Kempton Steam Museum - The Mercury Arc Rectifiers

Kempton Steam Museum volunteer David Walker describes the history and operation of the museum's Mercury Arc Rectifiers.

Mercury Arc Rectifiers are designed to convert AC to DC. The units at Kempton Steam Museum were originally installed at the Royal Opera House in Covent Garden to drive stage winches and motors. When they became redundant, they were rescued by museum volunteers and installed at Kempton to replicate units that were once used on the site. They are still regularly used to power the museum's heavy duty electrical equipment and can be seen operating on open days.

[JUANKERR]

Even in my late 70s and after nearly 50 years as a professional engineer I still find these alien-looking devices quite fascinating.

[remek_ember]

I love that the cooling fans are actually solid wood propellers

[grayeaglej]

And this children is why Museums are still an absolute NECESSITY in the digital age.

[calvinnickel]

I love how modern solutions are so simple… like solid state vs tubes, fuel injection vs carburation, turbine engines vs reciprocating engines, internal combustion vs external combustion, etc etc.. but engineers had to figure the difficult way that was technologically feasible first before things like materials and processes and tolerances allowed simpler things to be developed.

[swordfishtrigger]

the mercury vapor bulbs are about the coolest version of real science being as wild as science fiction. but personally i find all those well maintained, now-antiquated switches and meters to be the most beautiful part of this display.

[johnbridgman]

I hope we never need these videos to help us crawl back up from the stone age but I'm really glad that they are being made.

[km]

i think photonicinduction just broke the algorithm with his mercury arc rectifier

[deaconfrost]

Ancient tech still kicking around and being useful..and they say old technology isn't cool...definitely cool😎

[tomroland]

A work colleague told me he was at a power station which used these devices. I guess possibly to provide excitation for an alternator. One day he had to take a party of school children around the station, all of whom he thought were pretty disinterested. He showed them the steam driven alternator and said this is where we make the electricity and then pointed to the rectifier and said this is where we bottle it. The next day he was taken to task by the station manager...clearly their teacher wasn't happy.

[johnwinters]

When I was a boy there was a man in Bamber Bridge (nr. Preston, Lancs) who manufactured car batteries in a big shed by the railway line. To charge his batteries he had one of these rectifying the mains, and then simply put about 15-20 batteries in series on the output. I remember being fascinated by that shimmering dot of blinding light.

[rayhunter]

My late grandfather was an engineer and was involved as a consultant in the construction of our local museum of transport and technology in Auckland, NZ. He explained to me that when the trolley buses were phased out in Auckland in the 70' - 80's the mercury arc rectifiers were relocated to a building at the museum to supply DC to the trams that run from the museum to the Auckland zoo and on to the aircraft museum down the road. Visitors to the museum are able to stand and watch them operating.

[effyleven]

I saw rectifiers of this type during a school trip to the GPO's Doddinghurst Long Distance Radio Station, near Brentwood, Essex.
For a 14 year old, they were fascinating devices to watch as the glowing cyan light danced about in the bottle!
The Radio Station is long gone.. part of the site being under a housing estate...
... and I am now 76!

[acolytetojippity]

I watched this, and still have no idea how these things work. but they have to be the single most steampunk devices I have ever seen.

[philorkill]

This video humbles me in how much I still don't know. We stand truly on the shoulders of giants.

[bernardchorley]

It's great to see such an impressive bit of kit restored by the museum. A very well produced and informative video. Well done.

[biohazardousBiker]

I've seen one in person, the video can never do them justice for how amazing they look when they load up. it ran a historical tram bus in New Zealand

[BitTwisted]

These were really common on power stations, generating DC for the instrumentation battery backed up DC supply buses. The were a reliable and efficient way of generating large amounts of DC before silicon rectifiers appeared. I worked at Dungeness Magnox power station in the early 2000s. (On a completely separate project but engineers talk). I believe there were a suite of large mercury arc rectifiers supplying power to the instrumentation buses. Apareltly they occasionally blew out, which made for an interesting time I'm sure, (Let them cool down, replace fuses, then restart them and they were good for another few years). The station was scheduled for shut down in 2006 and Magnox were somewhat reluctant to spend millions replacing them with a new silicone rectifier system with so little time left. Obviously there were multiple redundant parallel systems but there were no spares available. Then some identical spare units turned up from the London underground which had never actually been turned on. I'm not sure if they needed to be fitted before the station was decommissioned, that part would have been turned off sometime after the fuel was removed, so probably 2012 ish. The trials and tribulations of keeping 50 year old equipment running :¬)

[GTASWcity]

I actually just saw Photonicinduction's new vid the other day powering up a mercy arc rectifier. I had never seen one in action before, though I'd seen several on display before throughout my adult life.

Truly fascinating to behold. Works of art, now. These are treasure now. For a time nixie tubes were also in this vintage category until that Czech fellow began producing them again.

To be honest, I do think we should interest future generations whatever way we can for fields like these.

[flyingmerkel]

And a big thank you to whoever saved this equipment from the scrap heap.

[KWfly]

One of my local museums has a set of these supplying power to a heritage street tram system. As the trams accelerate and decelerate, the arc changes. Very cool to see working!