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Old 13th Dec 2016, 7:38 pm   #121
Lucien Nunes
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Default Re: Mercury Arc Rectifier? Where to start

Update: information corrected.

A picture of the winding house reveals a drum controller placed behind the winding gear, which presumably served the two Westinghouse motors that drove it in tandem. It looks too chunky to be the field control for a Ward-Leonard set so presumably the drive was fixed-voltage with resistance control, rather than variable-voltage. Westinghouse were champions of metal rectifiers although perhaps they would have used MARs for the voltages involved here. Apparently when the new drives were installed in 2010 the original components were left in situ for heritage reasons and could be re-connected to the drum by refitting the motor couplings, so it might still be possible to see the bulbs if indeed they were bulbs.

I have thought about a directory of rectifier installations before; it would be nice if people could look up the names and addresses of their local bulbs and pay them a visit. Perhaps we should start a thread for people to report current status of any they know about?

Last edited by Lucien Nunes; 13th Dec 2016 at 7:51 pm. Reason: Updated information
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Old 13th Dec 2016, 8:58 pm   #122
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Quote:
it would be nice if people could look up the names and addresses of their local bulbs and pay them a visit.
Paranoid mode... then the "powers" would demand a clean up.
 
Old 13th Dec 2016, 10:33 pm   #123
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Default Re: Mercury Arc Rectifier? Where to start

It would be interesting to see how many glass type MAR's are still around.

I think most would have been decommissioned from the 1980's - 2000's with the closure of a lot of traditional engineering and manufacturing companies coupled with the advances in 3 phase inverter motor controls and PLC controls, plus the phasing out of high power DC motors during works refurbishment programmes.

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Old 14th Dec 2016, 5:38 am   #124
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Default Re: Mercury Arc Rectifier? Where to start

Just read a piece online about the Deep level air raid shelter that is below Belsize Park tube station. There are two Mercury Arc Rectifiers down there, one of which is still running to provide power for the lifts. The sites author visited recently and saw/photographed it working.

They look otherworldly.
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Old 14th Dec 2016, 9:38 am   #125
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Hi From Ash .. I just picked up on this as I have been off my Radio stuff temporarily, whilst chasing a shed load of abandoned Honda motorbikes. What a remarkable & enthusiastic young lady and what I wealth of knowledge Lucien is. I just wish my two daughters who get more involved in technical things. Soak up all the knowledge you can from the guys on here particularly Lucien and in a few years time I am sure you will be one of the resident experts too. I was lucky enough to see the MAR's controlling the stage at the old Royal Opera House in the very early '90's and I too was mesmerized by them..like something straight out of Igor's den in Frankenstein movies !
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Old 14th Dec 2016, 10:32 am   #126
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Default Re: Mercury Arc Rectifier? Where to start

Ash - for a moment I thought you were going to post that Cathy had picked up a MAR from a house clearance and handed it to you to get working, like the other items
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Old 18th Dec 2016, 3:55 pm   #127
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Default Re: Mercury Arc Rectifier? Where to start

(Hurried) pics as requested before it gets dark and damp.

Frying tonight!

type 100/2 S
15056.

Logo appears to be a circle (or two circles) inside a triangle with curved sides- This triangle resembles the end view of a 3 lobe camshaft.

Any information will be appreciated.

Dave
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Old 18th Dec 2016, 7:41 pm   #128
Lucien Nunes
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Looks like a Hewittic bulb although their logo is two interlocked H's. 100A output suitable for lower voltage applications due to straight arms. Don't let the endcaps take weight!
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Old 18th Dec 2016, 8:30 pm   #129
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Thanks Lucien, yes, i lifted by the big arms, the sealant twixt the glass and the terminals looks cementitious so i made a note to avoid putting any strain on it.

Just how low a voltage would this be able to produce without problems?

Last edited by The Philpott; 18th Dec 2016 at 8:33 pm. Reason: typo
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Old 18th Dec 2016, 8:46 pm   #130
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I don't know the official rating but I wouldn't exceed about 150 PIV on the main anodes. The forward drop is likely to be a volt or two lower than Steph's bulb due to the reduced arc length, somewhere around the 15V. 55-0-55 (i.e. tool transformer voltage) might be suitable with an upstream ballast and a short-circuit on the DC side. I expect the more inductance you add the less critical it would be and you could go considerably lower.

