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  1. #1
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    Will Thomas Edison's D/C dream come true?

    In the early days of electricity distribution there was almost a war between AC and DC electricity distribution between Edison's DC and GE/Teslas A/C Electrical distribution. In the end alternating current won due to Direct current's inability to travel efficiently over long distances at the time.
    It is now possible to run long distances with DC power. The problem seems to be in stepping down the high voltage, although any Electrical Engineer maybe able to correct me on this regarding the latest technology.
    With the huge take up of Solar panels and the fact that many appliances need DC power and require rectifiers to work on A/C power. Should we start to look at wiring houses in DC? This would allow more efficient use as there are always losses in rectifying and inverting electric current. There are many other reasons such as reduced "noise" etc. It would also be possible to run many appliances at lower non lethal voltages.
    I would be interested in other member's views. Any member's view who is more versed on the subject than I would be appreciated.

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    Thailand Expat David48atTD's Avatar
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    I have roof solar panels which produce DC, which is then run through an Inverter to connect to the power grid which is then inverted
    again to run the DC motor in the Washing Machine.

    Advantages of DC motors:

    • Speed control over a wide range both above and below the rated speed
    • High starting torque:
    • Accurate steep less speed with constant torque

    “Someone is sitting in the shade today because someone planted a tree a long time ago”

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    All appliances in our households are presently built for AC power. It will be very hard to change. But with solar roofs and battery storage long term it may be different.

    About transmission. The reason for AC was transformers which could step up voltage for transmision lines and then step down for houshold and industrial consumption. That way with voltage up and current down losses on electric cables were smaller. The same was not possible for DC. High voltage means low current and low losses on transmission lines. But over very long distances, thousands of km AC has problems as soon as the transmission line gets to the AC wavelength.

    For that reason today to transport power over very long distances actually DC is used. Google HVDC or look into this link. This has become possible because modern electronics are capable of transforming DC. Or not really directly, they first produce very high frequency DC which can then be transformed to the desired voltage and rectified to output DC.

    How Does HVDC Work

    The same method is used in modern power supplies. They are now much smaller and lighter and cheaper than they used to be, using the same method. First produce high frequency AC, transform then in small cheap transformers then rectify them.

    But building AC motors is also possible by modulating the AC frequency dynamid to needs. That method is used in electric cars, I believe. But I am not really sure without looking into it some more.
    "don't attribute to malice what can be adequately explained by incompetence"

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    Quote Originally Posted by David48atTD
    I have roof solar panels which produce DC, which is then run through an Inverter to connect to the power grid which is then inverted
    again to run the DC motor in the Washing Machine.
    This is my point. If you have solar panels and battery storage it would make more sense to have household electronics plugged directly into a DC power outlet rather than inverting the power to A/C then rectifying A/C bacK to DC to run your TV,computer etc even many refrigerators can run on DC power now. Also low power lighting such as LEDs etc run on DC. Electric ovens and hot plates can run on DC power. Air conditioners can also be made to run on DC power, so there is not much in a house where DC power cannot be utilised. I am interested to know what would be the downsides if any, as on my knowledge of electricity I cannot see any.

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    Thailand Expat VocalNeal's Avatar
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    Quote Originally Posted by Hugh Cow
    Also low power lighting such as LEDs etc run on DC.
    They do if you buy a DC "bulb" but the common ones found in Tesco are designed to plug into AC. They have all the conversion and drivers built in.

    Until such time as convenient manufacture, supply and price catches up it is easier to use "conventional" wiring.

    But yes you can buy small 12VDC fridges for camper vans etc. Washing machines I don't know.

    Quote Originally Posted by Takeovers
    But building AC motors is also possible by modulating the AC frequency dynamid to needs.
    DC motors are controlled by PWM (Pulse width Modulation) so that exists but maybe at smaller power levels like model electric trains and maybe even drones etc...
    Better to think inside the pub, than outside the box?
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    Quote Originally Posted by VocalNeal
    But yes you can buy small 12VDC fridges for camper vans
    But 12V means high current and a lot lof thick wiring. Not suitable for general household use. You need at least 120V to limit wiring cost. Which means you need conversion for almost any use. Sure it is possible to build any appliance for DC. With the same amount of mass production it would not be more expensive. It would be slightly more efficient when using solar panels and batteries. But it would mean the whole industrial production needs to change.

