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So Where’s My Low Voltage DC Wall Socket?

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Re: So Where’s My Low Voltage DC Wall Socket?

#61

Post by Wowfunhappy »

MisterTea wrote: post #46

We don't need DC sockets as they dont solve any problems. The stupid simple AC mains distribution system is well tested and proven. Who cares that they provide up to 3kW. The "last meter" problem is perfectly solved using AC-DC wall warts and bricks. If the power supply dies, you buy a new one and just plug it in. No electrician required. Putting things in wall or central distribution is not a solution to any existin…

Wouldn't it be more efficient to have e.g. one DC power supply for the house that can power everything that needs DC power, instead of lots of individual (and likely cheap/inefficient) power supplies?

Re: So Where’s My Low Voltage DC Wall Socket?

#62

Post by steve19 »

mark-r wrote: post #54
steve19 wrote: post #48

Earlier quoted context omitted.

I am not sure how Wikipedia can be more explicit, they even have a table showing the voltages and wattages of the different standards. [0] According to that table, the latest standard, 802.3bt Type 4, can provide 71 W to the device at the end of the cable (and inject 100W into the otherside). [0] https://en.wikipedia.org/wiki/Power_over_Ethernet

Clicking on the link "Power capacity limits" brings you to nothing useful. Are you looking elsewhere?

Scroll down to the table "Comparison of PoE parameters".

Re: So Where’s My Low Voltage DC Wall Socket?

#63

Post by NwtnsMthd »

ethagknight wrote: post #10

Is "Digital Electricity" a real thing? Its billed as an alternative to AC or DC. This may be as good a place as any to ask this question, but I am a hotel developer, and we've had a few people reaching out to us trying to sell "digital electricity" that sends high voltage over cat5 (up to 2000w per the Belden materials) by essentially sending high voltage for very brief blips with the ability to switch off before any…

My first impression is that it smells like BS but let's take a closer look.

CAT6 cabling uses 4 pairs of AWG 24 wire. This type of wire typically comes with two options for insulation 250V and 600V, Let's be optimistic and use the latter. The maximum recommended current for AWG 24 wiring is 0.577A [1], as a reference PoE specs use 0.3A (if I remember correctly). Using these assumptions our maximum power transmission would be 4 (pairs of wire) * 600V * 0.577A = 1384.8W, this doesn't include power losses inside the wire itself. Belden's descriptions seem to indicate that power transmission is multiplexed in the time domain, which would reduce the power transmission capability even further.

Current limits on wiring are semi-arbitrary, what it really comes down to is how much heat generation is tolerable in the wires and the environment in which they reside. If we were to ignore the suggested current limit of 0.577A per core then it is possible to transmit 2000W. More specifically you would need 0.833A at 600V in 4 pairs of wire to get 2000W.

TLDR: The claims seem dubious. It is possible if the current limits for AWG 24 wire are are exceeded by about 2x.

[1] https://www.powerstream.com/Wire_Size.htm

Re: So Where’s My Low Voltage DC Wall Socket?

#64

Post by lostlogin »

Johnny555 wrote: post #56
lostlogin wrote: post #31

Earlier quoted context omitted.

Looking at that plug and how chunky the holes are for ac power, when access is limited and you can’t see, shoving a usb c plug into the ac hole is going to happen often.

You'd have to shove awfully hard -- hard enough to crumple the metal shell of the USB connector, since it's wider than the opening in 120VAC socket. (I just tried it with a spare electrical outlet, and even with a fairly hard push and wiggling it around, I couldn't make it fit)

Yikes and thanks - I’m in New Zealand and our plugs are way smaller so you couldn’t make that mistake here, but it’s good to know the terminals are far enough in that it’s safe. I’ve seen some surprising things people have forced into the wrong port. USB into Ethernet etc.

Re: So Where’s My Low Voltage DC Wall Socket?

#65

Post by [deleted] »

ethagknight wrote: post #10

Is "Digital Electricity" a real thing? Its billed as an alternative to AC or DC. This may be as good a place as any to ask this question, but I am a hotel developer, and we've had a few people reaching out to us trying to sell "digital electricity" that sends high voltage over cat5 (up to 2000w per the Belden materials) by essentially sending high voltage for very brief blips with the ability to switch off before any…

[deleted]

Re: So Where’s My Low Voltage DC Wall Socket?

#67

Post by sebazzz »

Wowfunhappy wrote: post #61
MisterTea wrote: post #46

We don't need DC sockets as they dont solve any problems. The stupid simple AC mains distribution system is well tested and proven. Who cares that they provide up to 3kW. The "last meter" problem is perfectly solved using AC-DC wall warts and bricks. If the power supply dies, you buy a new one and just plug it in. No electrician required. Putting things in wall or central distribution is not a solution to any existin…

Wouldn't it be more efficient to have e.g. one DC power supply for the house that can power everything that needs DC power, instead of lots of individual (and likely cheap/inefficient) power supplies?

The problem is the resistance of the wires which causes a measurable voltage drop. Try extending a USB cable 10 meters to have an idea.

Re: So Where’s My Low Voltage DC Wall Socket?

#68

Post by laurencerowe »

Wowfunhappy wrote: post #61
MisterTea wrote: post #46

We don't need DC sockets as they dont solve any problems. The stupid simple AC mains distribution system is well tested and proven. Who cares that they provide up to 3kW. The "last meter" problem is perfectly solved using AC-DC wall warts and bricks. If the power supply dies, you buy a new one and just plug it in. No electrician required. Putting things in wall or central distribution is not a solution to any existin…

Wouldn't it be more efficient to have e.g. one DC power supply for the house that can power everything that needs DC power, instead of lots of individual (and likely cheap/inefficient) power supplies?

Most electronic devices require low voltage DC, so resistance losses in cabling across even quite short distances (10+ metres) would be significant. This is why DC distribution in data centres if it is used is normally 48V.

Re: So Where’s My Low Voltage DC Wall Socket?

#69

Post by rwmj »

rhinoceraptor wrote: post #4

It seems like USB A/C are going to be that. You can already buy outlets that have both mains and USB ports, there are even dual USB C outlets now, that can do 30 watts: https://www.amazon.com/dp/B07PTWG5DV

I stayed in a newly built hotel a few years ago that had two USB-A sockets integrated in every single power outlet, both in the room and around the lobby.

What actually worries me about this is that they are all backed by tiny switch mode power supplies, and if not designed and built correctly they have a habit of exploding. So now your hotel has hundreds of potentially explody boxes hidden in the walls.

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