I really need to try this DIY control gear stuff before making any detailed suggestions. As per last week if I finish work before midnight I might try at least to get the first bit of the demo video done if not any actual experiments...
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Old 20th Dec 2016, 12:11 pm   #131
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How come there are two Mar threads now?
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Old 20th Dec 2016, 2:54 pm   #132
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Default Re: Mercury Arc Rectifier? Where to start

This is the newer of the two threads - and started as a specific enquiry about getting into the world of MARs.
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Old 20th Dec 2016, 6:29 pm   #133
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Default Re: Mercury Arc Rectifier? Where to start

Jeffrey Borinsky also has a MAR: http://www.borinsky.plus.com/mars.html

He can be found on the Golborne Vintage Radio forum.

N.
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Old 20th Dec 2016, 6:32 pm   #134
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He's away at the moment, on his way to Antarctica, he might already be there, last forum contact was a few days ago down South America way.

Lawrence.
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Old 20th Dec 2016, 6:57 pm   #135
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The thin arm is the ignition anode? A 'dipper' is a reference to an ignition anode from it's behaviour when not energised?

How far was it possible to automate the startup of a MAR? It certainly sounds like an enormous challenge to make the gear from scratch if we are talking about transformers, chokes and switchgear that'll handle a few hundred amps.

Last edited by Neil Purling; 20th Dec 2016 at 7:00 pm. Reason: removing typing error
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Old 20th Dec 2016, 7:22 pm   #136
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From my limited knowledge the dipper is pulled down into the puddle by an electromagnet to initiate the arc.
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Old 20th Dec 2016, 10:40 pm   #137
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How many steps are there in starting a MAR like the bulb in post #127?
I understand it that you have to have a some degree of load present all the time in order to keep a stable arc. Do they have to 'warm-up' before the rectifying behaviour is stable enough to go 'on-line'.
I am assuming the necessary control gear would have to be tailored to suit the particular rectifier to a large degree so getting the rectifier operable will involve a rather large outlay.

A M.A.R. and a Jacob's Ladder are essential items if you want to construct Dr Hans Zarkhov's laboratory after the original 1936 saturday morning cinema serial.
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Old 21st Dec 2016, 6:48 am   #138
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I have to LOL at this thread.
'Ive put many 866a tubes in my rubbish! Makes me feel bad!

Sad thing is it's not like you get in trouble in New Zealand for throwing these out in the rubbish!
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Old 21st Dec 2016, 1:22 pm   #139
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Default Re: Mercury Arc Rectifier? Where to start

866As are just mercury vapour rectifiers, not MARs. Quite beefy, though- good for over a kilowatt of HVDC.

http://www.r-type.org/pdfs/866a.pdf
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Old 21st Dec 2016, 1:47 pm   #140
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How many steps are there in starting a MAR like the bulb in post #127?
MAR starting is fully automatic, almost instant (<1/2 second) and the bulb is immediately ready to take load. Control gear for dipper-ignition bulbs is fairly standardised. The dipper is a springy electrode with an iron armature midway, set to hover above the cathode pool. Mounted on its arm is a solenoid that can pull the armature down so that the electrode tip dips into the mercury, hence 'dipper'. The solenoid coil is usually connected between dipper and cathode. Starting sequence:

1. Excitation supply sends current-limited AC through solenoid.
2. Solenoid pulls dipper down, shorting itself out and releasing the dipper.
3. Dipper emerges from pool and draws arc, forming emission hotspot instantly.
4. Emission / ionisation from spot allows excitation anodes to pass current.
5. Excitation current operates contactor to disconnect dipper and solenoid.
6. Main anodes can also pass current as soon as hotspot is formed.
7. Continuous current from excitation supply maintains hotspot in absence of load until shut down.

The difference between Steph's bulb and Dave's is that the former is designed for use in equipment for supplying a single carbon-arc light source. It takes advantage of specific characteristics of the load to simplify the control gear and do away with the excitation circuit and its energy consumption. The carbon-arc is open-circuit when not in use and can tolerate an AC voltage across it, then once in operation a certain minimum current is guaranteed. Thus the rectifier senses the state of the load much like an auto-start generating set, waking the bulb only when needed.

As for warm-up, I have seen mention in online descriptions about things taking time to establish ionisation / warm up etc. There is nothing to warm up in a bulb; the hotspot is truly hot but involves a tiny mass of mercury, thus can be established or quenched in a fraction of a second. Even if the dipper makes multiple strokes before the arc starts, which it can readily do as functions as a shunt-connected trembler, this is not really apparent. You throw the switch and immediately hear the clunk of the ignition cutout contactor, by which time the bulb is glowing happily ready for use.

Last edited by Lucien Nunes; 21st Dec 2016 at 2:03 pm.
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