How Long Until Low Volt DC dominates building power distribution?

[MichaelO13]

The recent advent of USB3 power deliver protocols delievering varying levels of low Volt DC power options which are delievering enough power to run most computer equipment, lighting, and many appliances combined with the fact that practically every modern device is taking th AC from outlets and converting it to lower volt DC, I am wondering when the fundamental change in load center solutions will begin to charge, particularly on the residential side of things. I can see future load centers doing All of the DC rectification centrally with low Volt USB power delivery lines being distributed thoughout the house. This avoids loads of switching power supplies all over the house from plug in hone chargers to switchng done in 120v/USB power plugs. Such ad hoc power conversion at everywhere endpoint is not efficient and just generally wasteful.

I could certainly see home load centers with designs providing USB power delivery to most common sockets though out the house with a few areas with normal 120/220v ac in Kitchens, wash rooms, and shops. Has anyone seen any info like this on next get load centers?

 

[Hv&Lv]

So your recommended side by side AC and DC home distribution lines?
AC outlet with a DC outlet next to each one?

 

[petersonra]

Other than computer power and lighting there isn't a whole lot of stuff that can be powered up off of 5 volts DC. I don't see anybody wanting to distribute it from a central location. I can see having outlets with USB power receptacles. I could also see outlets with class two power supplies built in but I just don't see any benefit ever to having Central 5-volt DC power in a building.

 

[Hv&Lv]

Other than computer power and lighting there isn't a whole lot of stuff that can be powered up off of 5 volts DC. I don't see anybody wanting to distribute it from a central location. I can see having outlets with USB power receptacles. I could also see outlets with class two power supplies built in but I just don't see any benefit ever to having Central 5-volt DC power in a building.

Quite honestly I’m not sold on the usb receptacles. I have them in my house, I can’t unplug the “energy vampires”
with a wall wart, I can.

 

[hbiss]

The way I see it, the push for USB and low voltage power systems is just an attempt by people outside the electrical industry to create a new market for themselves. I think they fail to realize that if it ever came to fruition, it would still be subject to the NEC and require a licensed electrical contractor to service and install.

Low voltage power is nothing new because actually low voltage was used decades ago to power many rural houses. If you look, you can find lighting and appliances like refrigerators and irons that were available at the time.

-Hal

 

[Fred B]

The way I see it, the push for USB and low voltage power systems is just an attempt by people outside the electrical industry to create a new market for themselves. I think they fail to realize that if it ever came to fruition, it would still be subject to the NEC and require a licensed electrical contractor to service and install.

Low voltage power is nothing new because actually low voltage was used decades ago to power many rural houses. If you look, you can find lighting and appliances like refrigerators and irons that were available at the time.

-Hal

Currently these non electricians are deeply involved in doing POE and similar lighting and other devices. Code enforcement and licensing hasn't caught up with it yet. Genie might be out of bottle by time they do.

 

[MichaelO13]

Other than computer power and lighting there isn't a whole lot of stuff that can be powered up off of 5 volts DC. I don't see anybody wanting to distribute it from a central location. I can see having outlets with USB power receptacles. I could also see outlets with class two power supplies built in but I just don't see any benefit ever to having Central 5-volt DC power in a building.

The thing is with the latest revision of USB power delivery, you are not limited to 5 volts. The current spec can supply 5v, 9v, 15v, and 20v with future specs possibly delivering 28, 32, and 48 volts DC with up to 240w of power. This is more than enough for everyday appliances in the house except for things like vacuum cleaners, power tools and major appliances. The whole point of doing the rectification in the panel is to do it in a highly efficient way to rid our homes of all the wall-wart energy vampires.

While I can see some of you aren't sold on this, I really think this will become more and more common once the USB power delivery protocol matures in a few years.

 

[Besoeker3]

This is more than enough for everyday appliances in the house except for things like vacuum cleaners, power tools and major appliances. The whole point of doing the rectification in the panel is to do it in a highly efficient way to rid our homes of all the wall-wart energy vampires.

And that's the rub.

 

[paulengr]

Ok time for some fundamentals here.

Why do utilities use say 115 kV or 230 kV or even higher, AC or DC for power distribution? Isn’t that far higher voltage and just plain dangerous and scary? Why not distribute power at say 48 VDC,a common voltage used in phone systems for years? In fact Edison started with DC and even Tesla later suggested high voltage DC is the way to go. Much of the transmission system in the US Midwest is high voltage DC and it gets used elsewhere around the world. There is no technical reason we can’t switch to DC.

The answer is quite simple, First off regardless of whether it is AC or DC, losses in a power line are proportional to the square of the current. If we double the voltage, we cut the losses by 75% irrespective of whether it is DC or AC. Furthermore although there is a ton of active research on high frequency electronic transformers because they are smaller and have low losses in the transformer itself, the ROI and the losses in efficiency in the electronic conversion far exceeds the efficiency improvement in the transformer itself. Simply put, two coils of wire wound on a common iron core can easily exceed 99% efficiency compared to at best around 97% for DC conversion. So it is trivially simple and neatly lossless to transform up to a higher transmission voltage then down to lower distribution and finally utilization voltages with neatly unlimited power capability.

