Is household DC in our future?

Dr. Keith

Not a doctor.
Dr. Keith
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After the riveting discussion of different AC voltage schemes used by different countries I thought a bit about what consumes electricity in my home. While the supply is purely AC, an awful lot of it is actually consumed as DC. Most of my electronics convert the AC to DC and most of my LED lights do the same. I was even looking at an AirCon unit that had a DC compressor. Admittedly, most of the fans and bigger appliances are built for AC and would be clumsy to manage on DC.

I remember watching a house being built over a decade ago and the owner paying for Cat-5 cable to every room to connect various computers. He has a wi-fi router now that makes all that wire superfluous so I asked him if he regrets it. He said the cost was rather minimal and seemed a good idea at the time.

That made me think that it would be a similar cost to run a parallel DC power system to handle the lighting and light electronics load of the home. The advantage would be a single high end central AC to DC converter instead of a hundred cheap ones throughout the house. It would also allow any onsite solar to be used as DC instead of inverting to AC and then converting back to DC.

I haven't really thought this all the way through or done the math on it, but when I count the number of small converters around my house it does seem odd. Every LED light, every wall wort, every USB converter, they just seem to add up to a lot of inefficiency. Maybe I'm completely wrong, maybe all those little converters are quite efficient.
 
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Current tech (ha ha) is to use DC for transmission lines. Seems they now have semiconductor based "transformers" to make up the voltage loss over the long distance lines. So, no need for AC just so we can use copper wound transformers.

So yeah, household DC may be in out futures.
 
It is very hard to change standardized infrastructure. You would have to throw out all of your electronics and/or buy multiple AC-DC converters.

Who pays for replacing AC generation and transmission systems, and why would they do it?
 
Motor options today include permanant magnet DC motors for greater efficiency. Used mostly in cordless tools now, to extend battery life. I wonder how much they would save for the biggest motor in any house, the air conditioner compressor?

Also, semiconductors are not 100% efficient, or they wouldn't need cooling. So yeah, some gains to having one DC voltage from generator to device.
 
slyjoe said:
Not all of your electronics would use the same DC voltage. Not all of your converters are the same are they?
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That was one of my first thoughts, but I figured there would be larger hurdles, frankly.

I assume a lot of the things I mentioned can be made to run efficiently within the USB standard, for instance. So that would give a place to start, but even USB-C may not allow for enough power for larger items. There is a ton of stuff made to run on 12 volts, but no, it is not uniform by any measure.

It's a half baked idea at best, more along the lines of a musing, really.
 
Is there any value in a dual system? A low voltage DC one for all the electronics and lighting and a higher voltage AC one for all the stuff that needs to heat or move stuff?

Is that just needlessly complicating things?
 
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3point14 said:
Is there any value in a dual system? A low voltage DC one for all the electronics and lighting and a higher voltage AC one for all the stuff that needs to heat or move stuff?

Is that just needlessly complicating things?
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I guess that is the question I'm asking.

Are all these converters inefficient or do they work just fine?
 
Dr. Keith said:
After the riveting discussion of different AC voltage schemes used by different countries I thought a bit about what consumes electricity in my home. While the supply is purely AC, an awful lot of it is actually consumed as DC. Most of my electronics convert the AC to DC and most of my LED lights do the same. I was even looking at an AirCon unit that had a DC compressor. Admittedly, most of the fans and bigger appliances are built for AC and would be clumsy to manage on DC.

I remember watching a house being built over a decade ago and the owner paying for Cat-5 cable to every room to connect various computers. He has a wi-fi router now that makes all that wire superfluous so I asked him if he regrets it. He said the cost was rather minimal and seemed a good idea at the time.

That made me think that it would be a similar cost to run a parallel DC power system to handle the lighting and light electronics load of the home. The advantage would be a single high end central AC to DC converter instead of a hundred cheap ones throughout the house. It would also allow any onsite solar to be used as DC instead of inverting to AC and then converting back to DC.

I haven't really thought this all the way through or done the math on it, but when I count the number of small converters around my house it does seem odd. Every LED light, every wall wort, every USB converter, they just seem to add up to a lot of inefficiency. Maybe I'm completely wrong, maybe all those little converters are quite efficient.
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It is a mess. Keep in mind I actually have installed such a system....in a 200+ ft mega-yacht. There actually are reasons for this in marine. But it is complicated and very expensive. I don't see it ever being common in residential at all.
 
