[seanalltogether]

AC is still way better for power transmission, and I don't mean giant power lines spanning from one city to another, I mean from the curb to your home, or within the walls of your home. Electroboom has a video on this topic https://www.youtube.com/watch?v=S7C5sSde9e4 and its been repeated elsewhere, but transmitting dc power with any meaningful voltage is dangerous, like burn your whole house down dangerous, and if its not high voltage, you're just losing too much power to resistance.

[danachow]

> AC is still way better for power transmission, and I don't mean giant power lines spanning from one city to another, I mean from the curb to your home, or within the walls of your home.

First you say AC is way better for transmission, which is false - you should look into what HVDC is.. and second what you’re talking about “curb to home” is power distribution, not transmission - so your post is confused on a few levels - it’s hard to understand what you’re trying to even claim.

> its been repeated elsewhere, but transmitting dc power with any meaningful voltage is dangerous, like burn your whole house down dangerous

Would you like to specifically reference in your linked video where that claim is made? Because I didn’t see that, and I am puzzled what you’re referring to. Quite the opposite he demonstrates at household voltage, DC is safer than AC from a shock standpoint (see 2:08). Why do you think high voltage DC is inherently less safe than AC?

This video seems to demonstrate the basic historical concept that AC is superior for transmission due to the typical ease in converting to high voltage low current and back - the key point is that it is high voltage for lower current and lower loss and this has traditionally been easier achieved with AC. It doesn’t really get into modern power conversion which has changed things somewhat.

[Arainach]

https://www.youtube.com/watch?v=S7C5sSde9e4&t=3m18s

https://www.youtube.com/watch?v=S7C5sSde9e4&t=7m34s

The thermal properties of AC for comparable amounts of power in a conductor are significantly better.

Copper is expensive, and having dealt with just the difference between connecting 12 gauge and 14 gauge to outlets and pulling it through conduits I'm certainly not enthusiastic about needing larger conductors.

[elihu]

He was running ten amps over thin wires; of course that doesn't work. The problem there was that he was transmitting significant power at low voltage and high current. That doesn't say anything about the superiority of AC or DC. AC has historically been the more practical choice because you can trade AC voltage for current easily with a transformer, but there are ways to do that with DC now too. Maybe there's an argument to be made that transformers are cheaper or more reliable than boost converters; I don't know one way or the other.

If wikipedia is to be believed, DC is better in terms of conductor material costs and transmission losses than AC, at least for long distance high-power high-voltage transmission lines.

> A long-distance, point-to-point HVDC transmission scheme generally has lower overall investment cost and lower losses than an equivalent AC transmission scheme. HVDC conversion equipment at the terminal stations is costly, but the total DC transmission-line costs over long distances are lower than for an AC line of the same distance. HVDC requires less conductor per unit distance than an AC line, as there is no need to support three phases and there is no skin effect.

> Depending on voltage level and construction details, HVDC transmission losses are quoted at 3.5% per 1,000 km, about 50% less than AC (6.7%) lines at the same voltage.

https://en.wikipedia.org/wiki/High-voltage_direct_current#Ad...

[dhdc]

> If wikipedia is to be believed, DC is better in terms of conductor material costs and transmission losses than AC, at least for long distance high-power high-voltage transmission lines.

This is correct. DC is a much better choice for long distance transmissions. You don't need to worry about reactive power, skin effect, reactive elements of the line, whether the generators and the grid are synced or not etc. The problem with DC voltage conversion are mostly solved as well.

[distortedsignal]

> The required converter stations are expensive and have limited overload capacity. At smaller transmission distances, the losses in the converter stations may be bigger than in an AC transmission line for the same distance. The cost of the converters may not be offset by reductions in line construction cost and lower line loss.

https://en.wikipedia.org/wiki/High-voltage_direct_current#Di...

Not to mention that circuit breakers are harder in DC.

[dhdc]

> Not to mention that circuit breakers are harder in DC.

[Citation needed]

[elihu]

I can believe this is true. It's easier to make reliable AC switches because whatever arcing you get is self-extinguishing because the voltage passes zero 120 times a second. With DC, if you get an arc it'll just keep going as long as conditions allow. That means if you use a designed-for-AC switch in a DC application with the same voltage, it's likely to destroy itself sooner or later.

(Apparently this is one of the reasons why cars stick with 12V for accessories, because if they used higher voltages the electrical switches would be more expensive and less reliable.)

I don't know how this is normally overcome. In a lot of cases, the solution might just be "use a fuse instead".

[distortedsignal]

https://en.wikipedia.org/wiki/High-voltage_direct_current#Hi...

[danachow]

He’s demonstrating the use of a transformer to step up the voltage. The thermal properties are because of the lower current - not the line frequency. The transformer requires AC to work, but that is not the only way to convert power, and once the voltage is stepped up, it can be rectified back to DC and will actually be more efficient than AC - hence the reason that HVDC is a thing.

High power DC-DC conversion equipment is still more expensive than AC and the technology simply didn’t exist during the current wars.

[elihu]

AC won out historically because it's easy to change the voltage of AC using a transformer. If we reach a point where modern DC-DC converters are cheaper or better than a traditional transformer, then I don't see why we wouldn't just use DC everywhere. (I don't know if we're actually there yet.) With DC, you can transmit more power over the same wire you'd use for AC (no skin effect), electric shock from moderate DC voltages isn't as bad as AC, and you mostly get rid of 60-hz RF noise.

One argument for AC though is that it's easier to make AC switches, since those have a self-extinguishing arc. Maybe even household light switches can be replaced by solid-state devices?

Aside from the difficulty of making reliable switches, I'm not aware of anything about DC that makes it inherently more dangerous than an equivalent AC voltage.

[ncmncm]

The physical design of the switch ought to be easy enough to make physically interrupt the arc.

[dudeofea]

I'm not sure if that's the moral of that video. Just watched (had seen before), and his conclusion is that you shouldn't transmit power with low voltage because it means you need lots of current.

HVDC has some tradeoffs over HVAC, but you should be able to transmit power just fine with either.

HVDC doesn't suffer from the skin effect that AC does: https://www.allaboutcircuits.com/textbook/alternating-curren...

HVDC is however harder to make/break contact with compared to HVAC as AC crosses zero volts many times: https://electronics.stackexchange.com/a/325608

EDIT: Sorry, didn't mean to pile on this comment with everyone else