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    The problem with DC in the home is arcing when switching.
    To get enough power, voltage must be high and with high (relatively speaking here) voltage, you will get a big arc every time you switch something on or off.
    Switches would not last long and there is a fire hazard.

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    Sorry, the closest I come is being able to sing Whole Lotta Rosie when pissed.

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    I have a book on Tesla. Many out there. It covers the AC/DC battle. It's a bit thick but then so am I.

    The couple in the video are now sailing. Another prime example of self sufficiency. It may be worth while to watch if it holds you interest. Or you could wait a day or two and cold pizza will undoubtedly post another prison video thay may spark your fancy, ha ha.

    Cheers.......fish.

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    Custom user Neverna's Avatar
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    Quote Originally Posted by Hugh Cow View Post
    This is my point. If you have solar panels and battery storage it would make more sense to have household electronics plugged directly into a DC power outlet rather than inverting the power to A/C then rectifying A/C bacK to DC to run your TV,computer etc even many refrigerators can run on DC power now. Also low power lighting such as LEDs etc run on DC. Electric ovens and hot plates can run on DC power. Air conditioners can also be made to run on DC power, so there is not much in a house where DC power cannot be utilised. I am interested to know what would be the downsides if any, as on my knowledge of electricity I cannot see any.
    From a safety point of view, I have always been led to believe that DC is a bit more dangerous than AC because the voltage is constant in DC whereas AC goes through zero (think Sine wave), albeit very briefly .

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    Thailand Expat David48atTD's Avatar
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    Quote Originally Posted by Neverna View Post
    Quote Originally Posted by Hugh Cow View Post
    This is my point. If you have solar panels and battery storage it would make more sense to have household electronics plugged directly into a DC power outlet rather than inverting the power to A/C then rectifying A/C bacK to DC to run your TV,computer etc even many refrigerators can run on DC power now. Also low power lighting such as LEDs etc run on DC. Electric ovens and hot plates can run on DC power. Air conditioners can also be made to run on DC power, so there is not much in a house where DC power cannot be utilised. I am interested to know what would be the downsides if any, as on my knowledge of electricity I cannot see any.
    From a safety point of view, I have always been led to believe that DC is a bit more dangerous than AC because the voltage is constant in DC whereas AC goes through zero (think Sine wave), albeit very briefly .
    Just some fundamentals.

    'Voltage' is about potential difference.

    So the voltage difference between the 'average' of the Alternating Current (AC) sine wave to 'ground', in Thailand is 220V, in the USA 110V, in Australia 240V



    In Thailand it cycles 50 times a sec, so it passes thought '0' voltage (potential difference) only for a nanosecond. In the USA it cycles 60 times a second.

    Going back to Neverna's questioning statement ... it's not the voltage that usually kills you ... it's the amperage.

    The common safety devices are triggered when 15 - 30 milliamps are not returning through the circuit.



    I could rabbit on, but it just gets a bit technical.

    I'm actually a sparkie, but when I worked in the trade decades ago, it was all high voltage ... I worked for the local utility company.


    EDITed to add ... have a look at Japan 50Hz on one side of Japan, 60Hz on the other ... incompatible! https://www.fepc.or.jp/library/pamph...lectricity.pdf

    .
    Last edited by David48atTD; 01-06-2017 at 04:33 AM.

  13. #13
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    I should clarify I did not mean 12VDC at the GPO/wall outlet. I meant a higher voltage that was not going to need wires the thickness of a finger. IE around 100 - 220 volts which is what most countries currently use.

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    Quote Originally Posted by Neverna
    From a safety point of view, I have always been led to believe that DC is a bit more dangerous than AC because the voltage is constant in DC whereas AC goes through zero (think Sine wave), albeit very briefly
    Correct. And that's why you get arcing when switching DC. Think of disconnecting a car battery while something is on and you remove the positive first. Or the movies when they are going to torture someone with a car battery and jumper leads and the torturer ominously taps the leads together.
    Quote Originally Posted by David48atTD
    In Thailand it cycles 50 times a sec, so it passes thought '0' voltage (potential difference) only for a nanosecond.
    In one second it passes through 0 100 times and reaches peak high 50 times and peak low 50 times. A bit longer than a nanosecond, but I guess you were exaggerating deliberately to make the point .



    Quote Originally Posted by David48atTD
    it's not the voltage that usually kills you ... it's the amperage.
    Slight correction, it's ALWAYS current (amperage) that kills. Technically. Ohms Law could, I suppose, be used to argue volts could kill, simply because V and I are inversely related, but it's the passage of electricity that stops the heart, not the potential difference.