Now moving onto the converters a switching power supply converting from AC to DC can do so in a single stage using a very efficient and cheap device like an SCR or power FET and one capacitor on the output. A DC-DC conversion requires two stages of conversion with double the losses. Most devices involved have a 10 year or 100,000 hour life industrially or about 20% of that for consumer grade equipment compared to 30+ YEARS for even transformers. And the USB3 standard limits us to 48 VDC so we have over 4 times greater losses and the wattage isn’t enough to run a hair dryer, any laundry equipment, or most kitchen appliances.

If you don’t believe me then why is it that the vast majority of hotel USB ports that I visit don’t work? Or that I have to replace frequently used “wall warts” every couple years? The reliability on these things is astoundingly bad. I can’t even imagine an entire house full of them.

Plus if we get away from USB and just consider DC distribution in general don’t forget that although DC won’t kill you outright by causing heart fibrillation, it rips muscle tissue and breaks bones and unlike AC, it does not let go or knock you away. Fuses are twice as big and breakers 4 times larger because an AC circuit goes to zero Volts 120 times a second so it is trivially easy to shut down an AC circuit where with DC you literally have to pull the arc apart while energized. Large DC breakers are genuinely enormous. A 50 A DC breaker is about the size of a 1000 A AC breaker with no way to reduce the size…it’s physics at work.

So the simple answer is AC is used because it is simpler, cheaper, more efficient, and already established. DC has and continues to be around but has no compelling advantage.

Now keep in mind I’m no stranger to DC. My grand father was a telephone tech for over 50 years. I work on DC motors, generators, and drives a lot. It’s anything but foreign to me. And I strongly discourage DC distribution.

 

[zbang]

The whole point of doing the rectification in the panel is to do it in a highly efficient way to rid our homes of all the wall-wart energy vampires.

Which has more loss- LV DC distribution with central conversion or HV AC with distributed conversion? (HV being 240/120v here.)
What is the expected DC load, anyway? Is it simply small electronics/TV/small computers or something else? Phones and tablets might need under 10 watts, but a TV or laptop could be over 100.
How lossy are the "energy vampires", anyway? Most of the wall-warts I have run cool, so they themselves probably aren't wasting much. I'll posit that most modern wallwarts are fairly efficient, anyway, although I don't have the gear to properly test a couple.

And.... you still have to either distribute multiple DC utilization voltages or push another step of voltage conversion at the devices, and at that point, might as well distribute 120v AC.

To all of that, add the cost of installing and maintaining the rectifier and LV wiring.

This can be a tough audience .

 

[petersonra]

Or that I have to replace frequently used “wall warts” every couple years? The reliability on these things is astoundingly bad. I can’t even imagine an entire house full of them.

I cannot recall ever having to replace a wall wart at all due to failure and I've had probably hundreds of them over the years. Does not count the one I stepped on and broke.

 

[zbang]

Maybe 2-3 WW failures in 30? years, they tend to long outlast the stuff they came with.

 

[MichaelO13]

And that's the rub.

I believe some of you are not quite getting at what I am trying to portray. Low volt DC is in no way going to replace mains AC all together, certainly not in power distribution networks to the home. They will still continue to also exist in residential buildings. My point is I can see a time in the near futrure where residential loads centers have a section within them to to handle AC to DC rectification at the panel and will utilize the modern USB power delivery spec that can provide negotiated DC voltages from 5 to 48 volts. Traditional 120v AC outlets will continue to be distributed in the house, though I can see them being something like 1 per room versus several on all ways. They will also exist in garages, laundry rooms, and kitchens, etc when mains power is needed. With that said I can also see low volt DC power delivery plugs being widespread in bed rooms, living areas and powering lighting systems. Modern LEDs will work fine in these DC watt ranges the power delivery spec provides in most areas with the advantage of not having switching power supplies on each and every LED light bulb (which tend to fail way before the actual LEDs).

As far as the robustness of USB DC outlets they would certainly need to be built to last, but at the same time they can be replaced like any other normal outlet. While I see there are doubters, I can see things going this way in the future as more and more electronics continue to run low vote DC. Its less about the wall wart failures and more about the millions that have to be made every year and that end up in landfills. It just does not seem like a sustainable model as more and more of these are needed every year.

 

[petersonra]

I don't know why you want to distribute low voltage DC power from a central location. Now you've created a single point of failure.

No reason you can't have an outlet that has a USB port on it or other voltages available, but I don't see your plan happening it's just not practical. It is also doesn't solve any serious problem. You can already add a class 2 power supply wherever you need it.

 

[macmikeman]

Join the yacht club. There is amazing things going on now in cruising craft and lithium ion batteries.

 

[MichaelO13]

I don't know why you want to distribute low voltage DC power from a central location. Now you've created a single point of failure.

No reason you can't have an outlet that has a USB port on it or other voltages available, but I don't see your plan happening it's just not practical. It is also doesn't solve any serious problem. You can already add a class 2 power supply wherever you need it.

