Siderod Electrics

[Anonymous]

The Fall Classic Trains has picturees of N&W & Virginian electric boxcabs with siderods. What was the thinking behind this arrangement? Why would they want larger diameter drivers for hauling coal or is this because of limitations in early traction motors. How many motors did these have and what kind of gearing did they have?

[CSSHEGEWISCH]

Side rods were used at the time because of the limitations of the technology regarding traction motors, among other things. In the case of the DD1, it was thought that large traction motors mounted above the frame would behave like an inverted pendulum and would consequently be easier on the track. It would also reduce unsprung weight since part of a nose-mounted traction motor's weight is unsprung.

[Hugh Jampton]

Plus the side rods connect the rotation of the wheel it's not possible for one axle to slip.

[M636C]

In some cases, it wasn't possible to fit a motor of adequate power in the space between the wheels, particularly in the case of alternating current motors with low frequency AC as many of the early electrifications used. Even the well remembered GG1 locomotives did not have axle hung motors. The motors on a GG1, six units each with two armatures (effectively twelve motors in all) were mounted in the frame above the axle and drove the axle through flexible gearing. A similar motor arrangement was used on some 3000V DC locomotives in Italy. Many German and Swiss AC locomtives had a similar arrangement but with a single motor mounted in the frame above the axle, driven by flexible gearing. This even applied to bogie locomotives up until the 1960s. It was only with the introduction of solid state rectifiers and the adoption of DC motors that this arrangement has been abandoned. Now. of course variable frequency inverters allow the use of very compact inducton motors with no commutator or slip rings. The inverters generally work on about 1500V DC input, and the power from the overhead is converted to this, and then output to the motors as variable voltage, variable frequency three phase AC.

Locomotives with axle hung motors using single phase AC directly from the overhead (even transformed to a lower voltage) have generally been unsuccessful.

Peter

[Anonymous]

The N&W and Virginian Boxcab electrics were set up to run at either 14 or 28 mph. This was adequate at the time for maintaining a steady traffic flow. Compared to the speed of the steamers on their heavy grades this was more efficient and saved the railroad from having 2 or 3 mallets pulling/pushing the trains. It also eliminated the smoke problems for the crews.

They were also very cool to watch. Look at Herron's Pocahontas Glory (Vol 6?). and you will catch them in action.

Roger

[Anonymous]

When the siderod electrics were made mainline electrification was a new concept. In order to maximise the probability of success of the venture the designers used proven designs as much as possible. One of the designs used was the running gear of a steam locomotive. But instead of a boiler and pistons, a large electric motor provided the power.

If you look at early electric locomotives they often are siderod connected. PRR had several designs with siderods, the DD1 being the most notable and at least one unit was in service until the PC days. N&W also had siderod electrics. There are far too may European examples to begin to list, and many of them lasted well into the 1970s.

[CSSHEGEWISCH]

The two-speed situation on the N&W/VGN boxcabs is due to their design as split-phase locomotives. The traction motors were three-phase designs which made them constant-speed devices, the second constant speed was allowed by an adjustment in the wiring, perhaps an electrical engineer can help me out here. The original GN Cascade Tunnel electrification was a straight three-phase system with double overhead. The Italian State Railways also used a three-phase electrification on its lines in Northern Italy but these were converted or discontinued by the mid-1960's.