Red Baron Farms said:
It is a mess. Keep in mind I actually have installed such a system....in a 200+ ft mega-yacht. There actually are reasons for this in marine. But it is complicated and very expensive. I don't see it ever being common in residential at all.
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That is an interesting take. Thanks for adding your experience. One of the places you see a lot of DC powered products is the RV/Marine market.

The trend I've seen in both seems to be moving everything possible over to the DC side of things and just having AC for high load items like AirCon, Microwaves and fridges. That makes it so most items are still workable when only on battery power and then you have a large converter for when you are on "shore" power.
 
Dr. Keith said:
Are all these converters inefficient or do they work just fine?
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Cost would be a complicating factor. Just a simple battery count (or power pack rating) for each DC device you have would show that they all run on different voltages ranging from 1.5V to 24V+.

Even if you could produce one of those voltages at 100% efficiency, you would need bloody thick wires to carry voltage that low around the house. Then you would need DC to DC converters to run the appliances that are not on this "standardized" voltage. And you are back to the converter efficiency issue again.
 
psionl0 said:
Cost would be a complicating factor. Just a simple battery count (or power pack rating) for each DC device you have would show that they all run on different voltages ranging from 1.5V to 24V+.

Even if you could produce one of those voltages at 100% efficiency, you would need bloody thick wires to carry voltage that low around the house. Then you would need DC to DC converters to run the appliances that are not on this "standardized" voltage. And you are back to the converter efficiency issue again.
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Thanks. That makes sense.
 
And while there are DC to DC transformers, see any phone charger in a car, you would need them on all devices, and transforming from AC isn't a big deal.

It seems like too much effort to rewire all houses and replace all major appliances. I do see those usb and 110 outlet becoming more common and so on. Maybe dedicated DC lines for running LED's.
 
casebro said:
Current tech (ha ha) is to use DC for transmission lines. Seems they now have semiconductor based "transformers" to make up the voltage loss over the long distance lines. So, no need for AC just so we can use copper wound transformers.

So yeah, household DC may be in out futures.
Click to expand...

There is no such thing as a DC transformer. Long distance high voltage DC power lines use large inverter/converter plants at either end to connect to power grids, and in lower power applications you can cut the DC using a semiconductor switch and run that though a transformer. Neither technology is suitable for residential power distribution. If you want USB, you can get wall plugs with built in USB adaptors right now for under $20.
 
What about in this scenario:
In the not so distant future, most households will own an electric car with a battery that can provide the power needs a household of four for about three days and combine that with a grid that has a lot of renewable/intermittent power.
We could have a house run on DC that is powered by the car, and have the car charged when electricity is cheap/abundant and the household could run off of DC at night and other times of low grid power.
Also, I thought AC is much better for long distance transmission of power.
 
portlandatheist said:
What about in this scenario:
In the not so distant future, most households will own an electric car with a battery that can provide the power needs a household of four for about three days and combine that with a grid that has a lot of renewable/intermittent power.
We could have a house run on DC that is powered by the car, and have the car charged when electricity is cheap/abundant and the household could run off of DC at night and other times of low grid power.
Also, I thought AC is much better for long distance transmission of power.
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Issues
1. Your energy storage system goes away if the car goes away.
2. Best for long distance transmission of power is high voltage DC.

Though there are a few devices in the house that does not need on demand power.
1. Fridges and freezers could be ok without power for a short time.
2. Hot water tanks could be made big and heated once every day or so.
3. Air conditioners could be made to run more moderately during peak times.
4. Recharging of batteries, especially electric powered car batteries.
 
rjh01 said:
Issues
1. Your energy storage system goes away if the car goes away.
2. Best for long distance transmission of power is high voltage DC.

Though there are a few devices in the house that does not need on demand power.
1. Fridges and freezers could be ok without power for a short time.
2. Hot water tanks could be made big and heated once every day or so.
3. Air conditioners could be made to run more moderately during peak times.
4. Recharging of batteries, especially electric powered car batteries.
Click to expand...

I assume you meant AC there? Or is there something I'm missing?
 
Hellbound said:
I assume you meant AC there? Or is there something I'm missing?
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HVDC is often used for long distance power transmission. The quick and dirty version is that the resistance of a power line goes up as frequency goes up due to skin effects and reactive losses. Because you require expensive inverter stations at either end of the HVDC line there are minimum break-even distances below which you are better off just accepting the additional losses of using AC.

https://www.energy.siemens.com/hq/en/power-transmission/hvdc/
 
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