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politick
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PowerBox and non-Poe devices: Will it damage devices like a laptop?

Wed Apr 10, 2019 8:20 pm

In a nutshell, I want to be reassured that I can plug any laptop into a powered powerbox and it won't blowup the laptop's ethernet port.

I know that Ethernet is an electrically differential signal. So each pairs can have a different potential and as long as the pairs are electrically isolated, then no current drawn (no short circuit).
Now what I don't know is if ethernet ports on normal computer have a high impedance and that all pairs are electrically isolated (so no current leaks between pairs)?

Yes, I could test this out with an old laptop and risk the port, but even if the first one survives, one is not enough to generalize to *ANY* laptop (or other device) will survive if there's 24V on different pairs. Can someone that has tried this many times tell me what has been their experience ? Have you ever had any damages ethernet ports ?



Kind Regards,
Martin Politick, April 2019.
 
Paternot
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Re: PowerBox and non-Poe devices: Will it damage devices like a laptop?

Wed Apr 10, 2019 8:44 pm

There is an auto detection system, to find out if the device uses POE, and what type of it. As long as the PoE out port is set as "auto on" (or "off"), You can plug anything you want.
 
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politick
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Re: PowerBox and non-Poe devices: Will it damage devices like a laptop?

Wed Apr 10, 2019 11:16 pm

There is an auto detection system, to find out if the device uses POE, and what type of it. As long as the PoE out port is set as "auto on" (or "off"), You can plug anything you want.

Hi Paternot,

But isn't what you're describing 802.3af ? The standard ($expensive$) power over ethernet.
The PowerBox only does Passive PoE.
From my understanding of Passive PoE, the Power is always there and no testing is done from the PowerBox before a voltage appears on the pairs.
From reading the doc, the potential that goes In to power the unit, is the potential (V) that appears on the PoE out.

Kind Regards,
Martin Politick.
 
Paternot
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Re: PowerBox and non-Poe devices: Will it damage devices like a laptop?  [SOLVED]

Thu Apr 11, 2019 12:12 am

Yes, the potential that goes through is the potential that goes in the power unit. BUT the device does test, to see if the other side is capable of PoE.

Check the manual:
https://wiki.mikrotik.com/wiki/Manual:PoE-Out

What you are looking for is at "Port Settings".
 
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politick
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Re: PowerBox and non-Poe devices: Will it damage devices like a laptop?

Thu Apr 11, 2019 1:24 am

Yes, the potential that goes through is the potential that goes in the power unit. BUT the device does test, to see if the other side is capable of PoE.

Check the manual:
https://wiki.mikrotik.com/wiki/Manual:PoE-Out

What you are looking for is at "Port Settings".
OK Thank you ! That's perfect.
Yes the negotiation is a resistance between the spare pairs [4,5 (+) and 7,8 (-)] should have range from 3kΩ to 26.5kΩ. The brochure was not so descriptive.
And worse case, if I'm paranoid, I can configure the spare ports for PoE Off.

Kind Regards,
Martin Politick. April 2019.
 
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vecernik87
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Re: PowerBox and non-Poe devices: Will it damage devices like a laptop?

Thu Apr 11, 2019 6:59 am

You got it exactly right!
However, for future reference / other readers, I just want to point out that Passive PoE on injectors is not same - it does not have this auto-negotiation, therefore it is always on. Only Routerboards have auto-negotiation support for passive PoE.
You may also find that some other manufacturers are compatible with mikrotik's Passive PoE (for example UBNT), but these don't have auto-negotiation for Passive PoE as well, not even on PoE Switches.

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