Will AC power distribution become obsolete?

[nigelwright7557]

Nobody mentioned billions of existing electrical devices that cannot function without AC current....

Most universal motors run on AC or DC anyhow.

A lot of motor driven systems use AC for timing of power control.

[Marco]

And the switchgear gets problematic fast.

If the devices in the video were compliant, this seems a standards issue. Make them have to protect against reverse polarity faults if that's what you want.

[EPAIII]

I^2*R

This hairy old chestnut.

DC power over very long distances is practical and efficient,  but not for final distribution.

The thing is that there are those who have little understanding of the technicalities and safety aspects in letting Joe public near high energy DC.

Why would it need to be high voltage? Joe Public won't get electrocuted from 30 volts. That's what I meant by safety, if you had read my post.

[David Hess]

Do you have an estimate of how much power is “saved” between a shaded-pole motor vs the BLDC one?

I could measure it, but the refrigerator is currently in my storage unit several states away.  I would guess 5 watts saved by the motor itself, and that is 5 watts less than the compressor has to move but the COP lowers that.

I don’t understand the EPA mandate,  the shaded-pole motor, which is quite inefficient, could be replaced with a permanent split capacitor one. The efficiency gains may not be as large, but have proven ruggedness.

The EPA evaluation process is required to ignore external costs; they may not be a factor in any decision.  It does not matter to the EPA how much the requirement costs of if it makes economic sense.

I do not know that a capacitor run motor would be any more efficient, and I have never seen one that small.

[schmitt trigger]

I don’t think that they exist, because the shaded pole one has fulfilled the requirement.
I don’t see any physical impossibility why they couldn’t be designed.

None of the single phase induction motors are efficient, but my understanding is that the shaded pole is  the least efficient. Having said this, they are electrically very reliable.

But given their small size, the actual power savings are really small.

[Halcyon]

The chances of AC disappearing in favour of DC has less chance of happening, compared to switching Australia from driving on the left hand side of the road, to driving on the right.

[TimFox]

That change is simple:  all passenger vehicles switch on Saturday, and commercial vehicles switch on the next day Sunday.

[johansen]

The EPA evaluation process is required to ignore external costs; they may not be a factor in any decision.  It does not matter to the EPA how much the requirement costs of if it makes economic sense.

I do not know that a capacitor run motor would be any more efficient, and I have never seen one that small.

They make miniature capacitor motors as small as you want to pay for it, and ive seen ones that are around 60mm diameter 40mm thick and they have a shaft power rating of 7 watts at 1400rpm.. 400rpm of slip.

I would speculate they would not be more efficient enough to pay for the second winding and the capacitor, when the equivalent additional cost could simply make a shaded pole motor large (and run it at a lower flux density), or make the fan blades more efficient.

The epa does not give a shit if the equipment will ever pay for itself, because they, along with the majority of folks on this forum, do not understand that money and energy are essentially the same thing. 

So the present narrative of we need to reduce energy consumption is the hill that society may die on..regardless the cost, human or otherwise

[Marco]

Nobody mentioned billions of existing electrical devices that cannot function without AC current....

All of those will get to the end of their economic life eventually.

The only likely way the world to transition to DC would be a steady ingress of DC microgrids and DC distribution. Then after the writing is on the wall, power companies can say "in ten years mains will start switching over to DC and you'll need an inverter to run AC loads".

So if industrialised society is still around in 50+ years and AI hasn't taken over, it could happen. If AI takes over I think they'll switch to DC earlier.

[nctnico]

That change is simple:  all passenger vehicles switch on Saturday, and commercial vehicles switch on the next day Sunday.

Yep. Switching from left hand side to right hand side has been done before in other countries. Tesla is no longer making right-hand-side drive versions of some of their models. Other car manufacturers may follow. So the idea of needing to switch from left side driving to right side driving may not be that far fetched.

[Xena E]

.
The only likely way the world to transition to DC would be a steady ingress of DC microgrids and DC distribution.

But why? For changes sake? Or to appease the criminally stupid in society?

[soldar]

I cannot see changing to DC distribution any time soon. There are millions of three phase motors.

It would have made more sense decades ago to change to 300 or 400 Hz and it was never done because of the transition costs.

[pcprogrammer]

That change is simple:  all passenger vehicles switch on Saturday, and commercial vehicles switch on the next day Sunday.

