Removing the AC/DC conversion seems hardly worth the trouble. High efficiency AC/DC converters can be constructed. It's rather a question on how much one is willing to spend on such.
So in the end, the article says: say good bye to your washing machine, dish washer, electric kettle, electric stove, etc. I mean, the site is called "low tech magazine" for a reason...
I was thinking more like 200-400V DC systems, that could power most devices, but comes with a lot of challenges.
why not? it works, it has industry wide support and a huge range of products, and it's safe without excess need for shielding and isolation. it's closer to the actual operating range of most equipment, so it produces , in most cases, less intrinsic need for shifting voltages around, and the wiring that would get substantially smaller is already near size limits for dealing with vibration and harshness.
aside from trying to get closer to the operating voltages of whatever arbitrary energy pack we're specifically talking about , what's the point? if anything it would just wreck any hopes of cross-industry compatibility for a long time for very little manufacturing efficiency gains or energy savings.
tl;dr: the vast majority of car 12v is lights and logic, and they're closer to 12v than 200v in the vast majority of cases.
One solution may be to make a cable with a step-up converter at the beginning and a step-down converter at the end.
(It's worth remembering that the "modern", i.e. 1930s, three-phase power grid is built primarily to power motors on factory floors. I don't know if these are the highest load these days, but wouldn't be surprised if not.)
Small nitpick, I don't believe 3 phase power was picked primarily because it was convenient for powering 3 phase motors - it was picked because it's convenient for generating and transmission. There is no need for a neutral conductor in a balanced AC transmission system for example and it can very efficiently be converted to high voltage and stepped down again. It also results in modest power pulses though the generator compared to single phase etc.
VFDs have made A/C motors far more efficient than one driven by an across-the-line starter.
Should switch to 400Hz like aircraft do. Not just comically huge transformers, but also motor/generator magnets.
> A special generator was designed to create an output of 400 Hz. This allowed a motor which was the size of a watermelon to be replaced by one the size of a one-pound coffee can which could do the same work.
> The saving of weight allowed increased cargo capacity and decreased fuel consumption. Power at 400 Hz for aviation was a success and became the standard of modern AC-powered aircraft.
> Airports all around the world standardized on the same power system. This included the physical plug and cable as well as the 400 Hz power so that aircraft from anywhere in the world could land and be serviced wherever they landed. The aviation power system of 400 Hz became one of the first worldwide-adopted standards.
https://fcxinc.com/why-the-aviation-industry-operates-on-400...
Higher frequency lets you get away with smaller transformers, but decreases the skin depth on transmission lines which increases losses.
When I was working at SAS in ATX circa 2013, the 2 manufacturing lines were responsible for something like 10% of the city's average power consumption. I can't imagine the bleeding edge will have improved much - EUV light sources aren't exactly Energy Star compliant.
What's NOT easy is efficiently making 60 Hz AC at low quiescent power. Most inverters always burn 2-5% of maximum power with no load, while 1% would be considered far excessive if the output was DC (maybe 0.1% would be generally okay?). Part of this is lack of regulation; consumer devices have low-quiescent power supplies originally because of government mandates and, now, economies of scale. The government mandate didn't apply to inverters so there isn't an initial push to shift to low-quiescent topologies and prevent the first movers from being undercut.
So just for that reason, lower-voltage DC distribution can overall be more efficient if you are off-grid, even if some other portions of the system have increased losses. 120Vdc distribution would be superior from an efficiency standpoint in every way, but you're going to spend a lot on switches and protection equipment.
That is actually not at all how switching converters work. Pulsed DC is not AC. Those are two very different things.
Since all such power supplies prominently feature transformers, they can't operate on DC alone. But the frequency they use is high (a few kHz), the transformers are small, unlike the huge beasts in traditional 50/60 Hz power supplies.
Heating elements can run on DC more or less unmodified. Also electric motors can run on DC efficiently (see electric cars). Back in the days 3-phase power was needed to run strong electric motors (very common in Europe, but i think it exists also in the US for factories and businesses). But there are many easy solutions nowadays to just run them on DC.
