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Old 26th Nov 2016, 12:55 pm   #21
Steph1997
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Default Re: Mercury Arc Rectifier? Where to start

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Stephanie - was your intent to electrically operate the rectifier, and if so was that just to achieve the aesthetically pleasing visuals?
Exactly! I don't have any thing to convert to DC...for now!
However my plan if I can't get it running for a while or until I can get the parts is to get a display case with lights to light underneath in blue purely as a display piece to satisfy my needs for now!

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Steph
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Old 26th Nov 2016, 1:30 pm   #22
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Default Re: Mercury Arc Rectifier? Where to start

Yes, the query I had with operation is that you need all the other 'bits' as well, even if it is only transformers with delay timers and a resistive load. Which quickly gets onerous if you have a 3ph valve, and want to operate it as 3 phase, and may need quite a high current level to get the aesthetics you are after.
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Old 26th Nov 2016, 1:33 pm   #23
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Default Re: Mercury Arc Rectifier? Where to start

One of the great benefits of seeing a bulb run, apart from admiring it, is that it proves the vacuum is intact, hence that there is no danger of escaping mercury vapour and that it is worth making control gear for. The quality of vacuum can also be gauged from the shape of the glowing region. Historically there was a method of testing the vacuum without power, called the 'click test', which I cannot now recommend as it carries a risk of damaging the seals especially now that they may be weakened.

The seals are the weakest point on a bulb and can be faulty without any visible sign of damage. The bulb itself is quite strong due to its shape, and will withstand some surprising impacts although I recommend carefully avoiding them. But the seals can be destroyed by incorrect handling - if you are there at the time you will know it by the hissing sound of air entering the bulb, otherwise the only sign might be suspicious looseness of the caps.

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I know mercury is dangerous but it's a risk I'm. Willing to take and if something happens it happen and I'll figure something out.
This is not a good strategy. You do not want to be ringing round for quotes on spill kits and information on how to use them while little shiny balls are escaping through the gaps between your floorboards. Understand the hazards in detail, and have control measures in place to mitigate the attendant risks to a sensible level.

I saw the bulb you mentioned trying to buy. I have no idea whether the vacuum was OK but those small Nevelin bulbs are quite a good bet, I have found them reliable and they benefit from simplicity. There are only four seals - the cathode, two main anodes and the ignition electrode - and the terminal caps seem to do a good job of supporting them, better than say a comparable Hewittic. That was from a unit-type rectifier that was intended to serve just one projector lamphouse, for which the circuit was arranged to start the bulb when the lamp arc was struck. This dispensed with the need for an excitation supply and the auxiliary anodes which are the most common failures on larger bulbs.

Making your own control gear is possible, what is your experience with power electronics?
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Old 26th Nov 2016, 1:35 pm   #24
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Default Re: Mercury Arc Rectifier? Where to start

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Exactly! I don't have any thing to convert to DC...for now!
There is a thought. There is a plethora of vintage electronics (TVs, radios, but not generally things with a motor) which are transformerless, and cleverly designed to work from AC or DC supplies, so you could match your project with contemporaneous appliances working as designed (and still have a significant surplus of current!)

Best wishes with a very interesting project
Rob

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Old 27th Nov 2016, 2:02 am   #25
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Default Re: Mercury Arc Rectifier? Where to start

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I was bidding on one of his MAR's the other day actually, I got out bid by around £10 off the £220 price
Off topic, but there is no way of knowing what the winning bid was. The final price was one increment above yours, but if they were serious (and for this they probably were) their max bid could have been anything.
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Old 27th Nov 2016, 6:58 pm   #26
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Default Re: Mercury Arc Rectifier? Where to start

I know this, however I bid max bid at £215 which outbid the current one that was on at £210 and they got it for £220 which makes me sad

Oh well, I have a life time left!
Onwards and upwards.
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Old 27th Nov 2016, 8:56 pm   #27
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Smile Re: Mercury Arc Rectifier? Where to start

Stephanie, I admire your vision and determination, and I really hope you can realise your project safely. It's bold and clear and I inspiring.

...I have a small EHT mercury vapour rectifier (not the same thing at all), and have deeply observed the operation and grown to understand it deeply. I did develop a risk management strategy, even though the thing is relatively small, especially as I am a single parent.

It is clear that there is a difference between say, dropping the thing and spilling droplets of cold mercury, and the envelope fracturing and dispersing droplets of hot mercury vapour into the air, into the lungs of those around, and coating all surfaces around so that a major contamination site is created. Huge difference.

Far from wanting to pour cold water on your project, but as Lucien says, you'd definitely need a very conscious, well-articulated dynamic risk management strategy and the facilities to call it into play instantly in the event of a fracture or similar.

Long-live inquisitiveness and determination and vision!
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Old 27th Nov 2016, 11:34 pm   #28
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Default Re: Mercury Arc Rectifier? Where to start

Although I shouldn't, in this age of PC and non compartmentalising, I just can't help but find it astonishing that a 20 YO female could be so fascinated by such a thing as a MAR!! I doubt that more than a fraction of a percent of the whole UK population would even know that such a thing ever existed, let alone actually want one!
Don't misunderstand me though Steph, I'm not criticising, far from it, I think it's also amazing and really hope that you satisfy your wish to find one.
There was a really impressive example in the Birmingham Science museum many years ago, which was an actually functioning display. The museum has since relocated though, to a swanky, purpose built 'experience' centre, which I haven't visited due to the extortionate entry fee now imposed
Thinking of a suitable application for your MAR, should you find one, how about an electroplating plant!
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Old 27th Nov 2016, 11:58 pm   #29
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Default Re: Mercury Arc Rectifier? Where to start

Threeseven, suggesting electroplating USUALLY means more nasty poisonous chemicals. Your H&S conscience is asleep I fear.
Les.

