Will we have HVDC in home socket one day?

[JHZR2]

I don’t think it makes sense.

AC is robust. You can easily protect with breakers. Transformers are very efficient and long lived.

And, it’s not really clear what OP is actually talking about powering...

20A at 120V is ubiquitous. And it’s over 2kW. OP have you ever handled something dissipating 2kW? It’s not easy or safe.

DC will require DC/dc converters, which do so via high frequency AC and a high frequency transformer. It’s reliant on switching which isn’t as robust or long lived.

What’s the problem we are trying to solve by creating another DC power distribution system in the home?

Sounds like a solution in search of a problem.

I can see the normal power for a home going from 200A to a higher amount, maybe 500A, to service EV charging better. Beyond some point you go three phase and breakers get $$$.. I’d have my doubts that this will happen, but I can envision 208 3-phase becoming the norm into homes to support EVs, if people are so inclined, neighborhoods are new and have the infrastructure, etc. With 208 3-phase you can get 120v so still use the perfectly fine legacy voltage.

SiC and GaN will shrink power conversion...

 

[PandaBear]

Also, there is a problem with running a switching power supply from a switching power supply. The first one has to have an extra large filter capacitor, or a battery on its output to handle the current spike load of the second switcher it is supplying power to.

There was a thread here on BITOG more than a year ago where someone was trying to run a switcher from a switcher and it would not work even though the output of the first one supplying power to the second one was rated at more than what the RMS draw of the second one. The pulse draw of the second one exceeded the amount of current the first one could supply, and the first one could not maintain voltage, and therefore the second one did not get a high enough input voltage and second one would not work.

In other words if somewhere further up the feed to the DC plug in the house there was a switcher reducing the voltage, and it was feeding a switcher in something like a computer, then the first one would have to have extra large output filter capacitor(s).

I see, so this is why a lot of the power supplies use "phases" of many VRMs instead of stages of high to low voltage conversion. Or in your example it likely needs both switchers to be controlled by the same controller and switched synchronously.

 

[PandaBear]

I don’t think it makes sense.

AC is robust. You can easily protect with breakers. Transformers are very efficient and long lived.

And, it’s not really clear what OP is actually talking about powering...

20A at 120V is ubiquitous. And it’s over 2kW. OP have you ever handled something dissipating 2kW? It’s not easy or safe.

DC will require DC/dc converters, which do so via high frequency AC and a high frequency transformer. It’s reliant on switching which isn’t as robust or long lived.

What’s the problem we are trying to solve by creating another DC power distribution system in the home?

Sounds like a solution in search of a problem.

I can see the normal power for a home going from 200A to a higher amount, maybe 500A, to service EV charging better. Beyond some point you go three phase and breakers get $$$.. I’d have my doubts that this will happen, but I can envision 208 3-phase becoming the norm into homes to support EVs, if people are so inclined, neighborhoods are new and have the infrastructure, etc. With 208 3-phase you can get 120v so still use the perfectly fine legacy voltage.

SiC and GaN will shrink power conversion...

Originally I though going to DC switching would be more efficient, at least at the last mile, by centralizing some (say 408V or 750V AC) to 120VAC conversion and make them a DC that can power heat pump like device (AC, water heater, fridge) more efficiently and let them have DC input for variable frequency / load running without an AC to DC then back to AC conversion.

I guess if this centralized DC last mile is not efficient, or safe, vs a 3 phase 208, then it really doesn't do much for the complexity. I guess it means 3 phase would make more sense than going DC based home unless you have solar (which from what I heard many have tried to power a switching power supply directly, and would work fine as long as it doesn't overheat by using only 2 of the 4 H bridge diodes instead of all 4 evenly.

Would this work? Using a computer SMPS as a DC-DC converter

I have this crazy idea of using a computer SMPS with active PFC boost to take high voltage DC battery banks (144V+) and drop it down to 3.3V, 5V and 12V. Here's my thinking: the power supply inter...

electronics.stackexchange.com

Maybe it really is a solution searching for a problem.

 

[OVERKILL]

Originally I though going to DC switching would be more efficient, at least at the last mile, by centralizing some (say 408V or 750V AC) to 120VAC conversion and make them a DC that can power heat pump like device (AC, water heater, fridge) more efficiently and let them have DC input for variable frequency / load running without an AC to DC then back to AC conversion.

I guess if this centralized DC last mile is not efficient, or safe, vs a 3 phase 208, then it really doesn't do much for the complexity. I guess it means 3 phase would make more sense than going DC based home unless you have solar (which from what I heard many have tried to power a switching power supply directly, and would work fine as long as it doesn't overheat by using only 2 of the 4 H bridge diodes instead of all 4 evenly.

Would this work? Using a computer SMPS as a DC-DC converter

I have this crazy idea of using a computer SMPS with active PFC boost to take high voltage DC battery banks (144V+) and drop it down to 3.3V, 5V and 12V. Here's my thinking: the power supply inter...

electronics.stackexchange.com

Maybe it really is a solution searching for a problem.

