Randy, The question first. It wouldn't matter how many more units are added after four. The unit selector switch is a current limiting switch which limits the current available in the field loop circuit between the units to compensate for the number of main generator field windings present. In the one unit position 3.6 ohms is in series with the circuit, two units 2.4 ohms, three units, 1.2 ohms and four units 0 ohms. Once you get to the fourth position how many more units can be controlled depends on the point where the current draw on the loop exceeds reliable operation. This is one of the reasons engineers of first generation diesel locomotives I have spoken with would say about five units mu'ed was about the reliable limit of control. Of course I suppose you could run more units mu'ed if you didn't need their dynamic braking capability and you didn't exceed the loading of other control circuits. Just short the field loop on the fourth or fifth unit. Now about the first comment...are you sure about that? In dynamic braking, with the possible exception of the very first FTs which used a two position brake, the traction motors are connected to the main generator through the series windings, the commutators are connected to the resistor grids. The series windings supply power to the main generator to run it as a motor. The generator, auxiliary generator, air compressor and in this case the cooling fans all depend on the rotation of the output shaft to continue to operate otherwise no air for train brakes, etc. From my understanding the incremental range increases of the dynamic brakes comes more from improvements in the electrical components. Resistor grids and fans better able to dissipate the heat, improved traction motor and main generator windings, that sort of thing. I'm always willing to learn and certainly don't know all of the answers, so if you can point me to a source I investigate it further. Regards, Will Janet & Randy Brown wrote: > The most significant change in dynamic braking was that, after the FT, excitation of the motor fields came from supplemental windings in the main generator. The FT used battery power for this excitation, which limited the range and power of the dynamic brakes; the engine would stay at "idle". > > The later design meant not only that the engine would run during dynamic braking, but also that the speed of the engine would vary the excitation and incresase the range of application. It would be noisier, too, accounting for the difference in sound. > > Randy Brown The Erie Lackawanna Mailing List Sponsored by the ELH&TS http://www.elhts.org ------------------------------ End of EL Mail List Digest V3 #2038 ***********************************
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