Related to "Cat 5 current carrying capacity"
We want to use ethernet as the means of communication to small peripheral control cards. We need however to supply power (24VDC) to each card, at 30W approx per card.
Has anyone done this? Is it wise to use the unused pairs in the CAT5 cable for the power supply? POE does not seem like a suitable solution, complexity, wrong voltage.
Suggestions please,
Michael.

The big problem will be the voltage drop. At 100' you will be dropping about 7.5 volts at 1.25a

Get some signal boosters. Like the ones for long TV runs.

To avoid possible problems with people plugging things in that aren't supposed to be connected to it (and that will happen), I would do it as "PoE on steroids" using the 48V POE standard, beefed up to supply the current you need.

You of course need to make sure that your power injector limits current to a safe value.

Edit: I observe that the TIA specifies that the max safe current for Cat 5 24 AWG conductors is 360 mils. There's no way you can get your 30 watts at 24 volts. Even at 48 volts, using both halves of a pair for each side (as does PoE), you'll be right up at that limit.

Dang it, the board won't let me edit my previous post again...

There is a reason for the "complexity" of PoE. The people who designed PoE were smart people, looking for a simple solution--they did not build in gratuitous complexity just to make things difficult for people. PoE has the complexity it has because people will inevitably plug any RJ-45 plug into any available RJ-45 jack, and if you don't design for that situation, you will end up destroying things, and quite possibly starting fires.

I wouldn't even bet you could shove 1.25 a through a regular RJ connector.
IMHO these were designed to hit a price point ... for telephone connections. It is far from my favorite connector. I am surprised we don't have more trouble with them, as if it isn't enough.

They undoubtedly were designed to meet a price point--at pre-breakup AT&T. As such, long-term maintenance costs were part of the "price point."

RJ connectors were designed to work, and to keep on working, decade after decade, without an expensive visit from a truck with a "Bell" logo on the side.

Would this do it?

Bad!

BAD!

Someone please take away his Photoshop for a week.

http://www.fiftythree.org/etherkiller/

Ian A.

The world is full of smart asses!!

I am not so worried about voltage drop or current carrying capacity. We use CAT5 at the moment for the same application. But it is not ethernet. We use 2 cores for 24V 2 for GND, the rest carry the RS422 data.
The bit I am concerned about is putting ethernet and power through the same cable, and ideally through the same connectors at the end.

I would not advise it. If the 24v is AC it may interfere with the ethernet too much and just cause collisions between your nodes. Cisco makes switches that have power over ethernet, which use all 4 pairs for data and power, but I believe it is DC power. I would say, if the data is critical, I wouldnt even attempt it.


~Matt

Matt,
It is 24V DC. I cannot see it causing too many problems for the data. Anyhow, isnt that the beauty of TCPIP, if messages get corrupted they are noted and retransmitted. It is such a wonderful, fast communication method, but we would prefer not to have to run seperate cables for power. It is a process control, factory application.
Has no adventurous soul tried this, or got a clever solution. I would even consider 2 connections at the end of the cables, one the ehternet RJ45, the second for 24V annd GND.
Michael.

DC shouldnt cause too many issues - if any. If data gets corrupted, it isnt due to TCP/IP, it is really CSMA/CD Carrier Sense Multiple Access/Collision Detection. CSMA/CD is a layer 2 protocol in the OSI model, where TCP is Layer 3, and IP is layer 2. Anyway - I got off subject. Your goal is to keep collisions and data corruption to a minimum to keep traffic down.

I have used 1 cat5 cable to transmit 2 phone lines and 100bT connection and it is stable.

I would say youre probably OK using one cable, just make sure you keep track of your pairs! I would build a custom breakout cable / box and make note of what pairs are what. You dont want 24v being sent to your data circuit.

Good luck!

~Matt

Somebody has been reading the BOFH stories..

(TOOL_5150) ..."If data gets corrupted, it isnt due to TCP/IP, it is really CSMA/CD Carrier Sense Multiple Access/Collision Detection. CSMA/CD is a layer 2 protocol in the OSI model, where TCP is Layer 3, and IP is layer 2."

Wow.
The more I learn, the less I know.


Shawn.

https://www.electrical-contractor.n...showflat/Number/132415/page/1#Post132415