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Old 26th Oct 2016, 10:26 am   #61
Tractorfan
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Smile Re: Mercury Arc Rectifier

Hi,
Mercury arc rectifiers have always fascinated me since seeing the ones used for battery charging at the power station I worked at years ago.
However, I've often wondered about steel tank rectifiers. Do they have an insulating liner of some sort? Or are just the anodes insulated with lead-through bushings?
Cheers, Pete.
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Old 26th Oct 2016, 7:48 pm   #62
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Default Re: Mercury Arc Rectifier

The main tank of a steel cased MAR or Ignitron would be at cathode potential as it would be in direct contact with the mercury. To electrically insulate the inside of the tank would be complicated and rather unnecessary. The anodes and all other electrodes would be connected to the main tank with large glass or ceramic beads acting as glass to metal seals. I would be interested to know how well the vacuum was maintained over time compared to glass bulb types.

Christopher Capener
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Old 29th Oct 2016, 9:45 pm   #63
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Default Re: Mercury Arc Rectifier

The attached excerpt provides basic information on the construction details of steel-tank ignitrons and excitrons.

Given that sealed ignitrons saw extensive industrial use, one might infer that vacuum retention was not a problem. I wonder though if vessel size was a factor here. I understand that the very largest industrial ignitrons were usually pumped. At the other end of the size scale, vacuum retention was evidently not a problem with the steel tubed nuvistors.

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Old 29th Oct 2016, 10:36 pm   #64
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Default Re: Mercury Arc Rectifier

Older than the nuvistors are the late thirties American metal valves, made in vast quantities and not in any shortage nowadays.

David
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Old 29th Oct 2016, 10:53 pm   #65
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Default Re: Mercury Arc Rectifier

Is there a MAR at Crich Tramway village or just a photograph. Possibly at the Wakebridge stop where the actual substation is.

I don't know whether it is true that a MAR would 'sing' when on load & you could deduce whether there was a tram in the vicinity by the change in pitch.
Would I be correct that a working MAR would be a powerful emitter of UV light, not infra-red?

As you mentioned the use of MAR's on the railways there is one as an exhibit in the store annexe at the National Railway Museum in York. I cannot remember where it was installed or what it supplied.
Maybe a source of DC for a traversing crane?
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Old 29th Oct 2016, 11:05 pm   #66
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Default Re: Mercury Arc Rectifier

I think you will find that the Railway MARs were used mainly for supplying 750 volt DC Traction Current to the Southern Railway later British Railways Southern Region, for the 3rd Rail Electrification scheme from the mid 1930s onward. The sub stations are every 3 miles or so and MARs were still in use in some of them in the dying years of the last century.

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Old 30th Oct 2016, 1:19 pm   #67
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Default Re: Mercury Arc Rectifier

It is the case that they light up like a beacon when the load increases, so i imagine the sound changes as well.
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Old 30th Oct 2016, 3:02 pm   #68
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Quote:
Originally Posted by Neil Purling View Post
I don't know whether it is true that a MAR would 'sing' when on load & you could deduce whether there was a tram in the vicinity by the change in pitch.
The sound does increase when on load.
https://www.youtube.com/watch?v=5a5lkharews
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Old 30th Oct 2016, 5:57 pm   #69
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When I worked for BR, the sack ware house had 3 wire DC, powered via two large MARs and two transformer in our own sub station. Lighting on one floor 220 volt outer Positive to centre Neutral, another floor other outer Negative to Neutral. Motors nominal 440/460 volt. The motor were Early 1900 era with exposed brush gear in a very dusty environment, ring lubrication and never gave a bit of trouble. Oh, face plate starters, a real fire/explosion risk but it never happened. The building is now listed.Ted
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Old 9th Nov 2016, 12:27 am   #70
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Some info about Mercury Arc Rectifiers from 1907:
http://chestofbooks.com/crafts/popul...ectifiers.html
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Old 20th Dec 2016, 10:32 am   #71
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Default Re: Mercury Arc Rectifier

Quote:
Originally Posted by peter_scott View Post
Michael Bennett-Levy lived (or possibly still lives in) Monkton House, Old Craighall before he sold off his collection and moved to France for reasons of ill health.
I hadn't realised that Michael Bennett-Levy had died just a few days after this thread was current. His obituary in the BVWS Bulletin gives 28th September 2016.

Peter
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Old 20th Dec 2016, 11:57 am   #72
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Default Re: Mercury Arc Rectifier

Was saying to Steph that there was a MAR at the tram museum in Crich, saw it in the mid 90s but no idea if it's still there.
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Old 22nd Dec 2016, 1:19 am   #73
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Default Re: Mercury Arc Rectifier

The Crich tram power station has been upgraded, no MAR in operation or visible.
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Old 27th Dec 2016, 9:39 pm   #74
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Default Re: Mercury Arc Rectifier

If you're in the proximity of Crich, there is Midland Railway Centre that has one that works! and they also have one that's never been used and still in its box - How ever I believe the unused one is behind closed doors but the working one powers around Halloween time if I remember rightly!
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Old 27th Dec 2016, 10:30 pm   #75
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Default Re: Mercury Arc Rectifier

As an apprentice, back in the 50's, we serviced several lifts (elevators) in the London area that had Mercury Arc Rectifiers. Most were installed during the Victorian era. They were contained in metal cabinets and the glow was bright enough to shine out through the tiny holes in the hinges of the door.
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Old 28th Dec 2016, 2:14 pm   #76
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Quote:
Originally Posted by Steph1997 View Post
If you're in the proximity of Crich, there is Midland Railway Centre that has one that works! and they also have one thats never been used and still in its box - How ever i believe the unused one is behind closed doors but the working one powers around halloween time if i remember rightly!
So they have a sense of theatre then! What a time to power it up! Proper spooky when they are running.
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Old 31st Dec 2016, 8:12 pm   #77
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Default Re: Mercury Arc Rectifier

Frankensteiny objects aren't they once working!
Mine looks all ghostly at the moment, I'm reluctant to get her working in case something happens so I'm getting the set up and looking out for another as a spare just in case until then I will keep her glossy!
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Old 31st Dec 2016, 8:24 pm   #78
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Default Re: Mercury Arc Rectifier

Really hope you can get yours going. It will really be something.

Happy New Year.
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Old 1st Jan 2017, 7:07 pm   #79
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Default Re: Mercury Arc Rectifier

I will do eventually!
Happy New Year as well!
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Old 19th Mar 2017, 5:54 pm   #80
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Default Re: Mercury Arc Rectifier

Just wondering if anyone is progressing with getting one of these rectifiers up and running
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