It's quite likely that the motors on electric cars (and other efficient electric motors) are actually using an inverter to turn the DC into multi-phase AC and power an AC motor; this allows varying both the voltage and frequency of the AC fed into the motor.
My fridge is "inverter drive" and just runs continuously at a low duty cycle all day. Most heat pumps are like this too to dial up and down instead of strictly being on or off.
(Unsure what voltage the motors are running at though, so maybe AC-in is preferred to step it down before rectifying and chopping)
..but to get the same power (heat) output you need more current in a low voltage DC system. And power loss in the supply cables scales with the square of current, so you'll need thick (expensive) wiring in the wall or you'll risk the walls becoming an equally effective heating element.
Electric motors that run on DC are either brushed or have extra driver/conversion circuitry to pulse their coils in the right order. Both of these are not perfectly efficient.
(Also dumb that electric codes require dedicated circuits for many of these things, despite them not having the surge like they used to)
An electric resistance stove (radiant or exposed coil) would work just fine on DC, although, if it’s controlled using a TRIAC, that would need to change.
An induction stove uses rather high frequency AC, and that could be generated just fine from a DC supply.
Modern air conditioners use variable frequency drives, and those generally work by first converting the AC supply to DC.
I imagine that many modern washing machines also use some sort of variable frequency drive or DC-powered motor.
This is simply wrong. It is true that modern MPPT solar regulators use PWM to extract the maximum power, but for years, a simple on/off regulator was used to prevent overcharging.
The reality is that a solar panel is essentially a "Constant Current" supply, so the panel puts out the same current over a wide range of battery voltages. It is the battery which puts out a Constant Voltage at whatever current the load requires.
Maybe outputting a square wave from that solar generator would be optimal.
I do wonder how much in practice would be gained given the DC to DC conversions are guaranteed for every device.
But running low voltage DC power wiring is still probably not the best plan.
It turns out that there is a small industry out there that serves both RVs (and boats as well) that is 12V/DC based. Lights, pumps, refrigerators, fans, all running straight off a 12V power bank. "Cigarette lighter" outlets stand in for wall outlets for USB-style chargers, etc.
The 12V/DC battery system in the van is of course charged from both solar on the roof of the van and from the van's alternator (when the van battery is topped off and the van is under power of course).
I did add an inverter to supply 110V/AC for a pair of traditional electrical outlets I installed in the kitchen area of the van/RV. These are primarily used for plugging in wall-wart style chargers for the laptops.
(My Kill-A-Watt suggests that my rice cooker and even the electrical kettle would, just barely, function on the current provided by the inverter but RV-life tends toward minimalism so those extra appliances I've left behind.)
In any event, the whole experience did have me wondering if I could run a parallel 12V/DC electrical system in a new home and do away with a lot of the step-up/down of AC.
Definitely could do with some kind of modern outlet (USBC?) rather than the cigarette lighter outlets, ha ha.
Some advantages power limited and low voltage means it's safer[1]. Ethernet means you can control lights and other devices. Smaller diameter wiring means it's cheaper. Not needing a licensed electrician to install it saves $$$.
[1] Can imagine for a non North American not having to deal with 230VAC would be a big bonus.
The standard AC wiring is probably enough for 720W with 48V. The problem with choosing 48V is lock to medium power. Appliances would require 240V or 480VDC to get enough power.
The big problem is that there is no standard for DC power outlets or plugs. Would need to be different from AC and would also need to be different for different voltages.
Also, PoE is pretty high losses running power over Ethernet cable. The max power at source is 100W. PoE puts in higher voltage for account for the losses which means it isn't a straight 48V input to 48V output.
Now this is dedication ...
So they sacrificed the freedom of design to save €100?
My mom is in a typical suburb tract housing development, and the kitchen is right above the service entrance and the HVAC/mechanical room is right at it.
Great they're applying the same logic to solar-first systems, but it's not a new concept at all.
That limits the high gauge wire to the short run from battery to inverter, otherwise you'd need very expensive and heavy large gauge cable running to those high power devices.
And 12V in a vehicle makes little sense if the vehicle’s battery operates at 24V or 48V — it requires DC/DC conversion for no real benefit.
In the USA we have both ground and neutral wires at every outlet along with the hot (120VAC nominal) wire.
