Switching from AC grids to DC grids

[HAL-42b]

I am not really advocating a move to DC, just enjoying the conversation so far. Blindly sticking with old ideas will get us nowhere while change for the sake of change is not helpful either. The question is: With all the new tech and knowledge from the past 100 years, is AC outdated so bad that there is a real tangible benefit to such a massive change? Clearly there are some benefits and some drawbacks.

There is a demand towards incorporating renewables and making local storage easier. We also have many small gadgets that need energy. Whoever meets that demand will make money.

Other than that we already have time proven DC distribution onboard every vehicle, the outlets suck though.

[Monkeh]

Do the DC fanboys here realize that a typical 16A household circuit breaker (of which you will have dozens in a typical distribution box for a family home) for 230V AC here is rated to reliably interrupt short-circuit currents of up to 10000A, has the size of a box of cigarettes and cost 2.95EUR retail.

That a PIA* (1 phase or 2 phase)cost 2.95€ will be from the china, because in Spain it costs over 12€ of the Merlin-Gerin corporation

http://www.portalelectricidad.es/fabricante/merlin-gerin-automaticos

* PIA = Small Automatic Interrupt

That's because you're getting screwed, not because they're expensive.

[sync]

That is true about the isolation, and maybe an argument for a dedicated high power rail. Although 4 element resistive heater is not that big of a deal. For the connectors, there is no need to have all of them available on all outlets. Only the high power loads need the high power. Normal around the house outlets would be fine with only 4 wires

What a regression. Here in Germany we have one type of outlets at home. We use them for low power devices up to kettles, washing machines, dryers, (mobile) space heaters, etc. This is a flexibility I didn't want to give up.

[rx8pilot]

That is true about the isolation, and maybe an argument for a dedicated high power rail. Although 4 element resistive heater is not that big of a deal. For the connectors, there is no need to have all of them available on all outlets. Only the high power loads need the high power. Normal around the house outlets would be fine with only 4 wires

What a regression. Here in Germany we have one type of outlets at home. We use them for low power devices up to kettles, washing machines, dryers, (mobile) space heaters, etc. This is a flexibility I didn't want to give up.

A 30A dryer uses the same plug as a 10A kettle?

In the US, we have 15A, 20A 120v plugs in houses but mainly 15A. Then there are 30A, 40A 220v types for dryers and stoves. At least those are the common ones seen in houses. 3-4 different types.

[TassiloH]

Do the DC fanboys here realize that a typical 16A household circuit breaker (of which you will have dozens in a typical distribution box for a family home) for 230V AC here is rated to reliably interrupt short-circuit currents of up to 10000A, has the size of a box of cigarettes and cost 2.95EUR retail.

That a PIA* (1 phase or 2 phase)cost 2.95€ will be from the china, because in Spain it costs over 12€ of the Merlin-Gerin corporation

Ripoff. I'd think Eaton a reasonable brand, and here you go:
http://www.pollin.de/shop/dt/Mjg5OTM3OTk-/Haustechnik/Installationsmaterial/Schaltgeraete/Leitungsschutzschalter_EATON_PXL_B16_1.html
Retail 2.50 in a shop selling to private customers.

[sync]

A 30A dryer uses the same plug as a 10A kettle?

Yes dryers, kettles use the same plug. We have 3 types of plugs which fit into the same type of outlet: 10A/16A with PE, 10A/16A without PE and the smaller 2.5A europlug.

Our dryers at home don't need 30A because of 230V mains voltage.
edit: I didn't noticed that your 30A dryer sockets are 220V. So our dryers didn't have as much power available.

[rx8pilot]

They electric dryers here are on 220-240v at 30A. Maybe we are less patient and feel the need to blast our clothes with near thermonuclear heat. 

In our daily life though, the vast majority of people are only seeing one type of plug - the NEMA 5-15 15A/120v for just about everything. The high power plugs for stoves or dryers are hidden and rarely noticed.

[HAL-42b]

They electric dryers here are on 220-240v at 30A. Maybe we are less patient and feel the need to blast our clothes with near thermonuclear heat. 

This explains why dryer lint catching fire and burning down the house is so common 

[sync]

Back to the DC only powered home. IMHO a standard outlet should provide 2kW or more.

[rx8pilot]

Back to the DC only powered home. IMHO a standard outlet should provide 2kW or more.

Here in the US, we get 1875W from a normal outlet and it does not feel like a major limitation.

[vodka]

They electric dryers here are on 220-240v at 30A

That bestly, you leave more profitable  have a thripahsic conection

[sync]

Back to the DC only powered home. IMHO a standard outlet should provide 2kW or more.

Here in the US, we get 1875W from a normal outlet and it does not feel like a major limitation.

That's about 2kW. We have nominal 2.3kW (10A) continuously.

[HAL-42b]

Back to the DC only powered home. IMHO a standard outlet should provide 2kW or more.

How about this?



At 16A per phase it could provide 3000W total. Accepts any combination of loads. Just an idea.

[rx8pilot]

The downside would be load balancing, if all the loads were on a single leg that leg would be over loaded while the others idle.

[HAL-42b]

That would be a problem on an AC system but not as much here. The real problem would be the number of conductors.

[rx8pilot]

If you have 4 isolated supplies and only one of them is loaded with the all the things in the house, you would need supplies that are each capable of supplying the whole house = a huge waste. Some sort of smart management would be needed OR you would need 48v supplies that are 4x the needed size.

The load, ideally, would be reasonably distributed among the (4) 48v rails.

[ndunnett]

Like we save energy by boiling kettles slower?

No by using low power kettles.

Energy is a function of power and time. Using a lower power kettle will use at least as much (probably more) energy as a higher power kettle.