The problem with trying to frame grid policy around rooftop solar is that at some point penetration will need to be curtailed for grid-tie systems, which dovetails into my next point:

Big spinny things.

AC grid equipment, mostly large turbines, keep the grid stable. While HVDC is a good fit for long transmission hauls between disparate grids (intentionally not synch'ing their frequency) that doesn't mean that HVDC is a viable, or even logical, option for grid construct.

AC has numerous benefits that @JHZR2 has touched on, including the ability to be phased, stepped...etc. Most large generators (nuke plants, gas plants, coal plants, hydro dams...etc) are AC and play that critical role in providing inertia and stability to balance the loads coming on and off the grid.

I see no benefit in trying to reinvent the grid to better fit a technology that will never be able to provide the value necessary to make the investment worthwhile. The mild complication of conversion behind the meter for VRE installs is far better kept there then trying to make everything DC to avoid that IMHO.

 

[JHZR2]

Originally I though going to DC switching would be more efficient, at least at the last mile, by centralizing some (say 408V or 750V AC) to 120VAC conversion and make them a DC that can power heat pump like device (AC, water heater, fridge) more efficiently and let them have DC input for variable frequency / load running without an AC to DC then back to AC conversion.

I guess if this centralized DC last mile is not efficient, or safe, vs a 3 phase 208, then it really doesn't do much for the complexity. I guess it means 3 phase would make more sense than going DC based home unless you have solar (which from what I heard many have tried to power a switching power supply directly, and would work fine as long as it doesn't overheat by using only 2 of the 4 H bridge diodes instead of all 4 evenly.

Would this work? Using a computer SMPS as a DC-DC converter

I have this crazy idea of using a computer SMPS with active PFC boost to take high voltage DC battery banks (144V+) and drop it down to 3.3V, 5V and 12V. Here's my thinking: the power supply inter...

electronics.stackexchange.com

Maybe it really is a solution searching for a problem.

Again, what’s the problem you’re trying to solve?

I think you’re saying that since VFDs are more prevalent, and VFDs take AC, make dc on an internal link, then make AC with a varying wave form, why not take care of one of those steps elsewhere?

But rectification is lossy. And if your rectified AC isn’t exactly what a load wants, then it just needs to be changed again. And, not everything is fed from the VFD.

Could there be some efficiency from fewer big rectifiers versus more small ones? Maybe. But there’s also the chance of more/different harmonics at different points in the grid, more lossy and noisy rectification when the loading is low, etc. If it was a panacea, the concept would be broadly pushed. It isn’t Some level of local micro grid, with dc for common renewables connection, energy storage, vehickes charging and dispatching back to the grid, etc. has been looked at. But again, if the interface isn’t right, another set of conversions still needs to be done. And that’s for other reasons than what you’re asking.

 

[PandaBear]

Again, what’s the problem you’re trying to solve?

I think you’re saying that since VFDs are more prevalent, and VFDs take AC, make dc on an internal link, then make AC with a varying wave form, why not take care of one of those steps elsewhere?

But rectification is lossy. And if your rectified AC isn’t exactly what a load wants, then it just needs to be changed again. And, not everything is fed from the VFD.

Could there be some efficiency from fewer big rectifiers versus more small ones? Maybe. But there’s also the chance of more/different harmonics at different points in the grid, more lossy and noisy rectification when the loading is low, etc. If it was a panacea, the concept would be broadly pushed. It isn’t Some level of local micro grid, with dc for common renewables connection, energy storage, vehickes charging and dispatching back to the grid, etc. has been looked at. But again, if the interface isn’t right, another set of conversions still needs to be done. And that’s for other reasons than what you’re asking.

Yeah I think you pretty much sums up what I was thinking of. In a way it is likely not worth the trouble outside of solar home between the panel and VFD devices. Maybe a point to point link between them is all that's needed (say, a standard between Carrier / Trane / Tesla / Panasonic / LG), or maybe other DC electronics with battery backup moved internal to the system (like laptop battery based UPS sitting between power supply and the server / computer).

Sounds like if we ever need more power and efficiency, 3 phase AC is the better choice.

 

[MolaKule]

In this way it only requires a small trigger pulse on the gate to turn the thyristor on. Once switched on, the thyristor can only be turned off by removing the supply voltage.

That was the point I was making. In an AC system you have a positive excursion of the Sine Wave from 0 voltage to maximum positive, then it goes from maximum to zero, then it goes to a maximum negative value, then back to zero.



It is the negative voltage excursion of the sine wave in an AC system that switches "OFF" the thyristor.

The AC voltage available in our local home sockets averages 122Vrms or 173 volts peak, so the power transformer secondary that feeds the house is putting out 345 volts peak, or 244 Vrms.

Split-phase electric power - Wikipedia

en.wikipedia.org

The primary side of the power transformer transformer outside is being fed 14.460kV which is "stepped-down" to 244V using the theory of voltage transformation via induction, a voltage reduction (voltage transformation) ratio of 60 to 1 (60:1).

