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Comment by ethagknight | Hacker News Reader

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 damage occurs if a short is detected. they claim it is supposed to be significantly more efficient, doesn't require electricians to run cables, and its safer. I declined... but im still curious. basically every device in the room is connected via lan to a power server.

https://www.belden.com/blog/smart-building/digital-electrici...

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Looks like buzzword marketing bullshit to me. Apparently they're just sending pulsed DC power over Ethernet cables? Nothing else in that article is as new or exciting as they dressed it up to be. GFCI outlets are standard in modern houses, they claim to be safely transmitting "high voltage" but 120V is not, and the "digital" buzzword stinks of marketing.

>It transfers high levels of power over non-power cable

You can't beat physics. Wires heat up from current, regardless of whether it's AC, DC, or "digital" pulsed DC. I doubt Ethernet cable is rated for any significant amount of power, but searching for "cat6 max power" doesn't return any relevant results because search is broken in 2019.

It's also likely to be rather inneffecient, as they are converting from AC to DC and then potentially back to AC? There may be an advantage to pulsing DC but I'm not sure, typically AC is more efficient for power transmission because of lower losses for the same power over distance and higher transformer efficiency (no need for an inverter).

You can get 100W over Cat5 with 802.3bt, but I can't tell if there are any special requirements for that cabling: https://en.wikipedia.org/wiki/Power_over_Ethernet#Standard_i...

It sounds like "digital electricity" is a more advanced sort of GFCI: instead of verifying that the two pins are carrying equal current, it verifies that the expected amount of power makes it all the way to the receiving end.

Normally, running high voltage through a wire is dangerous because a fault can dump power into the middle of the wire (starting a fire) or into a person (stopping their heart), but perhaps with end-to-end active monitoring, it's possible to operate safely at much higher voltages?

If this technology works, I think it would also be useful for powering a tethered drone from the ground.

[Edit: according to lopmotr's link, they are using this for drones and balloons already.]

It's apparently a bit smarter than GFCI. [1] says it measures the loss in the wire to determine if a person or whatever is touching it. So that would protect people against shocks from touching both wires, which GFCI can't do.

[1] http://magazine.connectedremag.com/publication/?i=488126#{%2...

I think this is a pretty nice idea except for the patents and only having one or two suppliers and lack of technical details.

That sounds like the sort of thing your local electrical code authority might get very upset about. It's not clear what the actual voltage is? But if it's over "SELV" ratings different rules are going to apply.

From the material it sounds interesting but I'd be leery of the 600 Hz switching generating a ton of electrical noise and relying on the upstream systems to keep everyone safe. The idea sounds good but I can see a lot of ways this can go wrong outside of very controlled environments.

Oh wow, I would not want 2000w going through Ethernet. Both for the obvious electrical issues, and for the dangerous mixing of safe sockets and hot sockets.

No idea how this would be more efficient. Bursting voltage will lead to higher loses versus a continuous voltage. Are they claiming efficiency thanks to a centralized AC->DC converter?

Cat5 doesn't imply RJ45, so that confusion could be easily averted if people with brains developed that stuff. 2000w constant power transmission on a Cat5 sounds dubious, though. I don't know at what the voltage such a cable gives in and shorts wires. It would have to be pretty high to get the current to something the wire crossection can handle.

It's not the wattage that is going the be the problem, but either the high current or the high voltage (arcing).

I would check you local codes. Running Cat5 might not require an electrician, but that doesn't mean it doesn't mean it doesn't require a licensed installer. Especially if you want to run network over that Cat5, you'll want someone who knows what they're doing.

That said...Belden is reputable, but this doesn't sound like it's fully baked.

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

I've come around to the idea that some type of power over Ethernet is probably the correct solution for low voltage house wiring. There is an automotive standard IEEE 802.3bu-2016 which supports up to 55 watts.

The other advantage it that solves a lot of the IoT last 25 feet problem. Because it's both power and a data link.

There are special thicker 16 and 18 AWG Digital Electricity cables [1], so you probably wouldn't get that 2kW with CAT6 unless it's just peak power with a low duty cycle. They are rated for 300V so they might actually use close to that.

[1] https://www.belden.com/products/enterprise/copper/cable/de-c...

Oh, that makes more sense!

4 * 300V * 2.3A = 2.76kW

It looks like it's totally doable with those cables! But if they're running 300V DC through there... may as well just run 120Vac. The only benefit I see is that they can detect faults on the transmitting end in a sophisticated manner.

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