Steam turrets and dynamos

This supports the 1000 kW maximum load of the train power line... So, I support this facts as plausible and a good "role of thumb" for determine the power demands of a modern passenger car.
Maybe for long distance runs like in the US this value may increased, but for the distances within Germany this value may decrease thru modern and more economic systems, but I guess this value makes sense and shows why a locomotive mounted generator won't make this task, because it would be a huge and heavy machine

Was the steam locomotive the principal source of heating for passenger cars? Was a separate generator needed for this function or was the steam from the boiler used ? If so How did this affect performance in cold weather ?

Thanks to all.
Septa Fan

Well, I cannot speak for the US, because i am lacking reference books and descriptions.
So I speak for Germany and here the primary source for heating was during the age of steam logically steam. We had steam couplings between the locomotive and the cars, and if coupled giving a main steam line thru the train.
From this main line steam was taken into radiators for heating. Manually or thermomechanically operated valves open the steam supply tubes to the radiators, just to ensure a good warmth within the car.
With the upcoming of diesel and electric locomotives the main heat source steam was kept up - thus those early electric and diesel locomotives get additionally steam boilers mounted. Those little steam generators were coal fired for the electric locomotives, and diesel fired for the diesel locomotives - and those boilers only feed the steam line for heating.
Later some steam boilers were electricity driven for heating purposes and the development after world war 2 lead to the main 1000 Volt train power line - and the steam heating declined and ended in the 21. century - thus steam heating can only be found on museal trains and cars.

So, for electricity - especially illumination, all cars got their own generators and batteries. Older cars got oil lamps, which had to be lit by the conductor of the car at dusk. But most get converted to electric illumination. So there were generators mounted, which were belt driven from an axle shaft mounted drive gear. With the upcoming of trucks there were truck mounted generators, but still given from the main axle shaft.
Those feed their power into batteries and from there to the illumination or later to audio electronics. The conductors could use switches to enable illumination. And usually the train supervisor at the train switched on the illumination for the whole train at the master car. So lights went on and were powered by the power from the car mounted generators during the travel. On station stops batteries took over and powered the illumination for those short periods of time.
The train supervisor was also able to dim the lights... so there was the possibility to go from full illumination to a eco mode with less lights on. Also there was the possibility to set the lights to emergency lights, which illuminate only the most necessary vital parts and points of the car.
In the stations or shops the cars were connected to the local grid by electrants - now the AC power was send thru a rectifier to load the batteries - and to power the lights for maintenance.

This is, how it was during the age of steam... and still today we have batteries in the cars, which can be load by the main train power line from the locomotive, but today electronic control and air condition is the common.... but many cars have still today auxiliary generators, just as safety, if the main power line is fail, just to ensure illumination and some security installations were still on power.

Steam heating of passenger cars was used long after the demise of steam power. A lot of the diesel locomotives built for passenger service from the 30's thru the 60's, maybe into the early 70's were equipped with auxiliary steam boilers. A number of steam locomotive tenders were converted to auxiliary steam boiler units for diesel engines without on board auxiliary steam boilers used in passenger service. I think the total phaseout of stream heated passenger cars wasn't completed until sometime in the 80's.

(A footnote to Mikado 2-8-2's post with some more details

Re: "A lot of the diesel locomotives built for passenger service ... maybe into the early 70's were equipped with auxiliary steam boilers."

Called "stem generators." (During the U.S. Bi-Centennial celebrations in 1976, a streamlined Southern Pacific 4-8-4 was serviced at EMD's La Grange plant for use on special trains-- a (too young to have been acquainted with working steam?) EMD employee asked "What's in the long hood?" Possible answer that someone thought of later: "The largest steam generator ever used on a unit from this factory!")

As for when it ended... Gradually, delayed by the fact that the national passenger rail system had an inherited fleet of cars equipped for locomotive-supplied steam heat: in the 1970s, Amtrak converted many of these and replaced others with new cars equipped to accept electricity instead of steam: "HEP," for "head-end power." As long as steam-heated passenger cars were in use, there was a need for steam-generator equipped locomotives. Amtrak's first new diesel locomotives, the 150 SDP40F built by EMD between June 1973 and August 1974, came with steam generators. (I think the idea was that they could be removed and replaced with auxiliary diesel-generator sets for HEP when Amtrak got rid of steam heat on its passenger cars; in the event the SDP40F were scrapped instead.) Later Amtrak diesels were built with HEP.

