POE over a long run with cat6

[r3ddyfire]

I will start by thanking everyone for their time and consideration regarding this issue.
I have 3 laptops and 1 desktop all running windows 7 ultimate 64bit.
My ISP is Comcast and i have a docsis 3.0 cable modem from motorola as well as two routers Dlink dir 655 and dir 615 both of these are n300 routers and use a 5v wallwart.
I currently have the power supplies for the modems in the basement hooked up to a battery backup. Power runs through a POE splitter with cat6 to the two routers.

For whatever reason the DIR 615 does not get enough power or the correct amount of power via my 200 ft of cat6. The 655 however is doing perfectly. I tested the 615 with a 6ft cat6 with no issues however when i switch it to the longer run it does not startup. I have tried several runs of cat6 and neither of them work. All of these runs were previously tested and currently work with another 12v cisco router just fine. The plan was to replace the older G cisco router with the newer dlink n router.

What am i doing wrong ? What else can i check ?

Again any help with this would be greatly appreciated !

 

[Alabalcho]

Did you measure the voltage at the other end of that 220ft drop?
If Wikipedia is correct, Cat5 cable has "0.188Ohm/m DC Loop resistance", which would make about 14Ohm over 220ft of cable. Depending on your router' power consumption, there might be lot of loss (I x R) in that drop of cable.

 

[bill001g]

Unfortunately a bunch of vendors have hijacked the term PoE. When you read all the specs the PoE is referring to 48volt power. This form of PoE can go to the same distance as the ethernet cable or 100m. Now when you drop the voltage to say 12 volts to get the same watt rating you must push more current. The wires can only pass so much current so you get a much shorter distance at lower voltages.

Not much you can do to fix it other than buy non standard ethernet cable that uses larger wires.

 

[r3ddyfire]

Did you measure the voltage at the other end of that 220ft drop?
If Wikipedia is correct, Cat5 cable has "0.188Ohm/m DC Loop resistance", which would make about 14Ohm over 220ft of cable. Depending on your router' power consumption, there might be lot of loss (I x R) in that drop of cable.

so if i have the 14 ohm resistance do i get a different wallwart that will push more power and if so more of what ? amps or volts ? and how much ?

 

[r3ddyfire]

Unfortunately a bunch of vendors have hijacked the term PoE. When you read all the specs the PoE is referring to 48volt power. This form of PoE can go to the same distance as the ethernet cable or 100m. Now when you drop the voltage to say 12 volts to get the same watt rating you must push more current. The wires can only pass so much current so you get a much shorter distance at lower voltages.

Not much you can do to fix it other than buy non standard ethernet cable that uses larger wires.

The router in question here is using a 5v 2.5amp power supply. would a different power supply that pushes more amps or volts do the trick rather than different cabling ? if so what could i measure to figure out exactly how many more volts or amps i need ?

 

[bill001g]

You take big risk messing around with using power supplies not designed for the equipment you are plugging in to. You pretty much need to increase the voltage but the actual voltage drop you get in the wire is partially fixed and partially related to how much amps you pull though the wire. You run the risk of burning out either the power supplies or the router if the voltage gets wrong.

Your largest issue is that the wire itself is absorbing some of the power and if you keep trying to force it though it will at some point damage the wire.

Although you might be able to design something yourself the safest and easiest way to make this work is to use standard PoE power injectors and use 48volts. Then use a DC-DC converter to reduce the voltage at the far end. They make PoE converters to do exactly this. You will likely spend $100 on the PoE injector and the converters but you will get clean power out the far end.

 

[r3ddyfire]

You take big risk messing around with using power supplies not designed for the equipment you are plugging in to. You pretty much need to increase the voltage but the actual voltage drop you get in the wire is partially fixed and partially related to how much amps you pull though the wire. You run the risk of burning out either the power supplies or the router if the voltage gets wrong.

Your largest issue is that the wire itself is absorbing some of the power and if you keep trying to force it though it will at some point damage the wire.

Although you might be able to design something yourself the safest and easiest way to make this work is to use standard PoE power injectors and use 48volts. Then use a DC-DC converter to reduce the voltage at the far end. They make PoE converters to do exactly this. You will likely spend $100 on the PoE injector and the converters but you will get clean power out the far end.

