With the recent discussion about a rotary converter that was saved, got me wondering if there are any mercury arc rectifiers (also called mercury arc valves or Hewittic rectifiers) saved or even operating in North America. Doing a quick google search indicates a number have apparently been saved in the UK and Australia, but I didn't stumble on any listed in the US. If you haven't seen one operating, its something that looks like it belongs in Frankenstein's lab, but I can imagine the large amount of mercury each one contains isn't something to be taken lightly from a safety or liability standpoint.

I don't know of any mercury arc rectifiers at any trolley museum. They were not that common in the U. S. Considering that only around 10 rotary converters were saved. it is not surprising that there are none around. The last system to have one that I know of was the Vancouver trolleybus operation in the 1980's.

Here is a video of one operating in a railway-

http://www.youtube.com/watch?v=yjMZ5qtyCUc

But this video demonstrates how it works a bit better...6 arc tubes in a 3 phase bridge rectifier showing the hetrodyne between some classic music and the 50hz mains in his country.

http://www.youtube.com/watch?v=G7qMVYf85sM&list=UUZP_rK4U2A_n7NrvzxMeVyQ

The Toronto Railway Museum has this:

http://torontorha.blogspot.ca/2013/12/a ... ssive.html

Not sure what the current status of it is, but there was a campaign to save the mercury arc rectifier substation on the Manx Electric Railway at Laxey. It does indeed look like something from Dr. Frankenstein's laboratory. When I visited there in 1993, it was very much in service.

How do thoes compair to diodes. Also if you want a rotery converter (low power though) elevator mechanics are constentely tossing them when they do upgrades.

Did I really read 'current' status a few posts above? Was I the only one that caught that? With regards to elevators, I used to work for a company that built three phase to DC rectifiers, a project underwritten by Con Ed in NY. The idea was that Con Ed wanted to phase out the DC service that they were providing to lower Manhattan, apparently since the days of Edison himself. Not only elevators, but fire pumps as well used DC.

And I loved the J.S. Bach, especially the 128 foot 'earthquake' stop on the pedalboard.

Mercury vapor rectifier tubes had a number of drawbacks. They were used for many different devices including broadcast transmitters. The biggest problems was what was called an arc back. One of the tubes would arc internally conducting power in the opposite direction. This was like a short circuit on the output of the entire rectifier. Often it caused damage to the other tubes before circuit breakers could shut off power. The anodes would look like pacman had been chewing on them.

Manufacturers made solid state rectifiers that were plug-in compatible with the mercury vapor tubes. They cost about the same as a replacement mercury vapor tube. No one was happier than I was to replace all the mercury vapor rectifiers in several broadcast transmitters that I had to maintain.

The color inside a mercury vapor rectifier tube would change with age. A new tube had a deep glue color that gradually took on a green color as the tube aged. Some engineers had an ability to spot which tube was about to fail just by looking at the color.

The New Zealand Tramway Museum had a working mercury vapor rectifier with an excellent explanation posted how it worked.

As a note . . . I recall that the Iowa Terminal in Emery, IA had a mercury arc rectifier purchased second-hand from the Chicago North Shore & Milwaukee. This was mentioned in the Trains magazine article on this operation that was published in the late 1980s.

The National Tramway Museum at Crich, Derbyshire, UK operates from a mercury arc rectifier. I got to watch it being "lit up" during a 1998 visit.

Impressive!

I always thought that elevators used motor-generator sets rather than true rotary converters.

Some members of the Branford Electric Rwy. Ass'n. bought the mercury arc rectifier from an old drawbridge that had needed it after 600 Volt Direct Current trolley car power was no longer available. When more modern power supplies became practical for the Museum's line, they recovered their money by selling the mercury. The bridge motor could be used to restore a trolley! Edward "Sheraton" in his autobiography "The world of Mr. Sheraton", mentions that his Toronto hotel used mercury arcs to rectify the elevator power.

Pretty likely that the mercury arc rectifier used by the streetcars at Fort Edmonton, Alberta, Canada (Edmonton Radial Ry. Soc.) was the last one in use for traction purposes in the US or Canada. IIRC. it was last used late in 2012 and some of the setup was slated for static display. You can see this unit in operation on you tube.

The streetcar operation at Heritage Park, Calgary, Alberta, Canada also used a mercury are rectifier for traction power until a few years ago.

Gord

I briefly saw a vacuum tube rectifier device in a small building at the Nevada Northern. Anyone know what it may have been?

Robert Yuill

Not electrical but mercury related, the United States Lighthouse Service used mercury floats mechanisms at some of their later lighthouses to rotate the fresnel lens. Basically the lens sat on a platform that floated in a tub of mercury. You can imagine how much mercury it took to float a 6,000 pound lens. Offshore lights that were equipped with mercury float mechanisms had a tendency to lose mercury during storms, as the force of the waves impacting the towers would cause the mercury to splash out of the tub.

Needless to say, all of the mercury float mechanisms have been removed from service-some of them replaced with electric motors.