mixed consists

[Anonymous]

I have read quite a number of sources which point out that running DC traction motor units with AC units can cause problems. This is due to the difference in performance between the two systems,particularly in reference to acceleration and dynamic breaking in high tonnage,low speed service,where an AC unit can keep lugging where it's DC equivalent will stall.
Norfolk Southern is trying to institute a matched consist policy,with units grouped by horsepower,axle count,and intended service,but not manufacturer and model(i.e SD70s should operate with Dash 9-40CW but not GP38-2). They only have a small number of AC drive locos(SD80MAC,ec-Conrail) which operate in sets,so this isn't as big a concern as for CSX,UP,BNSF,CP who have big fleets of ACs.

[wabash1]

to answer your question if i have a sd70 and a sd60 and a gp38 the 2 big units will basiclly share the load and the gp38 will be over worked to a point but it tries to do its share. then when you get them on flat ground the gp 38 will do its best to keep up. and yes you can burn them up. i was told to run a gp 38 behind a dash 9 and i told them it wont make it the trainmaster took the responsibility for it and halfway up the grade i smoked it. litterally its now scrap iron its is best to stay with same power and maker if possible all ge or all emds.

[Anonymous]

My biggest question is how can locos of different power levels be made to pull the same amount. For example if a 2500hp loco and a 4000hp loco are hooked together and each is set on run 5 there will be a differece in tractive effort; is this an issue? What about different loading speeds; can this cause problems? I read in Trains magazine that traction motors in older units can be burned out when controlled by newer units. Is this true? Thanks for your help. Ron

[CShaveRR]

I guess I didn't really answer your questions about how the locomotives are controlled. The hoses between units (there are about four of them) connect functions such as braking and sanding, which are pneumatically controlled. Electrical controls, such as throttle position, dynamic brakes, headlights, etc., are controlled with a large cable that runs between units. The cable itself is very much standardized, and the "pins" inside it are usually standardized, so that the entire consist functions as one locomotive. If the engineer opens his throttle to Run 5, for example, every unit's engine will operate at that speed. There are switches that have to be positioned properly in each unit to make some of this happen (such as headlight controls), but if an engineer should want to turn on the rear headlight, the rearward-facing light on the last unit in the consist should be the one that lights up (regardless of the direction the unit itself is facing). If there is a problem with one of the units, the alarms should go off in the lead unit to make the engineer aware of the problems (and newer units will display the nature of the problem on their screens).

Hope all of this is clear!

[CShaveRR]

The hoses and cable that connect the multiple units to each other are standardized, so there really is no problem any more. Trains Magazine had an article about this 'way back in the mid-1960s (when there still were some non-standard things going on); it might be time to revisit the topic.

A few years back you'd have more problems between locomotives of different railroads than you would with locomotives of different builders. The Chicago & North Western had an electric gong instead of a bell, and this was trainlined (the gong would ring in all units of an all-CNW lashup). And it was no problem to run a UP unit in the CNW consist. But if you had a Chessie unit m.u.ed with a CNW unit, and rang the bell, I think you'd lose the load on the Chessie unit.

Nowadays, besides controlling units in a lashup, an engineer can control units not connected to his own, either in the middle or at the other end of his train (again, it's the control systems specified by the railroads, rather than by the locomotive builders, that cause compatibility problems). Why, even the engineers on the UP's steam locomotives can control trailing diesels from their cabs (4449, too)!

[Anonymous]

I believe that in a perfect world all consists would be made up of like locomotives. What problems do mixed consists have? How are different loco types and brands controled when hooked together(how are they regulated to pull in unison)? Do they share electrical power, or do they act independently?