It's almost like they're having mini-seizures. It happens with the SD40-2, Class 66, AC4400CW and others that I don't remember by name right now. You are accelerating gently, adding up more notches as the train gains speed, and suddenly the amps go to zero momentarily(and train loses all traction power) and then it starts climbing slowly again. I think Class 66 is the worst when it comes to this. And no, I don't suddenly put the throttle to notch 8 while stationary(some here may assume I abuse the throttle lever but I don't), and it doesn't only happen at notch 8, it occasionally happens at notch 4 and lower. It doesn't always happen while accelerating, it very often happens during normal cruising at set speed as well. Major pain in the ass when climbing a hill, you lose 5 mph before you know it, even if it feels like a momentary event.
I don’t know for sure but it might be something to do with switching to a different power mode. Afaik it’s true to life
Yes, it's switching from one mode to another. It's like changing gears on a car. Series to parallel I think although I could be entirely wrong.
I think that only occur to older or DC traction equipped engines. Never experienced it on AC44CW, SD70ACe & ES44. But i did experienced it when driving Class 66, GP38 & SD40.
It definitely happens with AC44CW and SD70, I agree that it doesn't happen with ES44C4 but it has a very delayed throttle response time as well(due to emissions regulations probably). Class 66 isn't that old(but surely looks like it in the cab) and I don't think it's DC as well
"Transition is the process by which the transmission of a diesel-electric locomoitve is brought from series wiring to parallel wiring. When in series, all current in the locomotive pass through all motors: this produces maximum low-speed force in the motors, i.e., maximum starting torque. When in parallel, current is divided among the motors: this produces maximum high-end efficency, i.e., highest motor speed. This is just as with the wiring internal to DC motors, where having the motor wound in series develops high starting torque, while placing the motor in parallel will develop high speed. Electrically, as current increases through the motors in a circuit with a given total current and voltage, the voltage drop across each motor will decrease: parallel circuits apply the total voltage to each load (i.e., in this case, motor), while series circuits apply the total current to each load."
Why do DC locomotives still have notched throttles and not continuous? After all they don't have to run their motors at certain preset frequencies like the AC motors
It never had anything to do with AC or DC. 8 throttle notches have been standard on US diesels since the FT in 1937, because of the ease of multiple-unit operation from a single cab (three wires can transmit 8 binary states). And on the other side of the coin, none of the UK DC D/Es had notched throttles, since except for the Class 20 they weren't originally designed with MU operation in mind.
Can you run AC currents non-discretely? Without some serious PCB of embedded work at least, which wouldn't be a thing in the early days of diesel locomotion. Is there an example of a pre-1980s AC diesel with continuous throttle?
No. Of course, there weren't many (if any) AC diesels of any sort, for that reason. Nobody could figure out how to build one that wouldn't self-destruct. The breakthrough was the German experimental DE 2500 in the mid 70s. Its use of thyristor control of voltage and current provided the conceptual framework for the 3-phase AC diesels which started appearing around 1990 (as well as all the German AC electrics from the 120 on).
Yes, but as a DC engine its designers were free to use stepped control, rheostatic control or a combination of both.
To explain the notched throttle, in all diesel locos the engine rpm is controlled by a governor. Early US diesel locos used "Woodward" electro/hydraulic governors, with this design solenoids are used to select the target rpm. Each solenoid can be either on or off. Hence a Woodward governor will always require a notched throttle. Modern locos tend to use electronic governors, so a continuous throttle is possible. I think a lot of modern US diesel locos stick with the notched throttle simply because it is what the crews are used to. Some early UK diesels used a centrifugal governor, this also allows for a continuous throttle.
The Woodwards were a first-generation thing; from at least the early 1960s they (or rather, the solenoids) were gone; and dynamic-brake control systems were continuous starting with (IIRC) the EMD GP-30. The notches have stuck around because there was little point in changing the simple, reliable 28-pin MU cable- still used even today in the age of wireless digital.
