But, nowadays, many of those devices use some form of switch mode supply, using a DC power supply would be no more complicated than for AC.

so how many circuits would need to run around the house to provide all of the different voltages? AND, what advantage is gained by having the supply remoted from the device using the power?
The concept of DC distribution is simply not ever going to work for normal households. It does work in military aircraft and in space stations, though.

 

so how many circuits would need to run around the house to provide all of the different voltages? AND, what advantage is gained by having the supply remoted from the device using the power?
The concept of DC distribution is simply not ever going to work for normal households. It does work in military aircraft and in space stations, though.

The one supply voltage runs round the house. Each device may need to convert that to some other voltage(s). That is the case whether the supply voltage is AC or DC.

With an AC supply you can use a heavy, expensive iron-cored transformer to producr other AC voltages. Then you can use a rectifier and large electrolytics to smooth it followed by a regulator to get what the device needs.

With a DC supply a switch mode supply, using a small light transformer and smaller capacitors (because of the higher frequency), can produce whatever voltages are needed cheaper and smaller than with an AC supply.

Looking around the house, most electrical items first rectify and smooth the AC input to a DC voltage and then produce whatever they want from that DC voltage. Why not cut out the middleman and eliminate all that rectifier, smoothing stuff and feed DC round the house.

 

The lack of an efficient conversion method is what lost the battle for Edison and DC.

You must have read different history than I did. And at the time of the Edison-Tesla(Westinghouse really) battle the few electric devices were DC. The problem with the Edison DC generation/distribution was the distance power could be transmitted not any conversion nonsense like your saying.

 

so how many circuits would need to run around the house to provide all of the different voltages? AND, what advantage is gained by having the supply remoted from the device using the power?
The concept of DC distribution is simply not ever going to work for normal households. It does work in military aircraft and in space stations, though.

More nonsense. How many circuits do we use now around a house to provide the power/voltages needed. Maybe your area of Detroit is different than Ohio, we only have two, 120V and 240V. The device appliance it self is made to use what ever voltage is available.

And your lack of knowledge to military aircraft is like that of Mig welding. "With over 70-years of experience, Collins Aerospace continues to develop and improve how generator products supply power to aircraft. Our solution for supplying constant frequency AC electrical power simplifies the design of the aircraft’s complete electrical system. " from - https://www.collinsaerospace.com/en...-Controls-Actuation/Electric-Power-Generation That link was chosen only because it was the first one that wasn't a PDF.

 

The problems with DC distribution are at the ends of the line, because converting the DC power back to a conveniently usable voltage is a lot more complicated than with AC power. The 380 KV AC power just takes a big transformer to step it down, while with the DC system it takes some sort of inverter. And what sort of electronic devices are suitable for such high voltages? Probably much less efficient than a good transformer, no doubt.

The province here has several hydro generating stations that are many kilometres distant, they have mostly all been converted or new installations to DC transmission, which has been around a long time.
The saving in conductors etc is very significant, the conversion to DC and back to AC is done with invertors using solid state principles, previously done with mercury ignitrons.
Max.

 

Power Transformers are a totally mature technology, while a good switch mode power supply takes some excellent design engineering, and a good amount of expertise in the PCB layout. In addition, they require a fair amount of filtering to keep from being producers of RFI. Just check out the non-approved but still very much used growlights that have been a problem for a while. And that bit of weight from those small and cheap transformers is not a big deal, except to the producers of JUNK. Just imagine the RFI racket if every house had 15 or 50 noisy switcher supplies. WiFi would not work, over the air entertainment would be obliterated, and no telling what other problems there might be. Certainly all of the wireless everything would have it's range shortened quite a bit.
In addition, consider the poor reliability of those small cheap switchers. Six months at the most.

 

OK, Max. For long distance power transport DC can make sense. But not for neighborhood distribution. And certainly not in the houses. WAY to complex for that.

 

Just imagine the RFI racket if every house had 15 or 50 noisy switcher supplies. WiFi would not work, over the air entertainment would be obliterated, and no telling what other problems there might be.

In the room in which I am sitting there are no less than 14 devices with SMPS (some of which are cheap from China - incidentally with good reliability) including the laptop on which I am typing this. In the loft just above me is the 3.6kW inverter feeding power from the solar panels on the roof back into the main supply. The WiFi works just fine otherwise you would not see this message. The only interference problem I have noticed is the inverter in the roof wipes out the 60kHz time transmissions during the day.