To bad for some of the passenger vehicles that business in some commercial sectors is 24/7. 

What a mistakea to makea, small 3 door car head on a big delivery van.

[pcprogrammer]

Nobody mentioned billions of existing electrical devices that cannot function without AC current....

Most universal motors run on AC or DC anyhow.

A lot of motor driven systems use AC for timing of power control.

What about all those ovens and other appliances that rely on 50 or 60Hz for their timekeeping device. These are still fairly common because they are cheap.

[TimFox]

In his brave new world, your old appliances have no place.

[Marco]

But why?

Why is telecom -48V? Distribution because silicon is cheaper than copper/cabling. Microgrids because of SELV, renewable power, batteries and EVs.

DC will ingress regardless, if it manages to ingress far enough that keeping AC in the middle stops making sense, you slowly switch over. Over a long enough timeline it could happen, though I don't think there is any likely long timeline without apocalyptic change.

[TimFox]

But why?

Why is telecom -48V? Distribution because silicon is cheaper than copper/cabling. Microgrids because of SELV, renewable power, batteries and EVs.

DC will ingress regardless, if it manages to ingress far enough that keeping AC in the middle stops making sense, you slowly switch over.

See  https://www.britishtelephones.com/howtele.htm
48 VDC is an appropriate voltage to operate traditional land-line telephones and is supplied from a bank of storage batteries at the local switching office that can supply power (< 70 mA, depending) when the local utility supply fails.
The negative voltage has to do with electrolytic corrosion concerns.
Don't operate your refrigerator or teakettle from the phone line.

[tooki]

Let’s not forget that it was only a few years ago that the last remnants of the DC grid in New York City were shut down. The remaining DC customers had to get rectifier units installed.

[TimFox]

Let’s not forget that it was only a few years ago that the last remnants of the DC grid in New York City were shut down. The remaining DC customers had to get rectifier units installed.

Those final DC customers included high-power DC motors (easily controlled) used for elevators and similar applications.
75 years ago or so, some New York residents had to use "AC-DC" radios (with tube half-wave rectifiers that could pass DC without transformers) because of DC distribution.
That led to a now-obsolete form of jokes about AC or DC in other unrelated topics.

[Marco]

Don't operate your refrigerator or teakettle from the phone line.

On the other hand on a long enough timeline on a DC microgrid it might make sense to drop to 48V at the socket so most appliances become SELV. DC-DC buck is cheap and reliable, electrolytics are an AC problem.

Just like 48V busbars work well for datacenters long after POTS has stopped mattering.

[TimFox]

Don't operate your refrigerator or teakettle from the phone line.

On the other hand on a long enough timeline on a DC microgrid it might make sense to drop to 48V at the socket so most appliances become SELV. DC-DC buck is cheap and reliable, electrolytics are an AC problem.

Just like 48V busbars work well for datacenters long after POTS has stopped mattering.

Again, for domestic loads between, say, 1500 and 3000 W, the mains-cable wire gauge will need to be large with only 50 V (60 A for 3 kW, using round numbers here).
Given full flexibility for supply voltage, it's an engineering calculation to choose the appropriate value depending on actual loads.

[Marco]

It's also a political one.

Data centers would save on copper with higher voltage busbars, but technicians are expensive. SELV saves lives and make servicing more efficient.

[IanB]

Data centers would save on copper with higher voltage busbars, but technicians are expensive. SELV saves lives and make servicing more efficient.

During my life, I have known many people die from cancer, and several people die from road collisions, but I have known no one die from or be injured by electricity.

I think electricity is one of those dragons that is disproportionately scary compared to the actual risk.

[madires]

Data centers would save on copper with higher voltage busbars, but technicians are expensive. SELV saves lives and make servicing more efficient.

I've seen the result of a technician working on a -48V DC PDU and causing a small oopsie with a wrench. The wrench was vaporised, the PDU's inside got a nice metal coating, and the guy was thrown back a few meters (luckily he wasn't injured). Even with -48V DC you need safety measures.

[madires]

On the other hand on a long enough timeline on a DC microgrid it might make sense to drop to 48V at the socket so most appliances become SELV. DC-DC buck is cheap and reliable, electrolytics are an AC problem.

Will you pay for replacing the mains wiring in all buildings worldwide with new wires with five times the cross section? Copper is expensive! And remodeling buildings too.