How do you do Power over Ethernet Cable (Only Power no Data)  - Page 1
Forum section: electronics / beginners

author: tompl
author_rank: Contributor
timestamp: February 27, 2016, 05:30:56 pm
content: How do you do Power over Ethernet Cable (Only Power no Data) the cable is CAT5 24AWG.I need 12v 2A and 5v 2A at the cable end (Connecting to raspberry pi, some solenoids and maybe a water pump) ?Distance is about 20m.

author: Cliff Matthews
author_rank: Unknown
timestamp: February 27, 2016, 05:43:58 pm
content: The AWG 24 will carry the current, fuse the feed end against shorts use 2-pair for GND and 1 pair each for 12 and 5v. Forget about using the RJ crimp connectors though... Typical PoE uses 48v and dedicated circuitry to negotiate power budget (I think each cable run tops out at 15watts, so you can see that even PoE standards keep amperage levels under 1 amp).

author: tompl
author_rank: Contributor
timestamp: February 27, 2016, 05:53:20 pm
content: Thanks how would I avoid voltage drop?

author: Richard Crowley
author_rank: Super Contributor
timestamp: February 27, 2016, 05:54:39 pm
content: It might be better to knock the 12V down to 5V at the far end and use 2-pair (4 wires) for ground/return, and the other 2-pair (4 wires) for the main voltage feed.If you have only crude loads at the far end (solenoids, motors, etc.) then you probably don't need to worry that much about some voltage droop and irregularities. Otherwise, you could send a higher voltage (and lower current) like 24V or even 48V and use a regulator at the far end for the 12V also. DC/DC converter boards are dirt-cheap these days and make a very convenient way to exchange voltage for current when using a limited wiring scheme.

author: Zbig
author_rank: Frequent Contributor
timestamp: February 27, 2016, 05:56:26 pm
content: With 5V@2A you could experience quite significant voltage drop over 20m. It could fall outside the target device's tolerance. Just send the 12V (ideally, use more than just one pair if you don't need them for anything else) and regulate it down to 5V locally using a step-down DC/DC converter on the remote end. I have done the similar thing when I was powering 5V Ethernet switch through a wimpy telephone cable. I ended up using 12V AC/DC adapter and a buck converter just before the switch. This way I don't have to worry about the device having to work on marginal voltage. And BTW, that's not "Power over Ethernet" - that's "powering random thing using some cable that happens to lie there already" ;-)EDIT:Richard beat me to it

author: Cliff Matthews
author_rank: Unknown
timestamp: February 27, 2016, 06:40:56 pm
content: Oops! 20 meters... I live in Canada, but every now and then my old-fart brain reads feet and not meters..For mere technicality sake, this shouldn't be called PoE (since that accommodates a center voice-pair and super-imposes DC on the orange/green data pairs). It's more like a power extension using 4-pair Ethernet cable, since OP hasn't stated if there is a need for voice pairs or the typical use of RJ-type jacks

author: tompl
author_rank: Contributor
timestamp: February 27, 2016, 06:46:01 pm
content: Going to try the 12v route and use a voltage reg at the other end (this one DROK&reg; Voltage Regulators Voltmeter Gauge 4.0-40V to 1.25-37V Voltage Step Down Converter LM2596 DC 5/12 Volt Adjustable with Heatsink and Screwhttps://www.amazon.co.uk/dp/B00RGK5G3I/ref=cm_sw_r_cp_awd_H6E0wbF1KHJXD)

author: Monkeh
author_rank: Super Contributor
timestamp: February 28, 2016, 10:28:51 am
content: 2A over 18AWG (24AWG x4) for 20m, will drop the best part of 2V. I hope you don't actually need 12V..

author: tompl
author_rank: Contributor
timestamp: February 28, 2016, 04:33:47 pm
content: Done it 12.2V in 11.9V at the other end Raspberry PI boots fine now just need to hook up the 12v stuff