PoE Tester Schematic

[nickbrown_500]

Hello All,

I'm looking at wanting to build a quick PoE tester just to let me know the power is getting through my device and which pairs this is running on.

I know there can be a couple of options depending on whether A or B wiring is been used.

Does anyone have a schematic etc of how this can be done, or any links to somewhere that it has been done.

Cheers

 

[Kripton2035]

you can this two schemes - it's easy to test with a voltmeter only. no schematic required.

 

[nickbrown_500]

I know it is easy to test with a volt meter, but to test numerous connections it gets a bit tedious.

Will have to just put together a design to light up some LED's for each just for quick checking. Just wanted to see if anyone had already done this.

 

[pplus]

Something like this



It must detect - change polarity, low supply voltage, lost connection on lines.

 

[nickbrown_500]

Thanks for the schematic, thats exactly like what I was thinking,

This will then allow for quick and easy diagnosis to which wiring is in place and also if power is going through.

Do you have any more information on this circuit, as you have put about detecting low supply voltage, lost connection etc. What are the signs of each.

Thanks

 

[pplus]

If supply voltage less then 2*1.4+43~46V zener diodes D17-D120 will be closed, LEDs no light.
If one of lines lost connection LEDs attached to this line will no light.
If polarity on lines 4 and 8 is normal, will light D1 (green) and D8 (red), if the opposite will light D2(red), and D7(green).

 

[Kripton2035]

hi,
I'm not sure your tester will work as a poe switch is intelligent
it only send the 48v supply if the poe device replies a certain sequence. the 48v are not always present on the wires.

 

[pplus]

hi,
I'm not sure your tester will work as a poe switch is intelligent
it only send the 48v supply if the poe device replies a certain sequence. the 48v are not always present on the wires.

Yes, my fault. But in IEEE 802.3af PSE is very simple mechanism of classification.

To determine whether a PD is connected, the following input parameters are checked:
• characteristic resistance = RGOOD (19k − 26, 5k),
• typical resistance value = RTY P (25k),
• characteristic capacitance = CGOOD (max.150nF).
This method is called "Resistive Power Discovery".

PD rejection criteria
• resistance less than or equal RBADmin (<= 15k) or
• resistance greater than or equal RBADmax (>= 33k) or
• capacitance greater than or equal CBADmin (>= 10μF)

Hence it is necessary to connect the parallel resistor value 2 * RGOOD to inputs 4-7,5-8,1-3, 2-6, or use LTC4257