I think something else DC fanatics are overlooking is infrastructure - for Australia at least (European homes are probably very similar) your typical circuit for 2.3kW socket outlets will be on a 20A circuit breaker ($20-30) with approx. 100 metres of 2.5mm2 twin core and earth cable ($100-150). By going from 230VAC to even 100VDC, you will need a 50A DC circuit breaker (unknown, at least triple the cost of AC C/B) and at least 10mm2 cable ($500). The cost difference is going to be similar for all circuits as well as your consumer mains, sub mains, etc. so for a new house, what might have been an $8000 invoice from the electrician is now going to be $40000-50000 simply due to extra cost of materials. Galvanic isolation and fault current protection are additional issues that have already been mention and will cost more on top of that. From there, the local distribution network is going to be nowhere near big enough, and neither is the transmission system feeding it, not to mention lots utilities actually generate power in AC so either massive rectification plants or new utilities would have to be built. Costs for that would run a long way into the billions for a place like Australia or Europe. Never going to happen.

[rx8pilot]

Whaaaa?

20A at 220v = 4.4Kw
100VDC at 50A = 5Kw

That sounds fanatic to me. In the USA, we use 120V at 15A for the vast majority of household needs. Only hairdryers and toasters max a circuit like that. Circuit protection is CHEAP whether its DC or AC.

[HAL-42b]

If you have 4 isolated supplies and only one of them is loaded with the all the things in the house, you would need supplies that are each capable of supplying the whole house = a huge waste. Some sort of smart management would be needed OR you would need 48v supplies that are 4x the needed size.

The load, ideally, would be reasonably distributed among the (4) 48v rails.

This reduces the number of conductors to 5 but still doesn't solve the load balancing issues.



For load balancing the most sensible way would be to have one single phase. But then the voltage would have to be high.

[krish2487]

Or,


It is as good (or as dumb, can be seen either way really) - start with the DC equivalent of 110/220V really.
Since most of the household appliances are designed for 340V+ DC (in case of 220V AC).
Dispense with the input bridge rectifier (or keep it) and switch to DC grid.


As far as I can forsee (not too far really), the only major concern will be that of switchgear and circuit breakers. Since the rest of the electronics are designed to run off the rectified DC anyway.

[/size][size=78%]It is as good a start as any. [/size]

[rx8pilot]

In my proprietary system, I use bi-directional communication to determine the voltage/current that will be delivered. It takes all human decisions out, they just plug in and go. My design is for a specific commercial use, but the concept could work in a house. It would allow low-voltage/low power up to high voltage/high power to be automatically negotiated and managed while using existing 3 wires and a single plug.

It does buy a substantial safety benefit because all the lines are very low power until they are activated by a successful negotiation. When the system is active, it sends a heartbeat pulse and if that heartbeat is disturbed, the branch shuts off. I am not saying this is a reason to go DC, its just an existing device that I build that has some merit.

I like the safety component that makes it very difficult to get electrocuted - even if you stick a piece of metal into the connector.

[ndunnett]

Whaaaa?

20A at 220v = 4.4Kw
100VDC at 50A = 5Kw

One circuit has more than one outlet on it (usually 10 or more), and miniature circuit breakers are generally only available in common sizes. 4.4kW at 100V is 44A, next biggest size of commonly available protective device is 50A. Smallest cable with a great enough CCC before taking into account derating factors is actually 16mm2 (I made a mistake before) and that is without considering fault loop resistance and voltage drop.

That sounds fanatic to me. In the USA, we use 120V at 15A for the vast majority of household needs. Only hairdryers and toasters max a circuit like that. Circuit protection is CHEAP whether its DC or AC.

As I've said above, that one circuit might have your hair dryer, hair straightener, toaster, TV, xbox, microwave oven, and PC all on the one circuit, all running at the same time. Putting a single outlet on a circuit is just silliness. In Australia we have a similar system to Europe, our general purpose outlet is 230V 10A, and that is what is used for >90% of domestic appliances. You might need a 15A or 20A outlet for welders, small lathes, etc. or large kitchen appliances for example, and generally those outlets have dedicated circuits. I suppose if an entirely new system was introduced you could get away with smaller general purpose outlets, but I (as well as probably a lot of people) really like the simplicity of only needing one type of outlet for most commonly used items

[sync]

Since most of the household appliances are designed for 340V+ DC (in case of 220V AC).
Dispense with the input bridge rectifier (or keep it) and switch to DC grid.

My central heating, dish washer, washing machine, refrigerator, fans, audio amp, turn tables, alarm clocks and most of my test gear is definitive AC only. That's way over 20000€ of devices. And probably the SMPS powered gear doesn't work on DC as well because the PFC doesn't like it.
That's the real problem for a transition to DC only. Backwards compatibility. It doesn't make sense to invest tens of thousands for the installation and new devices to save a few hundreds.

[rx8pilot]

My central heating, dish washer, washing machine, refrigerator, fans, audio amp, turn tables, alarm clocks and most of my test gear is definitive AC only. That's way over 20000€ of devices. And probably the SMPS powered gear doesn't work on DC as well because the PFC doesn't like it.
That's the real problem for a transition to DC only. Backwards compatibility. It doesn't make sense to invest tens of thousands for the installation and new devices to save a few hundreds.

There is little question that a transition would be costly. The only way it will be acceptable on a large scale is that is gradually changes over time. Even that would only happen if the general public saw a benefit - which most wont care.

[sync]

There is little question that a transition would be costly. The only way it will be acceptable on a large scale is that is gradually changes over time. Even that would only happen if the general public saw a benefit - which most wont care.

Is there real, big enough benefit? I doubt it. For some niches sure. But not general.