Honey, I blew up the RT-AC86U! (Passive PoE blunder)

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HBZ

New Around Here
Gutted and feeling very silly.

After reading plenty on the topic, for wiring reasons, I bought a pair of passive PoE adaptors
https://www.amazon.co.uk/dp/B076LR5KMF/?tag=smallncom-21
..where i planned on using the original Huawei PSU downstairs, next to my Asus rt-ac86u router and the existing cat5e cabling to power the HG612 modem in the attic where it currently connects to the incoming 'BT' signal.

I understood these adaptors would make use of unused copper in the cat5e to carry my modem PSU current up to the modem, whilst isolating those conductors from my fragile router and the modem.

With the upstairs end of the cat5e cable unplugged for now, I came downstairs and I plugged the Huawei PSU into the female PoE 'injector', the female rj45 of that injector to my cat5e cable (which goes upstairs), and the male rj45 of the PoE injector into the WAN socket of my Asus.

Immediately, the Asus lost all power and wouldn't come back.

The end.

A. What on earth did I do wrong other than trust reviews. Did I misunderstand these passive PoE setups?
B. I don't suppose there's a tiny link in the Asus which pops under this circumstance, which I can replace and be on my way?

I've already ordered a shiny new replacement router from Amazon :(

Thanks for any non-insulting input!
 

alex1236hk

Regular Contributor
PoE is for standalone AP like UniFi and Ruckus that require power from the Ethernet cable, not routers.
Consider it was an actual damage made by your own mistake, it should consider as outside of warranty.
Buy a new one and act smart next time.
 
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HBZ

New Around Here
Hi Alex,

Thanks for the comment. I understand regular PoE and it's purposes. This is 'just' passive PoE which should be more straight forward.

Yes, agree it was my mistake :)

Was hoping for constructive input but appreciate I'm a newbie here so maybe I haven't earned support yet, from the regulars.
 

Tucu

Regular Contributor
What is the voltage of the Huawei PSU? Does it match the voltage of the the Asus router?

Also, there are no unused wires in gigabit ethernet; the passive adapters are only useful for 100Mbps devices.
 

HBZ

New Around Here
Hi thanks for reading.

The modem voltage is supposed to be isolated from the router in this example so there's no need for voltage matching.
Also, this isn't using a gigabit port. This is using the link from the WAN port of the router to the LAN of the modem.

Thanks again
 

alex1236hk

Regular Contributor
Hi Alex,

Thanks for the comment. I understand regular PoE and it's purposes. This is 'just' passive PoE which should be more straight forward.

Yes, agree it was my mistake :)

Was hoping for constructive input but appreciate I'm a newbie here so maybe I haven't earned support yet, from the regulars.
You may try RMA it, pretending you don't know anything after you got a new one from Amazon,
but don't hope too much:D
 

Tucu

Regular Contributor
Ah, I misread your description of the connections.
In any case, it looks like the power from the injector fed back into the WAN ethernet port of the Asus. If the other end of the long CAT5e was not connected in any way, everything point at a defective PoE injector. As a warning: the WAN port of your router is a gigabit port so all wires are connected; It is not unusual to see posts of people blowing up their switches, routers and adapters with passive PoE.
 

bbunge

Part of the Furniture
Your Asus router will work on two pair of the CAT5e for 100 Mbps. I ran that way for a year on my 100/100 FIOS. The phone company installer split the CAT5 for Internet and phone. The new AX86U had some issues with that so I ran another CAT5 to the ONT which improved the bandwidth by 10 per cent. Is worth using all 4 pair between router and modem!
 

CaptainSTX

Part of the Furniture
I have used this gigabit POE injector to power various devices with no issues. It transmits data and the power using all eight conductors.


I use the inserter with the power supply of the device I want to power remotely. I install the inserter and the power supply either at the sending end or if the distance is to great I sometimes need to insert the power inserter mid-span. With an ASUS router you would use its 19V power supply by either modify the plug or finding an adapter. The power and data are combined at the sending end and broken out at the far end.

One thing to keep in mind the lower the input voltage the shorter the distance you can deliver the power to the device at the far end because of voltage drop. POE Texas has a calculator on their site to help you determine the maximum distance you can operate a remote device at. If the voltage drop is too great then you can try using a higher voltage power source but be very careful or you will let all the magic smoke out of your device.
 

thiggins

Mr. Easy
Staff member
A. What on earth did I do wrong other than trust reviews. Did I misunderstand these passive PoE setups?
As others have suggested, most likely it was the design of the adapter. If it were expecting to use "unused" pairs of a CAT5e cable, then that was the problem. The adapter likely just put the voltage directly on those assumed unused wires. Since the ASUS has gigabit Ethernet ports, you fried the Ethernet chip. There is no fuse/link to replace.

