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First of all I asked this question in DIY.stackexchange.com, because of the cabling in the house. Here I would like to ask about the electronics (or electrical) part of it.

And there is a very similar question here: Powering multiple devices from a single power supply

Yet there are some differences. First of all I was thinking to use 48V to transfer energy from a single power DC adapter, which I would like to place next to the main ethernet switch. Then I want to make a simple board, where I will split 48V DC output to 4-6 parallel wires. I would like to wrap these wires around Cat6 cables with tape (Cat6, because price it much higher for 50m cable, it is a good investment for the future and I don't want to replace these soon) and pull these combined cables through the walls (by replacing currently existing phone line or cable TV both of which I am not going to need).

My goal is here to provide 3 rooms with a pair of ethernet. One for personal computer or TV and the other one for a Raspberry Pi, which would run either as media center or security camera.

PoE is a more expensive alternative. I would like to use a gigabit switch for the future. Raspberry Pi's only support 100M but next model might be 1000M already. TV and PC's should definetely have 1000M. PoE switch 8 port is +100€s, 4 port is +50€. Then I need splitter for each Raspberry Pi (~4x), which is additional +60€ in total.

Since, I am enthusiastic about electronics, I thought I might try to do something on my own and learn more about it. So a single 48V power supply and wires around Cat6 around the house would solve my problem. Then I can solder my own small voltage regulator board. Which is even better, because I would like to attach infra red LEDs to my security cams, which will draw additional energy. My understanding is to feed them extra, since Raspberry Pi has a limited output energy. I can create the board in a way that the LEDs are controlled with a transistor (MOSFET?) and are fed with an extra voltage regulator (6V or something).

I know there are many aspects in this problem and I could split into different questions, but my original problem is to feed Raspberry Pi's with less adapters/cables as possible and with least costs. Is this possible at all? Do you think, this would be the optimal solution? Are there simpler ways to power my Raspberry Pis?

Here is a schematic:

Illustration of 48V power supply to feed RPi's

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    \$\begingroup\$ Why not just get a POE switch and use only the Ethernet cable? \$\endgroup\$ – R Drast Aug 27 '15 at 10:52
  • \$\begingroup\$ Be sure to use switching regulators (buck-converters) to convert 48V to 5V. \$\endgroup\$ – Golaž Aug 27 '15 at 11:09
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    \$\begingroup\$ @R Drast I explained above that PoE solutions are way more expensive. \$\endgroup\$ – Genom Aug 27 '15 at 22:19
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    \$\begingroup\$ @TedTaylorofLife I ended up using PoE as I have found a relatively cheap PoE switch and a relatively cheap PoE splitter. I have calculated and this was cheaper... However, I still think a 48V or 96V DC would be great to have for a smart home. I might actually do it anyway, if I extend my network with Arduinos etc. PoE switch (4+4) was about 50€ and the splitter 12€. And the advantage is, that it is an established technology and it is secure. I hope the prices go further down though. Also I have found a good IR USB camera for my Raspberry Pi, which can deliver enough current for it to operate. \$\endgroup\$ – Genom Aug 28 '16 at 19:31
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    \$\begingroup\$ @TedTaylorofLife I am using TP-Link TL-PoE10R PoE Splitter Adapter and this PoE splitter comes without a USB output format. There are however cheap DC to USB cables out there. I didn't find much time to invest in this yet but it works. When I finally have the time to complete other components, I will deploy them and see how it works. I did the math for the power consumption with Pis and PoE and my switch can supply more than enough power. \$\endgroup\$ – Genom Aug 29 '16 at 20:34
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Good ideas.

Remember to have rational size fuses at the supply end of your power cables to protect against fire due to shorts in the walls. Use the thickest wire for the power pair that you can afford and draw through the walls with ease to minimise losses.

You can add a 48->5V converter for your RPi and perhaps a higher power 48->12V converter for your IR illumination if suitable. Such converters are commodity items.

You could use a second Cat6 cable for the power and use two pairs for ground and two pairs for +48V but it will still be less copper than a dedicated pair of the same overall size.

EDIT:
As clarified by Golanz in the comments above the voltage converters should be of the switching type and not simple linear regulators so the current in the 48V link is reduced, a linear regulator would dissipate lots of energy as heat in the regulator and cause totally unnecessary load on the power supply and wiring by the same amount. Finding linear regulators with a 48V input for 5V output would be harder these days anyway and only appropriate for rare analogue applications.

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    \$\begingroup\$ Thanks a lot! I did not think about the fuzes. I think I will go with an extra power pair, because the cable "hoses" in the walls are narrow. \$\endgroup\$ – Genom Aug 27 '15 at 22:24
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The obvious question would be why? as a general rule the more conversion steops you have in your power chain the less efficient it will be. Lower voltage systems also suffer from greater resistive losses.

So unless you are planning to build in some form of backup power or you have reason not to want to run mains to the location of your adaptors it would seem far more sensible to just power the devices off local mains adaptors.

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  • \$\begingroup\$ Thanks that was another concern of mine... I am calculating how this will reflect in price... Each adaptor will also create loss. Then the question is, What is more efficient? Having 4-5x AC-5VDC adaptors or 1 AC-48VDC & 5x 48VDC-5VDC? I will read the datasheets and post my solution here... If anyone has already experience, suggestions are welcome! \$\endgroup\$ – Genom Nov 18 '15 at 8:05

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