Your solution is indeed the best way to go, however i was trying to do this on a budget. Considering i spent 8$ on the dir615 from goodwill and 70$ for 1000ft of cat6 cable, spending 100$ on an injector and converter somehow does not equal out. Im thinking if i measure output voltage at the end of the drop and figure out the overall loss i can get a wallwart that pushes a few more volts through. Considering i have 12v wallwarts functioning correctly i don't think a couple volts over 5 would cause any damage to the wire or the router as long as i make sure i am getting 5v at the end of it.

Just to clarify though i am losing volts not amps over the run of the cable correct ?

--UPDATE--

I just checked with a multimeter and i am getting 5.17v at the end of my drop which leads me to believe i am getting enough volts through the cable.

 

[bill001g]

Yes you are losing volts but the voltage loss is not a fixed value it is related to the amount of amps. As you increase the amps you lose more voltage. So if you were to measure the voltage with no load it could be 12volts but with a load it could be 4 volts. This is why power supplies have voltage regulators in them.

This is the device I was looking at

http://www.l-com.com/power-over-ethernet-100-1000-base-t-power-over-ethernet-poe-splitter-tap-with-adjustable-dc-output

You would need a 48volt PoE power injector on the far side.

 

[Alabalcho]

--UPDATE--
I just checked with a multimeter and i am getting 5.17v at the end of my drop which leads me to believe i am getting enough volts through the cable.

Is this with your router plugged in?
Imagine your router draws 1A at 5V. Power loss over the cable then would be 14Ohm x 1A = 14V, so in order for your router to get its 5V you have to supply 19V at the other end!
So: Check power draw from the router, and get DC-DC convertor to regulate the voltage at the router's end. Then plug appropriate-sized power supply at the other end (you are going to laptop-size power supply, 19V at 1A).

 

[r3ddyfire]

--UPDATE--
I just checked with a multimeter and i am getting 5.17v at the end of my drop which leads me to believe i am getting enough volts through the cable.

Is this with your router plugged in?
Imagine your router draws 1A at 5V. Power loss over the cable then would be 14Ohm x 1A = 14V, so in order for your router to get its 5V you have to supply 19V at the other end!
So: Check power draw from the router, and get DC-DC convertor to regulate the voltage at the router's end. Then plug appropriate-sized power supply at the other end (you are going to laptop-size power supply, 19V at 1A).

The 5v measured were without the router plugged in. I am not sure how to get my multimeter needles in there when i have the router plugged in...

I looked at the power supply and it says: Output 5V 3A
The back of the router asks for: 5V 2.5A

Just as a side note: This router has two lights that turn on when plugged in to show power. One is a D-Link logo and the other is a simple 1/0 (power logo). Without the ethernet cable both of these light up. With the cable only the Dlink logo lights up. Not sure if this will reveal anything but i figured i would mention it.

So then my follow up questions are:
- how do i measure voltage at the end of my run with the router plugged in ?
- if i plug in the 19v quoted above, wouldn't that surge the router (at first plug in anyways) ?
- how come i am not experiencing this same issue with my 12v dlink router ?

--UPDATE--
Well i got gutsy and plugged a 9v 1a power supply at the other end. My router boots up and works just fine for a little bit, but eventually freezes and requires a manual power reset (unplug then plug back in). I would like to try a 12v power supply but i am not sure what that will do to my little 5v router. However if it comes down to it ill chance and if i burn it ill just go hunt for another one at goodwill. PS: My questions above still stand...

--UPDATE 2--
Seeing that 9V was not providing consistent performance (no more than 15-20 minutes of uptime). I decided to try the 12v 1A power supply. With the 12v the router did not even turn on (i only did a quick plug check for lights and unplug). So i am thinking i could use a 9V power supply with more amperage than my current 1A one.

Again i don't understand why this issue is not happening with my other DIR 655 which also uses a 5v power supply over about 150 ft. The questions above still stand if anybody has an idea, i would be willing to try it out (provided it doesn't cost more than 15$ 😛 )