Re: arc headlights and dynamos

Posted by John Greenly on
URL: http://c-sng-discussion-forum.254.s1.nabble.com/arc-headlights-and-dynamos-tp15165p15170.html

Jim,

excellent!  Thanks so much for these photos.  Yes, I was coming to the same conclusion, but I didn't want to make a claim without good photographic evidence.  your photos are unquestionable. These headlights had to be kerosene lamps.  Here's an illustration I found yesterday:



I'm suspecting that the change from the big box headlights to these may have come with the introduction of better kerosene lamps like the central draft or "blast" burner types developed around 1890 that gave much more light than the early flat wick lamps.

So, yes: no wires, no electricity.  And acetylene lamps need a gas feed.  Typically the acetylene generator was located under a running board on the loco- this worked by dripping water on calcium carbide in a closed container, and the gas produced was piped to the light.

By the way, as to dynamos, the word refers to a generator using a commutator to produce DC current.  A dynamo is basically a brushed DC motor, but instead of supplying current to make it turn, you turn it to generate current.  Any permanent magnet DC motor will do this, but true dynamos did not use permanent magnets. They had field coils, electromagnets, that used the current generated by the dynamo itself to produce its own magnetic field-  a very clever "bootstrap" process.  

I also found reference to axle-driven dynamos in baggage cars, but it wasn't clear to me whether these were used just for lighting passenger cars, or for the loco as well.  Here's a detailed history and technical discussion of the Pyle steam-driven dynamo and arc light if anyone's interested:

https://books.google.com/books?id=fKZIAAAAMAAJ&pg=RA6-PA1&dq=electric+headlight&hl=en#v=onepage&q=electric%20headlight&f=false

go to the fourth result in this Google book and click on the "electric headlight" chapter.  

It's interesting that modelers seem always to refer to these shapes as arc headlights- PSC, Cal-Scale and others all do.  
These lights do look like they were configured in such a way that it was easy to replace the kerosene lamp with the vertically oriented arc electrode assembly, and the arc needed the cooling airflow allowed by this design.

By the way, that photo of C&S 44 is wonderful, I haven't seen it before.  All sorts of great details- the pilot, yes!  Also notice the riveted shotgun stack-  I've never seen one like that before.

thanks!
John