Steam train electricity generation

I assume that, at least in the later years, there were trains with steam locomotives that had electric power for lighting, cooking, fans, etc. How was the electricity generated? A generator powered by a wheel on the track, or by some sort of power take-off in the drive train? Batteries? Anybody know?

The technology changed over the years. In essence, any non-electric train has to find a way to deal with this, so even modern diesels need to cope somehow.

The modern way is to provide ‘head end power’ which is usually an auxilliary diesel engine running a generator in the back of the loco. In the steam days, power was often provided by dynamo-style generators and batteries which were inside the carriages themselves, connected to the axles. Some steam locomotives ran a small compressor to generate power, and others towed a power van behind in later years.

For most of the steam era, power demands were small because compartment heating was provided directly by steam from the locomotive via a ‘train pipe’, and in the early days, lighting was gas or oil. So, even into the 20th century, there was electric lighting, but the heating was taken care of by the steam, and there wasn’t any air-conditioning for the first few decades. This meant the small train-mounted generators were usually adequate.

The short answer is batteries.

In this shot the batteries would be located in the first rectangular container from the left. A generator was geared to one of the axles and fed power to a voltage regulator that provided constant voltage whether the train was moving or not. There is another battery box on the other side.

Electric generation at the head end of the train was virtually non-existent during the steam era. Generally there were two or three lines that ran the length of the train:
-The train line: this is the line for compressed air that provides air for braking and controls it as well.
-Steam: provides for heating, air-conditioning (yup!), and steam table heat for the diner.
-Signalling: An auxiliary air line for the conductor to signal up to the engineer and fireman.
Cooking was usually done with gas, supplied from tanks under the diner car.

And the use of steam didn’t end with the introduction of diesel power. The first passenger diesel equipment came with steam generators since the rooling stock was generally still equipped with steam powered accessories. Nowadays passenger equipment ia all electric and the locomotives have an alternator to provide power for the consist. Oftentimes these locomotives have an ‘H’ in their designations to indicate ‘head-end power’, such as the FPH-40.

I swear I was previewing…

Excellent answers, thank you.

<Nitpick> Most of the time, it’s written F40PH (F for full-width carbody, 40 because it is built around the GP40 freight engine, P for passenger gearing, and H for Head End Power, as stated.) </Nitpick>

Also correct is the use of batteries and axle generators in passenger equipment, steam generators in each car, or steam generators in the locomotive. Amtrak’s first custom-designed locomotive, the SDP40F (once again, SD40 based, passenger geared, full-with carbody) was probably fatally flawed because of its steam generator. All that water above the frame made for strange lateral motion going into curves, and the engines had a penchant for derailment. Amtrak got rid of them and went with the B-B trucked F40PH.

Steam locomotives often had a small[ish] turbine style generator attached on the outside of the boiler jacket to generate electricity for their headlight and instrument lights. Generally it was an open system, and constantly blew a small amount of steam exhaust, as seen in this photo:
UP 3985 Locomotive

I was under the impression that most diesel locomotives use a diesel generator and an electric motor to drive the wheels (i.e. like hybrid cars). Am I wrong on this?

Nope. Modern diesel’s are set up like that and have been for decades.

No, almost all American diesel locomotives are disel-electric. Surely you consider these locomotives to be modern?

Diesel-hydraulic locomotives (using torque converters) are common in some countries, like Germany and Japan. As I understand it, they are slightly more efficient than diesel-electric, but more complex, difficult to service, and don’t scale up to very large engines. Diesel-hydraulic is becoming less common as diesel-electric locomotive technology improves. Japan is replacing most of the DD51 diesel-hydraulic locomotives with the DF200 diesel-electric locomotives.

But I don’t think it’s a simple matter to take some of the electricity from the main generator and use it to power the passenger cars. The voltage would change as the engine is revved up, for one thing. (Unlike a hybrid car, there’s no battery to store power, so you still need to rev up the engine to accelerate.)

Um, isn’t that what I said? (Admittedly, one could construe I meant exactly like a hybrid car including battery pack, but in the general gist of things it’s still right.)

I’d think that you’d be able to fix that with a voltage regulator, which would clamp down on power surges and drop outs.

Sorry, my mistake. I guess I only read the first sentence of the above two posts.

We’re talking about 500kW of power here, about 500 times more than a 100-amp automotive alternator. I think power dissipation (i.e. wasted energy) from linear voltage regulators would be significant.

Well, one could make the argument that since the locomotives don’t have battery packs they’re wasting a lot of juice. (At least one design I’ve read about dumps the excess energy produced by the generators to heating coils simply to “burn off” the extra juice.) When you’re doing things like that, I don’t know if the losses caused by voltage regulators would be considered significant or not.

Not only that, but the electric traction motors in both electric and diesel-electric locomotives use stepped acceleration. The acceleration is not infinitely variable like a car’s. Imagine your gas pedal went ‘click, click, click’ through various set power levels as you depressed it with your foot. That’s how locomotives work. A typical electric passenger train (say a subway train) might have five ‘notches’. A diesel-electric locomotive used for freight will often have eight. Each time the driver notches up or down, the current takes a sudden hit rather than a gradual one, and this would make supplying head end power from the main generator very hard to do without frying all the electrical components in the rest of the train.

Just in case somebody nitpicks, many modern locomotives don’t have notch settings. The throttle can be smoothly opened and closed. This might seem like an infinitely variable power set-up, but it’s only an illusion. It’s just there to make life easier for the bloke in the driver’s seat. It’s called ‘chopper control’, and this name gives a hint as to how it works. Instead of pulling away from a station by gradually notching up through One Notch, Two Notch, etc up to Eight Notch, the driver just smoothly eases the throttle forwards, but as far as the traction motors are concerned, the notch settings still exist. Pulling out of the station, the motors will provide One Notch power to the wheels. As the driver eases the throttle further, the power remains on One Notch, but gradually starts ‘chopping in’ brief bursts of ‘Two Notch’ power. These bursts get longer and longer until they join together and the train is in Two Notch. So from the driver’s POV, he feels a smooth transition of power, but the electrical components are doing some wild stuff, and it’d be best to keep that away from the rest of the train, hence a separate diesel engine and generator for head end power. And even then, they recommend you don’t plug in your laptop.

We can go back to the F40PH and talk about Head End Power for a second.

Those locomotives were called “screamers” by engineers because when the HEP generator was engaged, the locomotive’s prime mover had to stay revved, even when sitting perfectly still at the station. It always sounded like they were in notch 8.

The F40’s replacement, the P40’s and P42’s, do not have to do this. I forget why, but I’m thinking there is a smaller diesel engine that powers the HEP generator.