Is Powering a device using POe more efficient than using an adaptor?

[darrenriley5]

Hi,

Is powering a power over ethernet device more efficient  than a powering a device using a power adaptor. I I've been asked to work out the energy costs we can save by using power over ethernet?

Thanks

Darren

[Thotsaphon Lueangwattanaphong]

Hello

    You might think how to get rid of power outlet and how to manage(on/off) power devices by remote access to switches.

Toshi

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[manju.cisco]

Also, when you have the link between the switch and the IP phone fails, the phones still remains powered on, wasting power..........

we can save atleast some amount of power with poe

[Latchum Naidu]

Hi Darren,

There are very good benefits with PoE than using adapter those are..

Simplicity and ease of deployment: In addition to providing the PoE benefit of network connectivity combined with power to a device over a single cable, Cisco PoE allows a device that requires as much as 20W per port to be connected to the network using a single switch port. This reduces the amount of cabling and power facilities that must be installed and managed, as well as simplifies installation and management of powered devices.

Investment enhancement: Throughout the industry, new applications for powered devices requiring more than 15.4W per port are under consideration. Cisco PoE could potentially provide support for these new applications such as video surveillance, remote video kiosks, and intelligent building management solutions.

Please rate the helpfull posts.
Regards,
Naidu.

[Edwin Summers]

You might be able to find some efficiency figures by digging through the Cisco site.  My recommendation would be to put your Cisco partner, or vendor partner, to work if you have one available.

One important thing to remember in this case would be "economy of scale".  While I would assume that the power supplying device (e.g. switch) power supply would be a bit more efficient than the "wall wort" for the phone, this should certainly be true as you scale.  Each wall wort will add it's own conversion loss, but the overall efficiency of the switch power supply should be better, and especially so when you consider a number of units.

At the very least, find the conversion efficiency of one phone power brick, and compare to the efficiency of your powering device's power supply, and scale from there.  That will give you a quick-and-dirty estimate.  Good luck!

[pascal]

When making your calculations don't forget to include the cable loss for PoE.  The original 802.3af standard specified switches should provide 15.4W, but to account for cable loss devices are only allowed to pull 12.95W.  Those same numbers for 802.3at are 34.2W and 25.5W respectively.

I don't know how these numbers compare to the conversion loss in a typical wall wort.

[Leo Laohoo]

Depends on how big your network and PoE requirement is.

Let me ask you this question:  How many powered-end-points do you have?  and How many watts of power do they consume?

The good part about PoE is that you turn on/off the power at your convenience.  Alternatively you can also SCHEDULE when you want the ports to power down and when the ports to power up.

I mean, let say that your office works 200 days in a year.  You have 100 powered-end-points using 7.5w of power.

This brings me:  200 (days) x 100 (end points) x 7.5 (watts) = 150,000 watts per day

Or 75,000 watts for 12-hours.

Compare that to leaving the power on all day for a year.  This brings to:  365 (days) x 100 (end points) x 7.5 (watts) = 273,750 watts

Nuts.  That's a huge discrepancy.