Why couldn't we raise the ground wire to +12VDC (or whatever) with regard to the neutral? The ground would have a very sensitive detector so that if electrical conditions exceeded some preset threshold it would collapse to zero nearly instantly, allowing the circuit protection to function as expected.
You could make a plug that only has a neutral and ground pin to tap into the low voltage side, or use all three pins to provide low power standby mode.
Now I'll do a search to find out that it is impossible because of a, b or c reasons or that it has already been patented somewhere and abandoned. Yay Internet...
In-house AC systems are designed to remain safe when that occurs. But it prevents using any of those wires in ways like what you suggested.
The standards for grounding make them unsuitable for running current. The ground wire in box are frequently bare. Metal boxes are grounded. The center screw is grounded. If you run current over the ground, those are live.
You have invented a way to electrocute lots of people.
The reason is that you don’t want to allow a fault which puts a line voltage (120VAC) onto the chassis of a piece of equipment waiting for a human to come along and complete the circuit to ground. So, you use the protective earth to connect to the chassis, such that if a power line ever did contact it, it would be a dead short to ground, which would trip the OCPD (over-current protection device, typically a circuit breaker), clearing the fault.
If you replace this safety mechanism with something that’s high-enough impedance to maintain a 12VDC differential, you’ve eliminated this important safety mechanism in your AC distribution system.
There are a few domestic circuit breaker teardowns on youtube. I suggest watching one and then asking the question: how can we break a high current _DC_ surge?
[1] switchgear use SF6. DC will require the SF6 at far lower V than AC
And neither type are a health hazard.
The WHO seems to think ICNIRPs concerns are valid:
https://www.icnirp.org/en/frequencies/low-frequency/index.ht...
Read papers 9-12 and let me know if you are still so certain.
Easily enough power for a monitor/TV, or for a small desktop computer.
https://audioxpress.com/news/usb-specification-revision-defi...
And Anker now makes the honkin’ big hubs you need for that: https://www.anker.com/products/a2342-240w-gan-charger
In situations where power source (solar!), storage and most consuming devices are low-voltage DC, just use a DC based setup if more practical.
I'm on a boat & most everything electric here is low voltage DC. But I do have a 12V->230V AC converter when needed.
In short: AC & low voltage DC can live happily side-by-side. The DC vs. AC debate is kind of a moot point these days.
Few devices other than switching power supplies are designed to work over a wide range of DC input voltages. There's an electric pump which will run slowly on an low input voltage and faster at a higher voltage.[1] Those are driven from windmills and solar. It's not cheap. It has to be self-protecting against too high and too low voltages.
[1] https://www.dankoffsolarpumps.com/product/solar-slowpump/
There is a telecom industry standard (perhaps only loosely standardized) for DC converters which are called "isolated DC-DC converters bricks."[2]. These are reasonably priced and reasonably high efficiency DC converters that fit into a set of standard form factors, e.g. 1/4 brick, 1/2 brick, etc. They are small sealed modules and a variety of outputs ratings are available for < $100 with efficiency > 85% and many newer examples are > 90% efficient.
The setup I've settled on is the following, based on 48v nominal[2] system.
Solar Array
80-100v
|
Solar Charger
|
LiFePo4
Battery
[40-53v]
|
Circuit
Protection
| <- Standard house wiring to point of use
|
| --- [12v DC Brick] -- short wire --> 12v devices
|
| --- [5v DC Brick] -- short wire --> 5v devices
1. There are lots of sources for dc-dc "brick" converter modules, such as these: https://www.artesyn.com/power-supplies/cat/148/isolated-dc-d...
1.1 Another affordable and available option is mean-well chassis-mount dc converters like this one: https://www.digikey.com/en/products/detail/mean-well-usa-inc...
2. "48v nominal" means anywhere from something like 44v to 60v depending on battery chemistry, state of charge and current loads on the system.
Slow Electricity: The Return of DC Power? (2016) - https://news.ycombinator.com/item?id=28216968 - Aug 2021 (230 comments)
Yes HVDC exist and are awesome for very long lines and for underwater uses. Yes, most appliances in a house today are DC.
That doesn't mean that making the in-between DC makes sense.