5 V home network
I've used power-over-ethernet successfully in various devices deployed around my house.
Advantages include:
- Can use any existing Cat-5 wiring you may have
- Any wiring you put in can be repurposed later if not needed.
- Off-the-shelf adapters for supplying and receiving power are readily available (usually sold for CCTV systems).
- You can use for wired network connections, which are generally more reliable than Wi-Fi
I'm using "passive" PoE (4 wires for network, 4 wires for DC +/-) at 24V, with local 5V stepdown at the receiving end. The PoE 'injector' runs off my UPS, so the gadgets stay powered over a power cut.
- A 5VDC network is liable to be "a bad idea".
- A somewhat higher voltage network with local regulators should be slightly better but adds electronic complexity.
- Local 5V psu's with a shortrange distribution system is liable to be better overall.
12 gauge cable has a resistance of ~= 1.6 Ohms per 1000 feet or per 500 "loop feet".
So you get 1.6V drop per amp for 500 loop-feet or about 3 mV per loop-foot per amp.
Option 1:
A 5V run of say 100 feet at 10 A will drop 3 mV x 100 x 10 = 3V.
That's obviously too much at 5V.
You MAY deciede that 5A max is OK - or that the mean current is half the max if ecenly distributed, and a max length of 50 feet may be acceptable.
But , making compromises will still give you drops in the 0.5 - 1.5 V range.
A few cameras at the far end are liable to 'spoil your day'.
Your network needs to either be "dumb" and able to supply max power at 5 VDC or intelligent and only supply power by negotiation. At 10A that's 5V x 10A = 50 W and probably double that to allow for drop and fusing and ... . 50 - 100W is enough to start a fire with a little ingenuity. Murphy has lots of ingenuity. It's not fatally flawed but care is needed. This is lower current and lower voltage than mains AC circuits provide - so if you take as much care with your DC network as your AC mains one it may be OK - noting the need for switches able to handle DC well at rated current (DC being substantially more difficult than AC).
Option 2:
Distribution at say 8VDC or higher (10-12VDC better) (or you can use AC) will allow freedom from voltage dropout issues. If you use linear local regulators then you lose efficincy with increasing feed voltage. If 8VDC is "just enough" you are losing (8-5)/8 ~= 40% of you power. And more again with more voltage. And you have added complexity and cost and a nonstandard system.
If you use switchmode local converters efficiency is relatively constant with feed voltage, and wiring losses drop as voltage increases due to resistive losses being proportional to current squared. But the converters add complexity and cost. POE (power over ethernet) is one version of this - and the cost per converter is liable to be substantial for off the shelf equipment, and compared to using mains powered commercial supplies.
Option 3:
A single power socket per location allows you to operate either a local 5v PSU OR a mains AC plugboard with a collection of plugpacks.
At the desk where I am typing this I have 18 x 12V powered USB hard drives on a shelf. I've considered the use of a 20A plus 12V supply, custom leads (std socket and cable from HDD to a connection system) but, so far, the 18 x 12V 1A powerpacks plus requisite mains plugboards has won through. Voltage drop is not an issue, I have excellent power supply redundancy either by providing say 2 spare 12V psus or by borrowing a supply from a less critical supply if needed.
My 5V "USB" supply needs are met by the several PCs with USB sockets, plus some of the HDDs have powered 5V outputs. And 5V "USB" psus are very very available, well priced (especially as used ones are usually reliable) and the connector is universal.
And mains AC (230 V 50 Hz in my case) is available throughout the house, or in any home or business I visit.
For me, and probably for you, option 3 makes most sense.
Voltage drop is the killer
The problem is, voltage drop is extremely acute at very low voltages, because currents are inherently higher, and voltage drop is a function of currents (E=IR). It's a square function against voltage. That means that distributing 5 V instead of 12 V is worse by a factor of 5.76. As a quick example, for a 100' (30 m) run with 3.6% voltage drop:
5 volts @ 12 amperes (60 W) needs 212 kcmil (4/0 AWG)
12 volts @ 5 amperes (60 W) needs 26 kcmil (6 AWG)
Don't "bomp the wah"; actually do the voltage drop calculation
One time I looked at a solar project. 15 A @12-19 V, 14 AWG wire would be fine. Except he was going 200' (60 m). So he gave it a wire size bump, and an extra one or good measure, clear up to 10 AWG wire. Of course, the system was a complete failure and didn't recharge his batteries as calculated. He couldn't understand. "Bat ah bomped the wah!"†
† Translation: "But I bumped up (increased the size of) the wire"
And you armwaved that too. You gave it a perfunctory bump to #10 and went "oughta be enough!" You actually have to go into the voltage-drop calculator and check. This should be based on actual current drawn by the loads on the wires, not breaker or supply rating. Rating a long branch for 20 A when it only needs to carry 2 A is a waste.
I've done bump calculations where it turned out I didn't need the bump.
Comply with Code ... But it's not too bad
You still need to follow the Electrical Codes for installation that is part of the building. Fortunately, the electrical codes are very relaxed for low voltage installations, and further relaxed for <55 W installations.
Neighbor site diy.stackexchange.com is a good one for Code questions.
12 V is so much better that you ought to do it.
As you saw from the 12/5 voltage drop calculation above, 12 V works worlds better. It has voltage drop considerations, still; but they are vastly reduced. Meanwhile, it is highly versatile, and the system can even be extended to be a whole-home backup system.
- LED 12 V lighting has huge variety and is more dimmable and hackable than mains lighting
- Most Internet routers and modems can run on it
- Some TVs can run on it
- Batteries are readily available for it cheap or in a number of chemistries
- Most solar charge controllers can supply it
- which means in a power outage, you have lights and Netflix
- Some smart doorbells can even run on it.
- That with a gas-only furnace like an Empire, gas water heater and stove can make a house perfectly livable with the grid down or absent
What's more, getting from 12 V to 5 V is really really not a problem. It is possibly the most commonly sold power converter anywhere!