Mercury-arc rectifier station under threat!

[Lucien Nunes]

If only that were true. If you can find me a sizeable redundant rotary converter a you win a mercury arc rectifier. If you can find a mercury arc rectifier, you win a thyristor bridge! There are still a few MARs operating in industry that I know of, but only a fraction of the number in use a decade ago. There are so many factors working against the survival of DC plant that we might never be able to put a decent display together at Electrokinetica because it's disappearing faster than I can recover it.

[broadgage]

Originally Posted by Brigham

I didn't even know that these were scarce. So what do major continuous-current machines derive their power from? Have we gone back to rotaries?

Heavy power DC is now much less common, being largely confined to railways and tramways. Solid state rectifiers are now the norm.
There are probably a few rotaries left working and maybe a few mercury arc rectifiers also, but these are now very rare.

The last largish rotary converter that I have seen working was for the lift in an office building, output 200 volts DC at about 100 amps.
This was energised from the standard 3 phase mains via a timming circuit that shut down the rotary if the lift had not been used for some time.
Still in use until the building was knocked down in about 2002.

"LEE LIGHTING" the film location lighting hire company still had a large DC generator for hire until recently, and may still have. The intended use was to power very large carbon arc lights for filming.
IIRC this machine was also hired for demonstarting or testing some large vintage DC powered machinery.

[Lucien Nunes]

largish rotary converter that I have seen working was for the lift in an office building

Unusual, was it a retrofit to an installation that was originally DC powered? This was the arrangement at the Midland Grand hotel from which we have preserved the resistance-controlled DC lifts. However the rotary converter had long gone by the time we got there.

Most later DC lifts and even early gearless ones used variable voltage control via a dedicated Ward-Leonard motor-generator set which enables full control of speed using the field of the generator. This obviously isn't possible with a rotary converter on which the DC and AC voltages are approximately proportional.

SCARCE ELECTRICAL PLANT ALERT! If any of you technical chaps ever see interesting old equipment like this, please drop me a line and let me know where it is, even if it is not scheduled to be removed yet. Most people wouldn't know they had a rotary converter in their building, so it is extremely difficult to find stuff to conserve. The more we know about, the greater the chances of success!

Lucien

[Sean Williams]

If you fancy a challenge, there is a huge DC generating set at the Strand Hotel in London.....

[Lucien Nunes]

Yes, that's exactly the kind of thing we're looking for (although we already know about that one). In a way what I'm after finding especially are the the real oddballs - who's got a LaCour converter? Kapp oscillatory phase advancer? A nice big Schrage motor? A dual-commutator plating dynamo?

Returning to the subject of lifts, which are a particular favourite of mine, definitely on the must-have list is a complete installation with an Otis Pie-Plate selector, e.g. 5850 type. This fascinating piece of electromechanical gadgetry generates an analogue of the lift shaft at about 1/4 real size in the form of virtual helix inside which sectors of a giant screw revolve on a spindle. Contact fingers on a moving carriage search for the ends of the sectors to precisely level the lift car at every landing. Then there's the Express DMR system, which uses a linear selector…

So much to do, so little time

Lucien

[Radio Wrangler]

I recall reading that the original positioning motors for Jodrell Bank were driven from Ward-Leonard sets.

I suppose it's the price of copper which is making large machines vanish so rapidly.

David

[Lucien Nunes]

That's certainly one of the main factors. Cash-strapped industries are not going to leave saleable material standing about, and on vacant sites anything shiny lasts about 5 minutes. Also there's a shift in methodology and a lack of available knowledge and skills in the front line. When machine X breaks down, instead of getting Fred to fix it, who looked after it for 40 years but retired last year, the job goes out to a 'facilities maintenance solutions provider'. Then they run into complications, e.g. 'We can't support that under ISO9001 because the manufacturer closed down 30 years ago and we can't get hold of the necessary documentation. So we'll have to change it.'

To be fair, some old electrical plant was fairly heavy on routine maintenance and that is costly to outsource. For accounting reasons, many operators would rather use a maintenance-free electronic drive that lasts 10 years, than an electromechanical one that lasts 50 years but requires brushes and contacts and regular greasing during that life.

Once the old plant is redundant it often has to follow the paper trail all the way to the recycler to comply with ISO14001 environmental management procedures, resulting in zero opportunities for it to be conserved.

[locoian]

With regard to Lucians request for a schrage motor, I believe that the Launceston steam railway has a cliff lift (I think Ex Scarborough) with a decent size variable speed motor.

Don't know if its a schrage or not and I think they are intending to use it so I don't suppose he wants to sell it.

Hope this dosn't tease you too much

Ian Howitt

[woodchips]

If you want large electrical equipment it is worth keeping an eye on the military sales and dealers. They used all sorts of odd things for even odder uses, and so much has come out of the military in the last 10 years some must have survived in the dealers' yards.

Try Jacksons at Mission, Woods Group in Crediton, Leavsley at Alewras, Withams at Colsterworth, Ramco at Skegness for dealers. Look on the historic military vehicle website for lots of dealers.

I no longer have anything much, but seen all sorts of interesting items come and go. The problem is usually moving it, once over a tonne or so and it gets difficult, can't trailer it with a car. If you use a truck then a forklift is needed to offload.

[woodchips]

Just looked on Woods Group ebay (yes, I know) listings and have a Omerod Hodgson fan, 220V @ 30A, price is a little steep, £1800, but make an offer, worth, what, £200 as scrap?

Forgot to say, other source of large DC generators is as scrap magnet dynamos used in excavator based scrap handlers.

[G6Tanuki]

Originally Posted by Lucien Nunes

Once the old plant is redundant it often has to follow the paper trail all the way to the recycler to comply with ISO14001 environmental management procedures, resulting in zero opportunities for it to be conserved.

The WEEE directive is indeed a real pain: recently I lost out on a 1600VDC@0.5A and various-associated-low-voltage-AC-outputs power supply which would have been the perfect PSU for a nice little quadruple-grounded-grid-813 HF linear-amp.

[Sean Williams]

Seeing as the purpose of this thread has been served it is now closed.