Power over Ethernet mod for Extender ?

[willplaice]

Hi

In a push to reduce power usage and adaptors, i was thinking it should be possible to use a POE feed to the extender location, and break out the power to feed the unit (i guess a simple power regulation circuit would be needed)

how come at uni i never had a clue what to build in electronics labs, and now i have loads of ideas ?


anyone else interested ?

[paulbeers]

Originally Posted by willplaice

Hi

In a push to reduce power usage and adaptors, i was thinking it should be possible to use a POE feed to the extender location, and break out the power to feed the unit (i guess a simple power regulation circuit would be needed)

how come at uni i never had a clue what to build in electronics labs, and now i have loads of ideas ?


anyone else interested ?

Power over ethernet (based on my understanding) is to offer you wireless access points, VOIP, and other networking gear to be setup where you may not have a plugin readily available (or for telephones on a VOIP system that do not have a plug at all). They do NOT reduce power usage (except for the case below). In fact, due to the resistance of the ethernet wire and the distances it needs to cover, you will actually have to use more power output in order to power your device.

See this link for an example of what would be necessary:
http://blog.fosketts.net/toolbox/pow...et-calculator/

For example, if I wanted to power one of my HD200 with a POE, over the the 50 ft length of ethernet from the where it sits to my main ethernet closet. That would require me to buy a new walwart that could supply an extra 1.2 volts of power (if all I did was use the ethernet as a means transmit power by having the walwart at one end of the run).

Now I know there are devices out there that can power several devices at once, and it can allocate power as needed to various devices (see POE for VOIP), but in those cases the idea is being used for devices that use varying amount of power (phones that aren't being used have the power of the system routed to the ones that are for example). For the HD200, it pretty much consistantly uses 6 to 7 watts of power (other than completely off when you actually pull the plug).

Even if the above isn't true and there was a power savings, by the time you run an extra ethernet cable, buy a new walwart, etc., etc., etc. it would take a considerable amount of time to recoup your costs. The unit has been measured to only use about 7 watt hours of power (6 at idle), that means it would take it 143 hours to use a killawatt hour. That means that over a course of a year it would use approximately 61 killawatt hours. Using .085 cents per killawatt hour = $5.185 (now I know in Eurpose the costs are higher), so how many years would I have to run the unit before I would break even?

You are better off replacing a couple of regular incandescent light bulbs then trying to do any crazy mojo with POE with the HD200.

If you really want to go green, you would be better off using a home automation system that would disconnect power to your entire home theater during hours you aren't home. My main home theater in the basement uses almost 90 watt hours of power even if everything is in "standby" (damn rear projection CRT).

This is just my .02 worth.

[freedml]

I have a switch in the attic where there is no outlet available, so I power it from the other end of the Ethernet cable using POE (but not an actual POE-ready device). It's pretty simple, put the power on an unused pair at one end of the cable and wire it into your device at the other end. You need dual Ethernet jacks where you can 'splice' the power in or out -- I found some at Fry's electronics. I don't know how practical it would be to power more than one device -- the power is only on that cable -- I don't think it is transferred to other branches of the netwok through switches or routers. With POE-ready devices you don't have to do any wiring but they may not have the voltage you need and they are more expensive. Devices 'draw' the amount of current they need as long as the power supply can supply it.

[paulbeers]

Originally Posted by freedml

I have a switch in the attic where there is no outlet available, so I power it from the other end of the Ethernet cable using POE (but not an actual POE-ready device). It's pretty simple, put the power on an unused pair at one end of the cable and wire it into your device at the other end. You need dual Ethernet jacks where you can 'splice' the power in or out -- I found some at Fry's electronics. I don't know how practical it would be to power more than one device -- the power is only on that cable -- I don't think it is transferred to other branches of the netwok through switches or routers. With POE-ready devices you don't have to do any wiring but they may not have the voltage you need and they are more expensive. Devices 'draw' the amount of current they need as long as the power supply can supply it.

Did you buy a higher voltage walwart for that switch? How long is the ethernet run carrying the power? Are any of your HD200's plugged into it? Just wondering if you might be undervolting that switch which is causing some of your stability issues (draw and voltage are two different things)

[Menehune]

Danger. PoE switches output 48V as part of the spec so they will definitely damage a 5V or 12V power input on your extender or switch. Using the unused pairs in the cable could be acceptable if you use the factory supply, are certain to maintain the correct polarity of the power plug and your cable run is short.
Personally, I would keep it under 25 feet, maybe less depending upon the current flow and voltage drop at the far end of the cable..

The reason for the high voltage is the current squared losses in the tiny, 24ga CatV cable conductors. The higher the voltage, the lower the current flowing, the less heating in that conductor and the less power loss (cable heating) in the cable.
It's the same reason why power distribution lines are in the hundreds of thousands of volts and not 120/220V like your house appliances require.

Some background of PoE anyone is interested:
http://www.infocellar.com/networks/new-tech/PoE/PoE.htm

[freedml]

I am using the 12v converter that came with the switch, just cut-off the connector and wired it up. The run is about 30 ft. Not running anything else from that power supply. Yes, you need a voltmeter to get the polarity right and you need to know which pairs are carrying data and which are available.