So Where’s My Low Voltage DC Wall Socket? • Hacker News Board

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

#111

Post by m463 » Tue, Dec 17, 2019, 3:05 AM UTC

asteli wrote: post #79

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…

Wait, that exists. USB is the standard. The UPS with standardized DC-outs is a USB power bank with integrated pass-through charging.

also POE

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

#112

Post by 8bitsrule » Tue, Dec 17, 2019, 4:35 AM UTC

A DC solution is WAY overdue. Put your hand on your AC->DC converter, or your wall-wart. Above ambient room temperature? Wasted energy. "It's only 2-10 watts." Multiply by 5 units (underestimated) per 100 million households. That's >= a gigawatt. 8700+ GwH / year.

That's aside from the environmental costs of making & disposing of these pernicioius devices. Time for that decades-old solution to retire.

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

#113

Post by vetinari » Tue, Dec 17, 2019, 9:54 AM UTC

mark-r wrote: post #44

nickhalfasleep wrote: post #2

No mention of Power-over-ethernet?

What is the maximum power provided by PoE? Wikipedia is surprisingly vague on the subject, probably because there are multiple standards. PoE was never intended to power more than just network equipment.

Depends on how you define "network equipment" :)

Unifi is selling LED panels, that are powered over PoE and controlled over Ethernet.

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

#114

Post by MisterTea » Tue, Dec 17, 2019, 5:43 PM UTC

snuxoll wrote: post #87

laurencerowe wrote: post #68

Earlier quoted context omitted.

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.

It’s also more difficult do do straight transformation on DC voltages, it can be done but the reason our power grid settled on AC was getting high voltage transmission levels down to reasonable ones for use is simple with some wound coils. It’s really easiest to just keep everything AC until the point of use, putting a transformer and a bridge rectifier in most devices is a better solution than needing switching powe…

Dumb DC supplies using just a bridge rectifier and filter cap(s) isn't really ideal if you need a stable voltage. If the mains voltage sags, so does output. Then factor in ripple from the cap bank under higher loads and the associated nonlinear harmonics and power factor issues from the rectification. You could add a linear regulator and increase the transformer output and burn the excess off as heat but efficiency goes down the toilet.

Switchers, for all their complexity, are pretty damn clean in terms of output and input PF correction. Even in audio and sensitive analog applications where dumb supplies were preferred have been replaced by switchers. A good design goes a long way and it's unfortunately easy to design junk switchers because of the complexity involved.

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

#115

Post by NwtnsMthd » Tue, Dec 17, 2019, 8:03 PM UTC

lopmotr wrote: post #90

NwtnsMthd wrote: post #63

Earlier quoted context omitted.

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…

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.