What properly designed passive PoE injectors do is use transformers to inject the DC plus and minus lines into all 8 twisted pairs in the cable.
B. I don't suppose there's a tiny link in the Asus which pops under this circumstance, which I can replace and be on my way?
No.
 

CaptainSTX

Part of the Furniture
Just to be clear the inserter I use and posted a link to uses Mode B and puts + on Pins 4 & 5 and the negative on Pins 7 & 8. It can handle up to 650 mA.

At the far end It is my understanding that the data and the power are separated so you are not feeding DC voltage to the Ethernet port other than the voltage which represents the state of 0 or 1.

The inserter you tried is for Fast Ethernet so as Tim stated it might have assumed that there were unused pairs which could be the reason you blew up your hardware.
 

thiggins

Mr. Easy
Staff member
Just to be clear the inserter I use and posted a link to uses Mode B and puts + on Pins 4 & 5 and the negative on Pins 7 & 8. It can handle up to 650 mA.

At the far end It is my understanding that the data and the power are separated so you are not feeding DC voltage to the Ethernet port other than the voltage which represents the state of 0 or 1.

The inserter you tried is for Fast Ethernet so as Tim stated it might have assumed that there were unused pairs which could be the reason you blew up your hardware.
Yours works like this:
poe_right_way.jpg


OP's worked like this:
poe_wrong_way.jpg

The difference in the injectors is that there are jacks at each end to inject DC and recover it.
 

CaptainSTX

Part of the Furniture
OP's worked like this:
I think you switched the the labels around. Mine works like the the second diagram the OPs works like the first diagram.

Also you may need to use a pair of POE injectors. One at each end because if you plugged a device into a device directly that wasn't POE ready the Ethernet port would get fried as the DC voltage would still be on the data pairs.
 
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thiggins

Mr. Easy
Staff member
I think you switched the the labels around. Mine works like the the second diagram the OPs works like the first diagram.
Don't think I did. He fried his router because the DC voltage was applied directly to the Ethernet port without being balanced across the pairs.
There are no unused pairs in a Gigabit port.

PoE injectors always need to be used in pairs if you are not supplying power to a device capable of being powered via PoE.
 

Tucu

Regular Contributor
I think you switched the the labels around. Mine works like the the second diagram the OPs works like the first diagram.

Also you may need to use a pair of POE injectors. One at each end because if you plugged a device into a device directly that wasn't POE ready the Ethernet port would get fried as the DC voltage would still be on the data pairs.
Yours seems to be like the first diagram, but with the other two pairs used for data only (to be GbE). In the second one, wires 4,5,7,8 are power only.
 

CaptainSTX

Part of the Furniture
Yours seems to be like the first diagram, but with the other two pairs used for data only (to be GbE). In the second one, wires 4,5,7,8 are power only.
Go back to my post #11. I clearly stated that the injectors I linked to and use transfer power on 4,5,7 and 8. The injectors the OP linked to use 1-2 and 3-6 for data. The other pairs are used for power.

Also you don't always need to use power injectors in pairs. I used in the past an outdoor AP. It used an injector to power it, but the AP was designed to accept both power and data on its Ethernet port. Not common but it is possible..
 
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Tucu

Regular Contributor
Go back to my post #11. I clearly stated that the injectors I linked to and use transfer power on 4,5,7 and 8. The injectors the OP linked to use 1-2 and 3-6 for data. The other pairs are used for power.

Also you don't always need to use power injectors in pairs. I used in the past an outdoor AP. It used an injector to power it, but the AP was designed to accept both power and data on its Ethernet port. Not common but it is possible..
Yours use 4,5,7,8 for power and data, otherwise they would not be GbE.
 

thiggins

Mr. Easy
Staff member
It's not the specific pairs that are used. It's how the DC is coupled into the pairs.

My example diagrams may not match the design of your specific coupler. But any passive PoE device that is connecting DC directly to any wire is risking damage to the equipment it is used with.
 

CaptainSTX

Part of the Furniture
Let's summarize how to use POE injectors to hopefully prevent someone from damaging a device in the future.

1. If a device isn't designed to be powered directly using POE delivered to an Ethernet port then you need to use a pair on injectors. One to insert the power and the other attached to the device to be powered to separate the power from the data.

2. Injectors that are only capable of 100Mbps use four wires for data (1-2 & 3-6). The other four wires for power. This type of injector only terminates four pins in the Ethernet jacks in the injector to isolate the data from the DC power. If an injector is incorrectly terminated or there is a short a connected device could be damaged.

3. POE injectors capable 1000Mbps use all eight wires to transmit data.

4. The power source to inject voltage must deliver the DC voltage the device to be powered is designed for. To high and you destroy the device and if it is to low from voltage drop or an incorrect supply the device being powered by POE may not function correctly.
 

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