In Mexico there were still enough steam-heated passenger trains for NdeM and FCP to get 31 steam-generator equipped GP38-2 (often referred to as "GP38P," though apparently EMD didn't think they merited a separate model designation) in June 1975.

HEP is better: it was used on streamlined trains in the 1930s and recognized as superior to steam heat, and only the "inertia" of the existing fleet of passenger cars kept it from being adopted universally. A small-ish passenger operation with a dedicated fleet of cars, not exchanging cars with the rest of the continental network, could be converted to HEP comparatively easily. I believe that some commuter operations had HEP in the 1950s, using locomotives with auxiliary electric generators.

Going back to the steam turbo issue, watch any older VHS videos of steam and listen how the whine from the turbos is overpowering. Sometimes the sound could scramble the video images. Guys with video cams often asked us to shut the turbo down. (It depended on our mood - railfans often didn't buy tickets or even a souvenir, but they wanted perfect three-quarter shots with rods down and just the right amount of smoke from us.)

On our locos, the steam turbo powered the headlights (front and rear), cab lights, and lights used to illuminate the gauges and water column.

Allen Hazen wrote: HEP is better: ....June 1975... 1930s ... 1950s,...

Allen, apologies for the clipping. A pocket history of the volatility of oil price is concealed in your post!
This was simply true, from an operational standpoint, in the days of 9 cent/gallon diesel.
The thermal efficiency of electric heat is not better than 35%, where as for steam heat we can expect 85% at least.
One wonders if, in these days of 3 + dollars/gallon diesel if the operational convenience of HEP would still outweigh the fuel cost in a procurement decision.

in the Boston area, among many others, today, all trains are heated by HEP. Another downside of HEP - one class of MBTA's locos are called "screamers" because of their high rpm HEP engines in the long hood - something that has never been said of a steam generator.

Eliphaz--
Hmmm...
I hadn't thought about the fuel efficiency aspect. Getting heat from steam is efficient: does it matter that the steam is being produced in a locomotive boiler (i.e. a fire-tube boiler, very small by the standards of staionary plants, fired at a rate that loses large amounts of fuel up the stack)? I don't know the answer: I have some idea of the factors relevant to the calculation, but not of their numerical values.

I think there are a number of other aspects, however, that contribute to the "superiority" of HEP:
---Ease of control
---Possibility of having lighting and air conditioning as well as heat all from a single source (i.e., we are comparing a passenger car equipped for HEP with one which has steam heat AND axle-generators(?) for electricity AND who knows what for air conditioning)
---loss of power in transmission (i.e. along the line, particularly between cars, from the head end to the rear of the train) is probably less with electrical connections between cars than with (often leaky) steam connections
---even with an auxiliary engine-generator set, I suspect (suspect: don't claim to know) that HEP can come from a lighter locomotive than one with enough water on board to supply steam for a long-distance run.

As for the "screamers"... that's what you get from primitive technology! For simplicity, the designers made the HEP alternator run off the main engine, and then, to ensure constant frequency (60 hz?) of the HEP current, had to make the main engine run at a constant speed! Several work-arounds are now possible: use of separate engine-alternator sets for HEP (as on most of MBTA's newer power), or (this one involves technology American locomotive builders didn't have when HEP became standard for passenger power in the 1970s) HEP AC "created" by solid state invertors.

(Thanks for your comment: as usual, real life is more complicated than I was thinking! Lots of things have to be considered before one can say that one technological option is "better," and I wasn't thinking through them all.)

Eliphaz wrote: in the Boston area, among many others, today, all trains are heated by HEP. Another downside of HEP - one class of MBTA's locos are called "screamers" because of their high rpm HEP engines in the long hood - something that has never been said of a steam generator.

NJ Transit had them as well, "Screaming F40s". Hard on the eardrums.