No more of a single point a failure than your entire power supply going through a single transformer, over a single wire run, through a single head meter unit, through a single panel breaker. Rectification units of this size can be made to a high standard to a point where their failure rate would be on par with every other component in the system., More over it could be modular and easily field probably unlike thinks like transformers. It may not "solve problems" but the cost savings is pretty compelling.

1. Greatly reduce power adapters by the millions
2. Reduce power lose from these adapters (while minuscule in scales of this size it will add up)
3. Reduce fire and electrical shock hazards from cheap Chinese USB power adapters
4. Save huge amounts in copper as this DC circuits will not require the same guages of copper wire, particularly in thinks like large office buildings
5. Greatly reduce LED lightbulb failures and almost make the entire idea of changing a buld obsolete as LEDs can last decades and what always fails on them is th ier switching power supplies.
6. Reduce the cacophony of EM noises switch power supplies create.
7. Reduce the the strain on the supply change for the components to make these power adapters by the millions.
8. Reduce ewaste as switchpower supplies and amound th emost common things that end up in land files.
9. Less high voltage mains power in walls is going to in turn reduce fires. While modern electrical safty codes makes this a minor point, its certainly not worth ignoring.
10. Greating reduce copper cost in power cords for things like PCs and potentially eliminating additional internal components needed to regulate power within each unit (think ATX power supply's)
11. Eliminate the need for surge surpresion devices at every end point as power conditioning can be done at the panel as well as simplify UPS units for PCs and devices to be pure PC devices and thus reducing costs

Note I acknowledge high end computers and servers wil still need mans power but DC USB power deliever is plenty for most end user workstations and laptops.

 

[kwired]

I don't know why you want to distribute low voltage DC power from a central location. Now you've created a single point of failure.

And voltage drop issues become more severe at such low voltages. yes many these items being powered are low power, but it adds up when you have many of them. There may be several that draw pretty low for a LV system, but then add a higher power item (for LV systems) here and there and you will either need many branches through the house or a hefty circuit to avoid voltage drop.

USB hubs or similar supplied by local line voltage circuit in areas of higher usage does make some sense though

 

[zbang]

Michael,
As some of my old prof's would say- "Show your workings." Many of the predictions (assertions?) are attractive, but they need some numbers and back-up information.

For instance "Reduce fire and electrical shock hazards from cheap Chinese USB power adapters"-
Is this actually a problem?
Let's assume, I think correctly, that pretty much all USB power adapters are made in China. Some to higher quality than others, but the majority of them sold in the USA appear to be UL listed (based solely in checking all the ones I have at home). How much reduction is likely or possible? Is it an issue of non-listed adapters coming into the country? Controlling their entry might be a better way to manage that. Or are the listing requirements insufficient?

Or "Reduce the cacophony of EM noises switch power supplies create."
Again, is this an actual problem? I'd expect that USB supplies are generally FCC part 15 class B qualified, and if so, are those limits too high?

"Eliminate the need for surge surpresion[sic] devices at every end point as power conditioning can be done at the panel"-
That is already true, and the 2020 NEC requires them (SPDs).

While these kind of ideas deserve consideration, the first things to ask are what's the issue to be solved, is it an actual problem, and does the idea address the root cause of that problem in a rational manner.

 

[Besoeker3]

I believe some of you are not quite getting at what I am trying to portray. Low volt DC is in no way going to replace mains AC all together, certainly not in power distribution networks to the home. They will still continue to also exist in residential buildings. My point is I can see a time in the near futrure where residential loads centers have a section within them to to handle AC to DC rectification at the panel and will utilize the modern USB power delivery spec that can provide negotiated DC voltages from 5 to 48 volts. Traditional 120v AC outlets will continue to be distributed in the house, though I can see them being something like 1 per room versus several on all ways. They will also exist in garages, laundry rooms, and kitchens, etc when mains power is needed. With that said I can also see low volt DC power delivery plugs being widespread in bed rooms, living areas and powering lighting systems. Modern LEDs will work fine in these DC watt ranges the power delivery spec provides in most areas with the advantage of not having switching power supplies on each and every LED light bulb (which tend to fail way before the actual LEDs).

As far as the robustness of USB DC outlets they would certainly need to be built to last, but at the same time they can be replaced like any other normal outlet. While I see there are doubters, I can see things going this way in the future as more and more electronics continue to run low vote DC. Its less about the wall wart failures and more about the millions that have to be made every year and that end up in landfills. It just does not seem like a sustainable model as more and more of these are needed every year.

OK.
Almost all residential homes have AC as the supply. That's the starting point. AC. If you want some DC in those homes you have to start with DC and then convert it. That's already reducing efficiency. Maybe not a lot but at least some. Then there are conductor losses for the low voltage DC.
How about commercial premises? Certainly we have halogen and LEDs. None of these require DC supplies. Not to mention there and residential. Again DC not required.

Then industrial. Where do we start? I did a lot of electrical plants. Paper mills, steel mills, but I suspect that is out completely outside what you are trying to portray. But maybe not I am.

 

[retirede]

My prediction is that wireless power transfer will become prevalent before running DC wiring ever takes hold.
WPC has already demonstrated 1KW wireless power transfer capability using an extension of the qi standard. A lot of details to work out, for sure, but it makes more sense than installing an second DC distribution system.