Wondering Wrote:
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> How was electrical power supplied to passenger
> cars back in the days of steam and no HEP units
> available?

Most passenger cars had large Edison batteries charged by a generator driven by a belt around a pulley on a car axle. A few train stations could supply power to the car batteries while it was sitting before an evening departure.

When light weight passenger cars came into use, many of them had propane engines connected to generators for lights and air conditioning. Some old heavyweight cars had propane engines installed for air conditioning power. They were called "ice engines" because they had evaporators in compartments that formerly had used ice for cooling. A Pullman car typically would carry eight tons of ice for cooling. Cold water from melting ice was circulated through radiators in the ventilating system.