Mercury Arc Rectification

Discussion in 'General Electronics Chat' started by Nicholas K. Heinrich, Nov 9, 2012.

  1. Nicholas K. Heinrich

    Thread Starter Member

    Feb 25, 2012
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    As I'm sure some of you are aware, Mercury Arc rectifiers look really cool. (One of my friends went as far as to liken it to an "Alien Uterus") I have been designing a coal gasification plant with power generation from the waste heat. I will have a large battery storage capacity, so all pumps and equipment will be DC. I was trying to justify to myself the use of Mercury Arc Rectifiers to convert 3 phase AC to DC when in reality I could just use a dynamo, simply because they look cool. Then I realized that all dynamos have commutators, and a rectifier could serve the same purpose. Am I correct in this thought?
     
  2. Kermit2

    AAC Fanatic!

    Feb 5, 2010
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    That was true, until Edison lost the AC/DC battle and AC generators and transformers became the method of least cost to distribute electricity.

    Sadly, the primacy of the commutated DC generator ended with him.

    Long live 3 phase AC

    All Hail Tesla!


    :)



    So, yea. A rectifier connected to an AC generator will serve the same purpose as a commutator, provided you have enough filter capacity and don't overload it. If to much current is drawn the filter will not function properly and you will have AC riding on a DC level above ground.
     
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  3. Nicholas K. Heinrich

    Thread Starter Member

    Feb 25, 2012
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    Filter? Hahaha, no, I am talking 500kw... And Mercury Arc Rectifiers are capable of 250A at 240V each. However many I need I will use. It will have a 7.92 million amp-hour battery bank, that should smooth it out right? The battery bank will be able to supply the 500kw for 24 hours if the plant goes down.
     
  4. Kermit2

    AAC Fanatic!

    Feb 5, 2010
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    500 Kilowatts!

    Where are you getting the 700-1000 horsepower needed to turn a 500KW genny?
     
  5. crutschow

    Expert

    Mar 14, 2008
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    250A silicon rectifiers are readily available in the voltage you need. I hope your are not seriously considering using mercury arc rectifiers with their reduced reliability, hazardous content, and higher forward voltage drop (11V or so compared to 1V or so) just because mercury vapor rectifiers are "cool".

    Is this some type of homework project?
     
  6. Nicholas K. Heinrich

    Thread Starter Member

    Feb 25, 2012
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    Accounting for an 80% efficiency, I was going for a raw 660kw. Or maybe a raw 666kw for kicks. Anyways, gasifying coal requires burning coal, also it produces coal tar, and hydrogen sulfide, all of which burn. Waste heat = Steam. A heavy oil engine will burn the coal tar. It may also gasify some biomass for another engine. So I could probably easily produce more than 1000Hp. Mercury arc rectifiers and Mercury vapor rectifiers are different things, and Mercury are rectifiers are far from unreliable, they used them for subway systems all the way into the 2000's... This plant would be utilizing waste heat, so voltage drop and efficiency is not my main concern. Half the purpose of the design is to be "cool". The process of coal gasification produces toxic waste anyway, so mercury isn't a big concern, if handled safely and responsibly. This is not a school project, rather something for my own enjoyment, which I will build when I have $3m+ to do so with.
     
    Last edited: Nov 9, 2012
  7. vk6zgo

    Active Member

    Jul 21, 2012
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    Although they were used for many years,they can be ,& mainly have been, replaced by solid state devices.

    Gaseous Rectifiers may be made still for replacement purposes,but I suggest you look around & see what devices are used in those Electric Railway systems which still use DC,as they would be of a similar order of magnitude to what you want to do.

    Many modern Railway systems use AC,with the rectification done on board the train,which would have been difficult to do with gaseous rectifiers.
     
  8. Nicholas K. Heinrich

    Thread Starter Member

    Feb 25, 2012
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    I know it can be replaced with solid state, however it is designed to be reminiscent of the early to mid 1900's. It will have brickwork, cast iron, piston steam engines, brass, fuses, old incandescent lighting, motor-generator sets, knife switches, etc. Hence the 80% projected efficiency. I am aware of the typical configuration of a 3 phase full wave bridge rectifier, however, it eludes me how that would work with mercury arc rectifiers.
     
    Last edited: Nov 10, 2012
  9. Nicholas K. Heinrich

    Thread Starter Member

    Feb 25, 2012
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    A mercury arc rectifier or (MAR) as I am now going to abbreviate them, have all phases going from one anode per phase, to one cathode for all phases, that being the liquid mercury pool.
     
  10. Kermit2

    AAC Fanatic!

    Feb 5, 2010
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    Then, if you don't need our help right now, what was the purpose of this post?

    Bragging rights?
     
  11. Nicholas K. Heinrich

    Thread Starter Member

    Feb 25, 2012
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    The purpose of this post is that I wanted to know, it is simply a question, purely out of curiosity. I have no idea how asking the question or making the post would give me any bragging rights... If I needed help right now, I would have posted this in the projects forum, not general electronics chat. I asked a question, that being "Will a rectifier serve the same purpose as a commutator?" I was given the answer yes. I then posed another question, that being "How would I achieve full wave rectification with MAR's?". I have yet to receive an answer. The point of this thread is that of asking a question, the point of which is to learn the answer from knowledgeable people whether I need to know or not. Surely you are not implying that asking a question out of curiosity is wrong?
     
  12. BillB3857

    Senior Member

    Feb 28, 2009
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  13. Nicholas K. Heinrich

    Thread Starter Member

    Feb 25, 2012
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    Ignitrons are similar to MAR's, however because they are single phase devices, they work like a diode. In a bridge rectification circuit, each phase is connected to the cathode of one diode, and the anode of another. This allows the current to be "pushed" into diode with its anode connected while the voltage is on the positive part of the sine wave, and "pulled" through the diode with its cathode connected while the current is on the negative part of the sine wave. However because MAR's have one anode per phase, but only one cathode for all phases, it would be required that one connect all phases to the cathode lead. Connecting all phases to one wire is simply a massive short circuit. I have decided to use 6 phases produced by two staggered three phase generators to produce a smoother DC current. I have also decided to use an MAR to rectify the voltage when it is on the positive side of the sine wave, and standard high current diodes for the negative half of the wave. This allows for easier maintenance of the setup, as well the preservation of the look of MAR's.
     
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