, it would seem the cleanest solution is to use the PD controller chips; perhaps multiple in parallel if you need higher current, though customers may object, as the PSE ports aren't cheap.
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