That's an apt description of a dynamotor. The Sacramento Northern 1005 also has the same setup and I believe it was common on SN cars. However a dynamotor has two complete armatures, and I would expect the South Shore would avoid the expense if they could. I can't imagine, though, how you set up a DC motor to be tolerant of either 600 or 1500. History sure has interesting secrets, too bad nobody puts them in books...

2 sets of field windings, in series with each other for 1500V operation, and in parallel with each other for 600V operation. Switching between the 2 could be done by reconfiguring the wiring, or by a set of 3 contactors, 1 "series" contactor for 1500V, 2 "parallel" contactors for 600V, just like a traction motor transition circuit.

Jeff

But, Chicago, South Shore & South Bend may have had dual voltage steeple cab freight locomotives, so that Mr. Insull could have the option of lending them to his 600 companies. Were the similar Chicago Rapid Transit locomotives, some of which are in museums, also dual voltage?

Now we enter into the magical Land of Conjecture, home of "What ifs....?", Wild Ass Guess's, and other outright guesswork. (see my signature, for pictures of your transportation in this land.)


No.

Jeff

I'll say. I might point out that the South Shore locomotives, even the steeple cabs that were replaced by the 700 series boxcabs in the sixties, were an order of magnitude bigger than anything on the other Insull roads; the CRT locos were fifty tonners, as were the BW steeplecabs on the CA&E and GE "pups" on the North Shore. The South Shore steeple cabs were all 80 ton or larger. Interestingly, the NYC class R locomotives the 700's were rebuilt from started life as 600V machines, while the 800 series locos were either 3000V or 3300V when they were destined for the USSR. This just all points out that it's no big deal to revise circuitry for different voltages, and 750V (1/2 voltage across a 1500V line) is close enough to 600V that it's within the tolerance for the motor design.

All this is besides the point, because it's the IC cars that had easily convertible compressors, not the South Shore cars, and there's no easy explanation why, except that they were.

Some histories claim that the South Shore steeple cabs were as I described, but I want better proof before I agree. The trolley poles on one end of them were also cited as proof, but the steel passenger cars in the late 1920s also has a pole on one end. I think that it was so they could share track, but not wire and voltage, with South Bend street cars.

This has been an interesting discussion. I thought I would put my two cents worth in. What I have to say is based on my experience, which is limited to just a couple of electric railway museums and a couple of transit systems.

A dynamotor is an interesting machine designed to be simple, light and inexpensive. It is two series wound motors wound on the same rotor with a commutator at each end and a shunt field to control the speed. The two motors do not have to be designed for the same voltage. If the two motors are designed to run at the same voltage and are run in series, voltage can be drawn from between the two motors that will be half the line voltage. So if 1200 VDC is across the two motors in series, the voltage taped from the center will be 600 VDC. If one motor is design for 600 VDC and the other for 900 VDC, the line voltage can be 1500 VDC and the center taped voltage can be 600 VDC. But being a proportional machine, as the line voltage goes down so does the center voltage. So on a 600/ 1200 VDC machine, if the line voltage goes down to 900 volts, the center voltage to ground will go to 450 volts.

Typically 600 VDC electric railway equipment is designed to run with line losses down to 400 volts. But the drop out voltage for the contactors is probably less than 200 volts. In the old days low line voltage was a problem that the railways lived with. Low voltage came with several problems including a noticeable loss in horsepower and speed, significant reduction in lighting, and the splash lubricated air compressors would stop lubricating at very slow speeds. With modern electronic control systems low voltage presents greater problems and can not be tolerated like the cars from the electro-mechanical era could.

When batteries were introduced to the electric railway industry, they could not use a dynamotor for charging because of the voltage drop on the output, so the motor generator was introduced with a voltage regulator to provide a proper charging voltage for the batteries. Lots of other schemes were used to charge batteries including putting them in series with a lighting string, taping the air compressor fields for a lower voltage source, series resisters, voltage dividers, axle driven generators, and charging at the carhouse at the end of the day. Batteries were used on third rail systems to avoid the control contactors from dropping out at every third rail gap, and later for car lighting and various train control and signaling systems.