StackPath

 

[sdowney717]

High voltage DC is about impossible to switch off reliably, it just arcs and burns up switches. AC since it cycles thru zero voltage, it is much safer plugging-unplugging and switching off. So mechanical switches are OUT of consideration. Plugs will burn up fast if you unplug a working high amp appliance.

 

[Fitter30]

Downtown saint louis missouri had dc in some office buildings in 1973. Think they ran elevators the ones that still had operators.

 

[4WD]

SCR or mosfet current controllers.

We have some older SCR/DC equipment and it’s getting harder to find techs who know these systems.
Everything newer is AC/VFD/IGBT.

 

[brianl703]

20A at 120V is ubiquitous. And it’s over 2kW. OP have you ever handled something dissipating 2kW? It’s not easy or safe.

If the 80% rule applies (a continuous load, defined as one exceeding 3 hours in duration), then it's not quite 2kW because you can only pull 80% of 20 amps, or 16 amps.

 

[brianl703]

Transformers are far more reliable than anything electronic that might be used to convert DC to DC (buck or boost converter).

 

[JHZR2]

If the 80% rule applies (a continuous load, defined as one exceeding 3 hours in duration), then it's not quite 2kW because you can only pull 80% of 20 amps, or 16 amps.

Very few loads in a home are considered continuous in that regard. But point taken.

 

[brianl703]

Very few loads in a home are considered continuous in that regard. But point taken.

There's also a UL standard involved as well, which is why with a very few exceptions you won't find any 120V appliance (with a 15 amp plug) that pulls more than 12 amps (which is 80% of 15 amps). One notable exception is hairdryers.

 

[JimPghPA]

Electric motors that are set up to run on 3 phase are easier to start, more efficient, and last longer than single phase electric motors.

Almost every home has a refrigerator and they have electric motors. One decent size one for the compressor, and one or two small ones for fans. Three are electric motors in AC systems, force air furnaces, attic vent fans, bathroom vent fans, freezers, sump-pumps, radon vent fans, washing machines, clothes dryers, small fans, and some other items.

So there are more electric motors being used in homes that first meets the eye.

 

[JimPghPA]

Transformers are far more reliable than anything electronic that might be used to convert DC to DC (buck or boost converter).

And simple AC transformers are much more tolerant of spikes in the line from distant lightning strikes.

 

[JimPghPA]

Just for the fun of it, how many of you out there know what a saturable reactor AC variable power controller is and how it works?

 

[ArrestMeRedZ]

I think I've figured out where home DC power makes sense. Solar produces low voltage DC, which is used to charge batteries (in some cases), but more often just converted to AC to power the conventional home and feed excess back into the grid. It is not an efficient process.
In that home are a number of devices (LED lighting, monitors, computers, etc.) that would work more efficiently on low volt DC.
Dedicated low voltage DC circuits would save the electrical and device inefficiencies of upconverting DC solar production to household AC and then downconverting it back to low voltage DC in each device.
Combine a few panels with a power wall and you could cheaply and efficiently provide for your household needs outside of HVAC and heavy appliances.

 

[JimPghPA]

I think I've figured out where home DC power makes sense. Solar produces low voltage DC, which is used to charge batteries (in some cases), but more often just converted to AC to power the conventional home and feed excess back into the grid. It is not an efficient process.
In that home are a number of devices (LED lighting, monitors, computers, etc.) that would work more efficiently on low volt DC.
Dedicated low voltage DC circuits would save the electrical and device inefficiencies of upconverting DC solar production to household AC and then downconverting it back to low voltage DC in each device.
Combine a few panels with a power wall and you could cheaply and efficiently provide for your household needs outside of HVAC and heavy appliances.

That would be a good direction to start in, but there may be some need for voltage regulation, or not. Some devices are quit happy with any DC voltage in a wide range, like 10 to 22 VDC ( just a wild guess on those values ). While others may only work if the incoming DC is within a very narrow range ( like 11.5 to 13.8 VDC ) ( another wild guess just as an example ). Though if home DC becomes popular and solar is a common supplier with a known normal range of voltage, it may be that makers of devices take that into consideration when designing the power-supply of devices.

 

[Skippy722]

I think I've figured out where home DC power makes sense. Solar produces low voltage DC, which is used to charge batteries (in some cases), but more often just converted to AC to power the conventional home and feed excess back into the grid. It is not an efficient process.
In that home are a number of devices (LED lighting, monitors, computers, etc.) that would work more efficiently on low volt DC.
Dedicated low voltage DC circuits would save the electrical and device inefficiencies of upconverting DC solar production to household AC and then downconverting it back to low voltage DC in each device.
Combine a few panels with a power wall and you could cheaply and efficiently provide for your household needs outside of HVAC and heavy appliances.

You would still need individual power supplies, like what we currently have, for your LED lights. You wouldn’t be able to just plug them directly into a low voltage DC circuit without frying the LED’s. Same with computer monitors and PC’s.