3 ms·

Remember that these were installed ~50 years before the transistor was invented. At the time, the hardware was very expensive. It was more economical to have a

Remember that these were installed ~50 years before the transistor was invented. At the time, the hardware was very expensive. It was more economical to have a single centralized rectifier than multiple distributed rectifiers. Since they were installed, it comes down to maintenance costs vs gutting and installing a brand new system. Maintaining an older system was apparently the choice these building owners made.

cnvogel 13y ago
At that time, rectifiers often consisted of a AC motor driving a DC generator. Which probably could have been moved to customers, but was avoided for maintenance and reliability reasons (more easy to service one big generator/motor pair than a few hunderes scattered aound the city, making noise in residential homes, ...) Nowadays it would be trivial, a complete motor control for variable-speed 3-phase motors, that could technically of course also drive DC, costs a few hundred dollars/euros. But probably not possible for certification reasons, as soon as you mess around with an old system you have to upgrade it to correspond to contemporary safety standards.
keithpeter 13y ago
Yes, I accept your point for when the system was originally provided. But now it strikes me that the older systems could be run from a power cabinet with a step up transformer and a rectifier running off AC mains given a supply with sufficient current capacity.
- Aloha 13y ago
  They could have then, but mercury vapor rectifiers are/were expensive, mogen sets are noisy and need service - its far easier to put a big one in, than lots of little ones.
bobdvb 13y ago
Many DC elevator systems also included Mercury Arc Valve rectifiers: http://en.wikipedia.org/wiki/Mercury-arc_valve http://en.wikipedia.org/wiki/Mercury-arc_valve They are still in use in some places and a few can be found in abandoned stations on the London Underground: http://www.eetimes.com/author.asp?section_id=36&doc_id=1319738 http://www.eetimes.com/author.asp?section_id=36&doc_id=13197...

cnvogel 13y ago

At that time, rectifiers often consisted of a AC motor driving a DC generator. Which probably could have been moved to customers, but was avoided for maintenance and reliability reasons (more easy to service one big generator/motor pair than a few hunderes scattered aound the city, making noise in residential homes, ...) Nowadays it would be trivial, a complete motor control for variable-speed 3-phase motors, that could technically of course also drive DC, costs a few hundred dollars/euros. But probably not possible for certification reasons, as soon as you mess around with an old system you have to upgrade it to correspond to contemporary safety standards.

keithpeter 13y ago

Yes, I accept your point for when the system was originally provided. But now it strikes me that the older systems could be run from a power cabinet with a step up transformer and a rectifier running off AC mains given a supply with sufficient current capacity.

Aloha 13y ago
They could have then, but mercury vapor rectifiers are/were expensive, mogen sets are noisy and need service - its far easier to put a big one in, than lots of little ones.

bobdvb 13y ago

Many DC elevator systems also included Mercury Arc Valve rectifiers: http://en.wikipedia.org/wiki/Mercury-arc_valve http://en.wikipedia.org/wiki/Mercury-arc_valve They are still in use in some places and a few can be found in abandoned stations on the London Underground: http://www.eetimes.com/author.asp?section_id=36&doc_id=1319738 http://www.eetimes.com/author.asp?section_id=36&doc_id=13197...