On those systems that used dynamotors, they have a dual voltage motor sitting there and it frequently was also used to also drive the air compressor through an air operated clutch. When the air compressor was connected, the dynamotor speed would drop due to the increased load, but since the dynamotor is a proportional device the output voltage would not go down as the speed did, making its use to drive the compressor practical.

With respect to tractive power, dual or multiple voltage systems are not as simple as they might appear. In the beginning most street railways started out as 500 VDC systems. As insulation systems improved and power demands increased the design voltages increased pretty much in 50 volt increments until we get to today’s 750 volt systems. There are two mathematical relationships that need to be kept in mind here. First is that voltage times current results in power. The second is that resistance times current it equal to voltage. If these two equations are combined you discover that a change in voltage makes an exponential change in power. So running a 500 VDC motor on 600 VDC or a 600 VDC motor on 750 VDC are significant changes in the performance of the motor. This also makes a significant change in the various stressed on the motor’s design parameters.

The common dual voltage system was 600 and 1200 VDC. This would allow motors designed to run on 600 VDC to be run in series on 1200 VDC. In this case the motors, or at least one motor, would have to be insulated for 1200 volts to ground. A car designed to run on either 600 or 1200 VDC using 600 volt motors has a fairly complicated change over system. The motors have to be reconnected from series to parallel and some changes to the acceleration resistors are usually made. On cars designed to run on 1200 VDC only using 600 volt motors usually have the motors permanently connected in series. The control system is set up like a two motor car with a two motor reverser. The control system has to be designed for only half the current since there is twice the voltage. To convert this car to run with full performance on 600 VDC requires a major modification, as the control system has to be change from a two motor system to a four motor system. Then all wiring and control contactors have to be changed to handle twice the current. The series acceleration resistors will have to be resigned to accommodate the new current requirements. The compressors and lighting also have to be changed.

Some systems used traction motors designed for 1200 VDC. The bar to bar commutator voltage on most DC traction motors is kept to about 20 volts to control sparking on the commutator. The typical antique DC traction motor is a four pole motor which means that the line voltage is seen on the commutator 90 degrees apart. To keep the bar to bar commutator voltage to 20 volts, there would have to be 30 bars in 90 degrees or about 120 bars around the commutator. Using this same 20 volt limit on a 1200 volt motor would result in about 240 bars around the commutator. This means that the commutator is much larger in diameter and more expensive.

At the Western Railway Museum there is one locomotive, Sacramento Northern 654, that was purchased after the merger of a 600 volt railroad and a 1500 volt railroad. It was built as a 600/1500 volt locomotive. The traction motors are 750 VDC traction motors reconnected in various series and parallel combinations to get the dual voltage. To get a reasonable speed out of the 750 volt motors running on 600 volts, there is field shunting. The compressed air source is dealt with in a similar manor. There are two 750 volt air compressors, electrically insulate for 1500 volts to ground, run in series when the locomotive is set for 1500 volts. In the 600 volt mode the air compressors are run in parallel with field shunting to get them running at the proper speed.

There is nothing simple about dual voltage equipment or converting equipment from one voltage to another.

As I recall from the GE Review articles (reprinted by CERA as "Electrification by General Electric" bulletin 116), even though 1500 volt traction motors were offered by both GE and Westinghouse (and were in successful use on MILW) they didn't trust them and went with 750 volt traction motors insulated for 1500 V. The "most parallel" they get is paired in series. I'll have to look to see if anything is said about the M-G or compressor but with their choice about the traction motors in mind it makes sense that they would do some sort of similar dual/series thing with the auxiliary machines.

Steve

Necroposting, but CSS&SB cars #102 and #109 were scrapped at Boone, IA in the Fall of 2023. They are no longer extant, though a few components from each were salvaged before they were cut up.

The roofs and floors had rotted away to the point of nonexistence and they had already become immobile eyesores some years back after tarpaulins covering them disappeared.

The other CSS&SB cars at Boone are still extant, and #106 supposedly can run "slowly" under the overhead from what I was told.