PoE Requests

[jnesbitt1]

I have a camera that I know needs 25.5 Watts of power to work. This camera is connected to a 3750X switch with PoE+. However, only the layer 2 portion the camera comes up (Low power mode). When I look at the power inline, the switch is reporting 15.4 Watts even though it can go up to 25.5 Watts. Needless to say the camera does not work and power inverter had to be installed.

Why would the 3570X not give the full 25.5 Watts to the camera. Is it the resistance in the cable? When I put a Fluke on the line and requested class 4 power I only received 22.5 Watts over a 3' patch cable. Any thoughts?

[Reza Sharifi]

I don't have a 3750x to test, but can you try adding:

int gix/x/x

power inline static max <max number>

to the port and test the camera again?

HTH

[jnesbitt1]

Okay, so did some more testing and found the following:

1.) With the switch port in default PoE settings (auto) and request class 4 power my results are 22.5 - 24.7 Watts. I ran the test 24 times and never hit anything greater than 25.

2.) Setting the max power consumption to 30 Watts had the same effect as Auto.

     -power inline static max 30000

3.) Setting the consumption to what I need gave me full class 4 power of 25.5 - 27.78 Watts of power

     -power inline consumption 25500

These tests were conducted in my lab with a Fluke. I have not had a chance yet to try them on the camera. From the test results though, I'm thinking statically setting the power requirements should work.

Is there an answer as to why Auto mode on a PoE+ switch does not give full class 4 power and why I have to statically set it?

[Joseph W. Doherty]

Is there an answer as to why Auto mode on a PoE+ switch does not give full class 4 power and why I have to statically set it?

Might be a bug.  Might also behave differently in a different IOS version.

[Reza Sharifi]

Is there an answer as to why Auto mode on a PoE+ switch does not give full class 4 power and why I have to statically set it?

I have seen the same thing when connecting 3rd party devices (Cameras, badge reader, vending machines etc..) to Cisco switches, specially if the device needs higher wattage (20-30).

HTH