Last edited by AC/HL; 28th Nov 2016 at 12:55 am. Reason: OT aside edited
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Old 28th Nov 2016, 12:24 am   #30
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Default Re: Mercury Arc Rectifier? Where to start

It was said tongue in cheek Les! Excuse me, I should have made that clear.
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Old 28th Nov 2016, 4:58 pm   #31
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Default Re: Mercury Arc Rectifier? Where to start

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Although I shouldn't, in this age of PC and non compartmentalising, I just can't help but find it astonishing that a 20 YO female could be so fascinated by such a thing as a MAR!! I doubt that more than a fraction of a percent of the whole UK population would even know that such a thing ever existed, let alone actually want one!
Don't misunderstand me though Steph, I'm not criticising, far from it, I think it's also amazing and really hope that you satisfy your wish to find one.
There was a really impressive example in the Birmingham Science museum many years ago, which was an actually functioning display. The museum has since relocated though, to a swanky, purpose built 'experience' centre, which I haven't visited due to the extortionate entry fee now imposed
Haha I know it's a bizarre thing to be untreated in at 20, any everyone looks at me gone out when I try and explain the purpose of one to then so it's nice to have found a forum with people who know about them and can possibly help! I've been obsessed for ages sinces I saw a few in a museum, so I'm on a mission to have my own and maybe one day it can be in a museum for people to admire once I'm older and another 20 year old will have the same asperations!

I'm yet to see the one in Birmingham but it's not far away so I shall go and visit on my journeys!
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Old 28th Nov 2016, 5:02 pm   #32
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Default Re: Mercury Arc Rectifier? Where to start

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Threeseven, suggesting electroplating USUALLY means more nasty poisonous chemicals. Your H&S conscience is asleep I fear.
I fear I'm coming across as a danger mouse!
this is not the case, I know how dangerous things are and how to transport a MAR, I have spoken to a few people before joining here and museum staff so I'm not doing this project single handedly - sorry to cause fear :P
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Old 28th Nov 2016, 5:19 pm   #33
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Default Re: Mercury Arc Rectifier? Where to start

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I'm yet to see the one in Birmingham but it's not far away so I shall go and visit on my journeys!
If and when you decide to go see it, let me know and I'll meet you there. I'd like to see it again myself.
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Old 28th Nov 2016, 5:20 pm   #34
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Default Re: Mercury Arc Rectifier? Where to start

I'm sure I saw somewhere that there were baby ones used in some welding equipment. They're probably less likely to to have survived I guess, but might be easier to live with and run without needing massive supply currents and loads.

Or are they more likely to be Tungar Tubes, which are related but not quite the same?
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Old 28th Nov 2016, 5:44 pm   #35
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Default Re: Mercury Arc Rectifier? Where to start

NOS tubes? I'm no welder..hmmms... I think the smaller ones (and bigger by the looks of things) often get destroyed or smashed

I think you can get baby rectifiers in the old TV's!
May start a little collection going I could have a family of rectifiers - Woo!
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Old 28th Nov 2016, 5:52 pm   #36
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Default Re: Mercury Arc Rectifier? Where to start

Beware the distinction between mercury vapour rectifier, which has a heated cathode like any radio valve but no pool of liquid mercury and no arc, and a MAR. Many people incorrectly call vapour rectifiers MARs, so some of the small devices are not actually MARs at all. The devices used in welding sets were normally Ignitrons, which function like a half-wave grid-controlled MAR. However many had metal envelopes rather than glass so you can't see the glow! The rectifiers in TVs and radios are normally standard valve rectifiers without any mercury at all.

I am not sure the one at Birmingham is still there - they have closed the electrical gallery this year.
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Old 28th Nov 2016, 6:41 pm   #37
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Default Re: Mercury Arc Rectifier? Where to start

There are certainly a lot of hurdles to be overcome in terms of the health and safety implications. That doesn't mean you won't do it, it'll just take longer.

My own particular obsession is building a liquid fuel rocket engine. It is a significant engineering challenge, but that pails into insignificance compared to the legislative side of things. You just have to jump through the next hoop, then the next and so on.
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Old 28th Nov 2016, 7:20 pm   #38
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Default Re: Mercury Arc Rectifier? Where to start

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I am not sure the one at Birmingham is still there - they have closed the electrical gallery this year.
Typical! I wonder if they have retained the MAR in the stores?
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Old 28th Nov 2016, 7:49 pm   #39
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Default Re: Mercury Arc Rectifier? Where to start

STEPH!!! The object of your desire has just appeared on ebay, and IT IS IN DERBY!!!

http://www.ebay.co.uk/itm/RARE-Mercu...oAAOSw-0xYPBLu
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Old 28th Nov 2016, 8:09 pm   #40
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If that isn't a sign then I don't know what is.
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