    Quote Originally Posted by Hugh Cow
    IE around 100 - 220 volts which is what most countries currently use.
    Thus, see above.
    Last edited by Maanaam; 01-06-2017 at 06:33 AM.

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    Custom user Neverna's Avatar
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    Quote Originally Posted by Maanaam View Post
    Quote Originally Posted by David48atTD
    it's not the voltage that usually kills you ... it's the amperage.
    Slight correction, it's ALWAYS current (amperage) that kills. Technically. Ohms Law could, I suppose, be used to argue volts could kill, simply because V and I are inversely related,
    Yes, and as in many examples, like in this example (the human body), if the resistance is constant, when the voltage changes, the current changes.
    Nev has style

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    Custom user Neverna's Avatar
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    Quote Originally Posted by Maanaam View Post
    Quote Originally Posted by Neverna
    From a safety point of view, I have always been led to believe that DC is a bit more dangerous than AC because the voltage is constant in DC whereas AC goes through zero (think Sine wave), albeit very briefly
    Correct. And that's why you get arcing when switching DC. Think of disconnecting a car battery while something is on and you remove the positive first. Or the movies when they are going to torture someone with a car battery and jumper leads and the torturer ominously taps the leads together.
    You also get arcing when switching AC.

    I don't know how it compares in severity to arcing when switching DC.

  17. #17
    Thailand Expat David48atTD's Avatar
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    When ever you are switching off, you will get arcing.

    The reason being that the electricity will want to continue to flow until it is interrupted.

    In most cases, that interruption is the air gap between the contacts.

    The insulation qualities of 'air' is about 30,000v/cm between two flat plates of metal.
    If the contacts are shaped differently, that gap reduces.

    The more current that flows, the more intense the spark.


    So, when switching is done 'under load' in a transformer yard etc, that air gap interruption solution is insufficient for
    the long term use of the equipment, oil is usually used to 'quench the arc'.





    But we digress ...

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    Quote Originally Posted by Neverna
    I don't know how it compares in severity to arcing when switching DC.
    Quite a bit, as David pointed out, with AC, you have a 100 points in time in one second where the voltage is zero. He pointed out how the sine wave averages out to 240V, BUT, the average of one cycle (and you get 50 cycles per second) is in fact zero.
    With DC, it is constant, thus always a much bigger arc for equal current and volts.

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    Why not a small capacitor to stop arcing?

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    Quote Originally Posted by Hugh Cow View Post
    Why not a small capacitor to stop arcing?
    You could, but if I recall properly from all those years ago, a capacitor for the job (and the resistor) for a 240 V circuit would be quite cumbersome I think. Don't think of the little electronic capacitors in a radio, these would be quite big. Think 1 kg of circuitry all boxed up. OK for say farm equipment where you have one switch at the back of the shed as a stand-alone unit, but you wouldn't want one at each light switch around the house.
    Think, too, of appliances. Each power point would have to be turned on and off at the wall....you would have to remember to not just plug the toaster in. And then, once on at the wall, you are actually switching at the toaster when you pop it down. I'm not sure if the distance of the toaster from the capacitor will reduce it's effectiveness but I think it would.

    I forget, TBH...will have to google.

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    I think the switch problem can be solved. They could go electronic switch, like so many items.

    IMO it is really the task of changing all the electric appliances and keeping stock of both AC and DC appliances for a long time in parallel that will make it inpractical. At the same time converting solar and battery outputs to AC becomes easier with advancing power electronics.

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    Quote Originally Posted by Takeovers View Post
    I think the switch problem can be solved. They could go electronic switch, like so many items.

    IMO it is really the task of changing all the electric appliances and keeping stock of both AC and DC appliances for a long time in parallel that will make it inpractical. At the same time converting solar and battery outputs to AC becomes easier with advancing power electronics.
    Yeah. I did a bit of a google and they now have solid state relays (showing my age). That would do, but I have no idea of the cost. They would surely be smaller than a capacitor-resistor set-up.

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    I am not an expert. But I see that there were huge advances in power electronics over the last decade. Both on cost and on reliability. Electronic switches will still be a little more expensive than mechanical ones.

    There is also the tendency to switch everything remotely which requires electronics. I guess you really need to switch on the light in your living room using your smartphone before you arrive at home.

    BTW this remembers me of my father who used to build high power high voltage switches for power plants at Siemens in Berlin.

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