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Mercury arc valves


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#1 Kimmo

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Posted 06 May 2009 - 10:07 PM

A mercury arc valve (mercury vapor rectifier) is a type of electrical rectifier which converts alternating current into direct current. Rectifiers of this type were used in electric motor power supplies for industry, in electric railways, streetcars and electric locomotives. They also found use in static inverter stations and as rectifiers for high-voltage direct current power transmission. Mercury arc rectifiers were invented by Peter Cooper Hewitt in 1902 and further developed throughout the 1920s and 1930s by researchers in both Europe and North America. Before the advent of solid-state devices, mercury arc rectifiers were one of the more efficient rectifiers. By 1975, high-voltage solid state devices such as the silicon diode and thyristor made the mercury arc rectifier obsolete even in high-voltage DC applications.

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One type of mercury vapor electric rectifier consists of an evacuated glass bulb, with a pool of liquid mercury sitting in the bottom as the cathode. Over it curves the glass bulb, which condenses mercury evaporated in the course of operation of the device. The glass envelope has one or more arms with graphite rods as anodes. Their number depends on the application. If direct current is to be produced from single-phase alternating current, then two anodes are used, each connected to the outer ends of a centre-tapped transformer secondary winding. With three-phase alternating current three or six anodes are used, to provide a smoother direct current. Six-phase operation can improve the efficiency of the transformer as well as providing smoother DC, by enabling two anodes to conduct simultaneously.

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Operation of the rectifier relies on an electrical arc discharge between electrodes in a sealed envelope containing mercury vapor. A pool of liquid mercury acts as a self-renewing cathode that does not deteriorate with time. The mercury emits electrons freely, whereas the carbon anodes emit very few electrons even when heated, thus rectifying action occurs.

Once an arc is formed, electrons are emitted from the surface of the pool, causing ionization of mercury vapor along the path towards the anodes. The mercury ions are attracted towards the cathode, and the resulting ionic bombardment of the pool maintains the temperature of the 'emission spot', so long as a current of a few amperes continues.

The mercury ions emit light at characteristic wavelengths, the relative intensities of which are determined by the pressure of the vapor. At the low pressure within a rectifier, the light appears pale blue-violet and contains much ultraviolet light.

http://en.wikipedia....rcury_arc_valve

In operation, the pear-shaped bulb glowed a fiendish violet-green while tears of condensed mercury ran down within. Compared with the alternative rotary AC-to-DC converter based on heavy engineering electric motor technology, the somewhat awe-inspiring mercury vapour rectifier was small, silent, vibration free, reliable and efficient.

http://www.abdn.ac.u...ected.php?id=46

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More: http://www.electrics...uk/mercarc.html

#2 LogicprObe

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Posted 06 May 2009 - 10:10 PM

How can you not love this stuff?

#3 Kimmo

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Posted 06 May 2009 - 10:11 PM

I dunno, maybe if you broke one...?

#4 LogicprObe

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Posted 06 May 2009 - 10:27 PM

I might have one among the heaps of valves I've got. Some boxes I haven't even opened yet!

#5 eveln

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Posted 06 May 2009 - 10:28 PM

They look like something out of Doctor Who. Evil looking.

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#6 LogicprObe

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Posted 06 May 2009 - 10:30 PM

They look like something out of Doctor Who.
Evil looking.


Bah!

They're beautiful!

#7 Hobo Man

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Posted 06 May 2009 - 10:31 PM

They look like something out of Doctor Who.
Evil looking.


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They look awesome though

Edited by Hobo Man, 06 May 2009 - 10:31 PM.


#8 Kimmo

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Posted 06 May 2009 - 10:35 PM



#9 eveln

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Posted 06 May 2009 - 10:37 PM

Don't get me wrong ,I read and understood a bit .... I'm just saying is all ....powerful. So that's complimentary. Right? :) Oh and evil. :) Edit: Well gees thanks Kimmo ! just posted this and played your vid Speakers were set loud from previous viewing.....I'm all here NOW Now it's abright evil contraption.........admittedly fascinating !

Edited by eveln, 06 May 2009 - 10:43 PM.

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#10 @~thehung

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Posted 07 May 2009 - 02:19 AM

aah...beautiful :) without being told otherwise, i wouldve thought they were props from old sci-fi films! which of course they probably were -- but its nice when technological reality is at least as weird as we might want to imagine. theres something exhilaratingly gothic about old analogue gear. it draws your mind back to the time when this stuff was at the fringes of new and scary science, and what it wouldve been like to have worked with the nuts and bolts of such devices in their infancy, when the phenomena was so raw and macroscopic. all those quirky contraptions of blown glass and metal rods, the electro-magnetic gadgets of the last century or so; despite being terribly new in the context of all history, seem to already possess an impossible sense of olde worlde charm, i suppose because they are relics of a startlingly brief "classical" age somewhere between steam and the transistor. nice one Kimmo.
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#11 Kimmo

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Posted 07 May 2009 - 02:22 AM

That pretty much sums up the appeal : )

#12 just_some_guy

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Posted 07 May 2009 - 02:26 AM

I saw one of those once. It must have been about a metre tall. I can't remember where I saw it. Perhaps a British Museum.
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#13 Kimmo

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Posted 07 May 2009 - 02:29 AM

It'd be groovy to see a three-phase one actually going, with the spinny pattern and stuff

#14 smithjoe1

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Posted 07 May 2009 - 04:10 AM

Those things look awesome but what can you do with them besides use them as a bridge recifier? I've just purchased a dozen IN9 Nixie bartubes to make a multi frequency VU meter, should look fantastic. Old vacuum technology seriously rocks.
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#15 waylander232

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Posted 07 May 2009 - 05:49 AM

Seriously freakin' cool, but probably not the best use of space... Imagine if you had one of those in your electric car, you'd need space for two engines. Though you could have it where your back seat would be, that'd look pretty sweet driving at night.
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#16 MrFriendly

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Posted 07 May 2009 - 11:12 AM

I do love old valve tech. They're grossly ineffecient, don't work well with high mechanical vibration, take up space, require ridiculous amounts of cooling, and have a tendency to blow up when you don't want them to. But they have a certain charm and romance. I think @~thehung put it beautifully. It's like when you catch the old trams or the Hitachi trains in Melbourne. You don't feel like they're being powered by modern technology, they sound and feel like they're being pulled along by some ancient magical force that only a privileged few knew how to wield for our convenience.
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#17 smadge1

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Posted 07 May 2009 - 11:57 AM

Like it says in Wikipedia, having a pool of mercury in a fragile glass container can be a recipe for disaster. Also, a lot of them leaked small amounts of mercury, and mercury compounds into their surrounds, requiring expensive clean ups.
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#18 bolt_krank

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Posted 07 May 2009 - 12:05 PM

That's cool. I love it.
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#19 Kimmo

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Posted 07 May 2009 - 01:25 PM

a lot of them leaked small amounts of mercury, and mercury compounds into their surrounds, requiring expensive clean ups.

Somehow, I reckon that adds to their coolness.

They look kinda menacing, and they actually are menacing.

#20 Taranthor

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Posted 07 May 2009 - 01:28 PM

I'm sure you could reproduce a fairly good and safe one with LED's rather than mercury. I think some modern tech custom designed to look antique would be great!




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