 

Correct me if I'm wrong, but doesn't HVDC also have less of an issue when it comes to corona discharge?

I believe it's only the high voltage peak that determines the degree of corona discharge, not whether it's AC or DC.

 

Running DC in the house for most small devices is fine but, of course, you would need a healthy inverter for any AC motors, such as the furnace or sump pumps.
However inverters are appearing in larger devices such as the refrigerator I just bought or some of the new microwaves ovens, so it would seem feasible to run DC into a house.
Of course the outside transmission lines would still need to be HV AC to minimize wire size.

 

One thing to keep in mind is that with DC, once an arc is struck it continues. AC passes through zero twice every cycle. That is not a problem until you accidentally strike an arc.

 

Some of the older off-gridders here have DC power for inside the house. Most use 12vdc for under 100W devices with RV and car electrical products. Once you move above a few hundred watts the wiring size requirements for 12vdc becomes expensive because of copper costs and if you increase the DC voltage to reduce copper losses the safety issues of DC sustaining arcs in plugs and switching becomes another cost factor for special DC rated components. Internal AC is what most people use today because the standard wiring is cheaper and safer for all power levels.

 

At one early point in my career we were given the task of converting the Old Oxford Observatory from 110v DC (Edison style Generator) to 230v AC mains supply..
Someone overlooked changing a couple of remote 110v incandescent lamps, they seemed fine on 230V!
Max.

 

Here: https://stephenstuff.wordpress.com/2016/06/11/dc-cable-selection-guide/ is an interesting read.

 

At one early point in my career we were given the task of converting the Old Oxford Observatory from 110v DC (Edison style Generator) to 230v AC mains supply..
Someone overlooked changing a couple of remote 110v incandescent lamps, they seemed fine on 230V!
Max.

I have seen, unfortunately, light wiring done inside a house using that older rubber covered telephone drop wire. The stuff with the #20 copper coated steel wires. Or they may be #22. Rather not a good choice. I suggested to that homeowner that they always have good batteries in their smoke detectors.

 

I would add that there is the hidden consideration of reliability when it comes to voltage conversion apparatus.

Simple magnetic devices like line frequency transformers and (quality) induction motors often provide decades or even centuries of reliable service with minimal periodic maintenance.

...Whereas finding a computer PSU that lasts more than 10 years feels like hunting a unicorn.

K.I.S.S.

 

I would add that there is the hidden consideration of reliability when it comes to voltage conversion apparatus.

Simple magnetic devices like line frequency transformers and (quality) induction motors often provide decades or even centuries of reliable service with minimal periodic maintenance.

...Whereas finding a computer PSU that lasts more than 10 years feels like hunting a unicorn.

K.I.S.S.

Certainly correct! Also, transformers are much more forgiving of momentary overloads and voltage spikes.
As for Unicorns, they are fairly common on the kingdom of Utopia.

 

I have seen, unfortunately, light wiring done inside a house using that older rubber covered telephone drop wire. The stuff with the #20 copper coated steel wires. Or they may be #22. Rather not a good choice. I suggested to that homeowner that they always have good batteries in their smoke detectors.

This was a complete re-wire, up to code installation.
Max.

 

I realize this is a very old thread, but the point about DC transmission is merely one of economics. Yes, there is the expense of the converter stations, which are very expensive. The break even point for switching to HVDC is simply due to there only being two power conductors resulting in a full 1/3 fewer insulators, 1/3 less conductor, narrower rights of way, lower installation cost due to not stringing and pulling that last phase, and leaner towers not needing to be strong enough to support that third conductor. I do not recall the distance where the DC line makes more sense, but there's nothing magical about it beyond economics.

There is the use of AC/DC/AC interconnection stations throughout the near western US between the western and eastern grids. This is to prevent the catastrophic collapse of the US grid under "perfect storm" conditions. The decision to use these isolation ties came after a significant outage back in the 60's gave federal officials a wake-up call. For national security, we needed to separate things a bit.

 

More nonsense. How many circuits do we use now around a house to provide the power/voltages needed. Maybe your area of Detroit is different than Ohio, we only have two, 120V and 240V. The device appliance it self is made to use what ever voltage is available.

I realize this thread is old, Shortbus, but there is something that must be addressed. In the US and Canada, 120V and 240V appliances cannot just accept whatever voltage is present in the dwelling. Smoke tends to get released when you connect a 120V appliance across 240.